Experimental Physiology

Published by Wiley
Online ISSN: 0958-0670
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Article
The renin angiotensin system (RAS) plays a crucial role in erectile function. It has been shown that elevated angiotensin II levels contribute to the development of erectile dysfunction both in human and in aminals. On the other hand, the heptapeptide angiotensin-(1-7) appears to mediate penile erection by activation of receptor Mas. Recently we have shown that the erectile function of Mas gene-deleted mice was substantially reduced, which was associated with a marked increase in fibrous tissue in the corpus cavernosum. We have hypothesized that the synthetic non-peptide Mas agonist, AVE 0991, would potentiate the penile erectile function. To evaluate that, intracavernosal injection of AVE 0991 potentiates the erectile response of anesthetized Wistar rats, measured as corpus cavernosum pressure/mean arterial pressure (CCP/MAP) upon electrical stimulation of the major pelvic ganglion. The facilitatory effect of AVE 0991 on erectile function was dose-dependent and completely blunted by the nitric oxide (NO) synthesis inhibitor, L-NAME. Importantly, concomitant intracavernosal infusion of the specific Mas receptor blocker A-779 abolished the effect of AVE 0991. We demonstrated that AVE 0991 potentiates penile erectile response through Mas in a NO dependent manner. Importantly, these results suggest that Mas agonists, such as AVE 0991, might have significant therapeutic benefits for the treatment of erectile dysfunction.
 
Article
It has been suggested that the glucose transport system of human erythrocytes contains an arginine shield to prevent the leak of potassium through the transporter. To investigate this suggestion we treated human erythrocytes with the specific arginine reagent 1,2-cyclohexanedione. Under conditions which produce a covalent reaction between arginine and the reagent, a steady leak of potassium occurs. If glucose, maltose or the inhibitor phloretin are present during the reaction the extent of the leak is reduced. These findings support the view that arginines have a role in preventing potassium loss through the glucose transporter.
 
Article
The C3 neurone, which acts as a motoneurone for the tentacle retractor muscle in Helix aspersa, contains both Phe-Met-Arg-Phe-NH2 (FMRFamide) and acetylcholine (ACh). Each of these transmitter substances evokes contraction of the isolated muscle. FMRFamide induces a delayed rise in tension followed by phasic contractions. Unlike the response to ACh, this response is not associated with a depolarization of the muscle cells. Here we show that FMRFamide stimulates the inositol phosphate second messenger system in the muscle and causes a significant increase in total inositol trisphosphate (InsP3) levels. The isomer which releases intracellular Ca2+ stores, inositol 1,4,5-trisphosphate (Ins(1,4,5)P3), is increased in a similar proportion to the total InsP3. The production of Ins(1,4,5)P3 is therefore likely to be involved in the response of the muscle to FMRFamide and may account for the oscillatory nature of the mechanical response. The N-terminally extended heptapeptide pGlu-Asp-Pro-Phe-Leu-Arg-Phe-NH2 (pQDPFLRFamide), which relaxes the muscle, had no acute effect on InsP3 levels. Indirect evidence also indicates that intracellular Ca2+ stores are required for the generation of the FMRFamide response.
 
Article
The CellML language was developed in response to the need for a high-level language to represent and exchange mathematical models of biological processes. The flexible structure of CellML allows modellers to construct mathematical models of the same biological system in many different ways. However, some modelling styles do not naturally lead to clear abstractions of the biophysical concepts and produce CellML models that are hard to understand and from which it is difficult to isolate parts that may be useful for constructing other models. In this article, we advocate building CellML models which isolate common biophysical concepts and, using these, to build mathematical models of biological processes that provide a close correspondence between the CellML model and the underlying biological process. Subsequently, models of higher complexity can be constructed by reusing these modularized CellML models in part or in whole. Development of CellML models that best describe the underlying biophysical concepts thus avoids the need to code models from scratch and enhances the extensibility, reusability, consistency and interpretation of the models.
 
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Corrigendum for DOI: 10.1113/expphysiol.2009.048082"Stearic acid-induced cardiac lipotoxicity is independent of cellular lipid and is mitigated by the fatty acids oleic and capric but not by the PPAR agonist troglitazone" Author name Lodha should be Lodhia.
 
Article
5-[5-(2-Nitrophenyl) furfuryliodine]-1,3-diphenyl-2-thiobarbituric acid (UCF-101) is a protease inhibitor which was reported to protect against ischaemic heart damage and apoptosis. This study evaluated the impact of UCF-101 on steptozotocin (STZ)-induced diabetic cardiomyocyte dysfunction. Adult FVB mice were made diabetic with a single injection of STZ (200 mg kg(1)). Two weeks after STZ injection, cardiomyocytes from control and STZ-treated mice were isolated and treated with UCF-101 (20 mum for 1 h). Cardiomyocyte contractile properties were analysed, including peak shortening (PS), maximal velocity of shortening/relengthening (+/-dL/dt), time to PS (TPS) and time to 90% relengthening (TR(90)). Steptozotocin-induced diabetes depressed PS and +/-dL/dt and prolonged TPS and TR(90) in cardiomyocytes, all of which were significantly alleviated by UCF-101. Immunoblotting analysis showed that UCF-101 significantly alleviated STZ-induced loss of phospholamban phosphorylation without affecting sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA2a) and phospholamban. Steptozotocin reduced AMP-activated protein kinase (AMPK) phosphorylation at Thr172 of the catalytic subunit without affecting total AMPK expression, which was restored by UCF-101. Short-term exposure to UCF-101 did not change the expression of X-linked inhibitor of apoptosis protein (XIAP) and Omi stress-regulated endoprotease, high temperature requirement protein A2 (Omi/HtrA2), favouring an apoptosis-independent mechanism. Both the AMPK activator resveratrol and the antioxidant N-acetylcysteine mimicked the UCF-101-induced beneficial effect in STZ-induced diabetic cardiomyocytes. In addition, UCF-101 promoted the phosphorylation of p38 mitogen-activated protein kinases and c-Jun N-terminal kinase (JNK) after 15 min of incubation, while it failed to affect the phosphorylation of extracellular signal-regulated kinase (ERK) and glycogen synthase kinase-3beta (GSK-3beta) within 120 min in H9C2 myoblasts. Taken together, these results indicate that UCF-101 protects against STZ-induced cardiomyocyte contractile dysfunction, possibly via an AMPK-associated mechanism.
 
Article
EB 1089 is a calcitriol analogue with low calcaemic activity, which inhibits parathyroid hormone-related peptide (PTHrP) secretion in rats implanted with the Leydig cell tumour H-500. We have studied its effect on maternal and fetal plasma PTHrP concentrations and on fetal calcium and phosphorus contents in rats. Three groups of six pregnant rats were injected I.P. daily with EB 1089 (0.10, 0.25 and 0.50 microgram kg-1 in groups 1, 2 and 3, respectively, from day 12 to day 20 of gestation). The control group received an equal volume of solvent alone. On day 21 of gestation the animals were anaesthetized with chloral hydrate and blood samples were taken. Fetuses were collected, weighed and ashed for Ca and P measurements. PTHrP concentrations were measured by radioimmunoassay (RIA) in maternal and fetal plasma. Calcium content (mg (g fetal wt)-1; mean +/- S.E.M.) in control fetuses was not different from that measured in fetuses from dams given the lowest dose of EB 1089, but was higher than that in fetuses from rats injected with EB 1089 at 0.25 microgram kg-1 (1.18 +/- 0.20; P < 0.05) or 0.50 microgram kg-1 (1.08 +/- 0.29; P < 0.05). There was no difference in fetal P content between any of the groups of rats. The PTHrP concentration (pg equivalents human PTHrP(1-34) fragment ml-1) in maternal plasma from control rats (1.70 +/- 0.50) was not different from that in maternal plasma of rats given the lowest dose of EB 1089 (1.44 +/- 0.63).(ABSTRACT TRUNCATED AT 250 WORDS)
 
