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Krishnan JKS, Rice S, Mikes M, Sugiura MH, Drew KL, Barati Z, Oliver SR. Pre-hibernation diet alters skeletal muscle relaxation kinetics, but not force development in torpid arctic ground squirrels. J Comp Physiol B 2024; 194:65-79. [PMID: 38219236 DOI: 10.1007/s00360-023-01527-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2022] [Revised: 11/10/2023] [Accepted: 11/20/2023] [Indexed: 01/16/2024]
Abstract
During the hibernation season, Arctic ground squirrels (AGS) experience extreme temperature fluctuations (body temperature, Tb, as low as - 3 °C), during which they are mostly physically inactive. Once Tb reaches ~ 15 °C during interbout arousals, hibernators recruit skeletal muscle (SkM) for shivering thermogenesis to reach Tb of ~ 35 °C. Polyunsaturated fatty acids (PUFA) in the diet are known to influence SkM function and metabolism. Recent studies in the cardiac muscle of hibernators have revealed that increased levels of ω-6 and the ω-6:ω-3 PUFA ratio correlate with sarco/endoplasmic reticulum calcium ATPase (SERCA) activity and hibernation status. We hypothesized that diet (increased ω-6:ω-3 PUFA ratio) and torpor status are important in the regulation of the SERCA pump and that this may improve SkM performance during hibernation. Ex vivo functional assays were used to characterize performance changes in SkM (diaphragm) from AGS fed the following diets. (1) Standard rodent chow with an ω-6:ω-3 ratio of 5:1, or (2) a balanced diet with an ω-6:ω-3 ratio of 1:1 that roughly mimics wild diet. We collected diaphragms at three different stages of hibernation (early torpor, late torpor, and arousal) and evaluated muscle function under hypothermic temperature stress at 4 °C, 15 °C, 25 °C, and 37 °C to determine functional resilience. Our data show that torpid animals fed standard rodent chow have faster SkM relaxation when compared to the balanced diet animals. Furthermore, we discovered that standard rodent chow AGS during torpor has higher SkM relaxation kinetics, but this effect of torpor is eliminated in balanced diet AGS. Interestingly, neither diet nor torpor influenced the rate of force development (rate of calcium release). This is the first study to show that increasing the dietary ω-6:ω-3 PUFA ratio improves skeletal muscle performance during decreased temperatures in a hibernating animal. This evidence supports the interpretation that diet can change some functional properties of the SkM, presumably through membrane lipid composition, ambient temperature, and torpor interaction, with an impact on SkM performance.
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Affiliation(s)
- Jishnu K S Krishnan
- Department of Chemistry and Biochemistry, University of Alaska Fairbanks, Fairbanks, AK, USA
| | - Sarah Rice
- Department of Chemistry and Biochemistry, University of Alaska Fairbanks, Fairbanks, AK, USA
- Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK, USA
| | - Monica Mikes
- Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK, USA
| | - M Hoshi Sugiura
- Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK, USA
| | - Kelly L Drew
- Department of Chemistry and Biochemistry, University of Alaska Fairbanks, Fairbanks, AK, USA
- Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK, USA
| | - Zeinab Barati
- Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK, USA
| | - S Ryan Oliver
- Department of Chemistry and Biochemistry, University of Alaska Fairbanks, Fairbanks, AK, USA.
- Department of Chemistry, United States Naval Academy, Annapolis, MD, USA.
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Bardsley OJ, Matthews HR, Huang CLH. Finite element analysis predicts Ca 2+ microdomains within tubular-sarcoplasmic reticular junctions of amphibian skeletal muscle. Sci Rep 2021; 11:14376. [PMID: 34257321 PMCID: PMC8277803 DOI: 10.1038/s41598-021-93083-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2021] [Accepted: 06/14/2021] [Indexed: 02/06/2023] Open
Abstract
A finite element analysis modelled diffusional generation of steady-state Ca2+ microdomains within skeletal muscle transverse (T)-tubular-sarcoplasmic reticular (SR) junctions, sites of ryanodine receptor (RyR)-mediated SR Ca2+ release. It used established quantifications of sarcomere and T-SR anatomy (radial diameter [Formula: see text]; axial distance [Formula: see text]). Its boundary SR Ca2+ influx densities,[Formula: see text], reflected step impositions of influxes, [Formula: see text] deduced from previously measured Ca2+ signals following muscle fibre depolarization. Predicted steady-state T-SR junctional edge [Ca2+], [Ca2+]edge, matched reported corresponding experimental cytosolic [Ca2+] elevations given diffusional boundary efflux [Formula: see text] established cytosolic Ca2+ diffusion coefficients [Formula: see text] and exit length [Formula: see text]. Dependences of predicted [Ca2+]edge upon [Formula: see text] then matched those of experimental [Ca2+] upon Ca2+ release through their entire test voltage range. The resulting model consistently predicted elevated steady-state T-SR junctional ~ µM-[Ca2+] elevations radially declining from maxima at the T-SR junction centre along the entire axial T-SR distance. These [Ca2+] heterogeneities persisted through 104- and fivefold, variations in D and w around, and fivefold reductions in d below, control values, and through reported resting muscle cytosolic [Ca2+] values, whilst preserving the flux conservation ([Formula: see text] condition, [Formula: see text]. Skeletal muscle thus potentially forms physiologically significant ~ µM-[Ca2+] T-SR microdomains that could regulate cytosolic and membrane signalling molecules including calmodulin and RyR, These findings directly fulfil recent experimental predictions invoking such Ca2+ microdomains in observed regulatory effects upon Na+ channel function, in a mechanism potentially occurring in similar restricted intracellular spaces in other cell types.
