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Lactate transporters (MCT proteins) in heart and skeletal muscles
Abstract
Lactate traverses the cell membranes of many tissues, including the heart and skeletal muscle via a facilitated monocarboxylate transport system that functions as a proton symport and is stereoselective for L-lactate. In the past few years, seven monocarboxylate transporters have been cloned. Monocarboxylate transporters are ubiquitously distributed among many tissues, and the transcripts of several monocarboxylate transporters are present within many of the same tissues. This complicates the identification of their metabolic function. There is also evidence that that there is some species specificity, with differences in MCT tissue distributions in hamsters, rats, and humans. MCT1 and MCT3-M/MCT4 are present in rat and human muscles, and MCT1 expression is highly correlated with the oxidative capacity of skeletal muscles and with their capacity to take up lactate from the circulation. MCT1 is also present in heart and is located on the plasma membrane (in subdomains), T-tubules, and in caveolae. With training, MCT1 is increased in rat and human muscle, and in rat hearts, resulting in an increased uptake of lactate from the buffers perfused through these tissues and an increase in lactate efflux out of purified vesicles. In humans, the training-induced increases in MCT1 are associated with an increased lactate efflux out of muscle. MCT3-M/MCT4 is not correlated with the muscles' oxidative capacities but is equally abundant in Type IIa and IIb muscles, whereas it is markedly lower in slow-twitch (Type I) muscles. Clearly, we are at the threshold of a new era in understanding the regulation of lactate movement into and out of skeletal muscle and cardiac cells.
... Lactic acid in the intracellular space used via oxidation as a respiratory fuel is one of the useful energy sources [128]. Thus, lactic acid produced in the cytosolic space of fast muscles contributing to relatively heavy exercise under physiological conditions is transported into the interstitial (extracellular) space via monocarboxylate transporter (MCT) ( Figure 3B) [141,142], and the extracellular lactic acid shuttles to oxidative tissues via the blood-delivered system [141]. Mitochondrial dysfunction in diabetes mellitus patients leads fast muscles to produce lactic acid even in cases of regular exercise without heavy muscle contraction [127,143]. ...
... Lactic acid in the intracellular space used via oxidation as a respiratory fuel is one of the useful energy sources [128]. Thus, lactic acid produced in the cytosolic space of fast muscles contributing to relatively heavy exercise under physiological conditions is transported into the interstitial (extracellular) space via monocarboxylate transporter (MCT) ( Figure 3B) [141,142], and the extracellular lactic acid shuttles to oxidative tissues via the blood-delivered system [141]. Mitochondrial dysfunction in diabetes mellitus patients leads fast muscles to produce lactic acid even in cases of regular exercise without heavy muscle contraction [127,143]. ...
... This means that HCO 3 − generated from CO 2 in peripheral tissues is not a net source of Lactic acid in the intracellular space used via oxidation as a respiratory fuel is one of the useful energy sources [128]. Thus, lactic acid produced in the cytosolic space of fast muscles contributing to relatively heavy exercise under physiological conditions is transported into the interstitial (extracellular) space via monocarboxylate transporter (MCT) ( Figure 3B) [141,142], and the extracellular lactic acid shuttles to oxidative tissues via the blood-delivered system [141]. Mitochondrial dysfunction in diabetes mellitus patients leads fast muscles to produce lactic acid even in cases of regular exercise without heavy muscle contraction [127,143]. ...
Blood contains powerful pH-buffering molecules such as hemoglobin (Hb) and albumin, while interstitial fluids have little pH-buffering molecules. Thus, even under metabolic disorder conditions except severe cases, arterial blood pH is kept constant within the normal range (7.35 ~ 7.45), but the interstitial fluid pH under metabolic disorder conditions becomes lower than the normal level. Insulin resistance is one of the most important key factors in pathogenesis of diabetes mellitus, nevertheless the molecular mechanism of insulin resistance occurrence is still unclear. Our studies indicate that lowered interstitial fluid pH occurs in diabetes mellitus, causing insulin resistance via reduction of the binding affinity of insulin to its receptor. Therefore, the key point for improvement of insulin resistance occurring in diabetes mellitus is development of methods or techniques elevating the lowered interstitial fluid pH. Intake of weak organic acids is found to improve the insulin resistance by elevating the lowered interstitial fluid pH in diabetes mellitus. One of the molecular mechanisms of the pH elevation is that: 1) the carboxyl group (R-COO-) but not H+ composing weak organic acids in foods is absorbed into the body, and 2) the absorbed the carboxyl group (R-COO-) behaves as a pH buffer material, elevating the interstitial fluid pH. On the other hand, high salt intake has been suggested to cause diabetes mellitus, however the molecular mechanism is unclear. A possible mechanism of high salt intake-caused diabetes mellitus is proposed from a viewpoint of regulation of the interstitial fluid pH: high salt intake lowers the interstitial fluid pH via high production of H+ associated with ATP synthesis required for the Na+,K+-ATPase to extrude the high leveled intracellular Na+ caused by high salt intake. This review article introduces the molecular mechanism causing the lowered interstitial fluid pH and insulin resistance in diabetes mellitus, the improvement of insulin resistance via intake of weak organic acid-containing foods, and a proposal mechanism of high salt intake-caused diabetes mellitus.
... Tais proteínas, conhecidas como transportadoras de monocarboxilato (TMC), dividem-se em 7 classes que já foram identificadas e clonadas [12][13][14][15]. A TMC1 é a proteína transportadora mais expressa, tanto em músculo estriado esquelético quanto em cardíaco, estando altamente relacionada à capacidade oxidativa dos músculos esqueléticos [16]. As proteínas da classe TCM3 e TCM4 são, juntamente com a TCM1, as mais expressas, tanto em tecido músculo esquelético animal quanto em humano. ...
... A abundância de TCM3 e TCM4 nos músculos ricos em fibras do tipo IIa e/ou IIb, concomitantemente com uma baixa expressão em fibras do tipo I, sugere que tais proteínas atuam como transportadoras de lactato para fora do tecido, em direção a circulação sangüínea. O treinamento com exercícios de alta intensidade parece induzir aumento de expressão destas proteínas transportadoras [10,16]. ...
... Sabe-se que o acúmulo reduzido de lactato em músculos oxidativos ou treinados aerobiamente durante exercício físico é devido a uma diminuição da atividade metabólica da via glicogenolítica e a um aumento da capacidade de oxidação de piruvato. Bonen [16] ressalta que as proteínas TMC1 possuem capacidade tanto de retirar o lactato da circulação como de removê-lo do tecido muscular. O aparente conflito é resolvido quando o autor explica que o aumento em consumo de lactato pelo músculo pode ser estratégico para restituir os níveis de glicogênio muscular. ...
Nosso estudo tem como objetivo desmistificar, para alunos de graduação quecursam a disciplina Bioquímica do Exercício Físico, a ação do lactato nos eventos dador muscular tardia (DMT) induzida pelo exercício físico. Para tanto, realizamos umexercício de corrida exaustiva (3 corridas intensivas de 250 metros, em pista oficial de400 metros, com intervalos de recuperação ativa de 150 metros de caminhada).Participaram do exercício 5 alunos (3 homens e 2 mulheres) com idade média de 21±2anos. A tentativa foi desenvolver uma atividade não habitual e exaustiva, a fim deelevar a concentração de lactato sangüínea e induzir um nível de desconfortomuscular. Coletamos 3 mL de sangue antes do esforço físico (valor controle – CO),imediatamente após (T0h), duas horas após (T2h) e quatro horas após a realização dacorrida (T4h), para obtermos, assim, as dosagens de lactato (em sangue total) e decreatina quinase (CK, no plasma). As análises de concentração de lactato no sangueforam realizadas através do aparelho AccutrendÒ Lactate (Roche) e as dosagens dosníveis de CK através do método reativo para determinação de quantidade plasmática(CK NAC – Método Cinético, Laborlab) por meio de espectrofotômetro. Houve umaumento significativo dos níveis de lactato no sangue imediatamente após arealização do exercício exaustivo, porém após o tempo T2h e T4h os valoresencontraram-se nos níveis detectados para o grupo controle (CO), revelando umaestratégia de remoção deste metabólito. Pudemos observar que houve umcomportamento idêntico quanto ao aumento de concentração de CK plasmática emtodos os indivíduos, após 4 horas da realização do exercício exaustivo, com aumentosignificativo em T4h em comparação ao grupo controle. A concentração plasmática delactato volta aos níveis pré-exercício 2h após a realização do exercício intenso e muitoantes da instalação dos primeiros sintomas da dor muscular tardia. Concluímos que aelevação das dosagens plasmáticas de CK após o exercício exaustivo pode ser emdecorrência de um aumento de permeabilidade ou perturbação mais efetiva dosarcolema, constituindo um primeiro evento participativo no desencadeamento daDMT.
... The MCT1 and MCT4 isoforms are co-expressed in skeletal muscle. MCT1 is ubiquitously expressed in a variety of human, rat tissues, including skeletal muscle and the heart (Bonen, 2000) and its expression is correlated with the oxidative capacity of various muscles (McCullagh et al. 1996;Baker et al, 1998). The MCT4 isoform is the predominant isoform in fast-twitch glycolytic muscle fibres, (Wilson et al, 1998) while the MCT1 isoform is more abundant in oxidative than glycolytic fibres. ...
... The fibre type distribution suggests that each MCT isoform may have distinct transport functions, with MCT1 acting more to take up lactate supplied to its interstitial fluids from the circulation or neighboring muscle cells, while MCT4 has a greater part in facilitating lactate efflux from the cells in which lactate production exceeds pyruvate oxidation. In accordance with this hypothesis is the fact that MCT4 is present in considerable quantity in intracellular pools, while no such presence was observed in the MCT1 isoform (Bonen, 2000). ...
... Taken together, these data support the notion that skeletal muscle cells may be dependent on MCT uptake for optimal volume regulation when the conditions are favourable in the presence of lactate. (Broer et al. 1997), while MCT4 has a larger role in lactate efflux, consistent with its high K m of 25-35 mM (Bonen, 2000, Dimmer et al. 2000. Since phloretin has a greater specificity towards MCT1 than MCT4, using 1 mM phloretin completely blocks MCT1. ...
... Einen wesentlichen Einfluss hat auch der Laktattransport, wobei der Monocarboxylat-Transporter (MCT) eine wichtige Rolle zukommen. Die Regulation der Muskellaktatkonzentrationen und damit auch der Blutlaktatkonzentrationen hängen dabei nicht nur von der Glykolyserate ab, sondern auch von der Effizienz des Laktattransports mittels MCT (Bonen, 2000). Juel (2008) fand heraus, dass vor allem bei Kurzzeitbelastungen die Leistungsfähigkeit des Transporters den leistungslimitierenden Faktor darstellt. ...
... Dabei befindet sich der MCT1 überwiegend in den oxidativen Muskelfasern und ist für die Laktataufnahme verantwortlich. Der MCT4 ist hauptsächlich in den glykolytischen Muskelfasern zu finden und ist für die Laktatabgabe zuständig (Bonen, 2000). Bonen et al. (2000) konnten in Untersuchungen einen großen Zusammenhang zwischen der MCT1-Dichte und der Laktatelimination und der Blutlaktatkonzentration nach supramaximaler Belastung nachweisen. ...
High-intensity interval training, characterized by repetitive short to long bouts of high-intensity exercise separated by recovery periods, represents a time-efficient training methodology for improving athlete performance. Previous research indicates that physiological and anatomical differences in men and women may result in divergences in training response. Furthermore, the state of research suggests that changes in skeletal muscle and different functional systems over the course of age may induce different responses to an exercise stimulus. In this regard, the results show that there is a sexual dimorphism in load and recovery during interval exercise. Furthermore, it was found that good trainability is possible in old age, which in turn may counteract age-related changes and their influence on load and recovery behavior.
... Much of the lactate produced in glycolytic fibers is taken up and oxidized in adjacent oxidative fibers [3]. Lactate is conveyed across the cell membrane by a family of monocarboxylate transporters (MCTs) [4]. Thus, MCTs have a significant function to maintain pH homeostasis inside the cells [5]. ...
... Among the known MCT isoforms, MCT1 and MCT4 are the main transporters in skeletal muscle [6]. MCT1 facilitates lactate influx mostly in oxidative fibers, while MCT4 is responsible for the extrusion of lactate mainly in glycolytic fibers [4,7]. Contractile activities of skeletal muscles appear to be significant for the regulation of MCTs [8]. ...
The research literature suggests that different training modalities cause various patterns in training-induced genes expression. This study aimed to investigate the effects of moderate intensity continuous training (MICT) and isocaloric high intensity interval training (HIIT) on gene expression of monocarboxylate transporter 1 (MCT1) and 4 (MCT4), Peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), and hypoxia inducible factor-1α (HIF-1α) in soleus and extensor digitorum longus (EDL) skeletal muscles of rats. Thirty male Sprague–Dawley rats were divided into 3 groups of control, MICT, and HIIT. Training protocols were performed according to the principle of overload for 8 weeks and 5 sessions per week. Then, the soleus and EDL muscles were extracted and the expression levels were analyzed using the real time PCR method. In the MICT group, only the EDL HIF-1α mRNA level was significantly higher than that of the control group (p < 0.05). In the HIIT group, however, mRNA levels of MCT4, PGC-1α, and HIF-1α in both muscles were significantly higher than those of the control group (p < 0.05). The comparison between the two training methods demonstrated that the gene expression levels of soleus and EDL MCT4, soleus PGC-1α, and soleus HIF-1α were significantly higher in the HIIT group compared to the MICT group (p < 0.05). There were also significant positive correlations between all mRNA levels of HIF-1α and corresponding mRNA levels of MCT4 (p < 0.05). HIIT caused greater positive responses in the gene expression of MCT4, PGC-1α, and HIF-1α compared to MICT.
... Lactate transport across the plasma membrane occurs via monocarboxylate transporters (MCT) (Bonen, 2000;Kitaoka et al. 2012). Among a family of MCTs (MCT1-14), MCT1 and MCT4 are thought to play an important role in skeletal muscle (Bonen, 2000). ...
... Lactate transport across the plasma membrane occurs via monocarboxylate transporters (MCT) (Bonen, 2000;Kitaoka et al. 2012). Among a family of MCTs (MCT1-14), MCT1 and MCT4 are thought to play an important role in skeletal muscle (Bonen, 2000). MCT1 is predominantly presented in the oxidative muscles and mainly facilitates lactate uptake, whereas MCT4 is abundant in the glycolytic muscles and mainly mediates lactate efflux from skeletal muscle (Dimmer et al. 2000;Bonen, 2001). ...
Abstract Growing evidence shows that lactate is not merely an intermediate metabolite, but also a potential signaling molecule. However, whether daily lactate administration induces physiological adaptations in skeletal muscle remains to be elucidated. In this study, we first investigated the effects of daily lactate administration (equivalent to 1 g/kg of body weight) for 3 weeks on mitochondrial adaptations in skeletal muscle. We demonstrated that 3‐week lactate administration increased mitochondrial enzyme activity (citrate synthase, 3‐hydroxyacyl CoA dehydrogenase, and cytochrome c oxidase) in the plantaris muscle, but not in the soleus muscle. MCT1 and MCT4 protein contents were not different after 3‐week lactate administration. Next, we examined whether lactate administration enhances training‐induced adaptations in skeletal muscle. Lactate administration prior to endurance exercise training (treadmill running, 20 m/min, 60 min/day), which increased blood lactate concentration during exercise, enhanced training‐induced mitochondrial enzyme activity in the skeletal muscle after 3 weeks. MCT protein content and blood lactate removal were not different after 3‐week lactate administration with exercise training compared to exercise training alone. In a single bout experiment, lactate administration did not change the phosphorylation state of AMPK, ACC, p38 MAPK, and CaMKII in skeletal muscle. Our results suggest that lactate can be a key factor for exercise‐induced mitochondrial adaptations, and that the efficacy of high‐intensity training is, at least partly, attributed to elevated blood lactate concentration.
