János Fodor

University of Debrecen, Debreczyn, Hajdú-Bihar, Hungary

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Publications (22)76.3 Total impact

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    ABSTRACT: The sarcoplasmic/endoplasmic reticulum Ca 2+ ATPases (SERCAs) are the main Ca 2+ pumps which decrease the intracellular Ca 2+ level by reaccumulating Ca 2+ into the sarco-plasmic reticulum. The neonatal SERCA1b is the major Ca 2+ pump in myotubes and young muscle fibers. To understand its role during skeletal muscle differentiation its synthesis has been interfered with specific shRNA sequence. Stably transfected clones showing significantly decreased SERCA1b expression (cloneC1) were selected for experiments. The expression of the regulatory proteins of skeletal muscle differentiation was examined either by Western-blot at the protein level for MyoD, STIM1, calsequestrin (CSQ), and calcineurin (CaN) or by RT-PCR for myostatin and MCIP1.4. Quantitative analysis revealed significant alterations in CSQ, STIM1, and CaN expression in cloneC1 as compared to control cells. To examine the functional consequences of the decreased expression of SERCA1b, repeated Ca 2+-transients were evoked by applications of 120 mM KCl. The significantly higher [Ca 2+ ]i measured at the 20 th and 40 th seconds after the beginning of KCl application (112±3 and 110±3 nM vs. 150±7 and 135±5 nM, in control and in cloneC1 cells, respectively) indicated a decreased Ca 2+-uptake capability which was quantified by extracting the maximal pump rate (454±41 μM/s vs. 144±24 μM/s, in control and in cloneC1 cells). Furthermore, the rate of calcium release from the SR (610±60 vs. 377±64 μM/s) and the amount of calcium released (843±75 μM vs. 576±80 μM) were also significantly suppressed. These changes were also accompanied by a reduced activity of CaN in cells with decreased SERCA1b. In parallel, cloneC1 cells showed inhibited cell proliferation and decreased myotube nuclear numbers. Moreover, while cyclosporineA treatment suppressed the proliferation of parental cultures it had no effect on cloneC1 cells. SERCA1b is thus considered to play an essential role in the regulation of [Ca 2+ ]i and its ab ovo gene silencing results in decreased skeletal muscle differentiation.
    Full-text · Article · Apr 2015 · PLoS ONE
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    ABSTRACT: The High-Mobility Group Box 1 protein (HMGB1) is a known nuclear protein which may be released from the nucleus into the cytoplasm and the extracellular space. It is believed that the mobilized HMGB1 plays role in the autoimmune processes as an alarmin, stimulating the immune response. In addition, muscle regeneration and differentiation may also be altered in the inflammatory surroundings. Biopsy specimens derived from patients with idiopathic inflammatory myopathies (IIM) such as polymyositis or dermatomyositis were compared to muscle samples from patients undergoing surgical interventions for coxarthrosis. The biopsy and surgery specimens were used for Western blot analysis, for immunohistochemical detection of HMGB1 in histological preparations and for cell culturing to examine cell proliferation and differentiation. Our data show lower HMGB1 expression, impaired proliferation and slightly altered fusion capacity in the primary cell cultures started from IIM specimens than in cultures of coxarthrotic muscles. The ratio of regenerating muscle fibres with centralised nuclei (myotubes) is lower in the IIM samples than in the coxarthrotic ones but corticosteroid treatment shifts the ratio towards the coxarthrotic value. Our data suggest that the impaired regeneration capacity should also be considered to be behind the muscle weakness in IIM patients. The role of HMGB1 as a pathogenic signal requires further investigation.
    No preview · Article · Mar 2015 · Journal of Muscle Research and Cell Motility
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    ABSTRACT: TASK-3 (KCNK9 or K2P9.1) channels are thought to promote proliferation and/or survival of malignantly transformed cells, most likely by increasing their hypoxia tolerance. Based on our previous results that suggested mitochondrial expression of TASK-3 channels, we hypothesized that TASK-3 channels have roles in maintaining mitochondrial activity. In the present work we studied the effect of reduced TASK-3 expression on the mitochondrial function and survival of WM35 and A2058 melanoma cells. TASK-3 knockdown cells had depolarized mitochondrial membrane potential and contained a reduced amount of mitochondrial DNA. Compared to their scrambled shRNA-transfected counterparts, they demonstrated diminished responsiveness to the application of the mitochondrial uncoupler [(3-chlorophenyl)hydrazono]malononitrile (CCCP). These observations indicate impaired mitochondrial function. Further, TASK-3 knockdown cells presented reduced viability, decreased total DNA content, altered cell morphology, and reduced surface area. In contrast to non- and scrambled shRNA-transfected melanoma cell lines, which did not present noteworthy apoptotic activity, almost 50 % of the TASK-3 knockdown cells exhibited strong Annexin-V-specific immunofluorescence signal. Sequestration of cytochrome c from the mitochondria to the cytosol, increased caspase 3 activity, and translocation of the apoptosis-inducing factor from mitochondria to cell nuclei were also demonstrated in TASK-3 knockdown cells. Interference with TASK-3 channel expression, therefore, induces caspase-dependent and -independent apoptosis of melanoma cells, most likely via causing mitochondrial depolarization. Consequently, TASK-3 channels may be legitimate targets of future melanoma therapies.