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Affiliation(s)
- Oliver J. Bardsley
- grid.5335.00000000121885934Physiological Laboratory, University of Cambridge, Downing Street, Cambridge, CB2 3EG UK
| | - Hugh R. Matthews
- grid.5335.00000000121885934Physiological Laboratory, University of Cambridge, Downing Street, Cambridge, CB2 3EG UK
| | - Christopher L.-H. Huang
- grid.5335.00000000121885934Physiological Laboratory, University of Cambridge, Downing Street, Cambridge, CB2 3EG UK ,grid.5335.00000000121885934Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QW UK
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Liu SX, Matthews HR, Huang CLH. Sarcoplasmic reticular Ca 2+-ATPase inhibition paradoxically upregulates murine skeletal muscle Na v1.4 function. Sci Rep 2021; 11:2846. [PMID: 33531589 PMCID: PMC7854688 DOI: 10.1038/s41598-021-82493-w] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2020] [Accepted: 01/11/2021] [Indexed: 12/18/2022] Open
Abstract
Skeletal muscle Na+ channels possess Ca2+- and calmodulin-binding sites implicated in Nav1.4 current (INa) downregulation following ryanodine receptor (RyR1) activation produced by exchange protein directly activated by cyclic AMP or caffeine challenge, effects abrogated by the RyR1-antagonist dantrolene which itself increased INa. These findings were attributed to actions of consequently altered cytosolic Ca2+, [Ca2+]i, on Nav1.4. We extend the latter hypothesis employing cyclopiazonic acid (CPA) challenge, which similarly increases [Ca2+]i, but through contrastingly inhibiting sarcoplasmic reticular (SR) Ca2+-ATPase. Loose patch clamping determined Na+ current (INa) families in intact native murine gastrocnemius skeletal myocytes, minimising artefactual [Ca2+]i perturbations. A bespoke flow system permitted continuous INa comparisons through graded depolarizing steps in identical stable membrane patches before and following solution change. In contrast to the previous studies modifying RyR1 activity, and imposing control solution changes, CPA (0.1 and 1 µM) produced persistent increases in INa within 1-4 min of introduction. CPA pre-treatment additionally abrogated previously reported reductions in INa produced by 0.5 mM caffeine. Plots of peak current against voltage excursion demonstrated that 1 µM CPA increased maximum INa by ~ 30%. It only slightly decreased half-maximal activating voltages (V0.5) and steepness factors (k), by 2 mV and 0.7, in contrast to the V0.5 and k shifts reported with direct RyR1 modification. These paradoxical findings complement previously reported downregulatory effects on Nav1.4 of RyR1-agonist mediated increases in bulk cytosolic [Ca2+]. They implicate possible local tubule-sarcoplasmic triadic domains containing reduced [Ca2+]TSR in the observed upregulation of Nav1.4 function following CPA-induced SR Ca2+ depletion.
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Affiliation(s)
- Sean X Liu
- Physiological Laboratory, University of Cambridge, Cambridge, CB2 3EG, UK
| | - Hugh R Matthews
- Physiological Laboratory, University of Cambridge, Cambridge, CB2 3EG, UK
| | - Christopher L-H Huang
- Physiological Laboratory, University of Cambridge, Cambridge, CB2 3EG, UK.
- Department of Biochemistry, University of Cambridge, Cambridge, CB2 1QW, UK.
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Vornanen M. Effects of acute warming on cardiac and myotomal sarco(endo)plasmic reticulum ATPase (SERCA) of thermally acclimated brown trout (Salmo trutta). J Comp Physiol B 2020; 191:43-53. [PMID: 32980918 PMCID: PMC7819936 DOI: 10.1007/s00360-020-01313-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2020] [Revised: 08/21/2020] [Accepted: 09/09/2020] [Indexed: 11/24/2022]
Abstract
At high temperatures, ventricular beating rate collapses and depresses cardiac output in fish. The role of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) in thermal tolerance of ventricular function was examined in brown trout (Salmo trutta) by measuring heart SERCA and comparing it to that of the dorsolateral myotomal muscle. Activity of SERCA was measured from crude homogenates of cold-acclimated (+ 3 °C, c.a.) and warm-acclimated (+ 13 °C, w.a.) brown trout as cyclopiazonic acid (20 µM) sensitive Ca2+-ATPase between + 3 and + 33 °C. Activity of the heart SERCA was significantly higher in c.a. than w.a. trout and increased strongly between + 3 and + 23 °C with linear Arrhenius plots but started to plateau between + 23 and + 33 °C in both acclimation groups. The rate of thermal inactivation of the heart SERCA at + 35 °C was similar in c.a. and w.a. fish. Activity of the muscle SERCA was less temperature dependent and more heat resistant than that of the heart SERCA and showed linear Arrhenius plots between + 3 and + 33 °C in both c.a. and w.a. fish. SERCA activity of the c.a. muscle was slightly higher than that of w.a. muscle. The rate of thermal inactivation at + 40 °C was similar for both c.a. and w.a. muscle SERCA at + 40 °C. Although the heart SERCA is more sensitive to high temperatures than the muscle SERCA, it is unlikely to be a limiting factor for heart rate, because its heat tolerance, unlike that of the ventricular beating rate, was not changed by temperature acclimation.
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Affiliation(s)
- Matti Vornanen
- Department of Environmental and Biological Sciences, University of Eastern Finland, P.O. Box 111, 80101, Joensuu, Finland.