Article
An AT1-specific angiotensin II receptor antagonist (GR117289; 1 mg/kg I.V. bolus) was administered daily to ten chronically catheterized, normotensive ewes during late pregnancy (from 126 +/- 1 days) until parturition (139 +/- 1 days); five control animals received an equivalent volume of vehicle solution. Following drug administration, mean maternal blood pressure decreased from 87 +/- 1 mmHg to a minimum of 79 +/- 1 mmHg at 0.5 h (P < 0.05; n = 10) and remained low for 4-6 h without any concomitant change in fetal blood pressure or maternal and fetal heart rates. In animals fitted with flow probes, uterine blood flow decreased from 443 +/- 21 to 363 +/- 27 ml/min at 0.5 h post-drug (P < 0.05; n = 6); this change was positively correlated with the reduction in maternal blood pressure. The mean decrements in uterine and umbilical blood flows measured by steady-state infusion of tritiated water were -611 +/- 171 ml/min at 4-6 h (P < 0.05; n = 5) and -71 +/- 19 ml/min at 0.5-1 h (P < 0.05; n = 5), respectively. Significant reductions (P < 0.05; n = 10) in fetal arterial oxygen tension (-1.6 +/- 0.4 mmHg), saturation (-6.6 +/- 1.6%) and content (-0.3 +/- 0.1 mumol/ml) were evident at 0.5 h post-drug and were maintained for 6-12 h. Umbilical oxygen delivery decreased at 0.5-1 h following drug administration (P < 0.01; n = 5), but was unaccompanied by any significant change in fetal oxygen consumption. Chronic decreases in daily fetal pH and blood oxygen content occurred in GR117289-treated ewes. There were no significant differences in gestational length or neonatal outcome between vehicle- and GR117289-treated groups of ewes with single fetuses.
 
Article
The aim of the present study was to investigate how early the onset of ischaemia-induced changes in gene expression is in remote myocardium, and whether these changes would be different for left and right ventricles. Wistar rats (n=27) were randomly assigned to left coronary artery (LCA) ligation for 30 or 120 min and sham groups. Evans Blue infusion revealed antero-apical left ventricle (LV) and left intraventricular (IV) septal ischaemia (35.5+/-0.6% of LV mass). LCA ligation induced transient LV systolic dysfunction and sustained biventricular slowing of relaxation. Regarding mRNA levels, type B natriuretic peptide (BNP) was upregulated in the LV at 30 (+370+/-191%) and 120 min (+221+/-112%), whilst in the right ventricle (RV) this was only significant at 120 min (+128+/-39%). Hipoxia-inducible factor 1alpha and interleukin 6 overexpression positively correlated with BNP. Inducible NO synthase upregulation was present in both ventricles at 120 min (LV, +327+/-195%; RV, +311+/-122%), but only in the RV at 30 min (+256+/-88%). Insulin-like growth factor 1 increased in both ventricles at 30 (RV, +59+/-18%; LV, +567+/-192%) and 120 min (RV, +69+/-33%; LV, +120+/-24%). Prepro-endothelin-1 was upregulated in the RV at 120 min (+77+/-25%). Ca2+-handling proteins were selectively changed in the LV at 120 min (sarcoplasmic reticulum Ca2+ ATPase, 53+/-7%; phospholamban, +31+/-4%; Na+-Ca2+ exchanger, 31+/-6%), while Na+-H+ exchanger was altered only in the RV (-79+/-5%, 30 min; +155+/-70%, 120 min). Tumour necrosis factor-alpha and angiotensin converting enzyme were not significantly altered. A very rapid modulation of remote myocardium gene expression takes place during myocardial ischaemia, involving not only the LV but also the RV. These changes are different in the two ventricles and in the same direction as those observed in heart failure.
 
Article
Experiments were undertaken using an ovarian adenocarcinoma cell line (A2780) and a drug-resistant strain (A2780.ad) derived from this line. P-glycoprotein could not be detected in A2780 cells but was essentially ubiquitous in A2780.ad cells, although removing the selective pressure for drug resistance led to reduced expression. However, the amount of P-glycoprotein present was used to predict the capacity of these cells to extrude rhodamine-123 (R-123) and their resistance to adriamycin, a cytotoxic drug. This accords with the role of P-glycoprotein as a drug pump. Although hypotonic solutions increased anion efflux from A2780 and A2780.ad cells, larger responses occurred in the parental line. Moreover, R-123 extrusion and anion efflux appeared to be mutually independent processes and so these data do not support the view that P-glycoprotein is involved in the control of volume-sensitive anion channels. Hypotonic solutions increased intracellular free calcium ([Ca2+]i) in drug-resistant cells but not in the parental line, and so establishing a drug-resistant strain may affect the control of [Ca2+]i during osmotic swelling. This could account for effects that were previously attributed to P-glycoprotein.
 
Article
We have explored the factors that may regulate membrane permeability in a cell line (NCL-SG3) derived from the human sweat gland epithelium. Ionomycin increased the rate of 125I-efflux from preloaded cells and this action appeared to be due to an increase in intracellular free calcium ([Ca2+]i). The ionomycin-evoked increase in 125I- efflux was reduced in cells that were exposed either to barium or to valinomycin in the presence of a high concentration of external potassium. It thus appears that a fraction of the ionomycin-evoked increase in 125I- efflux is due to the activation of potassium channels and experiments using 86Rb+ also suggested that ionomycin increased the rate of potassium efflux, an effect which was totally abolished by barium. Blockade of Na(+)-K(+)-2Cl- cotransport and of Cl- -HCO3- exchange reduced the basal rate of 125I- efflux and the ionomycin-evoked increase in 125I-efflux from control cells and from cells depolarized by valinomycin. These transport systems thus contribute to anion efflux, although [Ca2+]i-dependent chloride channels also appear to be present. Acetylcholine increases [Ca2+]i in the secretory cells of human sweat glands, but this neurotransmitter did not increase [Ca2+]i in NCL-SG3 cells and so membrane permeability was not under cholinergic control. Adrenaline did not increase [Ca2+]i, but this hormone did evoke cyclic-3',5'-adenosine monophosphate (cyclic AMP) production. However, membrane permeability was not under adrenergic control, as the cells did not appear to express functional, cyclic AMP-dependent anion channels. This may be because they were not fully differentiated under the culture conditions. ATP consistently evoked a dose-dependent increase in anion efflux that appeared to be mediated by [Ca2+]i. The increase in [Ca2+]i was initiated by the release of calcium from a limited internal store and was subsequently sustained by calcium influx. UTP and ADP also increased [Ca2+]i, whereas adenosine, AMP and alpha,beta-methylene ATP were without effect. These data thus suggest that a subclass of type 2 purine receptor, which is functionally coupled to phosphoinositidase C, is present in these cells.
 
Article
The present study was designed to test the hypothesis that the high renal vascular resistance characteristic of the newborn results from age-dependent changes in the responsiveness of the renal vasculature to kinins. Two studies were carried out in conscious, chronically instrumented lambs aged 1 and 6 weeks. Firstly, we measured the renal blood flow response to intra-arterial injection of the B2 receptor agonist bradykinin over the range of doses 0-800 ng x kg(-1). The ED50 renal blood flow response to bradykinin was 50 ng x kg(-1) in both age groups of lambs. Secondly, we measured the effects of intravenous administration of 12.5 microg x kg(-1) of the specific B2 receptor antagonist HOE 140; this dose attenuated the renal blood flow response to 50 ng x kg(-1) of bradykinin in both age groups. HOE 140 administration was associated with an age-dependent increase in mean arterial pressure, with little effect on heart rate or renal vascular resistance. This study provides new information regarding the effects of kinins in modulating renal haemodynamics during postnatal maturation. We reject our hypothesis and conclude that the high renal vascular resistance of the newborn does not appear to result from age-dependent changes in the responsiveness of the renal vasculature to endogenous kinins.
 