... This expression pattern indicates a potentially bigger role for MCT1 and MCT4 in cardiac lactate and ketone body uptake and/or efflux compared to other transporters. 48,49 Sarcolemmal expression, transporter activity, Figure 1 Schematic presentation of cardiac specific membrane substrate transporters and their distribution (endosomes vs. sarcolemma) within cardiomyocytes. GLUT 1 and GLUT4 are the predominant glucose transporters in the heart. ...
... 49,54 Moreover, exercise enhances MCT1 expression in the heart and skeletal muscle. 47,48 Although the exact mechanism still remains to be elucidated, there might be a role for AMPK, which stimulates the MCT1 promotor upon activation. An additional mechanism is elevated Ca 2þ levels that are able to activate the MCT1 promotor via the transcriptional factor nuclear factor of activated T-cells. ...
Cardiac pressure overload (PO), such as caused by aortic stenosis and systemic hypertension, commonly results in cardiac hypertrophy and may lead to the development of heart failure. PO-induced heart failure is among the leading causes of death worldwide, but its pathological origin remains poorly understood. Metabolic alterations are proposed to be an important contributor to PO-induced cardiac hypertrophy and failure. While the healthy adult heart mainly uses long-chain fatty acids (FAs) and glucose as substrates for energy metabolism and to a lesser extent alternative substrates, i.e. lactate, ketone bodies, and amino acids (AAs), the pressure-overloaded heart is characterized by a shift in energy metabolism towards a greater reliance on glycolysis and alternative substrates. A key-governing kinetic step of both FA and glucose fluxes is at the level of their substrate-specific membrane transporters. The relative presence of these transporters in the sarcolemma determines the cardiac substrate preference. Whether the cardiac utilization of alternative substrates is also governed by membrane transporters is not yet known. In this review, we discuss current insight into the role of membrane substrate transporters in the metabolic alterations occurring in the pressure-overloaded heart. Given the increasing evidence of a role for alternative substrates in these metabolic alterations, there is an urgent need to disclose the key-governing kinetic steps in their utilization as well. Taken together, membrane substrate transporters emerge as novel targets for metabolic interventions to prevent or treat PO-induced heart failure.
... Lactate is not only a final product (waste) of glycolysis but also may operate as a metabolic signal, a pseudo-hormone (Brooks, 2002). Lactate is continuously produced by skeletal muscle at all levels of muscle activity (McDermott and Bonen, 1992), and it serves as an energy substrate for cardiac and skeletal muscles (Wilson et al., 1998;Pilegaard et al., 1999;Bonen, 2000). The release of lactate from the muscle into the blood and its uptake by other muscle cells occur via monocarboxylate transporters (MCTs), which are proton-linked membrane carriers Gladden, 2000). ...
... The release of lactate from the muscle into the blood and its uptake by other muscle cells occur via monocarboxylate transporters (MCTs), which are proton-linked membrane carriers Gladden, 2000). Among the identified isoforms, MCT1 appears to be responsible for the influx of lactate predominantly in oxidative fibers, while MCT4 facilitates lactate extrusion mostly in glycolytic fibers (Wilson et al., 1998;Pilegaard et al., 1999;Bonen, 2000). ...
Although aerobic training has been shown to affect the lactate transport of skeletal muscle, there is no information concerning the effect of continuous aerobic training on spontaneous physical activity (SPA). Because every movement in daily life (i.e., SPA) is generated by skeletal muscle, we think that it is possible that an improvement of SPA could affect the physiological properties of muscle with regard to lactate transport. The aim of this study was to evaluate the effect of 12 weeks of continuous aerobic training in individualized intensity on SPA of rats and their gene expressions of monocarboxylate transporters (MCT) 1 and 4 in soleus (oxidative) and white gastrocnemius (glycolytic) muscles. We also analyzed the effect of continuous aerobic training on aerobic and anaerobic parameters using the lactate minimum test (LMT). Sixty-day-old rats were randomly divided into three groups: a baseline group in which rats were evaluated prior to initiation of the study; a control group (Co) in which rats were kept without any treatment during 12 weeks; and a chronic exercise group (Tr) in which rats swam for 40 min/day, 5 days/week at 80% of anaerobic threshold during 12 weeks. After the experimental period, SPA of rats was measured using a gravimetric method. Rats had their expression of MCTs determined by RT-PCR analysis. In essence, aerobic training is effective in maintaining SPA, but did not prevent the decline of aerobic capacity and anaerobic performance, leading us to propose that the decline of SPA is not fully attributed to a deterioration of physical properties. Changes in SPA were concomitant with changes in MCT1 expression in the soleus muscle of trained rats, suggestive of an additional adaptive response toward increased lactate clearance. This result is in line with our observation showing a better equilibrium on lactate production-remotion during the continuous exercise (LMT). We propose an approach to combat the decline of SPA of rats in their home cages. This new finding is worth for scientists who work with animal models to study the protective effects of exercise.
... Muskel-Laktat-Konzentrationen (und damit auch Blutlaktat-Konzentrationen) werden nicht nur durch die Glykolyserate, sondern auch durch die Effizienz des sarcolemmalen Laktattransports mittels Monocarbocylat-Transporter (MCT) reguliert. Ein Prozess der von der MCT-Menge abhängt [9]. 1994 wurde der erste MCT geklont und sequenziert. ...
... MCT1 kommt vornehmlich in oxidativen Fasern vor und ist für die Laktataufnahme zuständig (Km = ~3-5 mmol*l -1 ). MCT4 kommt vornehmlich in glykolytischen Fasern vor und sind für die Laktatabgabe zuständig (Km = 28 mmol*l -1 ) [9,10,11,32]. Im Tierexperiment zeigen oxydative Fasern eine um mehr als 50% höhere Laktattransportkapazität als glykolytische Fasern. So konnte gezeigt werden, dass die MCT1-Dichte stark mit Laktatelimination und den Blutlaktatkonzentrationen nach supramaximaler Belastung zusammenhängt [11,71]. ...
Blood lactate monitoring was and is widely used to evaluate training status and to set training intensity. Since its first documentation in the early 19 th century, the role of lactic acid has fascinated physiologists, biochemists, and coaches. Initial interpretation was that lactic acid appeared as a dead-end waste product and was responsible in some way for exhaustion and acidosis-dependent tissue damage (destruction of mitochondria). It was thought that the formation of lactic acid was due to an O 2 limitation in skeletal muscle. Recent evidence and new lines of investigation, now place lactate as an important metabolite capable of moving between cells, tissues and organs via lactate transporters, where it may be oxidised as a fuel. Lactate acts as a metabolic signal to specific tissues, becoming a pseudo-hormone ("lactormone"). Also the importance of lactate in muscle fatigue is now under scrunity. This article reviews the current state of the art about lactate.
... Improved O2 supply, as well as reduced need for the production of anaerobic ATP, must be considered. As a result, it has been suggested that the more endurance training is performed, the less lactate accumulates (Bonen et al., 2000;Joyner et al., 2008). ...
The blood lactate transfusion activity is characterized by triphasic nature. The required counterbalance between glycolysis and metabolism determines the flow of lactate into the muscles. Exercise (>80% of VO2max) has been observed to elevate the level of glycolysis and the gradual accretion of lactate to steadily higher levels, which consequently leads directly to fatigue. The purpose of this study was to investigate the influence of endurance training on the accumulation of lactate and whether it depends on the intensity of training or not. This study involved Sixteen participants, with mean age; 19.18 ± 1.0 years. Participants were asked to run at four various paces (9 km/h, 10.8 km/h, 12.6 km/h, and 14.4 km/h) for 60 minutes. After each exercise, blood lactate is immediately measured using Accusport and Polar devices. Statistically significant differences were seen in heart rate (HR), blood lactate (BL) and maximum lactate steady state (MLSS) after training (72.64 vs. 61.88), (158.22 vs 133.19), and (13.02 vs 8.41) > .01 respectively. Our results suggest that endurance training for 8 weeks can improve lactate threshold and blood lactate accumulation.
... In our study, there were no significant changes in the postexercise lactate removal rate after the 6-week IMT. Our initial hypothesis was that an increase in inspiratory muscle strength would accelerate the lactate removal rate by increasing the density of the transport protein of lactate through the lactate shuttle in the inspiratory muscles, 24 the monocarboxylate transporter type 1. 25 In our data, a nonsignificant tendency could be appreciated comparing HV-IMT and LV-IMT, respectively (Δ15.40 [21.49%] and Δ-4.14 [14.20%]; P = .338). ...
Purpose:
To analyze the effect of inspiratory muscle training (IMT) on the maximal inspiratory mouth pressure (MIP) and performance of elite swimmers.
Methods:
Eight participants performed a 3000-m swimming test (T-3000), followed by blood lactate measurements at 1 and 5 minutes postexercise.. The testing protocol was carried out before and after 6 weeks of IMT, in which a high-volume IMT group (HV-IMT) (n = 4) performed IMT twice a day-in the morning in a seated position and in the afternoon in a concurrent session of IMT and core muscle training. Also, a low-volume IMT group (LV-IMT) (n = 4) performed IMT in the morning session only.
Results:
After the intervention, both groups improved their MIP, HV-IMT (132.75 [27.42] to 156.75 [21.88] cmH2O; P = .010; d = 0.967) and LV-IMT (149.25 [22.82] to 171.50 [23.74] cmH2O; P = .013; d = 0.955), without a significant difference between groups (P = .855). Regarding swimming performance, there were no changes between groups in the T-3000 (P = .472) or lactate removal rate (P = .104).
Conclusion:
IMT increased inspiratory muscle strength in elite swimmers, but there was no association or meaningful impact on swimming performance.
... Lactate transport is mediated by a proton-linked monocarboxylate transporter (MCT1 & MCT4) [150]. Previous studies have demonstrated that MCT4 is related to lactate efflux from highly glycolytic muscle fibres, while MCT1 is associated with lactate uptake for further oxidation [150][151][152]. ...
A successful swimming performance is a multi-factorial accomplishment, resulting from a complex interaction of physical, biomechanical, physiological and psychological factors, all of which are strongly affected by the special medium of water as well as by genetic factors. The nature of competitive swimming is unique, as most of the competitive events last less than four minutes. Yet training regimens have an endurance nature (many hours and many kilometres of swimming every day), which makes it impossible to classify swimming by definitions of aerobic-type or anaerobic-type events, as in track and field sports. Therefore, genetic variants associated with swimming performance are not necessarily related to metabolic pathways, but rather to blood lactate transport (MCT1), muscle functioning (IGF1 axis), muscle damage (IL6) and others. The current paper reviews the main findings on the leading 12 genetic polymorphisms (located in the ACE, ACTN3, AMPD1, BDKRB2, IGF1, IL6, MCT1, MSTN, NOS3, PPARA, PPARGC1A, and VEGFR2 genes) related to swimming performance, while taking into consideration the unique environment of this sport.
... ,41 Forty-eight hours after OPBM, LDHA expression was significantly increased. Finally, the expression of monocarboxylate transporter 1 (MCT1) and MCT4, which are involved in the transport of lactate, increased markedly 48 h after OPBM.[46][47][48][49] 2.4 | Improved cell viability and angiogenic paracrine factor expression induced by OPBM after cell transplantation Next, we attempted to confirm the improved angiogenic paracrine factor expression, cell adhesion, and glycolysis observed in in vitro experiments. Accordingly, we used a mouse ischemic hindlimb model.Following the induction of ischemia, the mice were treated with a reduced number of cells (0.5 Â 10 6 cells; 150 μl), the conventional number of cells (1.5 Â 10 6 cells; 150 μl), or a reduced number of cells with OPBM (0.5 Â 10 6 cells; 150 μl) by injection into the gracilis muscle (Figure 4a). ...
Light‐based therapy such as photobiomodulation (PBM) reportedly produces beneficial physiological effects in cells and tissues. However, most reports have focused on the immediate and instant effects of light. Considering the physiological effects of natural light exposure in living organisms, the latent reaction period after irradiation should be deliberated. In contrast to previous reports, we examined the latent reaction period after light exposure with optimized irradiating parameters and validated novel therapeutic molecular mechanisms for the first time. we demonstrated an organic light‐emitting diode (OLED)‐based PBM (OPBM) strategy that enhances the angiogenic efficacy of human adipose‐derived stem cells (hADSCs) via direct irradiation with red OLEDs of optimized wavelength, voltage, current, luminance, and duration, and investigated the underlying molecular mechanisms. Our results revealed that the angiogenic paracrine effect, viability, and adhesion of hADSCs were significantly intensified by our OPBM strategy. Following OPBM treatment, significant changes were observed in HIF‐1α expression, intracellular reactive oxygen species levels, activation of the receptor tyrosine kinase, and glycolytic pathways in hADSCs. Additionally, transplantation of OLED‐irradiated hADSCs resulted in significantly enhanced limb salvage ratio in a mouse model of hindlimb ischemia. Our OPBM might serve as a new paradigm for stem cell culture systems to develop cell‐based therapies in the future. This article is protected by copyright. All rights reserved.
... Sox6 was previously reported as an important transcription factor involved in the regulation of slow myosin heavy chain gene [74], while Slc16a3 (MCT3-M/MCT4), which codifies for a lactate transporter, may be involved in the metabolism of specific myofibers. In fact, it is much more abundantly expressed in fast-twitch oxidative and fast-twitch glycolytic muscles than in slow-twitch oxidative muscles [75]. To validate this network and the suggested interactions between miRNAs and targets, we upregulated the expression of miR-208b or À214 in the C2C12 muscle cell line. ...
Non-coding RNAs represent the largest part of transcribed mammalian genomes and prevalently exert regulatory functions. Long non-coding RNAs (lncRNAs) and microRNAs (miRNAs) can modulate the activity of each other. Skeletal muscle is the most abundant tissue in mammals. It is composed of different cell types with myofibers that represent the smallest complete contractile system. Considering that lncRNAs and miRNAs are more cell type-specific than coding RNAs, to understand their function it is imperative to evaluate their expression and action within single myofibers. In this database, we collected gene expression data for coding and non-coding genes in single myofibers and used them to produce interaction networks based on expression correlations. Since biological pathways are more informative than networks based on gene expression correlation, to understand how altered genes participate in the studied phenotype, we integrated KEGG pathways with miRNAs and lncRNAs. The database also integrates single nucleus gene expression data on skeletal muscle in different patho-physiological conditions. We demonstrated that these networks can serve as a framework from which to dissect new miRNA and lncRNA functions to experimentally validate. Some interactions included in the database have been previously experimentally validated using high throughput methods. These can be the basis for further functional studies. Using database information, we demonstrate the involvement of miR-149, -214 and let-7e in mitochondria shaping; the ability of the lncRNA Pvt1 to mitigate the action of miR-27a via sponging; and the regulatory activity of miR-214 on Sox6 and Slc16a3. The MyoData is available at https://myodata.bio.unipd.it
... Si l'on s'intéresse maintenant à la localisation cellulaire, (Bonen, 2000) (Amemiya et al., 1995), NHE4 dans l'estomac et le rein (Orlowski et al., 1992), NHE5 se situe spécifiquement dans le cerveau (Baird et al., 1999). ...
Ce travail de thèse s’inscrit dans le cadre général de la physiologie énergétique, et comprend trois études, qui vont de l’exploration globale de l’Homme en mouvement (tests de terrain chez des athlètes de l’Equipe de France de Cyclisme, explorations à l’effort en laboratoire chez des cyclistes entrainés) jusqu’à des études du métabolisme musculaire par des techniques d’investigations cellulaires et moléculaires chez des sujets actifs. Ce travail a porté sur l’exercice de haute intensité générant de hauts niveaux de fatigue musculaire et sur les réponses adaptatives qui en résultent au niveau cardio-respiratoire et musculaire. La prise de bicarbonate de sodium contre placebo a permis d’étudier précisément le rôle de l’accumulation de protons au cours de séances de sprints en cyclisme. Grâce à ces travaux, nous avons pu montrer que si une alcalose induite n’améliorait pas systématiquement les performances de sprint en cyclisme, une perturbation importante du pH conduisait à des modifications du transport de l’oxygène pendant l’exercice, du fonctionnement des mitochondries après 24h de récupération, mais également de l’expression de certaines protéines impliquées dans la régulation du pH, à savoir le cotransporteur lactate/proton (MCT1) et sa protéine chaperonne CD147, ainsi que l’échangeur sodium/proton (NHE1). Ces modifications étaient en lien avec une réduction du stress oxydatif par l’alcalose induite, suggérant un rôle délétère de la carbonylation des protéines sur l’expression de ces protéines. Ces résultats permettent d’avoir un nouveau regard sur le rôle de l’acidose dans les mécanismes de régulation au niveau physiologique, cellulaire et moléculaire chez l’Homme.