    No preview · Article · Oct 2014 · Archives for Dermatological Research
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    ABSTRACT: Presence of the pituitary adenylate cyclase-activating polypeptide (PACAP) signalling has been proved in various peripheral tissues. PACAP can activate protein kinase A (PKA) signalling via binding to pituitary adenylate cyclase-activating polypeptide type I receptor (PAC1), vasoactive intestinal polypeptide receptor (VPAC) 1 or VPAC2 receptor. Since little is known about the role of this regulatory mechanism in bone formation, we aimed to investigate the effect of PACAP on osteogenesis of UMR-106 cells. PACAP 1-38 as an agonist and PACAP 6-38 as an antagonist of PAC1 were added to the culture medium. Surprisingly, both substances enhanced protein expressions of collagen type I, osterix and alkaline phosphatase, along with higher cell proliferation rate and an augmented mineralisation. Although expression of PKA was elevated, no alterations were detected in the expression, phosphorylation and nuclear presence of CREB, but increased nuclear appearance of Runx2, the key transcription factor of osteoblast differentiation, was shown. Both PACAPs increased the expressions of bone morphogenetic proteins (BMPs) 2, 4, 6, 7 and Smad1 proteins, as well as that of Sonic hedgehog, PATCH1 and Gli1. Data of our experiments indicate that activation of PACAP pathway enhances bone formation of UMR-106 cells and PKA, BMP and Hedgehog signalling pathways became activated. We also found that PACAP 6-38 did not act as an antagonist of PACAP signalling in UMR-106 cells.
    Full-text · Article · Aug 2014 · Journal of Molecular Neuroscience

  • No preview · Article · Aug 2014 · Acta Physiologica
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    ABSTRACT: Osteoarthritis (OA) is the most common form of chronic musculoskeletal disorders. A migratory stem cell population termed chondrogenic progenitor cells (CPC) with in vitro chondrogenic potential was previously isolated from OA cartilage. Since intracellular Ca(2+) signalling is an important regulator of chondrogenesis, we aimed to provide a detailed understanding of the Ca(2+) homeostasis of CPCs. In this work, CPCs immortalised by lentiviral administration of the human telomerase reverse transcriptase (hTERT) and grown in monolayer cultures were studied. Expressions of all three IP3Rs were confirmed, but no RyR subtypes were detected. Ca(2+) oscillations observed in CPCs were predominantly dependent on Ca(2+) release and store replenishment via store-operated Ca(2+) entry; CPCs express both STIM1 and Orai1 proteins. Expressions of adenosine receptor mRNAs were verified, and adenosine elicited Ca(2+) transients. Various P2 receptor subtypes were identified; P2Y1 can bind ADP; P2Y4 is targeted by UTP; and ATP may evoke Ca(2+) transients via detected P2X subtypes, as well as P2Y1 and P2Y2. Enzymatic breakdown of extracellular nucleotides by apyrase completely abrogated Ca(2+) oscillations, suggesting that an autocrine/paracrine purinergic mechanism may drive Ca(2+) oscillations in these cells. As CPCs possess a broad spectrum of functional molecular elements of Ca(2+) signalling, Ca(2+)-dependent regulatory mechanisms can be supposed to influence their differentiation potential.