Article
The role of the nuclear corepressor Receptor Interacting Protein 140 (RIP140) in metabolic regulation, gene and protein expression and insulin signaling in skeletal muscle cells remains to be delineated. To study this question, L6 myotubes were treated with or without an RNAi oligonucleotide sequence to down-regulate RIP140 expression and incubated with or without insulin (1 μM). RIP140 down-regulation increased (P<0.05) basal palmitate uptake (20%) and decreased (P<0.05) basal palmitate oxidation (38%). In control siRNA-treated cells, insulin increased (P<0.05) glucose (31%) and palmitate (20%) uptake and decreased (P<0.05) palmitate oxidation (35%). However, in RIP140 siRNA-treated cells, insulin did not affect (P>0.05) palmitate uptake and increased (P<0.05) palmitate oxidation (79%). Under insulin-mediated conditions, RIP140 down-regulation decreased (P<0.05) AKTSer473 and PKC-ζThr403/410 phosphorylation. As expected, RIP140 down-regulation was accompanied by an increase (P<0.05) in COX4 and PGC-1α mRNA content. RIP140 down-regulation increased (P<0.05) FATP1 mRNA content and CPT1b protein content and decreased (P<0.05) MCAD mRNA content under basal conditions. Under insulin-mediated conditions, RIP140 down-regulation increased (P<0.05) CPT1b, FATP1, and FGF21 mRNA content and decreased (P<0.05) MCAD mRNA content and plasma membrane FAT/CD36 protein content. Our data show that, in skeletal muscle cells, RIP140 expression significantly impacts palmitate uptake and oxidation and that alterations in gene expression and AKT-PKC-ζ signaling can partially explain these changes.
 
Article
Plasmalemmal Cl- -HCO3- exchangers regulate intracellular pH and [Cl-] and cell volume. In polarized epithelial cells, they contribute also to transepithelial secretion and reabsorption of acid-base equivalents and of Cl-. Members of both the SLC4 and SLC26 mammalian gene families encode Na+-independent Cl- -HCO3- exchangers. Human SLC4A1/AE1 mutations cause either the erythroid disorders spherocytic haemolytic anaemia or ovalocytosis, or distal renal tubular acidosis. SLC4A2/AE2 knockout mice die at weaning. Human SLC4A3/AE3 polymorphisms have been associated with seizure disorder. Although mammalian SLC4/AE polypeptides mediate only electroneutral Cl- -anion exchange, trout erythroid AE1 also promotes osmolyte transport and increased anion conductance. Mouse AE1 is required for DIDS-sensitive erythroid Cl- conductance, but definitive evidence for mediation of Cl- conductance is lacking. However, a single missense mutation allows AE1 to mediate both electrogenic SO4(2-) -Cl- exchange or electroneutral, H+-independent SO4(2)- -SO4(2-) exchange. In the Xenopus oocyte, the AE1 C-terminal cytoplasmic tail residues reported to bind carbonic anhydrase II are dispensable for Cl- -Cl- exchange, but required for Cl- -HCO3- exchange. AE2 is acutely and independently inhibited by intracellular and extracellular H+, and this regulation requires integrity of the most highly conserved sequence of the AE2 N-terminal cytoplasmic domain. Individual missense mutations within this and adjacent regions identify additional residues which acid-shift pHo sensitivity. These regions together are modelled to form contiguous surface patches on the AE2 cytoplasmic domain. In contrast, the N-terminal variant AE2c polypeptide exhibits an alkaline-shifted pHo sensitivity, as do certain transmembrane domain His mutants. AE2-mediated anion exchange is also stimulated by ammonium and by hypertonicity by a mechanism sensitive to inhibition by chelation of intracellular Ca2+ and by calmidazolium. This growing body of structure-function data, together with increased structural information, will advance mechanistic understanding of SLC4 anion exchangers.
 
Article
The intracellular concentration of cholesterol is regulated by the balance between endogenous synthesis and exogenous uptake. Oestrogens have been reported to be involved in the physiological regulation of cellular cholesterol content. Relevant reports have focused on long-term responses and there is a lack of information about the relationship between the timing of the oestrogen effect and the regulation of cholesterol homeostasis. The aim of this work has been to set up a systematic picture of the short-term effects induced by oestrogen on hepatic lipid metabolism in vivo and the involvement of some relevant signal transduction pathways. At intervals after oestrogen administration (30 min to 6 h), oestrogen receptor expression and changes in liver cAMP, IP(3) and protein kinase C-alpha (PKC-alpha) were followed. Changes in the expression of the low density lipoprotein receptor at mRNA and protein levels, and of hydroxy-methyl-glutaryl-CoA reductase activity have been verified. At the same time, the content of hepatic cholesterol, ubiquinone and dolichol and of plasma cholesterol have been determined. Changes of rab 5 and rab 8, small GTP-binding prenylated proteins involved in the transfer of neosynthesised proteins through the cell, have been also checked. In vivo treatment with oestradiol produced no change in cyclic AMP but a rapid increase in IP(3), increased PKC-alpha localisation on the membranes and enhanced expression of the low density lipoprotein receptor in the liver occurred. PKC inhibition completely prevented any increase in low density lipoprotein receptor mRNA in isolated and perfused rat liver. Early changes of ubiquinone and dolichol content and a later reduction in hepatic hydroxy-methyl-glutaryl-CoA reductase activity and plasma cholesterol content were also detectable. A functional role of the IP(3) -protein kinase C-alpha pathway in the induction of the low density lipoprotein receptor is suggested. Experimental Physiology (2001) 86.1, 39-45.
 
Article
17,18-Epoxyeicosatetraenoic acid (17,18-EETeTr) stimulates vascular large-conductance K(+) (BK) channels. BK channels are composed of the pore-forming BK alpha and auxiliary BK beta1 subunits that confer an increased sensitivity for changes in membrane potential and calcium to BK channels. Ryanodine-sensitive calcium-release channels (RyR3) in the sarcoplasmic reticulum (SR) control the process. To elucidate the mechanism of BK channel activation, we performed whole-cell and perforated-patch clamp experiments in freshly isolated cerebral and mesenteric artery vascular smooth muscle cells (VSMC) from Sprague-Dawley rats, BK beta1 gene-deficient (-/-), BK alpha (-/-), RyR3 (-/-) and wild-type mice. The 17,18-EETeTr (100 nm) increased tetraethylammonium (1 mm)-sensitive outward K(+) currents in VSMC from wild-type rats and wild-type mice. The effects were not inhibited by the epoxyeicosatrienoic acid (EET) antagonist 14,15-epoxyeicosa-5(Z)-enoic acid (10 mum). BK channel currents were increased 3.5-fold in VSMC from BK beta1 (-/-) mice, whereas a 2.9-fold stimulation was observed in VSMC from RyR3 (-/-) mice (at membrane voltage 60 mV). The effects were similar compared with those observed in cells from wild-type mice. The BK current increase was neither influenced by strong internal calcium buffering (Ca(2)(+), 100 nm), nor by external calcium influx. The 17,18-EETeTr did not induce outward currents in VSMC BK alpha (-/-) cells. We next tested the vasodilator effects of 17,18-EETeTr on isolated arteries of BK alpha-deficient mice. Vasodilatation was largely inhibited in cerebral and mesenteric arteries isolated from BK alpha (-/-) mice compared with that observed in wild-type and BK beta1 (-/-) arteries. We conclude that 17,18-EETeTr represents an endogenous BK channel agonist and vasodilator. Since 17,18-EETeTr is active in small arteries lacking BK beta1, the data further suggest that BK alpha represents the molecular target for the principal action of 17,18-EETeTr. Finally, the action of 17,18-EETeTr is not mediated by changes of the internal global calcium concentration or local SR calcium release events.
 