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Eshima H, Miura S, Senoo N, Hatakeyama K, Poole DC, Kano Y. Improved skeletal muscle Ca 2+ regulation in vivo following contractions in mice overexpressing PGC-1α. Am J Physiol Regul Integr Comp Physiol 2017; 312:R1017-R1028. [PMID: 28438761 DOI: 10.1152/ajpregu.00032.2017] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2017] [Revised: 04/04/2017] [Accepted: 04/12/2017] [Indexed: 01/13/2023]
Abstract
In skeletal muscle, resting intracellular Ca2+ concentration ([Ca2+]i) homeostasis is exquisitely regulated by Ca2+ transport across the sarcolemmal, mitochondrial, and sarcoplasmic reticulum (SR) membranes. Of these three systems, the relative importance of the mitochondria in [Ca2+]i regulation remains poorly understood in in vivo skeletal muscle. We tested the hypothesis that the capacity for Ca2+ uptake by mitochondria is a primary factor in determining [Ca2+]i regulation in muscle at rest and following contractions. Tibialis anterior muscle of anesthetized peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α)-overexpressing (OE, increased mitochondria model) and wild-type (WT) littermate mice was exteriorized in vivo and loaded with the fluorescent probe fura 2-AM, and Rhod 2-AM Ca2+ buffering and mitochondrial [Ca2+] were evaluated at rest and during recovery from fatiguing tetanic contractions induced by electrical stimulation (120 s, 100 Hz). In addition, the effects of pharmacological inhibition of SR (thapsigargin) and mitochondrial [carbonyl cyanide-4-(trifluoromethoxy) phenylhydrazone (FCCP)] function were examined at rest. [Ca2+]i in WT remained elevated for the entire postcontraction recovery period (+6 ± 1% at 450 s), but in PGC-1α OE [Ca2+]i returned to resting baseline within 150 s. Thapsigargin immediately and substantially increased resting [Ca2+]i in WT, whereas in PGC-1α OE this effect was delayed and markedly diminished (WT, +12 ± 3; PGC-1α OE, +1 ± 2% at 600 s after thapsigargin treatment, P < 0.05). FCCP abolished this improvement of [Ca2+]i regulation in PGC-1α OE. Mitochondrial [Ca2+] accumulation was observed in PGC-1α OE following contractions and thapsigargin treatment. In the SR, PGC-1α OE downregulated SR Ca2+-ATPase 1 (Ca2+ uptake) and parvalbumin (Ca2+ buffering) protein levels, whereas mitochondrial Ca2+ uptake-related proteins (Mfn1, Mfn2, and mitochondrial Ca2+ uniporter) were upregulated. These data demonstrate a heretofore unappreciated role for skeletal muscle mitochondria in [Ca2+]i regulation in vivo following fatiguing tetanic contractions and at rest.
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Affiliation(s)
- Hiroaki Eshima
- Department of Engineering Science, Bioscience and Technology Program, University of Electro-Communications, Tokyo, Japan
| | - Shinji Miura
- Laboratory of Nutritional Biochemistry, Graduate School of Nutritional and Environmental Sciences, University of Shizuoka, Shizuoka, Japan; and
| | - Nanami Senoo
- Laboratory of Nutritional Biochemistry, Graduate School of Nutritional and Environmental Sciences, University of Shizuoka, Shizuoka, Japan; and
| | - Koji Hatakeyama
- Department of Engineering Science, Bioscience and Technology Program, University of Electro-Communications, Tokyo, Japan
| | - David C Poole
- Departments of Anatomy and Physiology and Kinesiology, Kansas State University, Manhattan, Kansas
| | - Yutaka Kano
- Department of Engineering Science, Bioscience and Technology Program, University of Electro-Communications, Tokyo, Japan;
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Nasledov GA, Katina IE, Zhitnikova YV. Changes in the functioning of the electromechanical connection during tetanic contraction. NEUROSCIENCE AND BEHAVIORAL PHYSIOLOGY 2007; 37:153-9. [PMID: 17187207 DOI: 10.1007/s11055-007-0163-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2005] [Indexed: 11/26/2022]
Abstract
The functioning of the electromechanical connection during tetanic contraction in frog skeletal muscle was studied. Analysis using caffeine, calcium-free medium, the ryanodine receptor blocker dantrolene, and the Ca-ATPase inhibitor thapsigargin showed that the initial increase in tetanus, as in twitch contractions, did not require the presence of calcium ions in the surrounding medium, which is in agreement with published data. Contraction was accompanied by activation of potential-dependent release of calcium from the sarcoplasmic reticulum. In contrast, the secondary rise phase and/or the duration of the tetanus plateau were critically dependent on the present of Ca2+ in the surrounding medium. Given that contraction in this situation was inhibited by dantrolene, activation of prolonged contraction was also mediated by calcium released from the sarcoplasmic reticulum, though ryanodine receptors were now activated not by changes in the membrane potential but by the influx of external calcium. Thus, external calcium plays a significant role in the formation of prolonged contractile responses, providing for longer-lasting maintenance of power in contracted muscles.
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Affiliation(s)
- G A Nasledov
- I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, 44 M. Torez Prospekt, 194223, St. Petersburg, Russia
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Schuster F, Müller R, Hartung E, Roewer N, Anetseder M. Inhibition of sarcoplasmic Ca2+-ATPase increases caffeine- and halothane-induced contractures in muscle bundles of malignant hyperthermia susceptible and healthy individuals. BMC Anesthesiol 2005; 5:8. [PMID: 15946384 PMCID: PMC1175794 DOI: 10.1186/1471-2253-5-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2004] [Accepted: 06/09/2005] [Indexed: 11/17/2022] Open
Abstract
Background Malignant hyperthermia (MH) is triggered by halogenated anaesthetics and depolarising muscle relaxants, leading to an uncontrolled hypermetabolic state of skeletal muscle. An uncontrolled sarcoplasmic Ca2+ release is mediated via the ryanodine receptor. A compensatory mechanism of increased sarcoplasmic Ca2+-ATPase activity was described in pigs and in transfected cell lines. We hypothesized that inhibition of Ca2+ reuptake via the sarcoplasmic Ca2+-ATPase (SERCA) enhances halothane- and caffeine-induced muscle contractures in MH susceptible more than in non-susceptible skeletal muscle. Methods With informed consent, surplus muscle bundles of 7 MHS (susceptible), 7 MHE (equivocal) and 16 MHN (non-susceptible) classified patients were mounted to an isometric force transducer, electrically stimulated, preloaded and equilibrated. Following 15 min incubation with cyclopiazonic acid (CPA) 25 μM, the European MH standard in-vitro-contracture test protocol with caffeine (0.5; 1; 1.5; 2; 3; 4 mM) and halothane (0.11; 0.22; 0.44; 0.66 mM) was performed. Data as median and quartiles; Friedman- and Wilcoxon-test for differences with and without CPA; p < 0.05. Results Initial length, weight, maximum twitch height, predrug resting tension and predrug twitch height of muscle bundles did not differ between groups. CPA increased halothane- and caffeine-induced contractures significantly. This increase was more pronounced in MHS and MHE than in MHN muscle bundles. Conclusion Inhibition of the SERCA activity by CPA enhances halothane- and caffeine-induced contractures especially in MHS and MHE skeletal muscle and may help for the diagnostic assignment of MH susceptibility. The status of SERCA activity may play a significant but so far unknown role in the genesis of malignant hyperthermia.