... MCT1 belongs to proton-linked monocarboxylate transporters consisting of a family of 14 members within the MCT family of proteins as demonstrated by our phylogenetic analysis yielding 14 distinct clustering of mammalian taxa (Supplemental Fig. 7a). While the expression distribution of MCT isoforms has been shown to be organism and tissue specific, our RNA-Seq analysis of various tissues showed that MCT1 is the predominant MCT in both the fetal and adult heart (Supplemental Fig. 7b) 27 . ...
In the current study we examined several proteomic- and RNA-Seq-based datasets of cardiac-enriched, cell-surface and membrane-associated proteins in human fetal and mouse neonatal ventricular cardiomyocytes. By integrating available microarray and tissue expression profiles with MGI phenotypic analysis, we identified 173 membrane-associated proteins that are cardiac-enriched, conserved amongst eukaryotic species, and have not yet been linked to a ‘cardiac’ Phenotype-Ontology. To highlight the utility of this dataset, we selected several proteins to investigate more carefully, including FAM162A, MCT1, and COX20, to show cardiac enrichment, subcellular distribution and expression patterns in disease. We performed three-dimensional confocal imaging analysis to validate subcellular localization and expression in adult mouse ventricular cardiomyocytes. FAM162A, MCT1, and COX20 were expressed differentially at the transcriptomic and proteomic levels in multiple models of mouse and human heart diseases and may represent potential diagnostic and therapeutic targets for human dilated and ischemic cardiomyopathies. Altogether, we believe this comprehensive cardiomyocyte membrane proteome dataset will prove instrumental to future investigations aimed at characterizing heart disease markers and/or therapeutic targets for heart failure.
... Numerous studies show that MCT1 and MCT4 protein expression is increased in the skeletal muscle after exercise training and electrical stimulation in healthy humans [79][80][81]. MCT1 expression is increased after endurance training and its expression is correlated with the oxidative capacity [82], whereas MCT4 expression is increased following intensive exercise and related to the indexes of glycolytic metabolism [83]. Because MCT1 is mostly found in oxidative fibers and displays a higher affinity for L-lactate compared with MCT4, it has been suggested that MCT1 mainly handles the uptake of lactate and H + ions, whereas MCT4 is involved in lactate and H + efflux [84][85][86][87]. ...
Type 2 diabetes (T2D), along with obesity, is one of the leading health problems in the world which causes other systemic diseases, such as cardiovascular diseases and kidney failure. Impairments in glycemic control and insulin resistance plays a pivotal role in the development of diabetes and its complications. Since skeletal muscle constitutes a significant tissue mass of the body, insulin resistance within the muscle is considered to initiate the onset of diet-induced metabolic syndrome. Insulin resistance is associated with impaired glucose uptake, resulting from defective post-receptor insulin responses, decreased glucose transport, impaired glucose phosphorylation, oxidation and glycogen synthesis in the muscle. Although defects in the insulin signaling pathway have been widely studied, the effects of cellular mechanisms activated during metabolic syndrome that cross-talk with insulin responses are not fully elucidated. Numerous reports suggest that pathways such as inflammation, lipid peroxidation products, acidosis and autophagy could cross-talk with insulin-signaling pathway and contribute to diminished insulin responses. Here, we review and discuss the literature about the defects in glycolytic pathway, shift in glucose utilization toward anaerobic glycolysis and change in intracellular pH [pH]i within the skeletal muscle and their contribution towards insulin resistance. We will discuss whether the derangements in pathways, which maintain [pH]i within the skeletal muscle, such as transporters (monocarboxylate transporters 1 and 4) and depletion of intracellular buffers, such as histidyl dipeptides, could lead to decrease in [pH]i and the onset of insulin resistance. Further we will discuss, whether the changes in [pH]i within the skeletal muscle of patients with T2D, could enhance the formation of protein aggregates and activate autophagy. Understanding the mechanisms by which changes in the glycolytic pathway and [pH]i within the muscle, contribute to insulin resistance might help explain the onset of obesity-linked metabolic syndrome. Finally, we will conclude whether correcting the pathways which maintain [pH]i within the skeletal muscle could, in turn, be effective to maintain or restore insulin responses during metabolic syndrome.
... With the restoration of flow during reperfusion, the accumulating lactate and H + s can now be washed out and removed from cardiac myocytes through the actions of the monocarboxylic lactate transporters. 19 Furthermore, increased activity of the Na + /H + exchanger can reduce the cytosolic H + load in exchange for Na + , which causes an intracellular Na + overload. To reduce the Na + overload, the Na + /Ca 2+ exchanger can function in reverse mode, extruding Na + into the extracellular space while countertransporting Ca 2+ . ...
As an organ that must continuously pump oxygenated blood throughout the body, the heart has an enormous metabolic demand, which is primarily met via oxidative metabolism of fatty acids and carbohydrates. Because of its high metabolic demand, during times of reduced oxygen supply such as ischemia, the heart becomes highly susceptible to injury, and if flow is not re-established, myocardial tissue is lost and can result in death (myocardial infarction). Of interest, both myocardial ischemia and reperfusion are associated with a number of perturbations in energy metabolism that contribute to the pathology of ischemic heart disease. This includes marked elevations in glycolysis to counteract the reduction in oxidative metabolism, whereas fatty acids predominate as the primary fuel source for residual oxidative metabolism. During the early stages of cardiac recovery after successful reperfusion of the ischemic heart, fatty acid oxidation rates also rapidly recover at the expense of low glucose oxidation rates. These metabolic perturbations increase myocardial acidosis due to glycolysis being uncoupled from glucose oxidation, which impairs cardiac efficiency. As such, therapeutic approaches to stimulate glucose oxidation or inhibit fatty acid oxidation have the potential to correct dysregulated myocardial energy metabolism during ischemia and reperfusion, which improves cardiac efficiency and may lead to improved clinical outcomes in people with ischemic heart disease. L Heart Metab. 2020;81:xxx
... MCT1, which usually transports lactate in symport with a proton, is a potential carrier for this process. 28,31,32 As the first succinate pKa is $5.6, 33 at the pH within ischaemic tissues ($6.5) 26,27 $10% of the succinate in the myocardium would be in the monocarboxylate form, which may be transported by MCT1. 6,28,34 Supporting this possibility, expressing MCT1 in Xenopus oocytes led to succinate uptake into the cells, but only when incubated in a medium at acidic (pH $6) pH. ...
Aims:
Succinate accumulates several-fold in the ischemic heart and is then rapidly oxidised upon reperfusion, contributing to reactive oxygen species (ROS) production by mitochondria. In addition, a significant amount of the accumulated succinate is released from the heart into the circulation at reperfusion, potentially activating the G-protein coupled succinate receptor (SUCNR1). However, the factors that determine the proportion of succinate oxidation or release, and the mechanism of this release, are not known.
Methods and results:
To address these questions, we assessed the fate of accumulated succinate upon reperfusion of anoxic cardiomyocytes, and of the ischemic heart both ex vivo and in vivo. The release of accumulated succinate was selective and was enhanced by acidification of the intracellular milieu. Furthermore, pharmacological inhibition, or haploinsufficiency of the monocarboxylate transporter 1 (MCT1) significantly decreased succinate efflux from the reperfused heart.
Conclusion:
Succinate release upon reperfusion of the ischemic heart is mediated by MCT1 and is facilitated by the acidification of the myocardium during ischemia. These findings will allow the signalling interaction between succinate released from reperfused ischemic myocardium and SUCNR1 to be explored.
Translational perspectives:
In this study we demonstrate that succinate efflux upon reperfusion of the ischemic myocardium is mediated by the monocarboxylate transporter 1 (MCT1) and is enhanced by the ischemic acidification of the heart. These findings are an important advance in understanding how succinate is released upon reperfusion of ischemic organs. While this pathway is therapeutically tractable, greater understanding of the effects of succinate release is required before exploring this possibility.
... In skeletal muscles, MCT1 and MCT4 are present and both isoforms have a fibre specific distribution. MCT1 is responsible for lactate assimilation and mainly existing in oxidative muscle fibres, while MCT4 is basically in glycolytic muscle fibres and relevant for lactate depletion [26,27]. ...
PURPOSE: A number of physiological diagnostics were developed. However, the timeline-related diagnostics of maximal anaerobic glycolytic capacity remain unclear. The objective of this study was to evaluate the reliability and validity of a sprint running test to assess the anaerobic capacity.METHODS: The study was divided into three parts. Sixty-one male (24±4 years, 181.0±4.3 cm; 78.5±5.9 kg) and twelve female (25±3 years, 167.0±0.6 cm, 60.4±5.7 kg) sports students participated in this study. Twenty-five subjects (13 males, 24±2 years, 181.0±0.5 cm, 78.5±5.9 kg; 12 females, 25±3 years, 167.0±0.6 cm, 60.4±5.7 kg) performed incremental step tests at running track and several linear sprints on a running track (LSRT) with different time durations (8, 10, 12, and 14 seconds)(part I) on different days. Twenty-five male subjects (24±3 years, 180.7±6.7 cm, 84.6±8.8 kg) conducted a 10 or 12 second sprint running on a non-motorized treadmill (NMT)(part II). In part III, twenty-three male subjects (24±2 years, 181.4±5.8 cm, 74.5±7.4 kg) ran a 10 second LSRT and NMT on consecutive days. Capillary blood samplings were taken before (Lac<sub>r</sub>) and after the sprint running for ten minutes at one minute intervals to find out maximal lactate concentration after exercise and to calculate the maximum lactate production rate (LPR<sub>max</sub>).RESULTS: For all parts reliability for LPR<sub>max</sub> was proven (Part I: 8 seconds: ICC: r =.89; 10 seconds: ICC: r =.82; 12 seconds: ICC: r =.92; 14 seconds: r =.84, respectively; Part II: 10 seconds: ICC: r =.76; 12 seconds: ICC: r =.79). To analyze validity for LPR<sub>max</sub>, Part III was conducted and proven valid (ICC: r =.96, p=.074).CONCLUSIONS: We demonstrate that LSRT and NMT reliably determine anaerobic capacity and can be used as a valid tool for physiological performance diagnostics.
... Treatment with oligomycin led to a ~30% increase in the extracellular acidification rate (ECAR) of infarct organoids compared with the control organoids (Fig. 3e,f). This was accompanied by a biomimetic accumulation of l-lactate in infarct organoid medium (Fig. 3g), which was attributed to the enhanced production of lactic acid, supported by the increased ratio of LDHA:LDHB and decreased ratio of SLC16A1:SLC16A3 in infarct organoids 46,[49][50][51][52][53] (Fig. 3h). This evidence strongly supports a shift towards glycolytic metabolism in infarct organoids. ...
Environmental factors are the largest contributors to cardiovascular disease. Here we show that cardiac organoids that incorporate an oxygen-diffusion gradient and that are stimulated with the neurotransmitter noradrenaline model the structure of the human heart after myocardial infarction (by mimicking the infarcted, border and remote zones), and recapitulate hallmarks of myocardial infarction (in particular, pathological metabolic shifts, fibrosis and calcium handling) at the transcriptomic, structural and functional levels. We also show that the organoids can model hypoxia-enhanced doxorubicin cardiotoxicity. Human organoids that model diseases with non-genetic pathological factors could help with drug screening and development.
... This transporter is important in directing the energy-compound lactate between cells and tissues. The intervention of the Nano-tesla frequency on the thyroid gland of the IG after exercise, influences the creatine cyten (HaCat) and the oxidative transport of haemoglobin; these could be one of the reasons for reduction of the lactate value (Bonen, 1998). Combined, these results indicate an increased rate of rejuvenation of the test subjects exposed to Thyroid stimulation via Nano-tesla frequency. ...
This study seeks to answer the following question "Whether the application of the Thyreogym device (a non-invasive stimulation of the thyroid gland) can be proven to significantly influence the metabolic system, as indicated by measurable heart rate variability and lactate levels. The Thyreogym device s!mulates the thyroid in the low-frequency range. As has already been shown in preliminary studies (Wetzel et al. 2011), the light stimulation of the Tyroid (in Nano Tesla area) stimulates the metabolism, activates human fibroblast (AG01522), and creatincyten (HaCat). For this study, two physiological parameters (heart rate variability and lactate value) were collected from healthy subjects. At the beginning of the study we collected blood samples in order to analyse baseline TSH, T3 and T4 values. After all baseline measurements had been taken, test subjects were subjected to a three-week performance control utilising a treadmill-based tread test. The device was worn by the intervention group (Group A = IG) immediately between the 500 meter runs for eight minutes in the rest. The non-intervention control group (Group B = NIG) were subjected to the identical treadmill-based tread tests, however, they were not exposed to the device. The subjects of the study were athletes competing in triathlon, athletics, track and field, volleyball, hockey, football, and handball. Test subject with thyroid hyperfunction or hypofunction, infectious diseases, diseases of the immune-system or neurological diseases were excluded. Keywords: non-invasive stimulation of the thyroid gland in low-frequency range (Nano Tesla range), heart rate variability, HRV autonomic modulation, lactate value, recover from exercise , exercise intervention (running test distance 500 meters on an indoor treadmill). Aim: The purpose of this study was to monitor the level of influence of the stimulation of the thyroid gland and the subsequent effect on the rate of regeneration. By measuring heart rate variability (HRV) as a non-invasive approach to the ANS-function, and the lactate value as the threshold output, we could evaluate the loading work progress of the muscle system during exercise and after exercise. Method: An initial examination was conducted, utilising an anamnesis sheet, resting HRV, body height, body weight, as well as blood tests TSH, T3, T4 to exclude a metabolic disease or an overactive or hypothyroid condition. At this point, all study subjects who identified as having infectious diseases, or immune and nervous system diseases, were excluded from participation in the study. Statistical designed in accordance with ANOVA 2x3x5 to effective strength configuration to η 2 partial after η 2 p ≥.0099 low; η 2 p ≥.0588 middle; η 2 p ≥.1379 large was elected (Cohen, 1988). Results: The results of the study indicate that the stimulation of the thyroid by the device, has a positive effect on the athlete's ability to rejuvenate after being exposed to a load phase. Heart rate measurements during and after load phases were 8-10 BPM lower in the intervention group, indicating enhanced rejuvenation capabilities. In addition, subjects from the intervention group displayed lower lactate formulation during the load phase, and enhanced lactate reduction capabilities in the post load phase; tests showed reductions of-0.8mmol to-1.4mmol per 20μl capillary blood, when compared to baseline measurements. The results of this study enhance the existing state of research on the physical responses to thyroid stimulation. They also serve to illustrate a positive effect correlation between the applications of the device and enhanced metabolic system rejuvenation after exposure to load. Conclusion: Non-invasive stimulation of the Thyroid gland could be helpful to support or increase regenerative rates after periods of loads from sports activity. It could also play a helpful role in sports therapy. 2
... Direct inhibition of MCT transport activity by small molecule inhibitors like AR-C155858, AZD3965, syrosingopine or diclofenac is considered a therapeutic strategy for tumor treatment [47,[65][66][67][68]. Since metabolon disruption reduces, but not fully abolishes MCT transport activity, direct inhibition of MCT1/4 seems more efficient for cancer treatment on the cellular level. However, MCTs are ubiquitously expressed in the human body and play a central function in the energy metabolism of a wide range of tissues, including heart and skeletal muscle, liver and brain [68][69][70][71]. Therefore, systemic application of a high dose of MCT inhibitors, which would be required for full inhibition of MCT transport activity in a tumor, could be expected to produce severe side effects in other tissues. ...