Article
To examine whether obesity-associated leptin resistance could be due to down-regulation of leptin receptors (OB-Rs) and/or up-regulation of suppressor of cytokine signalling 3 (SOCS3) and protein tyrosine phosphatase 1B (PTP1B) in skeletal muscle, which blunt janus kinase 2-dependent leptin signalling and signal transducer and activator of transcription 3 (STAT3) phosphorylation and reduce AMP-activated protein kinase (AMPK) and acetyl-coenzyme A carboxylase (ACC) phosphorylation. Deltoid and vastus lateralis muscle biopsies were obtained from 20 men: 10 non-obese control subjects (mean +/- s.d. age, 31 +/- 5 years; height, 184 +/- 9 cm; weight, 91 +/- 13 kg; and percentage body fat, 24.8 +/- 5.8%) and 10 obese (age, 30 +/- 7 years; height, 184 +/- 8 cm; weight, 115 +/- 8 kg; and percentage body fat, 34.9 +/- 5.1%). Skeletal muscle OB-R170 (OB-R long isoform) protein expression was 28 and 25% lower (both P < 0.05) in arm and leg muscles, respectively, of obese men compared with control subjects. In normal-weight subjects, SOCS3 protein expression, and STAT3, AMPKalpha and ACCbeta phosphorylation, were similar in the deltoid and vastus lateralis muscles. In obese subjects, the deltoid muscle had a greater amount of leptin receptors than the vastus lateralis, whilst SOCS3 protein expression was increased and basal STAT3, AMPKalpha and ACCbeta phosphorylation levels were reduced in the vastus lateralis compared with the deltoid muscle (all P < 0.05). In summary, skeletal muscle leptin receptors and leptin signalling are reduced in obesity, particularly in the leg muscles.
 
Article
A functional -174 C/G polymorphism in the interleukin-6 gene (IL6) is a candidate to explain individual variations in exercise-related phenotypes. To replicate recent findings showing an association between the G allele and GG genotype of elite power sports performance in European (Spanish) Caucasian males, we compared allelic and genotypic frequencies of the IL6 -174 C/G polymorphism among elite endurance athletes (n = 74) and power athletes (n = 81) and non-athletic control subjects (n = 205) of both sexes from Israel. All subjects were Israeli Caucasians (with an equivalent ratio of non-Ashkenazi and Ashkenazi descent in each group; 2:1). We found no differences in the genotype or allele frequencies among groups (all P > 0.3). We further compared the genotype and allele frequencies between national- (n = 109) and international-level Israeli athletes (n = 46) in the endurance and power group, and found no significant genotype or allele differences after adjusting for multiple comparisons. We repeated all the analyses after pooling the Israeli and Spanish control subjects, endurance and power elite athletes, and found no genotypic and allelic differences among groups. The results did not change when the analyses were repeated including only the best Israeli athletes (i.e. the international-level group) together with the group of elite Spanish athletes (P > 0.2). In conclusion, the results of the present study did not show an association between the G allele of the IL6 -174 G/C polymorphism and power sports performance in the Israeli (Caucasian) population. Our findings support the need to replicate association results between genetic polymorphisms and athletic status in populations of different ethnic backgrounds with the largest possible population samples.
 
Article
17beta-Oestradiol (E2)-mediated inhibition of angiotensin-converting enzyme (ACE) protects the E2-replete kidney from the progression of hypertensive renal disease. Angiotensin-converting enzyme 2 (ACE2), a homologue of ACE, counters the actions of ACE by catalysing the conversion of angiotensin II (Ang II) to angiotensin(1-7) [Ang(1-7)]. We investigated E2 regulation of ACE2 in the renal wrap (RW) model of hypertension in rats. After 6 weeks on a high-sodium diet (4% NaCl), the activity of ACE2 was reduced in the renal cortex by 31%, which was mirrored by similar decreases in ACE2 protein (30%) and mRNA expression (36%) in the ovariectomized RW rat (RW-OVX); E2 replacement prevented these effects. The RW-OVX rats exhibited greater renal injury, including 1.7-fold more tubulointerstitial fibrosis and 1.6-fold more glomerulosclerosis than E2-replete females (RW-Intact and RW-OVX+E2). Angiotensin(1-7) infusion prevented these exacerbating effects of ovariectomy on renal pathology; no differences in indicators of renal injury were observed between RW-OVX-Ang(1-7) and RW-Intact rats. These renal protective effects of Ang(1-7) infusion were not attributable to increased ACE2 activity or to changes in heart rate or body weight, since these parameters were unchanged by Ang(1-7) infusion. Furthermore, Ang(1-7) infusion did not attenuate renal injury by reducing mean arterial pressure (MAP), since infusion of the peptide did not lower MAP but rather caused a slight increase during a 6 week chronic treatment for Ang(1-7). These results suggest that E2-mediated upregulation of renal ACE2 and the consequent increased Ang(1-7) production contribute to E2-mediated protection from hypertensive renal disease. These findings have implications for E2-deficient women with hypertensive renal disease and suggest that therapeutics targeted towards increasing ACE2 activity and Ang(1-7) levels will be renal protective.
 
Article
It has been reported that in streptozotocin (STZ)-induced diabetes, hyperglycaemia leads to progressive insulin resistance of the peripheral tissues. In this study, we tried to elucidate the effects of hyperglycaemia on insulin sensitivity and insulin signalling in ovariectomized (STZ)-induced diabetic rats. In addition, we attempted to demonstrate the role of 17beta-oestradiol and progesterone on insulin sensitivity, focusing on their effects on key proteins of skeletal muscle, insulin receptor (IR) and glucose transporter-4 (Glut-4). Our results show that hyperglycaemia could modulate insulin signalling, at the IR and Glut-4 level, in different ways depending on exposure time. 17beta-Oestradiol and progesterone have different effects on insulin signalling. 17beta-Oestradiol treatment improves insulin sensitivity, but its action is dependent on the exposure time and its plasma level. During the early period of treatment (days 6-11), this hormone counteracts the effects of hyperglycaemia downstream of the IR, whereas during the later period of treatment (days 11-16), it may counteract the effects of hyperglycaemia by modulating IR relative tyrosine phosphorylation. By contrast, progesterone only improves insulin sensitivity during the early period of treatment (days 6-11), and this effect is not associated with changes in IR and Glut-4 content. Both hormones have a protective role in skeletal muscle against the effects of glucose toxicity, but their effects begin at different stages of treatment. These new findings improve our understanding of insulin resistance in type 1 diabetes mellitus and of the risk/benefit ratio when 17beta-oestradiol and progesterone are used in oral contraceptives or hormone replacement therapy taken by menopausal women with controlled type 1 diabetes mellitus.
 
Article
The objective of this study was to investigate whether the acute haemodynamic effects of angiotensin-converting enzyme inhibition with captopril could be enhanced by oestrogen administration, and then to evaluate the mechanisms involved in this enhancement. All experiments were performed in 18-week-old female spontaneously hypertensive rats arranged in three experimental groups: intact; ovariectomized (OVX); and ovariectomized plus treatment with 17beta-oestradiol (OVX + E2). These groups were used to evaluate the effects of captopril administration alone, or following bradykinin B2 receptor blockade or nitric oxide synthase inhibition, on a number of haemodynamic parameters (mean arterial pressure, cardiac index, vascular resistance and heart rate). The drop in mean arterial pressure and vascular resistance index in response to captopril was more pronounced in intact and ovariectomized rats treated with 17beta-oestradiol than in ovariectomized animals. Blockade of bradykinin B2 receptors or inhibition of nitric oxide synthesis attenuated the synergy between 17beta-oestradiol and captopril. It is concluded that ovariectomy blunted the blood pressure and vascular resistance index drop observed in intact rats in response to captopril. Treatment with 17beta-oestradiol prevented the blunted response to captopril in ovariectomized rats. Kinins and nitric oxide may be involved in the mechanisms of 17beta-oestradiol potentiation of the haemodynamic effects of captopril.
 