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Affiliation(s)
- Frank Schuster
- Department of Anaesthesiology, University of Wuerzburg Oberduerrbacher Strasse 6, 97080 Wuerzburg, Germany
| | - Rainer Müller
- Department of Anaesthesiology, University of Wuerzburg Oberduerrbacher Strasse 6, 97080 Wuerzburg, Germany
| | - Edmund Hartung
- Department of Anaesthesiology and Intensive Care, Hospital of Stralsund, 18410 Stralsund, Germany
| | - Norbert Roewer
- Department of Anaesthesiology, University of Wuerzburg Oberduerrbacher Strasse 6, 97080 Wuerzburg, Germany
| | - Martin Anetseder
- Department of Anaesthesiology, University of Wuerzburg Oberduerrbacher Strasse 6, 97080 Wuerzburg, Germany
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Chawla S, Skepper JN, Huang CLH. Differential effects of sarcoplasmic reticular Ca(2+)-ATPase inhibition on charge movements and calcium transients in intact amphibian skeletal muscle fibres. J Physiol 2002; 539:869-82. [PMID: 11897856 PMCID: PMC2290190 DOI: 10.1113/jphysiol.2001.013095] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
A hypothesis in which intramembrane charge reflects a voltage sensing process allosterically coupled to transitions in ryanodine receptor (RyR)-Ca(2+) release channels as opposed to one driven by release of intracellularly stored Ca(2+) would predict that such charging phenomena should persist in skeletal muscle fibres unable to release stored Ca(2+). Charge movement components were accordingly investigated in intact voltage-clamped amphibian fibres treated with known sarcoplasmic reticular (SR) Ca(2+)-ATPase inhibitors. Cyclopiazonic acid (CPA) pretreatment abolished Ca(2+) transients in fluo-3-loaded fibres following even prolonged applications of caffeine (10 mM) or K(+) (122 mM). Both CPA and thapsigargin (TG) transformed charge movements that included delayed (q(gamma)) "hump" components into simpler decays. However, steady-state charge-voltage characteristics were conserved to values (maximum charge, Q(max) approximately equal to 20-25 nC microF(-1); transition voltage, V* approximately equal to -40 to-50 mV; steepness factor, k approximately equal to 6-9 mV; holding voltage -90 mV) indicating persistent q(gamma) charge. The features of charge inactivation similarly suggested persistent q(beta) and q(gamma) charge contributions in CPA-treated fibres. Perchlorate (8.0 mM) restored the delayed kinetics shown by "on" q(gamma) charge movements, prolonged their "off" decays, conserved both Q(max) and k, yet failed to restore the capacity of such CPA-treated fibres for Ca(2+) release. Introduction of perchlorate (8.0 mM) or caffeine (0.2 mM) to tetracaine (2.0 mM)-treated fibres, also known to restore q(gamma) charge, similarly failed to restore Ca(2+) transients. Steady-state intramembrane q(gamma) charge thus persists with modified kinetics that can be restored to its normally complex waveform by perchlorate, even in intact muscle fibres unable to release Ca(2+). It is thus unlikely that q(gamma) charge movement is a consequence of SR Ca(2+) release rather than changes in tubular membrane potential.
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Affiliation(s)
- Sangeeta Chawla
- Physiological Laboratory, University of Cambridge, Downing Street, Cambridge CB2 3EG, UK
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Même W, Léoty C. Cyclopiazonic acid and thapsigargin reduce Ca2+ influx in frog skeletal muscle fibres as a result of Ca2+ store depletion. ACTA PHYSIOLOGICA SCANDINAVICA 2001; 173:391-9. [PMID: 11903131 DOI: 10.1046/j.1365-201x.2001.00918.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We have investigated the influence of the sarcoplasmic reticulum (SR) Ca2+ content on the retrograde control of skeletal muscle L-type Ca2+ channels activity by ryanodine receptors (RyR). The effects of cyclopiazonic acid (CPA) and thapsigargin (TG), two structurally unrelated inhibitors of SR Ca(2+)-adenosine triphosphatase (ATPase), were examined on the SR Ca2+ content, the calcium current and contraction in single frog semitendinosus fibres using the double mannitol-gap technique. At moderate concentrations that only partially inhibited Ca2+ sequestration by the SR, CPA (2-4 microM) induces a concentration dependent depression of contraction and Ca2+ current amplitudes. When Ba2+ is the charge carrier, the inward current is not changed by CPA suggesting that this Ca(2+)-pump inhibitor does not directly affect dihydropyridine Ca2+ channels. Similar effects were obtained with TG (1-5 microM). Changes in Ca2+ currents and contraction were accompanied by a reduced Ca2+ loading of the SR. We attribute the modulation of the Ca2+ current to the selective inhibition of the SR Ca2+ ATPase, resulting in a decreased Ca2+ release and thereby a reduced activation of calcium inward currents. This is therefore taken to represent a calcium release-dependent modulation of skeletal muscle L-type Ca2+ channels.
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Affiliation(s)
- W Même
- Développement et Physiologie des Structures Contractiles, CNRS UMR 6018, Faculté des Sciences et des Techniques, Nantes, France
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Franklin IK, Winz RA, Hubbard MJ. Endoplasmic reticulum Ca2+-ATPase pump is up-regulated in calcium-transporting dental enamel cells: a non-housekeeping role for SERCA2b. Biochem J 2001; 358:217-24. [PMID: 11485570 PMCID: PMC1222050 DOI: 10.1042/0264-6021:3580217] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Dental enamel-forming cells face a major challenge to avoid the cytotoxic effects of excess calcium. We have characterized sarcoplasmic/endoplasmic reticulum calcium-ATPase pumps (SERCA) in rat enamel cells to address the proposal that non-mitochondrial calcium stores play a dominant role in transcellular calcium transport. A single major isoform, SERCA2b, was detected during the protein-secretory and calcium-transport stages of enamel formation using reverse-transcriptase PCR, cDNA cloning, Northern analysis and immunoblotting. Most importantly, SERCA2b exhibited a specific 3-fold up-regulation to high expression levels during calcium transport, as determined by quantitative immunoblotting and ATPase assays. Sensitivity of the calcium-dependent ATPase to thapsigargin and three other SERCA inhibitors was characterized. These findings indicate that enamel cells are well-equipped to sequester calcium in endoplasmic reticulum stores and so protect against calcium toxicity, associate SERCA with transcellular calcium transport for the first time, and establish SERCA2b as a molecular and pharmacological target for future investigations of calcium transcytosis. The observed physiological regulation in enamel cells contradicts the widespread perception that SERCA2b is restricted to general housekeeping duties.