    Full-text · Article · May 2014 · Pflügers Archiv - European Journal of Physiology
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    ABSTRACT: Myostatin, a member of the transforming growth factor β family was shown to be a potent negative regulator of skeletal muscle growth, as myostatin deficient mice have a great increase in muscle mass. Yet, the physical performance of these animals is not improved but suppressed. As an explanation, alterations in the steps in excitation-contraction coupling were hypothesized and tested for on mice with the 12-bp deletion in the propeptide region of the myostatin precursor (MstnCmpt-dl1Abc or Cmpt). In voluntary wheel running control C57/BL6 mice performed better than the mutant animals in both maximal speed and total distance covered. Despite the previously described lower specific force of Cmpt animals, the pCa-force relationship, determined on chemically permeabilized fibre segments did not show any significant difference between the two mouse strains. While resting intracellular Ca2+ concentration ([Ca2+]i) measured on single intact flexor digitorum brevis (FDB) muscle fibres using Fura-2 AM was similar to control (72.0±1.7 vs. 78.1±2.9 nM, n=38 and 45), the amplitude of KCl-evoked calcium transients was smaller (360±49 vs. 222±45 nM, n=22) in the mutant strain. Similar results were obtained using tetanic stimulation and Rhod-2 AM which gave calcium transients that were smaller (2.42±0.11 vs. 2.06±0.10 ΔF/F0, n=14 and 13, respectively) on Cmpt mice. SR calcium release flux, calculated from these transients showed a reduced peak (23.7±3.0 vs. 15.8±2.1 mMs-1) and steady level (5.7±0.7 vs. 3.7±0.5 mMs-1) with no change in the peak-to-steady ratio. The amplitude and spatial spread of calcium release events detected on permeabilized FDB fibres were also significantly smaller in mutant mice. These results suggest that reduced SR calcium release underlies the reduced muscle force in Cmpt animals.
    Full-text · Article · Jan 2014 · The Journal of Physiology
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    ABSTRACT: Chondrogenesis is known to be regulated by calcium-dependent signalling pathways in which temporal aspects of calcium homeostasis are of key importance. We aimed to better characterise calcium influx and release functions with respect to rapid calcium oscillations in cells of chondrifying chicken high density cultures. We found that differentiating chondrocytes express the α1 subunit of voltage-operated calcium channels (VOCCs) at both mRNA and protein levels, and that these ion channels play important roles in generating Ca(2+) influx for oscillations as nifedipine interfered with repetitive calcium transients. Furthermore, VOCC blockade abrogated chondrogenesis and almost completely blocked cell proliferation. The contribution of internal Ca(2+) stores via store-operated Ca(2+) entry (SOCE) seems to be indispensable to both Ca(2+) oscillations and chondrogenesis. Moreover, this is the first study to show the functional expression of STIM1/STIM2 and Orai1, molecules that orchestrate SOCE, in chondrogenic cells. Inhibition of SOCE combined with ER calcium store depletion abolished differentiation and severely diminished proliferation, suggesting the important role of internal pools in calcium homeostasis of differentiating chondrocytes. Finally, we present an integrated model for the regulation of calcium oscillations of differentiating chondrocytes that may have important implications for studies of chondrogenesis induced in various stem cell populations.
    Full-text · Article · May 2013 · Cell calcium
  • C. Matta · J. Fodor · T. Juhász · R. Zákány
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    ABSTRACT: It is well established that Ca2+ signalling mediates the effects of mechano-transduction in chondrocytes of mature articular cartilage. However, little is known about the precise regulation of Ca2+ homeostasis in differentiating cells of developing hyaline cartilage. Therefore, our research group is committed to characterise the Ca2+ homeostasis and to map the 'Ca2+ toolkit' of differentiating chondrogenic mesenchymal cells. High density cell culture system (HDC) established from chondrogenic mesenchymal cells isolated from limb buds of 4-day-old chicken embryos is a well-known model of in vitro cartilage differentiation, in which a spontaneous cartilage formation occurs in 6 days. We measured cytosolic free Ca2+ concentration ([Ca2+ ]i) in cells of HDC on different days of culturing. After an initial value of 80 nM, a significant transient elevation was detected in Fura-2-loaded cells on day 3 of culturing, when the majority of cells differentiate into chondroblasts and chondrocytes. This 140 nM peak of cytosolic Ca2+ concentration is a result of increased Ca2+ influx and