Article
At the outset, the Board decided to enhance the QJEP's content by publishing invited review articles, papers presented at selected symposia and, above all, the Sharpey-Schafer Lectures to honour the journal's founder. Volume 67, the second under our control, implemented this new policy with the publication of an influential review by the late Alan Brown on The Dorsal Horn of the Spinal Cord. This volume also had the full papers offered at a Physiological Society Symposium on Hormonal Control of Sodium Excretion held at Charing Cross Medical School on November 6th 1981, to mark the retirement of Professor H. E. De Wardener. Other review articles and symposia papers followed in volumes 68,69,70 and 71. Volume 68 was issued in 1983, the 75th anniversary of the QJEP. The journal celebrated 1983 by carrying a banner heading on the journal's cover, by holding a dinner for its Editors and Committee Members at Abden House in Edinburgh University and, more significantly, by publishing the Sharpey-Schafer lecture on Morphological Basis of Visual Control Function given by the Nobel Laureate Torsten N. Weisel and Charles D. Gilbert at UCL on 30th March, 1983. Volume 68 also contained David Whitteridge's revealing and much-quoted history of the QJEP entitled The Origin of the Quarterly Journal of Experimental Physiology. Volume 71 carried the next Sharpey-Schafer Lecture on Ion Channels and Signal Processing in the Outer Retina delivered by David Atwell at UCL on 25th March, 1986. The next volume, my last as Chairman, included a brief tribute to a fellow Editor - the highly gifted and respected Peter Baker who died suddenly on 10th March, 1987 on the eve of his 48th birthday. His loss was deeply felt by the QJEP Editors and Members of the Society; we can only imagine what his death meant to his family and friends. Although my period as an Editor ended on a tragic note, I feel that our Board ensured that the QJEP's early nurture from 1980 to 1987 under The Society's care was a healthy and pivotal one.
 
Article
During exercise the magnitude of the cardiovascular response is closely matched to the intensity of the exercise. In achieving this appropriate matching, an important role is played by the autonomic nervous system. Two mechanisms have been postulated to regulate this response. In one mechanism the changes in autonomic nerve activity to the heart and blood vessels are caused by signals arising in a central area of the brain and in the other mechanism the changes are caused by signals arising in the contracting skeletal muscle. In 1970-71 two studies were performed in Oxford which furthered our understanding of these two mechanisms. In one of these studies it was shown in cats that a reflex arising in the contracting skeletal muscle reflexly increased blood pressure and heart rate and that the thinly myelinated (Group III or A ) and the unmyelinated (Group IV or C) afferent nerve fibers were responsible. In the second of these studies it was shown in humans that a central mechanism could also increase the blood pressure and heart rate during static contraction at a fixed force. Tendon vibration of a skeletal muscle induces an involuntary reflex contraction. Utilizing this effect the central command needed to produce the same tension development was reduced or increased. When the same force was achieved with less central command the cardiovascular response was reduced and with more central command was increased. This demonstrated that descending motor commands from higher brain centers have an effect on the cardiovascular response to exercise.
 
Article
Inhibition of neurones in the ventral medulla accentuates the respiratory inhibition associated with acute blood pressure elevation in piglets. Activation of presynaptic 5-HT(1A) receptors inhibits serotonergic neurones in the ventral medulla and caudal raphé, and we tested the hypothesis that administration of 8-hydroxydipropylaminotetralin (8-OH-DPAT), a 5-HT(1A) agonist, within the rostroventral medulla and caudal raphé would enhance baroreceptor-mediated inhibition of respiratory activity in decerebrate, neonatal piglets. Baroreceptor stimulation was achieved by inflating a balloon in the distal aorta to elevate carotid blood pressure. After two to four control trials of baroreceptor stimulation, each piglet was given either a single intravenous (i.v.) dose of 10 microg kg(-1) 8-OH-DPAT or treated by adding 10 or 30 mm 8-OH-DPAT to the dialysate for approximately 10 min to inhibit serotonergic neurones, after which the baroreceptor stimulation trials were repeated. Baroreceptor stimulation reduced respiratory activity, particularly the respiratory frequency, which diminished from 35.7 +/- 3.3 to 33.8 +/- 3.1 breaths min(-1) (P < 0.02) and, following i.v. 8-OH-DPAT, baroreceptor-mediated inhibition of respiratory output was significantly accentuated (P < 0.05); the respiratory frequency declined from 34.5 +/- 3.6 to 26.5 +/- 2.9 breaths min(-1). Increasing aortic blood pressure reduced the respiratory frequency (P < 0.01), but focal dialysis of 10 or 30 mm 8-OH-DPAT had, on average, no effect on the ventilatory inhibition associated with an acute elevation of blood pressure. We conclude that activation of 5-HT(1A) receptors after systemic administration of 8-OH-DPAT enhanced baroreflex-mediated inhibition of ventilation, but this effect cannot be attributed to 5-HT(1A) receptor activation within the rostroventral medulla and caudal raphé.
 
Article
The T-type calcium channel (T-channel) is a low-voltage-activated channel. Whether T-channels are involved in sympathetic nerve discharge (SND), with subunits α1G and α1H differentially regulating SND genesis, was explored using in vitro brainstem-spinal cord-splanchnic sympathetic nerve preparations of wild-type and genetically modified B6 mice. Applications of 10-80 μm NNC 55-0396 to block T-channels in wild-type mice reduced SND in a concentration-dependent manner. Amounts of SND were measured in units of signal-to-noise ratio for objective comparisons between mouse groups. Comparable amounts of SND were observed in wild-type and α1G(-/-) mice. However, only ∼40% of the amount of SND of that in wild-type or α1G(-/-) mice was observed in α1H(-/-) mice. Whether a diminished excitatory drive originating in the brainstem could explain a low SND in α1H(-/-) mice was evaluated by cervical cord transections. Isolated spinal cord preparations of mice with different genetic backgrounds produced comparable amounts of SND. Excitability of the spinal circuitry was further explored by bath applications of 5 mm glutamate. Glutamate applications produced a prominent SND rise in all mouse groups. The ratios of glutamate-induced SND rise were similar between wild-type and α1H(-/-) mice, but significantly higher in α1G(-/-) mice. Taken together, these results suggest that α1H in mouse brainstem is essential for the genesis of presympathetic drive, whereas α1G in mouse spinal cord is functionally inhibitory for SND genesis. We conclude that α1H and α1G T-channel subunits may differentially regulate mouse SND genesis at different levels of the neuraxis.
 
Article
Both the (1S,3S) and (1S,3R) stereoisomers of 1-aminocyclopentane-1,3-dicarboxylate (ACPD), but not the (1R,3R) or (1R,3S) isomers, potently depress the fastest (presumed monosynaptic) component of dorsal root-evoked ventral root potentials in hemisected isolated spinal cord of the newborn rat. This effect is not due to antagonism of known excitatory amino acid (EAA) receptors on motoneurones and may reflect an action of the two ACPD isomers at presynaptic EAA receptors of the L-2-amino-4-phosphonobutyrate (L-AP4) type.
 
Article
We have reported that a change in muscle fibre type distribution is present in two strains of diabetic rats (Otsuka Long-Evans Tokushima Fatty and Goto-Kakizaki rats). In this study, we determined whether the change in soleus muscle fibre type distribution was caused by diabetes, using obese, diabetic (Zucker diabetic fatty, ZDF), obese, non-diabetic (Zucker fatty, ZF) and non-diabetic, non-obese rats (Zucker lean, ZL). Moreover, we investigated whether the gene expression levels of metabolic key molecules, namely the transcriptional factors of metabolic genes, exemplified by peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha), and the oxidative enzymes in mitochondria, exemplified by succinate dehydrogenase (SDH), were changed in type I and II muscle fibres in each type of rat, using the new technique of laser capture microdissection (LCM). Both plasma glucose and glucosylated haemoglobin levels were significantly higher in ZDF than in ZL and ZF rats. A lower percentage of type IIA fibres was observed in the muscles of ZDF rats than in those of ZL and ZF rats. The mRNA expression levels of SDH in type II fibres and of PGC-1alpha in type I fibres were significantly lower in ZDF than in ZL and ZF rats as assessed by LCM and real-time PCR analysis. We have shown, for the first time, that a lower percentage of type IIA fibres was observed in ZDF rats. We have also discovered that the expression levels of the oxidative metabolism-related genes, PGC-1alpha and SDH, decreased in type I and type II fibres, respectively, of ZDF rats.
 