Tumor cells rely on glycolysis to meet their elevated demand for energy. Thereby they produce significant amounts of lactate and protons, which are exported via monocarboxylate transporters (MCTs), supporting the formation of an acidic microenvironment. The present study demonstrates that carbonic anhydrase IX (CAIX), one of the major acid/base regulators in cancer cells, forms a protein complex with MCT1 and MCT4 in tissue samples from human breast cancer patients, but not healthy breast tissue. Formation of this transport metabolon requires binding of CAIX to the Ig1 domain of the MCT1/4 chaperon CD147 and is required for CAIX-mediated facilitation of MCT1/4 activity. Application of an antibody, directed against the CD147-Ig1 domain, displaces CAIX from the transporter and suppresses CAIX-mediated facilitation of proton-coupled lactate transport. In cancer cells, this “metabolon disruption” results in a decrease in lactate transport, reduced glycolysis, and ultimately reduced cell proliferation. Taken together, the study shows that carbonic anhydrases form transport metabolons with acid/base transporters in human tumor tissue and that these interactions can be exploited to interfere with tumor metabolism and proliferation.
... http://dx.doi.org/10.1101/625673 doi: bioRxiv preprint first posted online May. 2, 2019; 9 including heart and skeletal muscle, liver and brain [77][78][79][80]. Therefore, systemic application of a high dose of MCT inhibitors, which would be required for full inhibition of MCT transport activity in a tumor, could be expected to produce severe side effects in other tissues. ...
Tumor cells rely on glycolysis to meet their elevated demand for energy. Thereby they produce significant amounts of lactate and protons, which are exported via monocarboxylate transporters (MCTs), supporting the formation of an acidic microenvironment. The present study demonstrates that carbonic anhydrase IX (CAIX), one of the major acid/base regulators in cancer cells, forms a protein complex with MCT1 and MCT4 in tissue samples from human breast cancer patients, but not healthy breast tissue. Formation of this transport metabolon requires binding of CAIX to the Ig1 domain of the MCT1/4 chaperon CD147 and is required for CAIX-mediated facilitation of MCT1/4 activity. Application of an antibody, directed against the CD147-Ig1 domain, displaces CAIX from the transporter and suppresses CAIX-mediated facilitation of proton-coupled lactate transport. In cancer cells, this 'metabolon disruption' results in a decrease in lactate transport, reduced glycolysis and ultimately reduced cell proliferation. Taken together, the study shows that carbonic anhydrases form transport metabolons with acid/base transporters in human tumor tissue and that these interactions can be exploited to interfere with tumor metabolism and proliferation.
... Several drug transporters including oligopeptide transporters (PEPTs), breast cancer resistance protein (BCRP), organic cation transporters (OCTs), organic anion-transporting polypeptides (OATPs) and P-glycoprotein (P-GP) have been identified to account for intestinal absorption of drugs (Estudante et al., 2013). Monocarboxylate transporters (MCTs/SLC16A) have been identified to transport monocarboxylic acids, which are also associated with several diseases, such as atherosclerosis, cancer, mental retardation and cataract formation (Bonen, 2000;Bonen et al., 2006;Jones et al., 2017). MCT6 This article has not been copyedited and formatted. ...
Generally, diabetes remarkably alters the expression and function of intestinal drug transporters. Nateglinide and bumetanide are substrates of monocarboxylate transporter 6 (MCT6). We investigated whether diabetes down-regulated the function and expression of intestinal MCT6 and the possible mechanism in diabetic rats induced by a combination of high-fat diet and low-dose streptozocin. Our results indicated that diabetes significantly decreased the oral plasma exposure of nateglinide. The plasma peak concentration and area under curve in diabetic rats were 16.9% and 28.2% of control rats, respectively. Diabetes significantly decreased the protein and mRNA expressions of intestinal MCT6 and oligopeptide transporter 1 (PEPT1) but up-regulated peroxisome proliferator-activated receptor γ (PPARγ) protein level. Single-pass intestinal perfusion demonstrated that diabetes prominently decreased the absorption of nateglinide and bumetanide. The MCT6 inhibitor bumetanide, but not PEPT1 inhibitor glycylsarcosine, significantly inhibited intestinal absorption of nateglinide in rats. Coadministration with bumetanide remarkably decreased the oral plasma exposure of nateglinide in rats. High concentrations of butyrate were detected in the intestine of diabetic rats. In Caco-2 cells (a human colorectal adenocarcinoma cell line), bumetanide and MCT6 knockdown remarkably inhibited the uptake of nateglinide. Butyrate down-regulated the function and expression of MCT6 in a concentration-dependent manner but increased PPARγ expression. The decreased expressions of MCT6 by PPARγ agonist troglitazone or butyrate were reversed by both PPARγ knockdown and PPARγ antagonist 2-chloro-5-nitro-N-phenylbenzamide (GW9662). Four weeks of butyrate treatment significantly decreased the oral plasma concentrations of nateglinide in rats, accompanied by significantly higher intestinal PPARγ and lower MCT6 protein levels. In conclusion, diabetes impaired the expression and function of intestinal MCT6 partly via butyrate-mediated PPARγ activation, decreasing the oral plasma exposure of nateglinide. Copyright © 2019 by The American Society for Pharmacology and Experimental Therapeutics.
... The movement of lactic acid across the cell membrane is mainly mediated by proton-linked mono-carboxylate transporters (MCTs) [13][14][15], which are widely distributed throughout the body of all living organisms, even on circulating blood cells and brain astrocytes [16,17]. In total, 14 types of MCTs (MCT 1-14) have been identified, with each type showing specific tissue distribution across the body [18,19]. ...
Background
The central nervous system was previously thought to draw oxygen and nutrition from the arteries and discharge carbon dioxide and other metabolic wastes into the venous system. At present, the functional role of cerebrospinal fluid in brain metabolism is not fully known.
Methods
In this prospective observational study, we performed gas analysis on venous blood and cerebrospinal fluid simultaneously acquired from 16 consecutive preoperative patients without any known neurological disorders.
Results
The carbon dioxide partial pressure (pCO2) (p < 0.0001) and lactic acid level (p < 0.001) in the cerebrospinal fluid were significantly higher than those in the peripheral venous blood, suggesting that a considerable proportion of metabolic carbon dioxide and lactic acid is discharged from the central nervous system into the cerebrospinal fluid. The oxygen partial pressure (pO2) was much higher in the cerebrospinal fluid than in the venous blood, corroborating the conventional theory of cerebrospinal fluid circulatory dynamics. The pCO2 of the cerebrospinal fluid showed a strong negative correlation with age (R = − 0.65, p = 0.0065), but the other studied variables did not show significant correlation with age.
Conclusion
Carbon dioxide and lactic acid are discharged into the circulating cerebrospinal fluid, as well as into the venules. The level of carbon dioxide in the cerebrospinal fluid significantly decreased with age.
... MCT3, which is even less described, was also expressed in myotubes in the present study, but protein expression of this transport was unaffected by different concentrations of lactic acid. Higher abundance of MCT3 in fast-twitch glycolytic and fast-twitch oxidative than in slow-twitch muscle fibers has been reported, and it appears to be involved in the efflux of lactic acid 25 . It is important to keep in mind that in vivo, most muscles contain a mixture of both primarily glycolytic and primarily oxidative muscle fibers, and the proportion of each fiber type will depend on many factors from genetics to whether that particular muscle uses high-intensity exercise (glycolytic) or endurance exercise (oxidative). ...
Once assumed only to be a waste product of anaerobe glycolytic activity, lactate is now recognized as an energy source in skeletal muscles. While lactate metabolism has been extensively studied in vivo, underlying cellular processes are poorly described. This study aimed to examine lactate metabolism in cultured human myotubes and to investigate effects of lactate exposure on metabolism of oleic acid and glucose. Lactic acid, fatty acid and glucose metabolism were studied in myotubes using [14C(U)]lactic acid, [14C]oleic acid and [14C(U)]glucose, respectively. Myotubes expressed both the MCT1, MCT2, MCT3 and MCT4 lactate transporters, and lactic acid was found to be a substrate for both glycogen synthesis and lipid storage. Pyruvate and palmitic acid inhibited lactic acid oxidation, whilst glucose and α-cyano-4-hydroxycinnamic acid inhibited lactic acid uptake. Acute addition of lactic acid inhibited glucose and oleic acid oxidation, whereas oleic acid uptake was increased. Pretreatment with lactic acid for 24 h did not affect glucose or oleic acid metabolism. By replacing glucose with lactic acid during the whole culturing period, glucose uptake and oxidation were increased by 2.8-fold and 3-fold, respectively, and oleic acid oxidation was increased 1.4-fold. Thus, lactic acid has an important role in energy metabolism of human myotubes.
... This can be explained by the assertion that trained people experience lower serum lactate than untrained people when exercising at the same absolute workload (Triplett-McBride, 1996). This was in agreement with the result of the study done by Brooks, (2000) and Bonen, (2000) which revealed that athletes stay fit by training and such training generates big lactate load that the body adapt by building up mitochondria for quicker clearance of serum lactate to prevent accumulation. Tarnopolsky et al., 2006 andCarter et al., 2001 revealed that training enables growing of mitochondria in muscle cells, the mitochondria which is the power house of the cell where lactate is burned for energy. ...
Lactate is an end product of glucose metabolism that is usually produced in a larger quantity during exercise. This increase in production during exercise has been understood to be the reason for fatigue. The aim of this study is to determine the responses of serum lactate to aerobic exercise among amateur athletes and non-athletes. 48 consenting males (24 amateur athletes and 24 non-athletes) participated in this comparative quasi-experimental design. Subjects cycled on a bicycle ergometer to attain moderate intensity exercise target heart rate (MIETHR) and maintained the MIETHR till exhaustion (15 on Borgs scale or volitional exertion) while the serum lactate was measured at intervals. Data were analyzed with descriptive statistics and inferential statistics of Analysis of variance (ANOVA). Alpha level was set at p < 0.05. The mean age of the participants was 26.08±2.28 and 28.13±1.51 for the athletes and non-athletes respectively. There was a significant difference p=0.001 Training induced adaptations include a lower serum lactate level, a point that should be noted in studying of metabolic adaptations.
... Pela razão mencionada, durante um exercício contínuo, o "steady-state" das CSL apresenta-se como uma das condições para suportar uma carga correspondente à V4 por um tempo prolongado. A CSL reflete o equilíbrio entre a taxa de produção de lactato a nível muscular esquelético e os inúmeros mecanismos fisiológicos associados ao seu "clearence" A composição dos diferentes tipos de fibras ( Brooks & Mercier 1994;Ivy et alii, 1980), a capacidade respiratória muscular ( Ivy et alii, 1980), a densidade capilar ( Tesch, Sharp & Daniels, 1981), a mobilização preferencial de gorduras como substrato energético, relativamente aos hidratos de carbono, para a mesma intensidade relativa de exercício ( Beneke, Hütler & Leithãuser, 2000;Holloszy, 1996), assim como o transporte facilitado do lactato através das membranas celulares quer para a circulação quer para a mitocôndria (através da ação dos transportadores proteícos de monocarboxilato MCT) ( Bonen, 2000;Brooks, 2000;Gladen, 2000a,b), têm sido descritos como alguns dos fatores que podem influenciar as CSL. De fato, o treino de resistência induz modificações nos fatores acima mencionados, os quais se apresentam relacionados com a capacidade de oxidação do piruvato e com o aumento da eficiência das vias metabólicas conducentes à oxidação, libertação e consumo do lactato ( Brooks, 2000;Gladen, 2000a,b). ...
Tem sido assumido que a carga correspondente a uma concentração sangüínea de lactato (CSL) de 4 mmol/1, determinada a partir do limiar aeróbio-anaeróbio, pode ser mantida em adultos durante o teste constante de 30 min (“steady-state” CSL). A escassez de estudos que confirmem se tal fenômeno ocorre em jovens atletas, poderá justificar a possibilidade de considerar CSL diferentes para avaliação e desenvolvimento da capacidade aeróbia nesta população. Os objetivos do presente estudo foram: a) investigar a existência de um “steady-state” das CSL durante uma carga constante de 30 min (realizada a uma intensidade correspondente a 4 mmo/1) em jovens atletas; e b) verificar a existência de possíveis diferenças intra-individuais nas CSL durante o teste. Treze jovens atletas (idade: 16,07 ± 1,38 anos; massa: 61,0 ± 6,69 kg; 171,0 ± 5,6 cm) realizaram um teste incrementai e um teste de carga constante. O teste incrementai foi utilizado para determinar a carga correspondente a uma CSL de 4 mmol/1 ( V 4). Três dias depois os sujeitos realizaram um teste de carga constante de 30 min a uma intensidade correspondente à V 4 previamente determinada. No decorrer de ambos os testes foram recolhidas amostras de sangue capilar do lóbulo da orelha e imediatamente analisadas num analisador sangüíneo enzimático (YSI 1500 L - Sport) para determinação das CSL. Durante o teste constante, as amostras sangüíneas foram recolhidas aos 5o., 10o., 15o., 20o., 25o. e 30o. min. Como procedimentos estatísticos foram utilizados, para além das medidas descritivas, (média e desvio padrão), a análise de variância de medidas repetidas. O valor médio da V4 foi 3,9 ± 0,28 m/s. Dois dos 13 sujeitos foram incapazes de terminar o teste de 30 min (CSL finais de 9,82 e 7,25 mmol/1, respectivamente). De acordo com o critério de Heck et alli (1985c) os restantes sujeitos completaram o teste com CSL médias de 4,15 ± 1,11 mmol/1. As CSL médias nos diferentes momentos (5o., 10o., 15o., 20o., 25o. e 30o. min) do teste constante foram, respectivamente: 4,21; 4,50; 4,67; 4,57; 4,87 e 4,25 mmo/1. Não foram observadas diferenças significativas nas observações repetidas (F(5, 6) = 1,035; p = 0,474), indicando a inexistência de diferenças intra-individuais nas CSL durante o teste de 30 min. Deste modo, concluímos que a carga correspondente a uma CSL de 4 mmol/1 pode ser suportada, por jovens atletas, em condições de “steady-state” Os resultados sugerem que o referencial láctico a adotar na avaliação e treino da capacidade aeróbia em jovens não parece diferir do utilizado em adultos.
... They stated that training selectively enhanced tissue antioxidant defences by increasing the glutathione content and upregulating glutathione enzyme activities in the heart. Interestingly, lactate traverses the cell membranes of many tissues, including the heart and skeletal muscle via a facilitated monocarboxylate transport system MeT (54). Researchers had shown that with diabetes, MeT is reduced in the heart and exercise training alleviated these diabetesinduced reductions (55). ...
Consequently, physical exercise is frequently recommended for the treatment of type I and type II diabetes (6&7) and many investigators have demonstrated that exercise training is a cornerstone non-pharmacological treatment of cardiac and metabolic diseases (8&9). Regular physical exercise is an important component in the prevention and treatment of diabetes as it contributes to lowering blood glucose level and improving insulin action (10& 11). Moreover, physical training has a favorable effect on certain risk factors for coronary heart disease (e.g., lipids profile, arterial hypertension smoking (12). The molecular basis for exercise induced cardioprotection involves counteracting ischemia reperfusion injury and improving cardiac antioxidant capacity (13). Consequently, these benefits have been shown in the Diabetes Prevention Program in which physical activity in the form of walking 30 minutes/day on most days of the week was encouraged (10). Therefore, the aim ofthis work was to evaluate the effect of exercise on the structural changes As the rate of diabetes mellitus continues to increase, physical activity continues to he a fundamental form of therapy. Exercise influences several aspects ofdiabetes and these have led many diabetologists to consider exercise beneficial in treatment of diabetes. So, this study was conducted to investigate the role of exercise in treatment of cardiomyopathy due to type II induced diabetes in alhino rats. Forty rats were used and divided into two groups, control (1) and diabetic (H). Then, both groups were subdivided into two subgroups a&b, non exercised and exercised. Type II diabetes was induced in group II by oral 50% fructose solution for 8 weeks. Exercise training consisted of swimming for 4 weeks. It started in the exercise subgroups initially for 5min/day and ultimately reached Ihourl day for the last 2 weeks. In subgroup IIa, the mean blood glucose concentration was 263.8 mg% and there was a significant increase in the mean diameter ofthe cardiac muscle jibers (P<0.01). There were areas ofdegeneration in the cardiomyocytes together with disruption ofthe striated appearance. Electron microscopic examination revealed myofilamentous degeneration with deformed mitochondria. In subgroup lib, the mean blood glucose level was 108.6 mg% ami there was a non significant increase in the mean diameter ofthe cardiac musclejibers (P>O.OS). Exercise reversed the histopathological changes so that the myocardium was more or less normal in appearance. Therefore, it was concluded that exercise had a beneficial role in treating the diabetic induced changes in the cardiac muscle.