is found to be indispensable to proper chondrogenesis, because elimination of extracellular Ca2+ abolished the Ca2+ peak of day 3 and inhibited cartilage formation. Uncontrolled Ca2+ influx evoked by a Ca2+ ionophore (A23187) exerted dual effects on chondrogenesis in a concentration-dependent manner; low concentration of the ionophore increased [Ca2+ ]i up to 150 nM and facilitated cartilage formation, whereas high concentration of this compound elevated it over 250 nM and almost totally blocked cartilage formation. Proliferation of chondrogenic cells was more sensitive to modulation of [Ca2+ ]i then the viability of cells. Although chondrogenic cells express both IP3 and ryanodine receptors and can release Ca2+ from intracellular stores, these stores proved to play a minor role in the Ca2+ homeostasis of these cells. As the inhibition of the Ca2+ -calmodulin sensitive protein phosphatase calcineurin impeded the [Ca2+ ]i-peak in chondrogenic cells and reduced cartilage formation, we propose its contribution in the regulation of [Ca2+ ]i in these cells. We also found that chondrogenic cells secreted ATP and administration of ATP to the culture medium evoked Ca2+ transients exclusively in the presence of extracellular Ca2+ and on day 3 of culturing. Moreover, ATP caused elevated protein expression of the chondrogenic transcription factor Sox9 and also stimulated cartilage matrix production. ATP may exert these functions via acting through purinergic receptors; and indeed, expression of both ionotropic (P2X) and metabotropic (P2Y) purinergic receptors were detected. Metabotropic purinergic receptor agonist UTP caused a low level (60 nM) transient elevation of [Ca2+]i in 3-day-old HDC, without having an influence on cartilage matrix production. Application of suramin, which blocks all P2X receptors but not P2X4, did not impede the effects of ATP; furthermore, P2X4 appeared in the plasma membrane of differentiating cells only from day 3. In summary, chondrogenic cells possess a set of different molecules which enable them to modulate their Ca2+ homeostasis and [Ca2+ ]i was found to be kept in a narrow range during chondrogenesis. We present evidence on a significant new regulatory mechanism of chondrogenesis with revealing the role of Ca2+ influx of chondrogenic cells via P2X4 purinergic receptors.
    No preview · Chapter · Feb 2012
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    Dataset: Figure S2
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    ABSTRACT: Effects of TEA (2 mM) on cartilage matrix production and proliferation of HDC. (A) 2 mM TEA was applied continuously from day 1. Metachromatic cartilage areas in 6-day-old high-density colonies were visualized with DMMB dissolved in 3% acetic acid. Optical density (OD625) was determined in samples containing toluidine blue extracted with 8% HCl dissolved in absolute ethanol. Scale bar, 500 µM. (B–C) Effects of TEA treatment on the mRNA expression of Sox9, type II collagen and aggrecan on day 3, and protein expression and phosphorylation level of Sox9 in HDC on day 3 of culturing. For RT-PCR reactions, GAPDH was used as a control. (D) Effects of TEA treatments on cellular proliferation in HDC. Assays were carried out during the administration of TEA. (TIF)
    Preview · Dataset · Nov 2011
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    Dataset: Figure S1
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    ABSTRACT: Effects of TTX (60 nM) on cartilage matrix production of HDC. (A) 60 nM TTX was applied continuously from day 1. Metachromatic cartilage areas in 6-day-old high-density colonies were visualized with DMMB dissolved in 3% acetic acid. Optical density (OD625) was determined in samples containing toluidine blue extracted with 8% HCl dissolved in absolute ethanol. Scale bar, 500 µM. (B–C) Effects of TTX treatment on the mRNA expression of Sox9, type II collagen and aggrecan on day 3, and protein expression and phosphorylation level of Sox9 in HDC on day 3 of culturing. For RT-PCR reactions, GAPDH was used as a control. (TIF)
    Preview · Dataset · Nov 2011
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    ABSTRACT: Understanding the key elements of signaling of chondroprogenitor cells at the earliest steps of differentiation may substantially improve our opportunities for the application of mesenchymal stem cells in cartilage tissue engineering, which is a promising approach of regenerative therapy of joint diseases. Ion channels, membrane potential and Ca2+-signaling are important regulators of cell proliferation and differentiation. Our aim was to identify such plasma membrane ion channels involved in signaling during chondrogenesis, which may serve as specific molecular targets for influencing chondrogenic differentiation and ultimately cartilage formation.