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Affiliation(s)
- I K Franklin
- Department of Biochemistry, University of Otago, PO Box 56, 710 Cumberland Street, Dunedin, New Zealand
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Plattner H, Klauke N. Calcium in ciliated protozoa: sources, regulation, and calcium-regulated cell functions. INTERNATIONAL REVIEW OF CYTOLOGY 2001; 201:115-208. [PMID: 11057832 DOI: 10.1016/s0074-7696(01)01003-8] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
In ciliates, a variety of processes are regulated by Ca2+, e.g., exocytosis, endocytosis, ciliary beat, cell contraction, and nuclear migration. Differential microdomain regulation may occur by activation of specific channels in different cell regions (e.g., voltage-dependent Ca2+ channels in cilia), by local, nonpropagated activation of subplasmalemmal Ca stores (alveolar sacs), by different sensitivity thresholds, and eventually by interplay with additional second messengers (cilia). During stimulus-secretion coupling, Ca2+ as the only known second messenger operates at approximately 5 microM, whereby mobilization from alveolar sacs is superimposed by "store-operated Ca2+ influx" (SOC), to drive exocytotic and endocytotic membrane fusion. (Content discharge requires binding of extracellular Ca2+ to some secretory proteins.) Ca2+ homeostasis is reestablished by binding to cytosolic Ca2+-binding proteins (e.g., calmodulin), by sequestration into mitochondria (perhaps by Ca2+ uniporter) and into endoplasmic reticulum and alveolar sacs (with a SERCA-type pump), and by extrusion via a plasmalemmal Ca2+ pump and a Na+/Ca2+ exchanger. Comparison of free vs total concentration, [Ca2+] vs [Ca], during activation, using time-resolved fluorochrome analysis and X-ray microanalysis, respectively, reveals that altogether activation requires a calcium flux that is orders of magnitude larger than that expected from the [Ca2+] actually required for local activation.
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Affiliation(s)
- H Plattner
- Department of Biology, University of Konstanz, Germany
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Jaffe EH, Bolaños P, Caputo C. Amperometric characterization of exocytotic events from single mast cells: dependence on external and internal Ca++ sources. Cell Calcium 2001; 29:199-209. [PMID: 11162857 DOI: 10.1054/ceca.2000.0185] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Mast cells exocytotically release histamine/serotonin in response to different secretagogues. We have used substance P and compound 48/80 to study the Ca++ dependency of serotonin exocytosis from peritoneal mast cells using carbon fiber amperometric techniques. The exocytotic release pattern consists of a burst of events superimposed on a slow, transient, amperometric current baseline increase. Cellular re lease parameters (number, frequency and total charge of amperometric events) and individual event characteristics (charge integral, half width and peak amplitude) were similar for the two secretagogues used. Zero Ca++ conditions greatly reduced, without completely abolishing,cellular release parameters. Cyclopiazonic acid, an inhibitor of the endoplasmatic Ca++ ATPase, reduced the cellular exocytotic capacity and diminished the amplitude of individual exocytotic events more effectively than the 0 Ca++ condition. The cyclopiazonic acid effects occurred in the presence of external Ca++, indicating that this condition is not sufficient for maintaining full exocytotic capacity. The results confirm the importance of intracellular Ca++ for exocytotic activation. For the first time evidence is presented that the integrity of intracellular Ca++ pools determines the amplitude and frequency of individual exocytotic events. Saponin, a non-specific detergent, also induced quantal release similar to that obtained with substance P and compound 48/80. This release was not dependent on extracellular Ca++, but cyclopiazonic acid significantly reduced individual exocytotic release.
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Affiliation(s)
- E H Jaffe
- Centro de Biofísica y Bioquímica, Instituto Venezolano de Investigaciones Científicas, IVIC, Venezuela.
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Caputo C, Bolaños P, Escobar AL. Fast calcium removal during single twitches in amphibian skeletal muscle fibres. J Muscle Res Cell Motil 1999; 20:555-67. [PMID: 10555074 DOI: 10.1023/a:1005526202747] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Fluorescence signals from the calcium sensitive dyes Fluo-3 or Rhod-2 were obtained simultaneously with isometric tension in single fibres isolated from the anterior tibialis muscle of Leptodactylus insularis (20-22 degrees C). Fluo-3 fluorescence signals were transformed into [Ca2+]i transients as previously described. Most of the decay phase of single twitch transient is well fitted by a single exponential (tau of about 10 ms), followed by a slower declining component lasting tens of milliseconds. During short periods, 10 to 20 s, of low frequency stimulation, between 0.2 and 5 Hz, the basal [Ca2+]i increased slowly from 0.1 to about 0.4 microM, with only minor changes in the exponentially decaying phase. In fibres poisoned with thapsigargin or cyclopiazonic acid (1-2 microM) the tau of decay of fluorescence or Ca2+ transients of single twitches was very similar to that observed in non-poisoned fibres. Nevertheless, in poisoned fibres challenged with repetitive stimulation. the tau of Ca2+ transients decay increased from about 10 ms to >40 ms, while the basal [Ca2+]i increased from 0.1 to 2 microM. Short rest periods (about 5 min) could reverse these effects, indicating that they were not a direct consequence of SR Ca 2+ -ATPase inhibition. The correlation coefficient between tau of decay and basal [Ca2+]i was >0.8 (P<0.0001). Qualitatively similar results were obtained measuring Rhod-2 fluorescence signals. A lumped, two-compartment model could account for these results. Loading the fibres with EGTA-AM, diminished the effects of prolonged stimulation observed in poisoned fibres. Moreover, we show that the Na+ - Ca2+ exchange mechanism does not participate appreciably in fast Ca2+ removal.