... or gluconeogenesis (i.e., liver and kidney; Halestrap, 2012). Monocarboxylate transporter 4 increases in fast, glycolytic muscles as it primarily functions to transport lactate out of the cell (Pilegaard et al., 1999b;Bonen, 2000;Dimmer et al., 2000;Fox et al., 2000). ...
Acute activation of AMP-activated protein kinase (AMPK) increases monocarboxylate transporter (MCT) expression in skeletal muscle. However, the impact of chronic activation of AMPK on MCT expression in skeletal muscle is unknown. To investigate, MCT1, MCT2, and MCT4 mRNA expression and protein abundance were measured in the longissimus lumborum (glycolytic), masseter (oxidative), and heart from wild-type (control) and AMPK γ3R200Q pigs. The AMPK γ3R200Q gain in function mutation results in AMPK being constitutively active in glycolytic skeletal muscle and increases energy producing pathways. The MCT1 and MCT2 mRNA expression in muscle was lower (P < 0.05) from both wild-type and AMPK γ3R200Q animals compared to other tissues. However, in both genotypes, MCT1 and MCT2 mRNA expression was greater (P < 0.05) in the masseter than the longissimus lumborum. The MCT1 protein was not detected in skeletal muscle, but MCT2 was greater (P < 0.05) in muscles with an oxidative muscle phenotype. Monocarboxylate transporter 2 was also detected in muscle mitochondria and may explain the differences between muscles. The MCT4 mRNA expression was intermediate among all tissues tested and greater (P < 0.05) in the longissimus lumborum than the masseter. Furthermore, MCT4 protein expression in the longissimus lumborum from AMPK γ3R200Q animals was greater (P < 0.05) than in the longissimus lumborum from wild-type animals. In totality, these data indicate that chronic AMPK activation simultaneously increases MCT2 and MCT4 expression in skeletal muscle. © 2017 American Society of Animal Science. All rights reserved.
... The knowledge about these metabolic effects of different exercise training programs is of huge importance for the regulation of resistance training. Increased La associated with an increased IGF-1 level seems to be potent stimuli for effective responses to muscular adaptations [33,34]. Studies showed that lactate and a metabolic stress-induced reduced pH level plays a decisive role for the adaptation of muscles to exercise stimuli as well as for the hypertrophy [35][36][37]. ...
The knowledge about metabolic effects of different training programs is of huge importance for the regulation of resistance training. Most studies investigated the effect of the variation of a single load character on physiological parameters such as blood lactate and oxygen intake. Therefore, the present study investigates the physiological reactions on practice-oriented resistance exercise programs with different loads and training volumes. 24 male subjects (25.6 ± 5.9 years, 171 ± 4 cm, 74.3 ± 5.3 kg) were randomly assigned into three different resistance training groups (G1 = 30/30/3/60, G2 = 50/20/3/90, G3 = 70/10/4/90; respectively % of one repetition maximum /repetitions /number of sets /rest between sets). Exercises squats, bench press, biceps curl, french press, and rowing were completed in a randomized order. Heart rate (HR), breathing frequency (BF), oxygen uptake and blood lactate (La) were measured at the end of each set. Mean value of all sets in each exercise was used for statistical analysis (ANOVA). Performance was calculated using the relative power index (RPI). There were significant differences in the RPI (ANOVA p <0.01) between the three groups (G1 < G2 < G3). Mean values of all exercises showed a significant difference of the between G2 and G3 (ANOVA p<0.05), but no differences in other parameters were found (ANOVA p>0.05). The and HR showed significant differences between the exercises (ANOVA p<0.05). Independent of the three training programs, significant differences in HR, RF and but not in La were shown between the exercises. In summary, the present study shows, that the physiological effects of the three different strength training programs on HR, La and BF differs very little, despite the strongly differing RPI. The selection of the exercise seems to be especially important for the acute adaptations of and HR, but not for lactate accumulation.
... En el presente estudio el valor de lactato máximo aumentó significativamente tras la aplicación de la fase de entrenamiento, a diferencia de lo que se afirma en otros estudios 24,25 . Aunque se ha demostrado la importancia de aumentar el valor de lactato máximo, es verdad que puede mejorarse el rendimiento por el aumento del número de transportadores de lactato 26,27 . ...
Before an important competition, the training dose should be reduced with the intention of improving the performance. This study aims to determine the impact of the implementation of a mathematical model during the non-linear, progressive reduction of the training load or taper in young swimmers. Ten swimmers were tested before and after the taper. The control variables measured during the training were the volume, the relationship between the volume and the mean intensity of training season (MITS) and the frequency of training. The decrease in the volume of training after applying the mathematical model was of 30.9% in the first week, and of 71.2% in the second week. The decrease in MITS after applying the mathematical model was of 30.8% in the first week, and of 71.1% in the second week. The training frequency was decreased by 10% in the first week, and up to 40% in the second week. The records obtained between the first and the second tests were significantly better (p < 0.05). The maximum lactate production also increased significantly (p < 0.05), unlike the speed of lactate clarifying that it did not. The correlation between lactate and the maximum mark obtained was significant (p < 0.05). The value SPE (subjective perception of effort) after applying the mathematical model decreased, but not significantly (p > 0.05). These data indicate that the taper proposed does not cause loss of sensation or training, since the records improved significantly, as did the maximum production of lactate, showing a high correlation between maximum lactate and record.
... This family of transporters moves lactate and a proton down a concentration gradient, which determines the directionality of transport. Similar to LDH, different MCT isoforms are expressed in tissue types according to their oxidative capacity [233,234]. For example, MCT1 is high in oxidative cell types like muscle sarcolemma [235], and increases with training. ...
Cancer is a disease characterized by unrestrained cellular proliferation. In order to sustain growth, cancer cells undergo a complex metabolic rearrangement characterized by changes in metabolic pathways involved in energy production and biosynthetic processes. The relevance of the metabolic transformation of cancer cells has been recently included in the updated version of the review "Hallmarks of Cancer", where the dysregulation of cellular metabolism was included as an emerging hallmark. While several lines of evidence suggest that metabolic rewiring is orchestrated by the concerted action of oncogenes and tumor suppressor genes, in some circumstances altered metabolism can play a primary role in oncogenesis. Recently, mutations of cytosolic and mitochondrial enzymes involved in key metabolic pathways have been associated with hereditary and sporadic forms of cancer. Together, these results suggest that aberrant metabolism, once seen just as an epiphenomenon of oncogenic reprogramming, plays a key role in oncogenesis with the power to control both genetic and epigenetic events in cells. In this review, we discuss the relationship between metabolism and cancer, as part of a larger effort to identify a broad-spectrum of therapeutic approaches. We focus on major alterations in nutrient metabolism and the emerging link between metabolism and epigenetics. Finally, we discuss potential strategies to manipulate metabolism in cancer and tradeoffs that should be considered. More research on the suite of metabolic alterations in cancer holds the potential to discover novel approaches to treat it.
... For the aspect of inflammatory and oxidative stress dependent intensity of exercise (Azizbeigi et al., 2015), we suggested the different metabolic responses caused in elites and amateurs in different experiments. Lactate increases in mechanical overload to induce oxidation in heart and slow fiber by transporting monocarboxylate transporter (MCT) 1 and MCT4, which stimulates as a cascade of muscle hypertrophy regulation even though it was initially considered as a metabolic waste and a fatigue causing substance (Bonen, 2000;Bonen et al., 2000;Gladden, 2004;Kitaoka et al., 2011). It can be suggested that lactate is recognized as a signal medium involving protein anabolic mechanism to muscle hypertrophy (Enoki et al., 2006). ...
Horse riding (HR) is a sport harmonized with rider and horse. HR is renowned as an effective sport for young and old women and men. There is rare study regarding comparison between elite horse riders and amateurs. We aimed to investigate comprehensive ranges of parameters such as change of lactate, heart rate, calorie, VO2max, skeletal muscle mass, body water, body fat, etc between amateurs and professionals to emphasize HR not only as a sport training but also as a therapeutic aspect. We performed 3 experiments for comparing physical fitness, body compositions, lactate value, heart rate and calorie consumption change before and after riding between amateurs and elites. Around 3 yr riding experienced elites are preeminent at balance capability compared to 1 yr riding experienced amateurs. During 18 min horse riding, skeletal muscle mass and body fat were interestingly increased and decreased, respectively. Lactate response was more sensitive in elites rather than amateurs and its recovery was reversely reacted. Exercise intensity estimated from heart rate was significantly higher in elites (P<0.05). The similar pattern of calorie consumption during riding between amateurs and elites was shown. Horse riding possibly induces various physiological (muscle strength, balance, oxidative capability, flexibility, and metabolic control) changes within body and is thus highly recommended as combined exercise for women, children, and aged as therapeutic and leisure sport activity.
... Diaz-Herrera, et al 13 showed that aerobic training for 12 weeks increased oxidative fibers in rats, such as fiber type I 24%, type IIA 8%, and type IIX 16%, and decreased glycolytic fiber (type IIB: 20%). Bonen 14 showed that aerobic training increased monocarboxylate transporter (MCT) I in heart and skeletal muscles. Siu 15 found increases in mitochondria and oxidative enzymes in skeletal and heart muscles of rats after 8 weeks of aerobic training. ...
Background: Aerobic training can be done not only continuously, but also intermittently. Intermittent aerobic training aimed to get blood lactate level lower than continuous aerobic training. Blood lactate concentration in one of the various factors that determine training performance. However, until recently, little studies about intermittent aerobic training and blood lactate levels have been done. Therefore, this study aimed to measure blood lactate levels in Wistar rats after 4 and 12 weeks of intermittent aerobic training.Methods: 16 Wistar rats were divided into two groups, control and aerobic group. Every group was divided into two subgroups, 4-week and 12-week subgroup. Aerobic group performed training using T-6000 treadmill with a speed of 20 m/minute for 20 minutes, with resting period for 90 seconds every 5 minute. Measurements of lactate level was done with L-lactate (PAP) Randox kit (LC2389).Results: Blood lactate level in the 4-week aerobic group was 2.11 mmol/L, while that of the 4-week control group was 1.82 mmol/L (p > 0.05). Meanwhile, lactate level in 12-week aerobic group was 1.71 mmol/L (p < 0.05), and significantly lower than in 12-week control group, which was 3.03 mmol/L.Conclusion: This study showed that lactate level after 12-week intermittent aerobic training was the lowest compared to 4-week intermittent aerobic and 12-week control group. (Med J Indones. 2013;22:141-5. doi: 10.13181/mji.v22i3.582)Keywords: Blood lactate, intermittent aerobic training, Wistar rat
... This is because of a better O2 supply and so less need for anaerobic ATP-production. Moreover, they have suggested that a higher elimination rate of lactate, is the reason for a reduced lactate accumulation by endurance training ( Bonen A., 2000;Laurent et al., 2001). when interpreting blood lactate data, we should adopt a cautious approach. ...
... Senza scendere nel dettaglio della fisiopatologia e della medicina dello sport, è necessario riassumere brevemente i principali ruoli metabolici del lattato. È stato dimostrato che il lattato è in grado di entrare nelle cellule attraverso il sistema shuttle del trasportatore monocarbossilato e che lo "scambio" lattato-piruvato costituisce un sistema metabolico ben adattabile alle esigenze energetiche dell'organismo [5][6][7] : in determinate circostanze, il lattato diventa l'ultima ri-sorsa energetica e non un semplice prodotto di scarto del metabolismo cellulare 8,9 . Infatti, molte specie animali sono in grado di ottimizzare il rapporto produzione/consumo di ATP in modo da sostenere attività muscolari a elevata intensità, utilizzando il lattato come un trasduttore di energia, e non come un prodotto di rifiuto [10][11][12][13] . ...
Early goal directed therapy has been found to improve prognosis in septic patients, if the therapeutic goal is achieved within the first six hours. The aim of our study is to demonstrate that in patients with acute cardiorespiratory failure, rapid (within 2 hours) lactate clearance can help define patients’ prognosis. 67 consecutive patients, admitted to our 16-bed Emergency Medicine ward for acute cardiorespiratory failure (age 75,9 ± 9,8) (APACHE II score 19,0 ± 4,1), were included in the study. Blood lactate concentration was read at admission and after 2, 6 and 24 hours. We evaluated mortality at seven days and the use of orotracheal intubation (patients with negative outcome) vs. discharge or transfer to a non-emergency ward with subsequent discharge (patients with negative outcome). Lactate concentration at admission was 4,6 ± 2,5 mmol/l; lactate clearance (%) at 2 hours was 40,4 ± 32,1 in patients with a positive outcome and –8,3 ± 5,0 in patients with a negative outcome (p < 0,05). Lactate clearance at 2 hours < 25% is correlated to a negative outcome with an 84,2% sensitivity and a 79,2% specificity. The positive predictive value was 61,5% and the negative predictive value was 92,2%. Systematic lactate clearance monitoring can be used in cases of acute cardiorespiratory insufficiency to identify patients with a high risk of negative outcome. In our study, low clearance at two hours was associated with an increase in mortality and/or the need for orotracheal intubation. Conversely, a clearance at two hours of > 25% in most cases confirms the therapeutic strategy undertaken. Serial evaluation of blood lactate concentration may therefore be useful in guiding treatment strategies.
In diesem Kapitel werden die Prinzipien des kardiopulmonalen Ausdauerkapazitätstrainings erläutert. Bei Menschen mit pulmonaler, kardialer oder metabolischer Erkrankung steht die Ausdauerleistungsfähigkeit im direkten Zusammenhang mit Morbidität und Mortalität. Bereits niedrige Intensitäten können sowohl bei gesunden als auch chronisch erkrankten Personen effektiv eingesetzt werden und Anpassungsmechanismen auslösen. Das Programm zur Erreichung gesundheitsbezogener Endpunkte muss auf die individuellen Leistungslimitierungen des Patienten abgestimmt werden. Die Auswahl der Belastungsform hängt von Beeinträchtigungen der alveolären Ventilation, der Diffusion, des Herz-Kreislauf-Systems, der peripheren Muskulatur und der Atemmuskeln sowie von weiteren Krankheitsbildern, Alter, Leitungsfähigkeit und Dauer des bisherigen Trainings ab. Die positiven Effekte konnten sowohl im stationären als auch im ambulanten Bereich belegt werden.
The objective of this study was to determine if ractopamine (RAC) impacts postmortem muscle metabolism and subsequent pork quality in Halothane (HAL) and Rendement Napole (RN) mutant pigs. All RAC fed pigs had increased (P < 0.04) L* values. HAL and RN mutants muscle had lower (P < 0.01) pH values but RAC feeding had no effect. RN mutants had higher and lower (P < 0.05) muscle pH and temperatures, respectfully at 15 min and RN mutant pigs had greater (P < 0.0001) glycogen initially but lactate levels similar to wild type (WT) pigs at 24 h. RAC lowered (P < 0.05) glycogen in RN mutants but not in HAL mutated or WT pig muscle. These data show RAC feeding changes postmortem energy metabolism but does not change pH and pork quality hallmark of two major pig gene mutations and supports our contention that ultimate meat quality traits and their biochemical drivers may be more complex than originally reasoned.