    Full-text · Article · Nov 2011 · PLoS ONE
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    ABSTRACT: To date, four isoforms of triadins have been identified in rat skeletal muscle. While the function of the 95-kDa isoform in excitation-contraction coupling has been studied in detail, the role of the 32-kDa isoform (Trisk 32) remains elusive. Here, Trisk 32 overexpression was carried out by stable transfection in L6.G8 myoblasts. Co-localization of Trisk 32 and IP(3) receptors (IP(3)R) was demonstrated by immunocytochemistry, and their association was shown by co-immunoprecipitation. Functional effects of Trisk 32 on IP(3)-mediated Ca(2+) release were assessed by measuring changes in [Ca(2+)](i) following the stimulation by bradykinin or vasopressin. The amplitude of the Ca(2+) transients evoked by 20 μM bradykinin was significantly higher in Trisk 32-overexpressing (p < 0.01; 426 ± 84 nM, n = 27) as compared to control cells (76 ± 12 nM, n = 23). The difference remained significant (p < 0.02; 217 ± 41 nM, n = 21, and 97 ± 29 nM, n = 31, respectively) in the absence of extracellular Ca(2+). Similar observations were made when 0.1 μM vasopressin was used to initiate Ca(2+) release. Possible involvement of the ryanodine receptors (RyR) in these processes was excluded, after functional and biochemical experiments. Furthermore, Trisk 32 overexpression had no effect on store-operated Ca(2+) entry, despite a decrease in the expression of STIM1. These results suggest that neither the increased activity of RyR, nor the amplification of SOCE, is responsible for the differences observed in bradykinin- or vasopressin-evoked Ca(2+) transients; rather, they were due to the enhanced activity of IP(3)R. Thus, Trisk 32 not only co-localizes with, but directly contributes to, the regulation of Ca(2+) release via IP(3)R.
    Full-text · Article · Aug 2011 · Pflügers Archiv - European Journal of Physiology
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    ABSTRACT: When the intracellular calcium stores are depleted, a Ca(2+) influx is activated to refill these stores. This store-operated Ca(2+) entry (SOCE) depends on the cooperation of several proteins as STIM1, Orai1, and, possibly, TRPC1. To elucidate this role of TRPC1 in skeletal muscle, TRPC1 was overexpressed in C2C12 cells and SOCE was studied by measuring the changes in intracellular Ca(2+) concentration ([Ca(2+)](i)). TRPC1 overexpression significantly increased both the amplitude and the maximal rate-of-rise of SOCE. When YM-58483, an inhibitor of TRPC1 was used, these differences were eliminated, moreover, SOCE was slightly suppressed. A decrease in the expression of STIM1 together with the downregulation of SERCA was confirmed by Western-blot. As a consequence, a reduction in maximal Ca(2+) uptake rate and a higher resting [Ca(2+)](i) following the Ca(2+) transients evoked by 120mM KCl were detected. Morphological changes also accompanied the overexpression of TRPC1. Differentiation of the myoblasts started later, and the myotubes were thinner in TRPC1-overexpressing cultures. For these changes the observed decrease in the nuclear expression of NFAT1 could be responsible. Our results suggest that enhanced expression of TRPC1 increases SOCE and has a negative effect on the STIM1-Orai1 system, indicating an interaction between these proteins.
    Full-text · Article · Jun 2011 · Cell calcium
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    ABSTRACT: TASK-3 channel overexpression was shown to facilitate the survival of malignantly transformed cells, possibly by providing greater hypoxia tolerance through a still unknown mechanism. Although it has been suggested previously that TASK-3 channels are expressed in the mitochondrial membranes, their role here remains elusive. In this study, a transient transfection of TASK-3 knockdown melanoma cell cultures was produced to show the significance of TASK-3 expression. Reduction of the TASK-3 protein biosynthesis induced characteristic changes in cell morphology, reduced the amount of DNA and decreased metabolic activity and mitochondrial function of melanoma cells when compared with control. These findings indicate that TASK-3 channel expression and function is indispensable for the proliferation and/or survival of the melanoma cells, as they seem to contribute to their mitochondrial functions. The significance is that, in this study, we have shown that TASK-3 channels are expressed in the mitochondria of melanoma malignum cells, and they are essential for maintaining cellular integrity and viability. The TASK-3 knockdown melanoma cell line had altered morphology, reduced DNA content, decreased metabolic activity and impaired mitochondrial function. These data indicate that TASK-3 channels are functionally present in the mitochondria of the melanoma cells, and their function is essential for the survival of these cells, thus TASK-3 channels may be the possible targets of future anticancer therapy.