Article
The Na(+)-K(+)-2Cl(-) cotransporter (NKCC1) is responsible for ion transport across the secretory and absorptive epithelia, the regulation of cell volume, and possibly the modulation of cell growth and development. It has been reported that a variety of cells, including osteoblasts, contain this cotransporter. In this study, the physiological role of NKCC1 in osteoclastogenesis was exploited in a co-culture system. Bumetanide, a specific inhibitor of NKCC1, reduced the number of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells. In order to investigate the mechanism by which bumetanide inhibits osteoclastogenesis, the mRNA expressions of the receptor activator of nuclear factor (NF)-kappaB ligand (RANKL) and osteoprotegerin (OPG) were analysed by RT-PCR. Exposure of osteoblastic cells to a medium containing 1 micro M bumetanide reduced RANKL mRNA expression induced by 10 nM 1alpha,25-dihydroxyvitamin D3 (1alpha,25(OH)2D3, in a dose-dependent manner. In addition, RANKL expression was also analysed with enzyme-linked immunosorbant assay (ELISA) using anti-RANKL antibody. The expression of RANKL was decreased with the increase of bumetanide concentration. In contrast, the expression of OPG mRNA, a novel tumour necrosis factor (TNF) receptor family member was increased in the presence of bumetanide. These results imply that bumetanide inhibits osteoclast differentiation by reducing the RANKL/OPG ratio in osteoblastic cells. However, no significant difference in M-CSF mRNA expression was observed when bumetanide was added. Also, we found that the phosphorylation of c-Jun NH2-terminal kinase (JNK), which regulates the activity of various transcriptional factors, was reduced by bumetanide treatment. Conclusively, these findings suggest that NKCC1 in osteoblasts has a pivotal role in 1alpha,25(OH)2D3-induced osteoclastogenesis partly via the phosphorylation of JNK.
 
Article
Aim Interaction of peroxisome proliferator-activated receptor γ co-activator 1α (PGC-1α) with other cellular signaling pathways plays an important role in the training-induced mitochondrial adaptations. The purpose of this study is to examine whether pyrolidine dithiocarbamate (PDTC), a nuclear factor κB (NFκB) inhibitor and antioxidant, and β-adrenergic blocker propranolol (PROP) would affect PGC-1α-induced mitochondrial transcription factors, enzymes and proteins involved in energy metabolism and antioxidant defense in response to endurance training. Methods Female Sprague-Dawley rats (age 8 wks) were randomly divided into two groups (N=24): subjected to 8-wk treadmill training or remained sedentary. Each group of rats was injected (i.p.) daily with either PDTC (50 mg/kg body wt), PROP (30 mg/kg) or saline as control 1 h before daily exercise session. Results Sedentary PDTC rats showed 75% higher PGC-1α content (P<0.01) but lower mitochondrial transcription factor A (Tfam) and phosphorylated cAMP-responsive element binding protein (p-CREB) than control rats. Training increased PGC-1α by 57% (P<0.01), cytochrome c oxidase 4 (COXIV) by 30% (P<0.05) and p-CREB by 13% (P<0.05), whereas mitochondrial mitofusin-2 (Mfn2) level was decreased 24% (P<0.01). PDTC treatment decreased PGC-1α and p-CREB content by 34 and 53% (P<0.05), respectively, in trained rats and abolished training effects on COXIV and Mfn2. None of the training effects was abolished by PROP treatment. Mitochondrial superoxide dismutase activity was decreased with PDTC whereas training-induced glutathione peroxidase activity was unaltered by either drug. Conclusion NFκB-inhibitory and antioxidant properties of PDTC can attenuate PGC-1α mediated mitochondrial adaptation to endurance training, whereas the β-adrenergic pathway has little adverse effect.
 
Article
Experiments were carried out to determine if endogenous pyrogen-induced fever impairs protective responses of newborn rats to hypoxia. Twenty-seven 5- to 6-day-old conscious rat pups received a subcutaneous injection of 0.20 microg of recombinant rat interleukin-1beta (rrIL-1beta) per kilogram of body weight to induce fever, or an equal volume of vehicle. They were then either exposed to a single period of hypoxia produced by breathing an anoxic gas mixture (97 % N(2)-3 % CO(2)) and their time to last gasp was determined, or they were exposed repeatedly to hypoxia and their ability to autoresuscitate from primary apnoea was determined. Core temperature increased significantly following administration of rrIL-1beta but did not change following administration of vehicle (i.e. vehicle, 0.0 +/- 0.1 degrees C; rrIL-1beta, 0.7 +/- 0.3 degrees C; P < 0.001) before exposure to hypoxia. IL-1beta-induced fever did not alter the time to last gasp when the pups were exposed to a single period of hypoxia or the number of successful autoresuscitations upon repeated exposure to hypoxia. Thus, our data do not support the hypothesis that endogenous pyrogen-induced fever impairs the protective responses in newborns that may prevent death during hypoxia as may occur during single or repeated episodes of prolonged sleep apnoea.
 
Article
Heart failure is associated with a low grade and chronic cardiac inflammation that impairs function, however the mechanisms by which this sterile inflammation occurs in structural heart disease remain poorly defined. Cardiac-specific heterozygous overexpression of the calcineurin transgene (CNTg) in mice results in cardiac hypertrophy, inflammation, apoptosis, and ventricular dilation. We hypothesized that activation of the Nlrp3 inflammasome, an intracellular danger sensing pathway required for processing the pro-inflammatory cytokine interleukin-1β (IL-1β), may contribute to myocardial dysfunction and disease progression. Here we report that Nlrp3 mRNA was increased in CNTg mice compared to WT. Consistent with inflammasome activation, CNTg animals had increased conversion of pro-caspase-1 to cleaved and activated forms as well as markedly increased serum IL-1β. Blockade of IL-1β signaling via chronic IL-1 receptor antagonist (IL-1-ra) therapy reduced cardiac inflammation and myocyte pathology in CNTg mice, resulting in improved systolic performance. Furthermore, genetic ablation of Nlrp3 in CNTg mice reduced pro-inflammatory cytokine maturation, cardiac inflammation and improved systolic performance. These findings indicate that activation of the Nlrp3 inflammasome in CNTg mice promotes myocardial inflammation and systolic dysfunction through the production of pro-inflammatory IL-1β. Blockade of IL-1β signaling with the IL-1-ra reverses these phenotypes, and offers a possible therapeutic approach in the management of heart failure.
 
Article
Ca2+ mobilization by membrane depolarization or histamine application, was measured in isolated human uterine artery smooth muscle cells. Nifedipine, a Ca2+ channel blocker, was found to inhibit the depolarization-induced increase in [Ca2+]i but not the histamine-induced increase. This suggests the presence of functional voltage-dependent Ca2+ channels and agonist-induced mobilization of Ca2+ via a different mechanism. Caffeine inhibited both the depolarization- and histamine-induced increases in intracellular calcium. The mechanisms of inhibition do not involve cAMP and point to a complex action of caffeine at multiple sites. The dephosphorylating agent 2,3-butanedione monoxime (BDM) was found to block voltage-dependent Ca2+ changes but not agonist-induced changes suggesting a role for phosphorylation in the regulation of the Ca2+ channels in these cells.
 