Cadmium (Cd) is a non-essential heavy metal with many harmful effects, especially tumorigenesis. Previously we established that autophagy-dependent increasing of glycolysis played an important role in Cd-induced cell growth and migration of A549 and HELF cells. In this study, we found Cd could induce autophagy and mTOR in A549 cells, HELF cells and in lung tissues of BALB/c mice. More interestingly, Cd-induced elevation of mTOR was autophagy-dependent and autophagy-induced cell growth and glycolysis was mTOR-dependent. However, in A549 cells, besides the above mTOR-dependent pathway, Cd-induced autophagy could directly induce PKM2 and LDHA independent of mTOR. Further study showed that only in A549 cells could autophagy other than mTOR enable Cd to increase MCT1 expression and MCT1 was involved in autophagy-induced PKM2 and LDHA. Sodium lactate added in the culture medium promoted Cd-induced cell growth of A549 cells, while had no effect on HELF cells. Finally, the effect of autophagy/MCT1/PKM2 pathway on lactate utilization to facilitate Cd-induced A549 cell growth was determined. Above all, we concluded that in HELF cells, autophagy induced mTOR-dependent glycolysis in which GLUT1 and HKII was elevated to promote glucose intake to accelerate cell growth. Whereas, in A549 cells, besides the above pathway to use glucose, autophagy could induce an mTOR-independent glycolysis pathway in which lactate could be used as fuel through autophagy-MCT1-PKM2 to escape glucose deficiency.
There is evidence suggesting that the effects of diet and physical activity on physical and mental well-being are the result of altered metabolic profiles. Though the central and peripheral systems work in tandem, the interactions between peripheral and central changes that lead to these altered states of well-being remains elusive. We measured changes in the metabolic profile of brain (cortex) and muscle (soleus and plantaris) tissue in rats following 5-weeks of treadmill exercise and/or a high-fat diet to evaluate peripheral and central interactions as well as identify any common adaptive mechanisms. To characterize changes in metabolic profiles, we measured relative changes in key metabolic enzymes (COX IV, hexokinase, LDHB, PFK), substrates (BHB, FFA, glucose, lactate, insulin, glycogen, BDNF) and transporters (MCT1, MCT2, MCT4, GLUT1, GLUT3). In the cortex, there was an increase in MCT1 and a decrease in glycogen following the high-fat diet, suggesting an increased reliance on monocarboxylates. Muscle changes were dependent muscle type. Within the plantaris, a high-fat diet increased the oxidative capacity of the muscle likely supported by increased glycolysis, whereas exercise increased the oxidative capacity of the muscle likely supported via increased glycogen synthesis. There was no effect of diet on soleus measurements, but exercise increased its oxidative capacity likely fueled by endogenous and exogenous monocarboxylates. For both the plantaris and soleus, combining exercise training and high-fat diet mediated results, resulting in a middling effect. Together, these results indicate the variable adaptions of two main metabolic pathways: glycolysis and oxidative phosphorylation. The results also suggest a dynamic relationship between the brain and body.
PURPOSE: A number of physiological diagnostics were developed. However, the timeline-related diagnostics of maximal anaerobic glycolytic capacity remain unclear. The objective of this study was to evaluate the reliability and validity of a sprint running test to assess the anaerobic capacity.METHODS: The study was divided into three parts. Sixty-one male (24±4 years, 181.0±4.3 cm; 78.5±5.9 kg) and twelve female (25±3 years, 167.0±0.6 cm, 60.4±5.7 kg) sports students participated in this study. Twenty-five subjects (13 males, 24±2 years, 181.0±0.5 cm, 78.5±5.9 kg; 12 females, 25±3 years, 167.0±0.6 cm, 60.4±5.7 kg) performed incremental step tests at running track and several linear sprints on a running track (LSRT) with different time durations (8, 10, 12, and 14 seconds)(part I) on different days. Twenty-five male subjects (24±3 years, 180.7±6.7 cm, 84.6±8.8 kg) conducted a 10 or 12 second sprint running on a non-motorized treadmill (NMT)(part II). In part III, twenty-three male subjects (24±2 years, 181.4±5.8 cm, 74.5±7.4 kg) ran a 10 second LSRT and NMT on consecutive days. Capillary blood samplings were taken before (Lac<sub>r</sub>) and after the sprint running for ten minutes at one minute intervals to find out maximal lactate concentration after exercise and to calculate the maximum lactate production rate (LPR<sub>max</sub>).RESULTS: For all parts reliability for LPR<sub>max</sub> was proven (Part I: 8 seconds: ICC: r =.89; 10 seconds: ICC: r =.82; 12 seconds: ICC: r =.92; 14 seconds: r =.84, respectively; Part II: 10 seconds: ICC: r =.76; 12 seconds: ICC: r =.79). To analyze validity for LPR<sub>max</sub>, Part III was conducted and proven valid (ICC: r =.96, p=.074).CONCLUSIONS: We demonstrate that LSRT and NMT reliably determine anaerobic capacity and can be used as a valid tool for physiological performance diagnostics.
Nephrotoxic serum (NTS) nephritis occurs in three stages: inflammation, early kidney damage, and severe kidney damage. We quantified the temporal changes in the enantiomers of lactate (LA) and 3-hydroxybutyrate (3HB) in serum and urine during the progression of autoimmune kidney damage in mice with NTS nephritis. Two-dimensional and three-dimensional HPLC were used to quantify the enantiomers. The serum and urinary levels of LA and 3HB enantiomers significantly changed during the progression of NTS nephritis. Specifically, d-LA was significantly higher in the serum (131.8 ± 30.6, 123.7 ± 27.2, 109.3 ± 15.6 vs. 51.2 ± 7.5 μM; p < 0.05) and urine (222.2 ± 34.8, 197.4 ± 53.9, 214.8 ± 68.9 vs. 100.8 ± 37.7 μmol/g creatinine; p < 0.05) of the week 0 (W0), week 1 (W1), and week 2 (W2) groups than the normal group. The l-3HB/d-3HB ratio was significantly lower in the W0, W1, and W2 groups than the normal group in serum (0.0362 ± 0.0082, 0.0346 ± 0.0065, 0.0323 ± 0.0033 vs. 0.0602 ± 0.0214; p < 0.05) and urine (0.0591 ± 0.0304, 0.1524 ± 0.0365, 0.1232 ± 0.1066 vs. 0.3273 ± 0.1394; p < 0.05). The changes in serum and urinary d-LA and l-3HB/d-3HB ratios were stable before severe kidney damage. In conclusion, we successfully determined the levels of LA and 3HB enantiomers in NTS nephritis by HPLC. Serum and urinary d-LA contents and l-3HB/d-3HB ratios may have potential as biomarkers of early autoimmune kidney injury.
This review is made of two parts ; each one is presented under the form of questions to which, by using only published scientific data, we try to give up-to-date answers and to highlight the limits of theories sometimes easily admitted concerning lactic acid effects. The first part of the review is mainly focused on the study of lactate synthesis and metabolism during and after exercise. This study would allow us to built our criticisms concerning : several a priori about lactate effects, about the concepts of « anaerobic lactic thresholds », and on the theories underlining these ones. The second part of the review is focused on possible consequences, but not proved, of lactate accumulation on the skeletal muscle function. How should we accept anymore to ear that lactic glycolysis has a poor energetic yield, or that lactate accumulation leads to cramps, fatigue, and other differed muscular pains ?
The maximal lactate steady state (MLSS) is defined as the highest blood lactate concentration (MLSSc) and work load (MLSSw) that can be maintained over time without a continual blood lactate accumulation. A close relationship between endurance sport performance and MLSSw has been reported and the average velocity over a marathon is just below MLSSw. This work rate delineates the low-to high-intensity exercises at which carbohydrates contribute more than 50% of the total energy need and at which the fuel mix switches (crosses over) from predominantly fat to predominantly carbohydrate. The rate of metabolic adenosine triphosphate (ATP) turnover increases as a direct function of metabolic power output and the blood lactate at MLSS represents the highest point in the equilibrium between lactate appearance and disappearance both being equal to the lactate turnover. However, MLSSc has been reported to demonstrate a great variability between individuals (from 2–8 mmol/L) in capillary blood and not to be related to MLSSw. The fate of enhanced lactate clearance in trained individuals has been attributed primarily to oxidation in active muscle and gluconeogenesis in liver. The transport of lactate into and out of the cells is facilitated by monocarboxylate transporters (MCTs) which are transmembrane proteins and which are significantly improved by training. Endurance training increases the expression of MCT1 with intervariable effects on MCT4. The relationship between the concentration of the two MCTs and the performance parameters (i.e. the maximal distance run in 20 minutes) in elite athletes has not yet been reported. However, lactate exchange and removal indirectly estimated with velocity constants of the individual blood lactate recovery has been reported to be related to time to exhaustion at maximal oxygen uptake.
Biochemical studies were conducted to determine the location of a putative lactate transport protein in rat skeletal muscle plasma membranes (PM). PM (50-100 micrograms protein) were incubated with [U-14C] L(+)-lactate, in the presence or absence of unlabeled monocarboxylates or potential inhibitors, after which proteins were separated by SDS-PAGE. Gel slices (2 mm) were cut and analyzed for 14C. [U-14C] L(+)-lactate was bound to plasma membranes in the 30 to 40 kDa molecular mass range. Binding of [U-14C] L(+)-lactate was inhibited by N-ethylmaleimide, unlabeled L-lactate and pyruvate, and in a dose dependent manner by alpha-cyano-4-hydroxycinnamate (r = 0.995), but not by cytochalasin-B. The inhibition of [U-14C] L(+)-lactate binding was similar to the inhibition of lactate transport. Therefore the transport of L(+)-lactate across skeletal muscle plasma membranes involves a polypeptide of 30 to 40 kDa.
Members of the POU-domain gene family encode for transcriptional regulatory molecules that are important for terminal differentiation of several organ systems, including anterior pituitary, sensory neurons, and B lymphocytes. We have identified a POU-domain factor, referred to as sperm 1 (Sprm-1). This factor is most related to the transactivator Oct-3/4, which is expressed in the early embryo, primordial germ cells, and the egg. However, in contrast with Oct-3/4, rat Sprm-1 is selectively expressed during a 36- to 48-hr period immediately preceding meiosis I in male germ cells. Although the POU-domain of Sprm-1 is divergent from the POU-domains of Oct-1 and Oct-2, random-site-selection assay reveals that Sprm-1 preferentially binds to a specific variant of the classic octamer DNA-response element in which the optimal sequence differs from that preferred by Oct-1 and Pit-1. These data suggest that the Sprm-1 gene encodes a DNA-binding protein that may exert a regulatory function in meiotic events that are required for terminal differentiation of the male germ cell.
Purified sarcolemmal membranes from mixed rat hindlimb muscle were solubilized with octylglucoside and the extract subjected to hydroxylapatite (HA) chromatography. Following protein elution with a sodium phosphate gradient and detergent removal by dialysis, the HA eluate was reconstituted into asolectin liposomes using a freeze-thaw procedure. Specific L-[14C]lactate transport activity eluting from the 0.2 M sodium phosphate fraction was 30-fold higher compared with native sarcolemmal vesicles (31.64 versus 1.06 nmol/min per mg). The reconstituted carrier exhibited Michaelis-Menten saturation kinetics with Km and Vmax. values of 46.2 +/- 6.6 mM and 498.7 +/- 17.2 nmol/15 s per mg respectively. L-Lactate transport activity was inhibited 57% by preincubation of proteoliposomes with 10 mM alpha-cyano-4-hydroxycinnamate, a known inhibitor of lactate transport. Analysis of the HA eluates by SDS/PAGE showed the presence of a 34 kDa band corresponding to lactate transport activity. Reconstitution of lactate transport activity eluting from the HA column, together with SDS/PAGE analysis suggests the presence of a 34 kDa polypeptide mediating sarcolemmal lactate exchange in rat skeletal muscle.
The lactate carrier was solubilized from purified rat skeletal-muscle sarcolemma with the detergent decanoyl-N-methyl-glucamide and the solubilized carrier was reconstituted into phospholipid vesicles. Reconstituted proteoliposomes showed a faster time course of L-lactate uptake than did protein-free liposomes. The rate of L-lactate uptake into the proteoliposomes was inhibited by the lactate-transport inhibitors p-chloromercuribenzenesulphonate, diethyl pyrocarbonate, alpha-cyano-4-hydroxycinnamate and quercetin. In contrast, the anion-exchange inhibitor DIDS (4,4'-di-isothiocyanostilbene-2,2'-disulphonate) had almost no effect on the uptake. The extent of L-lactate uptake at equilibrium was not affected by the presence of the transport inhibitors, but was sensitive to osmotic strength. L-Lactate and pyruvate, but not D-lactate, inhibited L-lactate uptake when present at 10-fold excess. The properties of L-lactate transport in reconstituted proteoliposomes were similar to those observed in native sarcolemmal vesicles, i.e. the lactate carrier seems to retain its transport characteristics during the solubilization and reconstitution steps.
The structure, size, and surface density of the conspicuous flask-shaped structures called caveolae that are located under the plasma membrane of cardiac myocytes in intact rat atria were studied by electron microscopy after physiological perturbations designed to examine whether caveolae and/or their necks are fixed or mobile and whether the caveolar lumen is always open or can close off from the interstitial space. We showed that, in stretched and unstretched atria, horseradish peroxidase could enter or be washed out of caveolae at 37 degrees, 18 degrees, and 4 degrees C, but this finding does not rule out that caveolae and/or their necks can cycle rapidly between states closed and open to the interstitial space. Electron microscopy of thin sections revealed that exposure of atria at 37 degrees or 18 degrees C to physiological salt solutions made hypertonic by adding 150 mM sucrose or mannitol resulted in a striking enlargement of caveolar profiles within 1 to 5 minutes. Caveolar enlargement was rapidly reversible on return to control saline. After freeze fracture of atria exposed to these hypertonic solutions, quantitative analysis of electron micrographs of the fracture faces revealed statistically significant increases in cross-sectional diameter of cross-fractured caveolar necks and in mean number of caveolar necks penetrating per unit area of plasmalemmal fracture face. These results suggest that atrial myocyte caveolae are dynamic structures whose necks may be reversibly inserted into and withdrawn from the plasmalemma, possibly (but not necessarily) corresponding to states in which caveolae are, respectively, open and closed to the interstitial spaces.
We examined the expression of the monocarboxylate transporters in rat skeletal muscles. All skeletal muscles examined co-expressed MCT1 and MCT3. While MCT1 was highly correlated with the oxidative indices of rat skeletal muscles (muscle oxidative fiber composition, citrate synthase activity, and LDH-1). MCT3 was not correlated with these indices of the muscles oxidative capacities. MCT3 content in fast-twitch glycolytic and fast-twitch oxidative glycolytic rat hindlimb muscles were similar while MCT3 content of the slow-twitch oxidative muscle was markedly lower than in these other muscles. With 7 days of chronic electrical stimulation (10 Hz, 24 h/day) via the peroneal nerve, there was a 1.5 to 1.9 fold increase in MCT1 content of the chronically stimulated muscles (i.e. extensor digitorum longus (EDL), the red (RTA) and white tibialis anterior (WTA)). In contrast, no changes were observed in the MCT3 content of these 7 day, chronically stimulated muscles. Thus, the observed increase in lactate uptake by chronically stimulated muscles can be ascribed to increases in MCT1 (r=0.96) since no changes were observed in MCT3. Clearly, the expression of MCT1 and MCT3 are regulated differently.
The frequency dependent dielectric constant and loss of the unconventional bismuth cuprate glasses have been presented in wide temperature and frequency ranges. Alternating current dielectric loss peak has been observed in the measurable frequency range at higher temperatures, where the measured ac conductivity approaches the dc conductivity. The temperature range where ac loss peak has been observed, varies systematically with glass composition. The dielectric data at these temperature ranges have been analyzed in terms of different theoretical models to find out the possible relaxation mechanism. It has been observed that the dipolar relaxation model with a distribution of relaxation times can best explain the experimental data. The dipolar relaxation occurs due to the hopping of charge carriers between different localized valence states of copper ions within a range of energies near the mobility edge. High value of the dielectric constant observed in these glasses can be attributed to the influence of high polarizability of the Bi3+ ions of the unconventional network former Bi2O3 to the ac response. The higher distribution of the relaxation times in the present glasses compared to the unconventional lead cuprate glasses indicates less homogeneity of the bismuth cuprate glass system.