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Affiliation(s)
- C Caputo
- Laboratorio de Biofísica del Músculo, Centro de Biofísica y Bioquímica, Instituto Venezolano de Investigaciones Científicas, IVIC, Caracas, Venezuela
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14
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Duke AM, Steele DS. Effects of creatine phosphate on Ca2+ regulation by the sarcoplasmic reticulum in mechanically skinned rat skeletal muscle fibres. J Physiol 1999; 517 ( Pt 2):447-58. [PMID: 10332094 PMCID: PMC2269360 DOI: 10.1111/j.1469-7793.1999.0447t.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
1. The effect of creatine phosphate (PCr) on sarcoplasmic reticulum (SR) Ca2+ regulation was studied in mechanically skinned skeletal muscle fibres from rat extensor digitorium longus (EDL). Preparations were perfused with solutions mimicking the intracellular milieu and the [Ca2+] within the muscle was monitored continuously using fura-2. 2. Brief application of 40 mM caffeine caused a transient increase in [Ca2+] due to SR Ca2+ release, and an associated tension response. Withdrawal of PCr resulted in (i) a slow transient release of Ca2+ from the SR (ii) a marked prolongation of the descending phase of the caffeine-induced fluorescence ratio transient and (iii) a decrease in the Ca2+ transient amplitude to 69.2 +/- 2.7 % (n = 16) of control responses. 3. Prolongation of the caffeine-induced Ca2+ transient also occurred following application of the SR Ca2+ pump inhibitor cyclopiazonic acid (CPA). This suggests that (i) the descending phase of the caffeine-induced Ca2+ transient is dependent on the rate of Ca2+ uptake by the SR and (ii) prolongation associated with PCr withdrawal may also reflect a decrease in the net Ca2+ uptake rate. 4. The effects of PCr withdrawal were mimicked by addition of the creatine kinase (CK) inhibitor 2,4-dinitro-1-fluorobenzene (DNFB). Hence, reducing the [PCr] may influence SR Ca2+ regulation by limiting local ATP regeneration by endogenous CK. After treatment with DNFB, PCr withdrawal had no effect on the Ca2+ transient, confirming that PCr does not have an additional direct effect on the SR. 5. The Ca2+ efflux associated with PCr withdrawal was insensitive to ryanodine or Ruthenium Red, but was effectively abolished by pretreatment with the SR Ca2+ pump inhibitor cyclopiazonic acid (CPA). This suggests that the Ca2+ efflux associated with PCr withdrawal is independent of the SR Ca2+ channel, but may involve reversal or inhibition of the Ca2+ ATPase. 6. These data suggest that Ca2+ regulation by the SR is strongly dependent on the supply of ATP via endogenous CK. Depletion of PCr may contribute to impaired SR Ca2+ regulation known to occur in intact skeletal muscle under conditions of fatigue.
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Affiliation(s)
- A M Duke
- School of Biology, University of Leeds, Leeds LS2 9JT, UK
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15
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Bauer CS, Plieth C, Bethmann B, Popescu O, Hansen UP, Simonis W, Schonknecht G. Strontium-induced repetitive calcium spikes in a unicellular green alga. PLANT PHYSIOLOGY 1998; 117:545-57. [PMID: 9625707 PMCID: PMC34974 DOI: 10.1104/pp.117.2.545] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/29/1997] [Accepted: 03/03/1998] [Indexed: 05/22/2023]
Abstract
The divalent cation Sr2+ induced repetitive transient spikes of the cytosolic Ca2+ activity [Ca2+]cy and parallel repetitive transient hyperpolarizations of the plasma membrane in the unicellular green alga Eremosphaera viridis. [Ca2+]cy measurements, membrane potential measurements, and cation analysis of the cells were used to elucidate the mechanism of Sr2+-induced [Ca2+]cy oscillations. Sr2+ was effectively and rapidly compartmentalized within the cell, probably into the vacuole. The [Ca2+]cy oscillations cause membrane potential oscillations, and not the reverse. The endoplasmic reticulum (ER) Ca2+-ATPase blockers 2,5-di-tert-butylhydroquinone and cyclopiazonic acid inhibited Sr2+-induced repetitive [Ca2+]cy spikes, whereas the compartmentalization of Sr2+ was not influenced. A repetitive Ca2+ release and Ca2+ re-uptake by the ER probably generated repetitive [Ca2+]cy spikes in E. viridis in the presence of Sr2+. The inhibitory effect of ruthenium red and ryanodine indicated that the Sr2+-induced Ca2+ release from the ER was mediated by a ryanodine/cyclic ADP-ribose type of Ca2+ channel. The blockage of Sr2+-induced repetitive [Ca2+]cy spikes by La3+ or Gd3+ indicated the necessity of a certain influx of divalent cations for sustained [Ca2+]cy oscillations. Based on these data we present a mathematical model that describes the baseline spiking [Ca2+]cy oscillations in E. viridis.
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16
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Uttenweiler D, Weber C, Fink RH. Mathematical modeling and fluorescence imaging to study the Ca2+ turnover in skinned muscle fibers. Biophys J 1998; 74:1640-53. [PMID: 9545029 PMCID: PMC1299511 DOI: 10.1016/s0006-3495(98)77877-4] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
A mathematical model was developed for the simulation of the spatial and temporal time course of Ca2+ ion movement in caffeine-induced calcium transients of chemically skinned muscle fiber preparations. Our model assumes cylindrical symmetry and quantifies the radial profile of Ca2+ ion concentration by solving the diffusion equations for Ca2+ ions and various mobile buffers, and the rate equations for Ca2+ buffering (mobile and immobile buffers) and for the release and reuptake of Ca2+ ions by the sarcoplasmic reticulum (SR), with a finite-difference algorithm. The results of the model are compared with caffeine-induced spatial Ca2+ transients obtained from saponin skinned murine fast-twitch fibers by fluorescence photometry and imaging measurements using the ratiometric dye Fura-2. The combination of mathematical modeling and digital image analysis provides a tool for the quantitative description of the total Ca2+ turnover and the different contributions of all interacting processes to the overall Ca2+ transient in skinned muscle fibers. It should thereby strongly improve the usage of skinned fibers as quantitative assay systems for many parameters of the SR and the contractile apparatus helping also to bridge the gap to the intact muscle fiber.