Article
Procedures that reduce contraction are used to facilitate optical measurements of membrane potential, but it is unclear to what extent they affect the excitability of the heart. This study has examined the electrophysiological consequences of a range of extracellular [Ca2+] (0.7-2.5 mmol l(-1)), 2,3-butane-dione monoxime (BDM; 1-20 mmol l(-1)) and cytochalasin-D (Cyto-D; 1-5 micromol l(-1)). Monophasic action potentials (MAPs) were recorded from the basal epicardial surface of the left ventricle of isolated rabbit hearts. Conduction delay (CD) and time to 90% repolarisation of the monophasic action potential (MAPD90) were measured. The effects of BDM and Cyto-D on restitution were studied at a [Ca2+] of 1.9 mmol l(-1). Restitution curves for MAPD90 were generated using a standard S1-S2 protocol. All manoeuvres decreased left ventricular developed pressure (LVDP): 0.7 mmol l(-1) Ca2+ to 74.0 +/- 6.1%, 20 mmol l(-1) BDM to 4.5 +/- 1.0%, and 5 micromol l(-1) Cyto-D to 12.8 +/- 3.5% of control value. CD decreased from a control value (33.3 +/- 1.0 ms, n= 16) to 93.0 +/- 2.2% in 0.7 mmol l(-1) Ca2+, but increased to 133.7 +/- 10.5% in 20 mmol l(-1) BDM and 127.4 +/- 10.6% in 5 micromol l(-1) Cyto-D. At 350 ms pacing cycle length, MAPD90 (control = 119.6 +/- 1.7 ms n= 16) was prolonged by reduced extracellular [Ca2+]. BDM had no effects on MAPD90 at control pacing rates. Cyto-D caused a significant prolongation (to 115.0 +/- 3.0% of control, n= 6) at the highest concentration studied (5 micromol l(-1)). Both BDM (20 mmol l(-1)) and Cyto-D (3 micromol l(-1)) flattened the restitution curves but neither agent altered maximum MAPD90. Extracellular [Ca2+] of 1.9 mmol l(-1) in conjunction with a moderate dose of Cyto-D (3 micromol l(-1)) reduced contractility with minimal effects on action potential duration and conduction at a fixed pacing cycle length. However, both BDM and Cyto-D had pronounced effects on electrical restitution.
 
Article
The effects of 2,3-butanedione monoxime (BDM, 0.5-20 mM) on Ca(2+)-activated force in skinned muscle fibres, and force and Ca2+ responses in aequorin-injected intact fibres from the iliofibularis muscle of the cane toad Bufo marinus were investigated. Peak twitch force responses progressively decreased to 3% of the control response with increasing [BDM] up to 20 mM. Peak twitch aequorin light responses decreased to 65% of the control response in 10 mM BDM, but increased again to control values in 20 mM BDM. The duration of the twitch aequorin light response increased by up to 60% above 5 mM BDM. Tetanic (170 Hz) force and aequorin light responses reversibly decreased in a dose-dependent fashion to about 50% of the control response in 10 mM BDM. Failure of tetanic (170 Hz) stimulation was observed in the presence of 20 mM BDM. Intracellular [Ca2+] could be modified by changing the frequency of tetanic stimulation in the presence of BDM, permitting a study of the dependence of isometric force on intracellular [Ca2+] at different concentrations of BDM. In 10 mM BDM, the rate of force development in intact fibres was slower by a factor of two at saturating [Ca2+], and was up to one order of magnitude slower at non-saturating [Ca2+], when compared with control responses. At a similar intracellular [Ca2+] steady-state isometric force was reduced to about 85 and 50% of the control responses in 2 and 10 mM BDM, respectively. The effect of BDM on maximum Ca2+-activated force in skinned fibres paralleled the decrease in tetanic (170 Hz) force observed in intact fibres. The rate of force development in skinned fibres decreased with an increase in [BDM] at constant [Ca2+], and the sensitivity of the contractile apparatus to Ca2+ was shifted to a higher [Ca2+] by BDM. The results suggest that BDM reduces contractility in cane toad iliofibularis muscle by direct inhibition of the contractile apparatus, and reduction of the release of activator Ca2+ from the sarcoplasmic reticulum. Furthermore, BDM may be a useful tool to help study the relationship between force and [Ca2+] in intact muscle fibres.
 
Article
This study tested the hypothesis that prolonged physical deconditioning affects the coupling of left ventricular depolarization to its ejection (the pre-ejection period, PEPi) and that this effect is minimized by exercise countermeasures. Following assignment to non-exercise (Control) and exercise groups (Exercise), 14 females performed 56 days of continuous head-down tilt bed rest. Measurements of the electrocardiogram (ECG) and stroke volume (Doppler ultrasound) during supine rest were obtained at baseline prior to (Pre) and after (Post) the head-down tilt bed rest (HDBR) period. Compared with Pre, the PEPi was increased following head-down tilt bed rest (main effect, P < 0.005). This effect was most dominant in the Control group [Pre = 0.038 ± 0.06 s (s.d.) versus Post = 0.054 ± 0.011 s; P < 0.001]. In the Exercise group, PEPi was 0.032 ± 0.005 s Pre and 0.038 ± 0.018 s Post; P= 0.08. Neither the QRS interval nor cardiac afterload was modified by head-down tilt bed rest in Control or Exercise groups. Low-dose isoprenaline infusion reversed the head-down tilt bed rest-induced delay in the PEPi. These results suggest that head-down tilt bed rest leads to a delayed onset of systolic ejection following left ventricular depolarization in a manner that is affected little by the exercise countermeasure but is related to β-adrenergic pathways. The delayed onset of systole following head-down tilt bed rest appears to be related to mechanism(s) affecting contraction of the left ventricle rather than its depolarization.
 
Article
Vagus is Latin for Wandering and the vagus nerve fully deserves this name due to its extensive distribution through the body. Indeed, one of the lines of the song that accompanied the 2012 GL Brown Lecture exaggerates this diversity, "My function's almost anythin', and Vagus is my name" Altering vagal activity was first investigated in the 1880s as a treatment for epilepsy and vagus nerve stimulation (VNS) is now an approved treatment for refractory epilepsy and depression in the US, despite an incomplete understanding of the mechanisms involved. VNS could be beneficial in many other conditions including heart failure, tinnitus, chronic hiccups, Alzheimer's and inflammatory diseases. Inhibition of vagal activity could also be beneficial in some conditions e.g. reducing activation of vagal respiratory afferents to treat chronic cough. This review discusses evidence underlying some current and potential therapeutic applications of vagal modulation, illustrating the wonders of the Wanderer!
 
Article
Voltage-gated sodium channels initiate action potentials in nerve, muscle, and other excitable cells. Early physiological studies described sodium selectivity, voltage-dependent activation, and fast inactivation, and developed conceptual models for sodium channel function. This review article follows the topics of my 2013 Sharpey-Schafer Prize Lecture and gives an overview of research using a combination of biochemical, molecular biological, physiological, and structural biological approaches that has elucidated the structure and function of sodium channels at the atomic level. Structural models for voltage-dependent activation, sodium selectivity and conductance, drug block, and both fast and slow inactivation are discussed. A perspective for the future envisions new advances in understanding the structural basis for sodium channel function and the opportunity for structure-based discovery of novel therapeutics.
 
Article
We are endlessly fascinated by memory; we desire to improve it and fear its loss. While it has long been recognised that brain regions such as the hippocampus are vital for supporting memories of our past experiences - autobiographical memories - we still lack fundamental knowledge about the mechanisms involved. This is because the study of specific neural signatures of autobiographical memories in vivo in humans presents a significant challenge. However, recent developments in high-resolution structural and functional magnetic resonance imaging (MRI) coupled with advanced analysis methods now permit access to the neural substrates of memory representations that has hitherto been precluded in humans. Here I describe how the application of 'decoding' techniques to brain imaging data is beginning to disclose how individual autobiographical memory representations evolve over time, deepening our understanding of systems-level consolidation, prompting in particular new questions about the roles of the hippocampus and ventromedial prefrontal cortex, and offering new opportunities to interrogate the elusive memory trace that has for so long confounded neuroscientists.
 
Article
This is the first study using the selective agonist/antagonist stereoisomers of dihydropyridine 202791 to investigate stimulus-secretion coupling in pancreatic islet cells. We studied effects of the (+)(Ca2+ channel agonist) and (-)(Ca2+ channel antagonist) forms of the dihydropyridine, on 45calcium net uptake, insulin secretion, and membrane potential measured in rodent islets. The antagonist partially inhibited glucose-induced insulin secretion and Ca2+ uptake; however, the potassium-induced Ca2+ uptake was completely inhibited. The antagonist did not completely block glucose-evoked spike activity. Addition of the agonist enhanced insulin release and Ca2+ uptake in the presence of 5.6 mM-glucose, but did not increase insulin release or Ca2+ uptake in 16.7 mM-glucose. In the presence of tetraethylammonium (TEA), (+)202791 increased and (-)202791 decreased the duration of glucose-induced action potentials. The results again confirm the presence of a dihydropyridine-sensitive Ca2+ channel in pancreatic B-cells. In addition these data suggest that in these cells there is activation of a dihydropyridine-insensitive Ca2+ entry in the presence of glucose.
 