    No preview · Article · Apr 2011 · Melanoma research
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    Full-text · Article · Feb 2011 · Biophysical Journal
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    Preview · Article · Jan 2010 · Biophysical Journal
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    ABSTRACT: The immunosuppressant cyclosporine A (CsA) is a specific pharmacological inhibitor of calcineurin, the Ca2+-calmodulin activated phospho-Ser/Thr-specific protein phosphatase. Although calcineurin-inhibiting compounds are applied for local treatment of psoriasis or atopic dermatitis in dermatological practice, little is known about the functions of calcineurin in epidermis-derived malignancies. We investigated the effects of CsA on two human melanoma cell lines, the metastasis forming HT168 and WM35 established from an RGP primary lesion. CsA of 2 microM lowered the enzyme activity by 50% and caused elevation in both mRNA and protein expression of calcineurin. Cell proliferation was diminished, as well as the cellular morphology and the actin organization were altered in both cell lines. CsA increased cell death moderately in both cell lines and reduced the metabolic activity of HT168 cells, but not that of WM35 cells. CsA also elevated the expressions of both Bcl-2 and ERK1/2. Fibronectin guided migration of HT168 cells was stimulated under the effect of CsA, while that of WM35 cells was reduced, moreover, HT168 cells switched from the expression of beta3 to beta1 integrin, but WM35 cells continued to express beta3. Based on our results we propose a multiple, partly malignancy-dependent role of calcineurin in these melanoma cell lines.
    Full-text · Article · May 2009 · International Journal of Oncology
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    ABSTRACT: We have previously demonstrated that elevation of free cytosolic Ca(2+) concentration at the time of differentiation of chondroblasts was mainly due to a Ca(2+) influx and it was indispensable to cartilage formation in chicken high density mesenchymal cell cultures (HDC) [C. Matta, J. Fodor, Z. Szijgyarto, T. Juhasz, P. Gergely, L. Csernoch, R. Zakany, Cytosolic free Ca(2+) concentration exhibits a characteristic temporal pattern during in vitro cartilage differentiation: a possible regulatory role of calcineurin in Ca-signalling of chondrogenic cells, Cell Calcium 44 (2008) 310-323]. Here, we report that chondrogenic cells secreted ATP and administration of ATP to the culture medium evoked Ca(2+) transients exclusively in the presence of extracellular Ca(2+) and only on day 3 of culturing, when the final commitment of chondroblasts occurs. Moreover, ATP caused elevated protein expression of the chondrogenic transcription factor Sox9 and stimulated cartilage matrix production. Expression pattern of different types of both ionotropic and metabotropic purinergic receptors was detected. Agonists of metabotropic receptors, ADP and UDP did not evoke any Ca(2+) transients and had no influence on cartilage formation, while UTP caused transient elevation of cytosolic Ca(2+) concentration in 3-day-old HDC without stimulating matrix production. Suramin, which blocks all P2X receptors but not P2X(4) did not impede the effects of ATP, furthermore, P2X(4) appeared in the plasma membrane fraction and gave signals with immunocytochemistry only from day 3. In summary, we suggest a role of ionotropic purinergic signalling of P2X(4) in the generation of ATP-dependent Ca(2+) transients of differentiating chondroblasts.
    Full-text · Article · Apr 2009 · Cell calcium
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    ABSTRACT: The 95 kDa triadin (Trisk 95), an integral protein of the sarcoplasmic reticular membrane in skeletal muscle, interacts with both the ryanodine receptor (RyR) and calsequestrin. While its role in the regulation of calcium homeostasis has been extensively studied, data are not available on whether the overexpression or the interference with the expression of Trisk 95 would affect calcium sparks the localized events of calcium release (LCRE). In the present study LCRE and calcium transients were studied using laser scanning confocal microscopy on C2C12 cells and on primary cultures of skeletal muscle. Liposome- or adenovirus-mediated Trisk 95 overexpression and shRNA interference with triadin translation were used to modify the level of the protein. Stable overexpression in C2C12 cells significantly decreased the amplitude and frequency of calcium sparks, and the frequency of embers. In line with these observations, depolarization-evoked calcium transients were also suppressed. Similarly, adenoviral transfection of Trisk 95 into cultured mouse skeletal muscle cells significantly decreased both the frequency and amplitude of spontaneous global calcium transients. Inhibition of endogenous triadin expression by RNA interference caused opposite effects. Primary cultures of rat skeletal muscle cells expressing endogenous Trisk 95 readily generated spontaneous calcium transients but rarely produced calcium sparks. Their transfection with specific shRNA sequence significantly reduced the triadin-specific immunoreactivity. Functional experiments on these cells revealed that while caffeine-evoked calcium transients were reduced, LCRE appeared with higher frequency. These results suggest that Trisk 95 negatively regulates RyR function by suppressing localized calcium release events and global calcium signals in cultured muscle cells.
    Full-text · Article · Nov 2008 · The Journal of Physiology