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Affiliation(s)
- D Uttenweiler
- Ruprecht-Karls-Universität Heidelberg, II Institute of Physiology, Germany
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17
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Abstract
In porcine malignant hyperthermia-susceptible (MHS) skeletal muscles, calcium release is abnormal and resting calcium may be elevated. Thus MHS muscles may have prolonged twitch relaxation and lower fusion frequencies, which would be augmented by inhibition of sarcoplasmic reticulum (SR) Ca2+ adenosine triphosphatase (ATPase) activity; bundles of intact muscle cells from MHS and normal pigs were used to investigate this possibility. Cooling and low-frequency stimulation, in combination, enhanced twitch fusion and prolonged twitch relaxation significantly more in MHS than in normal muscles (e.g., 34 +/- 4% versus 16 +/- 4% fusion, and 82.4 +/- 9.4 ms versus 43.2 +/- 7.8 ms half-relaxation time, for MHS and normal muscles, respectively). Similarly, inhibition of the SR Ca2+ ATPase by cyclopiazonic acid resulted in significantly greater twitch fusion in MHS muscles. These results were consistent with predicted effects of enhanced SR Ca2+ release and/or elevated resting calcium in MHS muscles and indicate that cooling during a malignant hyperthermia crisis could actually increase the force of muscle contractures.
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Affiliation(s)
- N R Enzmann
- Department of Veterinary PathoBiology, University of Minnesota, St. Paul 55108, USA
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18
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Même W, Huchet-Cadiou C, Léoty C. Cyclopiazonic acid-induced changes in the contraction and Ca2+ transient of frog fast-twitch skeletal muscle. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 274:C253-61. [PMID: 9458735 DOI: 10.1152/ajpcell.1998.274.1.c253] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The effects of cyclopiazonic acid (CPA) were investigated on isolated skeletal muscle fibers of frog semitendinosus muscle. CPA (0.5-10 microM) enhanced isometric twitch but produced little change in resting tension. At higher concentrations (10-50 microM), CPA depressed twitch and induced sustained contracture without affecting resting and action potentials. In Triton-skinned fibers, CPA had no significant effect on myofibrillar Ca2+ sensitivity but decreased maximal activated force at concentrations > 5 microM. In intact cells loaded with the Ca2+ fluorescence indicator indo 1, CPA (2 microM) induced an increase in Ca(2+)-transient amplitude (10 +/- 2.5%), which was associated with an increase in time to peak and in the time constant of decay. Consequently, peak force was increased by 35 +/- 4%, and both time to peak and the time constant of relaxation were prolonged. It is concluded that CPA effects, at a concentration of up to 2 microM, were associated with specific inhibition of sarcoplasmic reticulum Ca(2+)-adenosinetriphosphatase in intact skeletal muscle and that inhibition of the pump directly affected the handling of intracellular Ca2+ and force production.
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Affiliation(s)
- W Même
- Laboratoire de Physiologie Générale, Centre National de la Recherche Scientifique, ERS 6107, Faculté des Sciences et des Techniques, Nantes, France
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19
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Makabe M, Werner O, Fink RH. The contribution of the sarcoplasmic reticulum Ca2+-transport ATPase to caffeine-induced Ca2+ transients of murine skinned skeletal muscle fibres. Pflugers Arch 1996; 432:717-26. [PMID: 8764974 DOI: 10.1007/s004240050190] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The present study was carried out to investigate the contribution of the Ca2+-transport ATPase of the sarcoplasmic reticulum (SR) to caffeine-induced Ca2+ release in skinned skeletal muscle fibres. Chemically skinned fibres of balb-C-mouse EDL (extensor digitorum longus) were exposed for 1 min to a free Ca2+ concentration of 0.36 microM to load the SR with Ca2+. Release of Ca2+ from the SR was induced by 30 mM caffeine and recorded as an isometric force transient. For every preparation a pCa/force relationship was constructed, where pCa = -log10 [Ca2+]. In a new experimental approach, we used the pCa/force relationship to transform each force transient directly into a Ca2+ transient. The calculated Ca2+ transients were fitted by a double exponential function: Y0 + A1 . (-t/t1) + A2 . exp(t/t2), with A1 < 0 < A2, t1 < t2 and Y0, A1, A2 in micromolar. Ca2+ transients in the presence of the SR Ca2+-ATPase inhibitor cyclopiazonic acid (CPA) were compared to those obtained in the absence of the drug. We found that inhibition of the SR Ca2+-ATPase during caffeine-induced Ca2+ release causes an increase in the peak Ca2+ concentration in comparison to the control transients. Increasing CPA concentrations prolonged the time-to-peak in a dose-dependent manner, following a Hill curve with a half-maximal value of 6.5 +/- 3 microM CPA and a Hill slope of 1.1 +/- 0.2, saturating at 100 microM. The effects of CPA could be simulated by an extended three-compartment model representing the SR, the myofilament space and the external bathing solution. In terms of this model, the SR Ca2+-ATPase influences the Ca2+ gradient across the SR membrane in particular during the early stages of the Ca2+ transient, whereas the subsequent relaxation is governed by diffusional loss of Ca2+ into the bathing solution.
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Affiliation(s)
- M Makabe
- II. Institute of Physiology, University of Heidelberg, INF 326, D-69120 Heidelberg, Germany
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20
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Du GG, Ashley CC, Lea TJ. Effects of thapsigargin and cyclopiazonic acid on sarcoplasmic reticulum Ca2+ uptake, spontaneous force oscillations and myofilament Ca2+ sensitivity in skinned rat ventricular trabeculae. Pflugers Arch 1996; 432:59-65. [PMID: 8662268 DOI: 10.1007/s004240050105] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Thapsigargin (TG) and cyclopiazonic acid (CPA) have been reported to be potent inhibitors of the sarcoplasmic reticulum (SR) Ca2+ uptake in isolated SR vesicles and cells. We have examined the effect of TG and CPA on (1) the Ca2+ uptake by the SR in saponin-skinned rat ventricular trabeculae, using the amplitude of the caffeine-induced contraction to estimate the Ca2+ content loaded into the SR, (2) the spontaneous Ca2+ oscillations at pCa 6.6 using force oscillation as the indicator, and (3) the myofilament Ca2+ sensitivity in Triton X-100-treated preparations. Inhibition of Ca2+ loading by TG and CPA increased with time of exposure to the inhibitor over 18-24 min. TG and CPA produced half inhibition of Ca2+ loading at 34.9 and 35.7 microM respectively, when 18-24 min were allowed for diffusion. The spontaneous force oscillations were more sensitive to the inhibitors: 10 microM TG and 30 microM CPA both abolished the oscillations in this time. The myofilament Ca2+ sensitivity was not affected by 10 and 300 microM TG or CPA. The results show that the concentrations of TG and CPA necessary to inhibit the SR Ca2+ uptake of skinned ventricular trabeculae are much higher than the reported values for single intact myocytes. One reason for this may be slow diffusion of the inhibitors into the multicellular trabecula preparation.