Article
The hypothesis that glucagon 1-21 (G1-21) is trophic to the gastrointestinal tract was investigated in the hypoplastic intestine of intravenously maintained rats. Three groups of eight rats were fed parenterally for three days and then were infused with either 0, 20 or 80 micrograms rat-1 day-1 of G1-21 for 3 days. No significant effect on the weight of the stomach, caecum or colon was observed, but both the weight and crypt cell production rate of the small intestine were significantly decreased by G1-21. Plasma enteroglucagon was also decreased by G1-21 treatment. It is concluded that G1-21 does not have a trophic effect on the gastrointestinal tract, and, in fact, has an antiproliferative effect on the small intestine, which could in turn be modulated by decreased levels of endogenous enteroglucagon.
 
Cumulative cisternal milk volumes during 24 h milk driainage from one udder half (details in text; data from two raindomly chosen cows are shown).
Article
Five primiparous and five multiparous cows were used to determine if mammary cisternal storage of milk during a 24 h period of milk accumulation limited milk secretion. In addition, we investigated if there is a parity effect for the capacity of the mammary cisternal compartment to hold a 24 h accumulation of milk secretion, and studied the movement of milk from the alveolar compartment into the cisternal compartment. All cows were fitted with catheters in all teats in order to collect cisternal and alveolar milk fractions separately. For a 24 h period of milk accumulation, the milk was drained once (after 24 h) from one side of the udder (OD), and continuously from the other side of the udder (CD). There was no significant parity effect for cisternal, alveolar and total milk volumes at 24 h. Therefore, data from primi- and multiparous cows were pooled for subsequent analyses. Cisternal milk volume from CD glands was higher than that from OD glands (P < 0.01), indicating that cisternal storage of milk in the mammary gland may be limiting to milk secretion during 24 h milking intervals. Alveolar volumes did not differ between OD and CD, but, as a result of the higher cisternal milk volume, total milk volume was highest in the CD glands (P = 0.05). Movement of milk from the alveolar into the cisternal compartment was intermittent. Moreover, analyses of the slopes of individual milk accumulation profiles of the first 6 h of accumulation revealed that the cisternal compartment starts filling immediately following milking, although the rate of filling is relatively low until 7-8 h postmilking.
 
Article
Previous studies have suggested that the uptake of prolactin from the blood into the milk may be restricted when the alveolus is distended with milk. Therefore the aim of this study was to determine the relationship between prolactin in milk and milk production by measuring the concentration of prolactin in samples of fore- and hind-milk as well as the volume of milk removed for each breast, at each breastfeed over a 24 h period. The mean (+/-S.D.) concentration of prolactin in milk for all women (n = 15) over the 24 h period was 18.5 +/- 11.6 mug l(-1) (fore-milk) and 16.8 +/- 12.8 mug l(-1) (hind-milk). The variation between women masked small changes within women in the concentration of prolactin in milk over the 24 h period, therefore a prolactin ratio (individual fore- or hind-milk value divided by the mean for all fore- or hind-milk samples collected over a 24 h period) was determined. The concentration of prolactin was highest in milk between 02.01 and 06.00 h (prolactin ratio for fore- to hind-milk, 1.5), and lowest between 10.01 and 18.00 h (prolactin ratio for fore- to hind-milk, 0.8). Furthermore, we observed that the difference in prolactin concentration between the fore- and hind-milk (fore-hind gradient) was greatest between 06.01 and 10.00 h (4 mug l(-1)). To ensure that this effect was not due to permeability in the paracellular pathway, the concentrations of serum albumin and sodium in milk were measured. No significant (P > 0.05) changes over the 24 h period, or with increasing time since last feed were observed. We therefore concluded that when the breast is most drained of milk (in the late evening), and the rate of milk synthesis is greatest, the fore-hind prolactin gradient in the milk of the following feed (in the early morning) is highest. This is consistent with the observation that prolactin uptake from the blood by the lactocyte is dependent on the fullness of the breast, such that prolactin uptake may be inhibited in full alveoli.
 
Article
Heat production was continuously measured from birth to 24 h after birth in pigs tube-fed 14 g kg-1 of colostrum or water (sham-fed animals) at hourly intervals, and maintained at thermoneutrality (34 degrees C) or in moderate cold (24 degrees C). Results indicate that colostrum was necessary to initiate and sustain the postnatal rise in metabolic rate observed at 34 degrees C. It provided about 75% of the energy required for heat production at 24 degrees C. Heat production was increased by 74% in the cold and decreased by 30% during starvation. In both cases, maintenance of the energy balance was achieved with a compensatory drop in body temperature. At 34 degrees C, variations in postmeal heat production represented 12% of the total 24 h energy expenditure and were almost equally due to the thermogenic effect of colostrum and to confounding factors, including physical activity. In the cold, calculated postmeal thermogenesis accounted only for 3% of 24 h energy expenditure and for 9% of the extra heat produced in the cold. Our results highlight the main role of colostral energy in the energy metabolism of the newborn pig in a typical birth environment (24 degrees C) and in thermoneutral conditions (34 degrees C). Thermoneutral postmeal thermogenesis is low and its contribution to the extra heat produced in the cold very limited.
 
Article
Cardiovascular arousal is associated with patterned cortical activity changes. Head-down tilt bed rest dimishes baroreflex-mediated cardiac control. The present study tested the hypothesis that head-down bed rest deconditioning would modify the forebrain organization for heart rate control during baroreflex unloading. Heart rate (HR) variability (HRV), blood pressure and plasma hormones were analyzed at rest whereas HR and cortical autonomic activation patterns (functional magnetic resonance imaging) were measured during graded and randomly assigned lower body negative pressure segments (LBNP, -15, and -35 mmHg) both before (Pre) and after (Post) a 24 hour head-down bed rest (HDBR) protocol (Study 1; n=8). An additional group was tested before and following diuretic-induced (Diuretic) hypovolemia (Study 2: n=9; Aldactone, 100 mg/day for 3 days) that mimicked the plasma volume lost during HDBR (-15% in both studies; P<0.05). HDBR with hypovolemia did not affect baseline HR, MAP, HRV or plasma catecholamines. HDBR augmented the LBNP-induced HR response (P<0.05) and this was associated with bedrest-induced development of i) enhanced activation within the genual anterior cingulate cortex (ACC) and the right anterior insular cortex (IC) and ii) deactivation patterns within the subgenual regions of the ACC. Diuretic treatment (without HDBR) did not affect baseline HR and MAP, but did reduce resting HRV and elevated circulating norepinephrine and plasma renin activity (P<0.05). The greater HR response to LBNP following Diuretic (P<0.05) was associated with diminished activation of the right anterior insula. Our findings indicate that a) 24 hours of HDBR minmized the impact of diuretic treatment on baseline autonomic and cardiovascular variables, b) despite the similar augmentation of HR responses to LBNP, and despite similar pre-intervention cortical activation patterns, HDBR and Diuretic produced different effects on the cortical responses with HDBR affecting ACC and right insula regions whereas Diuretic affected primarily the right insula alone but in a direction that was opposite to HDBR. The data indicate that physical deconditioning can induce rapid functional changes within the cortical circuitry associated with baroreflex unoading, changes that are distinct from diuretic-induced hypovolemia. The results suggest that physical activity patterns exert rapid and notable impact on the cortical circuitry associated with cardiovascular control.
 
Top-cited authors
Helmut Sies
  • Heinrich-Heine-Universität Düsseldorf
David A Jones
  • Manchester Metropolitan University
John H Coote
  • University of Birmingham
Peter E Hartmann
  • University of Western Australia
Robert D Guzy
  • The University of Chicago Medical Center