Skeletal muscle and most other tissues possess a membrane transport system mediating a coupled lactate and H+ translocation. Muscle possesses several lactate-proton transporter isoforms of which two have been cloned; however, the main isoform remains to be identified. The isoforms may have different properties and functional roles, but these have not been specifically characterized. The distribution of lactate-proton transport capacity in skeletal muscle is fiber type dependent, with a higher capacity in slow-twitch fibers compared with fast-twitch fibers. During intense muscle activity and in the recovery period, the lactate and H+ effluxes are mainly mediated by the lactate-proton transporter, which reduces the accumulation of lactate in muscle as well as the drop in internal pH suggested to be involved in muscle fatigue. Thus the lactate-proton transporter is of functional importance for pH regulation in association with muscle activity. This carrier is also important for lactate uptake into resting muscle and other tissues; therefore, the carrier distribution is important for the fate of lactate in the body. In addition, the capacity of the lactate-proton transporter can be increased by intense training and is reduced by inactivity; thus the lactate-proton transporter can undergo adaptive changes.
In isolated, blood perfused, supramaximally stimulated, isotonically working gastrocnemii of dogs lactic acid (LA) output and O2-consumption (V O2) were measured according to the Fick principle. Simultaneously concentration of muscle tissue was determined at rest and at different times during exercise. In one series of experiments metabolic alkalosis was induced by infusions of THAM of Na bicarbonate. As a result arterial pH increased to about 7.5 and standard [HCO3-1] to 31-35 mmol per 1. In another group of experiments metabolic acidosis was induced by HCl infusions. In these experiments pH decreased to 7.0-7.1 and standard [HO301] to 8-11 mmol per 1. During the first 3-4 min after the onset of exercise LA concentration of muscle tissue rose to 18-19 mumol per g wet weight in both series of experiments. During acidosis the highest average values for LA release from the muscle were about 1.1 mumoles per g per minute. During alkalosis LA permeation rate was nearly three times as high. As a consequence of increased rate of permeation, LA concentration of muscle tissue decreased more rapidly in alkalosis than in acidosis. In both series of experiments work per time and VO2 were practically equal during the first 5-6 min of exercise. Thereafter work per time and VO2 decreased more rapidly in acidosis than in alkalosis, a result which probably is due to higher LA concentration in muscle at this time in acidosis. It is concluded that LA permeation rate across muscle cell membrane is increased by high extracellular HCO3- concentration in combination with low H+ activity and vice versa.
In four healthy volunteers, muscle lactate concentration and the release of lactate from the leg were determined at rest and at 4 and 12 min of sitting bicycle exercise at four intensities (30, 50, 70, and 90% of maximal oxygen uptake). The muscle biopsies were obtained by needle biopsy technique from m. vastus lateralis. The rate of lactate release was calculated from the femoral venous-arterial differences of lactate and the leg blood flow was determined by constant rate dye infusion. Both leg blood flow and leg oxygen consumption increased linearly with work intensity. The release of lactate rose approximately linearly with the muscle lactate concentration up to about 4-5 mmol/min but then the relationship revealed a clear leveling off. These results indicate a maximal level for the lactate release from the exercising muscles with a translocation hindrance for lactate within the muscles.
1. Intact erythrocytes were incubated with 100 microM-4,4'-di-isothiocyanostilbene-2,2'-disulphonate (DIDS), a concentration sufficient to inhibit lactate transport irreversibly by 65%. DIDS-labelled proteins were detected by immunoblotting of erythrocyte membrane proteins with an anti-DIDS antibody. Labelled polypeptides of 35-45 kDa in rat erythrocytes, and of 40-50 kDa in rabbit and guinea pig erythrocytes, were detected by this technique. In human erythrocytes, which have 10-fold less transport activity, no labelled polypeptide in this molecular mass range was detected. 2. Labelling of these 35-50 kDa polypeptides was decreased markedly in the presence of the specific inhibitors of lactate transport alpha-cyano-4-hydroxycinnamate and 4,4'-dibenzamidostilbene-2,2'-disulphonate (DBDS), which compete with DIDS for binding to the transporter. However, the weakly bound inhibitor 4,4'-dinitrostilbene-2,2'-disulphonate (DNDS) afforded little protection against labelling by DIDS. 3. The lactate transporter from rat erythrocytes was solubilized with decanoyl-N-methyl glucamide (MEGA-10) and partially purified by Mono-Q anion-exchange chromatography, with transport activity eluting at 0.1-0.15 M-NaCl. The 35-45 kDa DIDS-labelled polypeptide from rat erythrocytes was eluted in the same peak of protein as lactate transporter activity during Mono-Q chromatography. 4. These observations provide strong evidence that the lactate transporter is a polypeptide of 35-45 kDa in rat erythrocytes and of 40-50 kDa in rabbit and guinea pig erythrocytes.
(1) The synthesis of the novel stilbenedisulphonate N,N,N',N'-tetrabenzyl- 4,4'-diaminostilbene-2,2'-disulphonate (TBenzDS) is described, and its interaction with the lactate transporter and band 3 protein of erythrocytes investigated. At 10% haematocrit the IC50 (concn. required for 50% inhibition) for inhibition of transport of 0.5 mM L-lactate into rat erythrocytes at 7 degrees C was approx. 1.6 microM, as low as any other inhibitor of the transporter. In human erythrocytes at 10% haematocrit the IC50 value was increased from approx. 3 microM to 9 microM upon raising the temperature from 7 degrees C to 25 degrees C. (2) TBenzDS inhibited transport of L-lactate into rat erythrocytes in a manner that was competitive with the substrate, as is the case for some other stilbene disulphonate derivatives (Poole, R.C. and Halestrap, A.P. (1991) Biochem. J. 275, 307-312). (3) Increasing the haematocrit from 5 to 20% caused a 3-fold increase in the IC50 value for inhibition of L-lactate transport in rat erythrocytes. (4) TBenzDS was found to bind to erythrocyte membranes, with a partition coefficient (Pm) of 6000-7000 under all conditions tested. (5) TBenzDS also inhibited band 3-mediated sulphate transport in rat erythrocytes; 50% inhibition required approx. 2.5 microM TBenzDS for cells at 10% haematocrit. (6) TBenzDS is fluorescent, and an enhancement of this fluorescence occurs upon addition of BSA or erythrocyte membranes. The fluorescence enhancement caused by erythrocyte membranes is due to binding of the inhibitor to the band 3 protein at the same site as the stilbenedisulphonate 4,4'-diisothiocyanodihydrostilbene-2,2'-disulphonate (H2DIDS).
Lactate transport was studied in sarcolemmal giant vesicles obtained from rat or rabbit skeletal muscle. With this technique it is possible to obtain quantitative information on sarcolemmal transport characteristics. In equilibrium exchange experiments with 10, 30 and 60 mM lactate, vesicles from 'red' rat muscles had a 50% higher lactate transport capacity than vesicles from 'white' muscles. Giant vesicles made from rabbit red muscles had a 39% higher lactate transport capacity than vesicles from white muscles. These differences probably reflect a different number of lactate transporters, whereas the lactate affinity in red and white muscles are identical. Lactate transport capacity decreased with age. Sarcolemmal giant vesicles made from 22-month-old rats had a 28% lower transport capacity than vesicles from 2-month old rats. In absolute terms, the initial exchange flux with 30 mM lactate was 92 and 127 pmol cm-2 sec-1 for old and young rats, respectively. In supplementary studies in which microelectrode measurements were made in single mouse muscle fibers, it was shown that the cellular acidification rate due to lactate incubation, was 38% lower in fibres from 18-month old mice than in fibres from 2-month old mice.
Lactic acid is produced and consumed under various metabolic and pathogenic conditions in numerous cell types of mammalian tissues. The movement of lactic acid and lactate anions within and between tissues depends, ultimately, on flux rates between intracellular and extracellular compartments. Flux rates themselves are dependent on several variables, including (but not limited to) exchange surface area, flow through the tissues of interest, lactate and proton concentration gradients across the cell membranes, and proton concentration gradients across the cell membranes, and permeability of the membranes to these ions. This review focuses on the selective permeability characteristics of the principal cells of lactate metabolism: skeletal muscle, heart, liver, kidney, and erythrocytes. Special attention will be paid to lactate uptake and release in skeletal muscle, the premier tissue of lactate production and consumption, and the regulator of whole body lactate dynamics during exercise and recovery from exercise.
1. Inhibition of L-lactate transport into rat erythrocytes by stilbenedisulphonates was studied under conditions which allowed the contribution of reversible and irreversible inhibition to be assessed. 2. At low temperatures (7 degrees C), 4,4'-di-isothiocyanostilbene-2,2'-disulphonate (DIDS) and other stilbenedisulphonates were found to inhibit lactate transport instantaneously, in a manner which was fully reversible. The most potent reversible inhibitors were 4,4'-dibenzamidostilbene-2,2'-disulphonate (DBDS), DIDS and 4-acetamido-4'isothiocyanostilbene-2,2'-disulphonate (SITS), for which apparent Ki values at 0.5 mM-L-lactate were approx. 36, 53 and 130 microM respectively. 3. DIDS and DBDS were competitive inhibitors with respect to L-lactate, with Ki values of approx 40 microM and 22 microM respectively. 4. After incubation for 1 h at 37 degrees C with DIDS or its dihydro derivative (H2DIDS), which contain the amino-reactive isothiocyanate group, most of the inhibition observed was irreversible. Under these conditions the IC50 value (concn. causing 50% inhibition) for irreversible inhibition by both compounds was approx 100 microM. SITS was much less potent as an irreversible inhibitor of L-lactate transport, approx. 20% inhibition being obtained at 100 microM. 5. The reversible inhibitor DBDS (1 mM) afforded protection against irreversible inhibition by DIDS and H2DIDS (100 microM); protection was 60 and 65% respectively after a 60 min incubation. This indicates that specific binding of the irreversible inhibitors is required before covalent modification can take place. 6. These compounds may be useful high-affinity probes for lactate transport in other tissues and might act as affinity labels for the transport protein(s).
Lactate transport was studied in giant (median diameter 6.3 microns) sarcolemmal vesicles obtained by collagenase treatment of rat skeletal muscle. The lactate transport displayed stereospecificity, had a high temperature coefficient, and could be inhibited up to 90% with known transport inhibitors (PCMBS and cinnamate). In equilibrium exchange experiments, the L-lactate flux demonstrated saturation kinetics with Km = 23.7 mM and Vmax = 108 pmol cm-2 s-1. With lactate present on only one side of the membrane, (zero trans conditions), Vmax was reduced to 48 pmol cm-2 s-1. The flux rate displayed transacceleration. The lactate flux was coupled to a parallel H+ flux. Under equilibrium exchange conditions, the carrier-mediated lactate flux was not pH-dependent. In the zero trans experiments, H+ on the trans side acted as an inhibitor. The loaded form of the carrier reorients faster than the unloaded form, and the protonated form with no lactate bound reorients slowly or is immobile. When compared to intact muscles, the giant sarcolemmal vesicles retain their transport characteristics both qualitatively and quantitatively.
Intracellular pH and [Na+] in the heart are regulated by the sarcolemmal membrane Na(+)-H+ exchange pathway. No data are currently available regarding the adaptation of this system to pathological conditions in the heart. Because ionic interactions with the heart are altered in cardiomyopathy during chronic experimental diabetes, it was hypothesized that Na(+)-H+ exchange may become abnormal. In addition, the effects of treating diabetic rats with daily injection of L-propionylcarnitine were investigated to determine whether alterations in lipid metabolism may be involved in any potential changes in ion transport. Rats were injected with streptozotocin (65 mg/kg) and killed 8-10 wk later, and sarcolemmal membrane vesicles were isolated from pooled ventricles. Significant depressions in Na(+)-K(+)-adenosinetriphosphatase (ATPase) activity and Na(+)-Ca2+ exchange were observed in the diabetic preparations in comparison to control. L-Propionylcarnitine treatment of the diabetic rats partially normalized these activities. A striking depression in cardiac sarcolemmal Na(+)-H+ exchange was observed in the diabetic animals in comparison to control, and this was not a result of a nonspecific increase in membrane permeability. L-Propionylcarnitine treatment of the diabetic rats did not improve sarcolemmal Na(+)-H+ exchange.
An Na(+)-H+ exchange inhibitor, 5-(N,N-dimethyl)amiloride (DMA), was used to probe the possible role of Na(+)-H+ exchange in ischemia-reperfusion injury in coronary perfused isolated rat right ventricular wall. In DMA-untreated hearts, 60 min of ischemia resulted in a significant rise in testing tension (RT: 174 +/- 8% of preischemic level). Thirty minutes of reperfusion further increased RT (273 +/- 12%) and induced a poor recovery in developed tension (DT: 28 +/- 4%). Both the rate of tension development and relaxation (+dT/dt and -dT/dt) recovered to a similar degree. When 1, 5, or 20 microM DMA was included in the perfusate (3 min before ischemia and in the first 3 min of reperfusion), the maximal postischemic RT of the heart was reduced to 204 +/- 21, 166 +/- 15, and 139 +/- 45% of the preischemic levels (P less than 0.05), respectively, and DT was 39 +/- 3, 63 +/- 10, and 79 +/- 8% of the preischemic levels (P less than 0.05), respectively. Similar qualitative recovery of +/- dT/dt was observed. Recovery was similar if DMA was present only during reperfusion. DMA treatment also significantly protected against creatine phosphokinase release during reperfusion. The results demonstrate that DMA can significantly protect the heart during the initial stages of reperfusion. The data suggest that Na(+)-H+ exchange may play an important role in the development of cardiac dysfunction and damage during the first minutes of reperfusion.
The mechanisms of lactate and pyruvate transport across the plasma membrane of rat skeletal muscle under various pH and ionic conditions were studied in skeletal muscle sarcolemmal (SL) membrane vesicles purified from 22 female Sprague-Dawley rats. Transport by SL vesicles was measured as uptake of L(+)-[U-14C] lactate and [U-14C] pyruvate. Lactate (La-) transport is pH-sensitive; stimulations to fivefold overshoot above equilibrium values were observed both directly by a proton gradient directed inward, and indirectly by a monensin- or nigericin-stimulated exchange of Na+ or K+ for H+ across the SL. Isotopic pyruvate could utilize the transporter, and demonstrated pH gradient-stimulated overshoot and cis-inhibition characteristics similar to those of lactate. Overshoot kinetics were also demonstrated by pH gradient formed by manipulation of external media at pH 5.9, 6.6, and 7.4 and intravesicular media at 6.6, 7.4, and 8.0, respectively. Carbonyl cyanide m-chlorophenylhydrazone, an H+ ionophore, was used as a "pH clamp" to return all stimulated uptake courses back to equilibrium values. Lactate uptake was depressed when internal pH was lower than external pH. These data strongly suggest that La- and H+ are either cotransported by the carrier, or transported as the undissociated HLa, and can account for the majority of the lactate uptake at pH 7.4. The mechanism does not require cotransport of either K+ or Na+. However, an inwardly directed Na+ gradient without ionophore in the absence of a pH gradient doubled La- transport; treatment with amiloride, an inhibitor of the Na+/H+ exchanger, abolished this stimulation, suggesting that this transporter may be an important coregulator of intracellular pH, and could disrupt 1:1 H+ and La- efflux stoichiometry in vivo. We conclude that the majority of La- crosses the skeletal muscle SL by a specific carrier-mediated process that is saturable at high La- concentrations, but flux is passively augmented at low intracellular pH by undissociated lactic acid. In addition, a Na+/H+ exchange mechanism was confirmed in skeletal muscle SL, does affect both lactate and proton flux, and is potentially an important coregulator of intracellular pH and thus, cellular metabolism.
To study the kinetics of lactate transport in an isolated, nonmetabolizing system, skeletal muscle sarcolemmal membrane vesicles were purified from 22 female Sprague-Dawley rats. L(+)-[U-14C] Lactate at 10 concentrations demonstrated saturation kinetics with a Vmax of 139.4 nmol/mg/min, and an apparent Km of 40.1 mM. Threefold higher initial rates of L(+)-lactate uptake were seen at 37 degrees C than at 25 degrees C, indicating temperature sensitivity. Transport was stereospecific for the L(+) isomer: isotopic D(-) uptake rates remained linear at concentrations from 1 to 200 mM, and 1 mM D(-) remained 6-fold lower in net uptake after 60 min than the L(+) isomer. Furthermore, unlabeled 10 mM D(-)-lactate in the external medium could only inhibit 1 mM isotopic (L(+) uptake by 12%, whereas unlabeled 10 mM L(+)-lactate and pyruvate inhibited 82 and 71%, respectively. Additionally, 10 mM beta-hydroxybutyrate and acetoacetate could moderately inhibit (27 and 32%, respectively) 1 mM L(+)-lactate transport, but the unsubstituted aliphatic monocarboxylates (formate, acetate, propionate), tricarboxylic acid cycle intermediates (malate, succinate, oxaloacetate, alpha-ketoglutyrate, citrate), amino acids (alanine, aspartate, glutamate), and palmitate or adenosine in 10-fold excess could not effectively inhibit 1 mM L(+)lactate uptake under cis-transport conditions. 4,4'-Diisothiocyanostilbene-2,2'-disulfonic acid could inhibit L(+)-lactate transport by only 13%, so that lactate transport does not appear to be affected directly by Cl- or HCO3- fluxes. It was demonstrated that KCl could not evoke a membrane potential-induced overshoot of lactate uptake in the presence or absence of valinomycin. Moreover, gluconate could substitute for Cl-, indicating that Cl- flux does not contribute to a membrane potential-dependent component of the transport mechanism, suggesting an electroneutral translocation process. Protein-modifying reagents significantly inhibited 1 mM L(+)-lactate transport during pH-stimulated conditions (p-chloromercuriphenyl-sulfonic acid, 83%; N-ethylmaleimide, 86%; HgCl2, 56%; mersalyl, 63% inhibition). We conclude that the skeletal muscle lactate transporter is a membrane-bound protein, specifically associated with the sarcolemma, that demonstrates saturation kinetics, competition, stereospecificity, and sensitivity to temperature as well as various ionic cis-inhibitors. The lactate transporter is a potentially important regulator of lactate flux across skeletal muscle, and may help to regulate intracellular pH and intermediary metabolism during lactic acidosis.
A range of short-chain aliphatic monocarboxylates, both unsubstituted and substituted with hydroxy, chloro and keto groups, were shown to inhibit transport of L-lactate and pyruvate into both guinea-pig cardiac myocytes and rat erythrocytes. The carrier of heart cells exhibited a higher affinity (approx. 10-fold) for most of the monocarboxylates than did the erythrocyte carrier. A notable exception was L-lactate, whose Km for both carriers was similar. The K1 values of the two carriers for inhibitors such as phenylpyruvate and alpha-cyanocinnamate derivatives were also different. The high affinity of the heart cell carrier for ketone bodies and acetate may be physiologically important, since these substrates are used as fuels by the heart.
The oxidation of glucose represents a major source of metabolic energy for mammalian cells. However, because the plasma membrane is impermeable to polar molecules such as glucose, the cellular uptake of this important nutrient is accomplished by membrane-associated carrier proteins that bind and transfer it across the lipid bilayer. Two classes of glucose carriers have been described in mammalian cells: the Na(+)-glucose cotransporter and the facilitative glucose transporter. The Na(+)-glucose cotransporter transports glucose against its concentration gradient by coupling its uptake with the uptake of Na+ that is being transported down its concentration gradient. Facilitative glucose carriers accelerate the transport of glucose down its concentration gradient by facilitative diffusion, a form of passive transport. cDNAs have been isolated from human tissues encoding a Na(+)-glucose-cotransporter protein and five functional facilitative glucose-transporter isoforms. The Na(+)-glucose cotransporter is expressed by absorptive epithelial cells of the small intestine and is involved in the dietary uptake of glucose. The same or a related protein may be responsible for the reabsorption of glucose by the kidney. Facilitative glucose carriers are expressed by most if not all cells. The facilitative glucose-transporter isoforms have distinct tissue distributions and biochemical properties and contribute to the precise disposal of glucose under varying physiological conditions. The GLUT1 (erythrocyte) and GLUT3 (brain) facilitative glucose-transporter isoforms may be responsible for basal or constitutive glucose uptake. The GLUT2 (liver) isoform mediates the bidirectional transport of glucose by the hepatocyte and is responsible, at least in part, for the movement of glucose out of absorptive epithelial cells into the circulation in the small intestine and kidney. This isoform may also comprise part of the glucose-sensing mechanism of the insulin-producing beta-cell. The subcellular localization of the GLUT4 (muscle/fat) isoform changes in response to insulin, and this isoform is responsible for most of the insulin-stimulated uptake of glucose that occurs in muscle and adipose tissue. The GLUT5 (small intestine) facilitative glucose-transporter isoform is expressed at highest levels in the small intestine and may be involved in the transcellular transport of glucose by absorptive epithelial cells. The exon-intron organizations of the human GLUT1, GLUT2, and GLUT4 genes have been determined. In addition, the chromosomal locations of the genes encoding the Na(+)-dependent and facilitative glucose carriers have been determined. Restriction-fragment-length polymorphisms have also been identified at several of these loci.(ABSTRACT TRUNCATED AT 400 WORDS)
Lactate transport across the sarcolemma of isolated mouse muscles was studied with a 14C tracer technique. The cellular tracer uptake could be inhibited by unlabelled L-lactate (and pyruvate) and to a lesser extent by D-lactase. The stereospecific fraction had a Km of 3.5 mM, and made up 50% of the total transport. The tracer uptake was unaffected by 0.05 mM DIDS and 0.2 mM amiloride, but was inhibited by cinnamate (Ki = 8 mM) and PCMBS (Ki = 0.8 mM). With high concentrations of the latter inhibitor compounds or with high concentrations of unlabelled L-lactate, the tracer uptake was inhibited 80%, which indicates that the main part of the transport involves facilitated diffusion. The remaining fraction (20%) was non-saturable, reduced at high pH, and could not be inhibited; it is probably mediated by diffusion of undissociated lactic acid. Lactate transport was pH-dependent, which is consistent with a lactate-H+ symport. The maximal transport capacity, as calculated from the pH changes measured with pH-sensitive micro-electrodes while the lactate gradient was 30 mM, was 11.8 mmol kg-1 min-1 (pH 6.2).
1. Rat and rabbit erythrocyte plasma-membrane proteins were solubilized with decanoyl-N-methylglucamide and reconstituted into liposomes. The procedure includes detergent removal by gel filtration, followed by a freeze-thaw step. 2. The rate of [1-14C]pyruvate uptake into these vesicles was inhibited by approx. 70% by alpha-cyano-4-hydroxycinnamate and p-chloromercuribenzenesulphonate. The extent of uptake at equilibrium was not affected by the presence of these inhibitors, but was dependent on the osmolarity of the suspending medium. 3. Reconstituted bovine erythrocyte membranes, which have no lactate carrier, showed a much slower time course of pyruvate uptake, with no inhibitor-sensitive component. 4. L- but not D-lactate competed for alpha-cyano-4-hydroxycinnamate-sensitive [1-14C]pyruvate uptake.
In situ muscle stimulation in trained and untrained rats was used to reevaluate whether adaptations induced by endurance exercise training result in decreased lactate production by contracting muscles. The gastrocnemius-plantaris-soleus muscle group was stimulated to perform isotonic contractions. After 3 min of stimulation with 100-ms trains at 50 Hz at 60/min, the increases in lactate concentration in the plantaris, soleus, and fast-twitch red muscle (deep portion of lateral head of gastrocnemius) were only approximately 50% as great in trained as in sedentary rats. In the predominantly fast-twitch white superficial portion of the medial head of the gastrocnemius the increase in lactate concentration was 28% less in the trained than in the sedentary group. The decreases in muscle glycogen concentration seen after 3 min of stimulation at 60 trains/min were smaller in the trained than in the untrained group. The reduction in lactate accumulation that occurred in the different muscles in response to training was roughly proportional to the degree of glycogen sparing. These results show that endurance training induces adaptations that result in a slower production of lactate by muscle during contractile activity.
Isolated canine gracilis muscles were perfused in situ with a free flow (systemic blood flow; FF) or a constant flow (blood from a reservoir; CF). The nervous supply was stimulated electrically for 60 min. A-V-concentration differences for glucose, pyruvate, lactate, glycerol, FFA and O2 were obtained as well as the concentrations of ATP, CP, glycogen and lactate in the muscle.Resting O2 uptake ranged from 4 to 11 moles100 g–1min–1 (FF; CF). A 30- and 5-fold increase in O2 uptake occurred during stimulation in the FF and CF-experiments, respectively. The release of lactate was, however, the same (20–40 moles100 gmin–1) although the muscle lactate concentration was much higher in the CF experiments. In the CF experiment stimulation did not significantly increase glucose uptake which ranged from 0.3 to 3.3 moles100 g–1 min–1 at rest. Conversely, stimulation resulted in a 6-fold increase in glucose uptake in the FF experiments. No definite tendency for a FFA uptake or a glycerol release was found in either experiment (FF, CF). Glycogen depletion during the stimulation period amounted to 20–30 molesg–1. Thus the glucose uptake could account for only 12% of the carbohydrate utilized during the stimulation period.
The effect of denervation on lactate transport capacity was studied in giant sarcolemmal vesicles obtained from rat muscle. The rate of lactate transport was determined in soleus and red (RG) and white gastrocnemius (WG) after 1, 3, and 21 days of denervation and in the corresponding contralateral muscles. In addition, muscle lactate dehydrogenase (LDH) and succinate dehydrogenase (SDH) activities were determined. After 1, 3, and 21 days of denervation the rate of lactate transport was lower (P < 0.05) in WG (9, 11, and 36%), RG (15, 21, and 41%), and soleus (12, 24, and 50%) compared with the contralateral muscles. After 21 days of denervation LDH activity was 26, 25, and 34% and SDH activity 33, 25, and 27% lower (P < 0.05) in WG, RG, and soleus, respectively, compared with the contralateral muscles. In the control muscles the lactate transport capacity was 20 and 32% lower (P < 0.05) in WG than in RG and soleus, respectively. The present findings provide support that the sarcolemmal lactate carrier is a plastic system; the transport capacity in soleus, RG, and WG already declines after 1 day of denervation and is further reduced after 21 days of denervation. In addition, the data suggest that the lactate transport capacity in fast-twitch glycolytic fibers < fast-twitch oxidative-glycolytic fibers < slow-twitch oxidative fibers.
PCR was used to amplify the coding region of CHO MCT1 cDNA. This was then used to screen a rat skeletal muscle cDNA library which lead to the isolation of a full length cDNA encoding MCT1 from rat. The cDNA derived amino acid sequence shows 94% and 86% identity to CHO and human MCT1, respectively.
Sarcolemmal giant vesicles obtained from rat hindlimb muscles were used as a model for the study of pH regulation in skeletal muscle. The transport systems involved in the recovery from 40 mM lactate and pHi 6.5 were quantified from both flux measurements of the co-transported ions and counter-ions, and from measurements of the rate of the internal pH change. The diffusion of lactic acid plus the carrier-mediated co-transport of lactate and H+ had the highest capacity to transport protons (240 nmol H+/mg protein per min). These systems are therefore responsible for a large part of the H+ efflux in periods with a high lactate production. The capacity of the HCO(3)- - dependent systems was 47 nmol/mg per min, and the capacity of the Na+/H+ exchange system was 33 nmol/mg per min in vesicles from mixed muscles. The capacity to remove H+ by the lactate/H+ co-transport system and by the bicarbonate-dependent systems was significantly higher in vesicles from predominantly red fibers than in vesicles from white fibers, whereas the distribution of the Na+/H+ exchange system was independent of fiber type. These observations demonstrate that the pH regulation during muscle activity in red muscles is more effective than in white muscles.
The purpose of this study was to investigate the effect of the neural regulation of contractile activity on lactate transport in skeletal muscle. Contractile activity of the rat soleus muscle was abolished by denervating the hindlimb muscles in one leg (3 days) while the sham-operated contralateral hindlimb muscles served as a control. Three days after surgery, lactate transport into the soleus muscle was measured in vitro, using incubated soleus muscle strips. Lactate uptake by the denervated soleus muscle was reduced compared with control (P < 0.05). The diffusive component of lactate transport was unaltered by denervation (P > 0.05). These results translated into a reduction in lactate carrier-mediated transport capacity (-68%) in the denervated soleus (P < 0.05). These studies indicate that loss of contractile activity results in a decrement of lactate transport, which is probably due to a reduction in the number of lactate carriers in the sarcolemma. Our results suggest that the inherent activity of the muscle is important in maintaining the lactate transport system.
Low stringency screening of a cDNA library from hamster liver yielded a cDNA encoding MCT2, a monocarboxylate transporter that is 60% identical to hamster MCT1, the first monocarboxylate transporter to be isolated. The functional properties of the two MCTs were compared by expression in Sf9 insect cells using recombinant baculovirus vectors. Like MCT1, MCT2 transported pyruvate and lactate. The two transporters were sensitive to inhibition by phloretin and by alpha-cyano-4-hydroxycinnamate. MCT1, but not MCT2, was sensitive to organomercurial thiol reagents such as p-chloromercuribenzoic acid. Immunoblotting and immunofluorescence studies revealed a strikingly different tissue distribution of the two MCTs. MCT1 was present in erythrocytes and on the basolateral surfaces of intestinal epithelial cells. MCT2 was not detectable in these tissues, but it was abundant on the surface of hepatocytes. In the stomach, MCT1 was present on the basolateral surfaces of epithelial cells; in contrast, MCT2 was expressed on parietal cells of the oxyntic gland. In the kidney, MCT1 was present on the basolateral surfaces of epithelial cells in proximal tubules, whereas MCT2 was restricted to the collecting ducts. MCT1 was expressed on sperm heads in the testis and proximal epididymis. In the distal epididymis, it disappeared from sperm and appeared on the microvillar surface of the lining epithelium. In contrast, MCT2 was present on sperm tails throughout the epididymis and not on the epithelium. Both transporters were expressed in mitochondria-rich (oxidative) skeletal muscle fibers and cardiac myocytes. These findings suggest that MCT1 and MCT2 are adapted to play different roles in monocarboxylate transport in different cells of the body.
Lactate and pyruvate are transported across cell membranes by monocarboxylate transporters (MCTs). Here, we use the recently cloned cDNA for hamster MCT1 to isolate cDNA and genomic clones for human MCT1. Comparison of the human and hamster amino acid sequences revealed that the proteins are 86% identical. The gene for human MCT1 (gene symbol, SLC16A1) was localized to human chromosome bands 1p13.2-p12 by PCR analysis of panels of human x rodent cell hybrid lines and by fluorescence chromosomal in situ hybridization.
A marked decrease in the activity of the amiloride-sensitive Na+/H+ exchanger has been demonstrated in hearts from streptozotocin (STZ)-induced diabetic rats. The aim of this study was to investigate the contribution of other specific sarcolemmal transport mechanisms to intracellular pH (pHi) recovery upon reperfusion in STZ-induced diabetic rat hearts and their relation to recovery of ventricular function. Isovolumic rat hearts were submitted to a zero-flow ischemic period of 28 min at 37 degrees C and then reperfused for 28 min. The time course of pHi decline during ischemia and of recovery on reperfusion was followed by means of 31P-labeled NMR. The perfusion buffers used were either HEPES or CO2/HCO3-. An HCO3(-)-dependent (amiloride-insensitive) mechanism contributed to pHi recovery after ischemia in the diabetic rat hearts. Even when the Na+/H+ exchanger was blocked by amiloride in nominally HCO3(-)-free solution, a rapid rise in pHi occurred during the first 3 min of reperfusion. The early rise in pHi was reduced by external lactate and inhibited by alpha-cyano-4-hydroxycinnamate. This suggested that a coupled H(+)-lactate efflux may be a major mechanism for acid extrusion in the initial stage of reperfusion. The observation of a higher functional recovery on reperfusion in diabetic hearts is in accordance with previous studies using HCO3- buffer. However, this study shows that a good recovery of function occurred even more rapidly in diabetic hearts receiving HEPES-buffered solution than in those receiving HCO3(-)-buffered solution. This suggests that the HCO3(-)-dependent mechanism of regulation may be depressed in diabetic rat hearts.