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Affiliation(s)
- G G Du
- University Laboratory of Physiology, Parks Road, Oxford OX1 3PT, UK
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Bakker AJ, Lamb GD, Stephenson DG. The effect of 2,5-di-(tert-butyl)-1,4-hydroquinone on force responses and the contractile apparatus in mechanically skinned muscle fibres of the rat and toad. J Muscle Res Cell Motil 1996; 17:55-67. [PMID: 8740432 DOI: 10.1007/bf00140324] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
In this study, we investigated the effect of the Ca2+ pump inhibitor, 2,5-di-(tert-butyl)-1,4-hydroquinone on the function of the contractile apparatus, Ca2+ uptake, the permeability of the sarcoplasmic reticulum to Ca2+ and excitation-contraction coupling, in mechanically skinned muscle fibres of the rat and toad. 2,5-di-(tert-butyl)-1,4-hydroquinone had no significant effect on the maximum force and Ca2+ sensitivity of the contractile apparatus in rat and toad fibres at concentrations of 20 and 5 microM respectively. In rat fibres, 2,5-di-(tert-butyl)-1,4-hydroquinone was found to inhibit sarcoplasmic reticulum Ca2+ loading in a dose dependent manner, with a half maximal effect at 2 microM. In toad fibres, 5 microM 2,5-di-(tert-butyl)-1,4-hydroquinone completely blocked sarcoplasmic reticulum Ca2+ loading. Exposure to 5 mM BAPTA revealed a small resting sarcoplasmic reticulum Ca2+ leak in unstimulated rat fibres. This Ca2+ leak was not significantly affected by the presence of 20 microM 2,5-di-(tert-butyl)-1,4-hydroquinone, suggesting that 2,5-di-(tert-butyl)-1,4-hydroquinone does not substantially block or activate the sarcoplasmic reticulum Ca2+ release channels. Depolarisation-induced force responses elicited in rat and toad skinned fibres were not significantly affected by 0.5 microM 2,5-di-(tert-butyl)-1, 4-hydroquinone. In the rat fibres, 5 and 20 microM 2,5-di-(tert-butyl)-1,4-hydroquinone greatly increased the peak and duration of initial depolarisation-induced force responses, while subsequent responses were reduced. 2,5-di-(tert-butyl)-1,4-hydroquinone did not affect excitation contraction coupling, as depolarisation-induced force responses similar to initial controls could be elicited after 2,5-di-(tert-butyl)-1,4-hydroquinone exposure, provided that the initial Ca2+ release in 2,5-di-(tert-butyl)-1,4-hydroquinone was chelated with 0.5 mM EGTA (to prevent Ca(2+)-dependent damage) and the sarcoplasmic reticulum was reloaded with Ca2+. In the toad fibres, 5 microM 2,5-di-(tert-butyl)-1, 4-hydroquinone had a similar effect on depolarisation-induced force responses to that observed at 20 microM 2,5-di-(tert-butyl)-1, 4-hydroquinone in rat fibres. This study shows that 2,5-di-(tert-butyl)-1,4-hydroquinone specifically and reversibly inhibits the sarcoplasmic reticulum Ca2+ pump in skeletal muscle and therefore, 2,5-di-(tert-butyl)-1,4-hydroquinone could be a valuable tool for investigating the role of the sarcoplasmic reticulum in Ca2+ homeostasis in skeletal muscle.
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Affiliation(s)
- A J Bakker
- School of Physiology and Pharmacology, University of New South Wales, Sydney, Australia
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22
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Länge S, Wissmann JD, Plattner H. Caffeine inhibits Ca2+ uptake by subplasmalemmal calcium stores ('alveolar sacs') isolated from Paramecium cells. BIOCHIMICA ET BIOPHYSICA ACTA 1996; 1278:191-6. [PMID: 8593276 DOI: 10.1016/0005-2736(95)00230-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Caffeine inhibits 45Ca2+ sequestration by subplasmalemmal calcium stores ('alveolar sacs') of low thapsigargicin sensitivity which we have isolated from the ciliated protozoan, Paramecium tetraurelia. Inhibition depends on caffeine concentration, with an IC50 of 31.8 mM. According to kinetic evaluation this is compatible with non-competitive inhibition of Ca2+ uptake, rather than with superimposed 45Ca2+ release during sequestration. It remains to be analysed whether this mechanism might be of possible relevance also for Ca2+-mediated activation in vivo in this or in any other secretory system. Such an effect could also operate indirectly, e.g., by Ca2+-release induction via sequestration inhibition. This is the first description of caffeine-mediated inhibition of Ca2+ uptake by calcium stores from a secretory system. Our data are compatible with some observations with sarcoplasmic reticulum from striated muscle fibers.
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Affiliation(s)
- S Länge
- Faculty of Biology, University of Konstanz, Konstanz, Germany
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Baudet S, Do E, Noireaud J, Le Marec H. Alterations in the force-frequency relationship by tert-butylbenzohydroquinone, a putative SR Ca2+ pump inhibitor, in rabbit and rat ventricular muscle. Br J Pharmacol 1996; 117:258-67. [PMID: 8789377 PMCID: PMC1909275 DOI: 10.1111/j.1476-5381.1996.tb15185.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
1. The effects of 2,5 di-(tert-butyl)-1,4-benzohydroquinone (TBQ), a putative inhibitor of the sarcoplasmic reticulum (SR) Ca2+ pump, on twitch tension, time course and SR Ca2+ content have been studied at different stimulation frequencies (0.5-3 Hz) in isolated preparations from the rabbit and rat right ventricle, at 37 degrees C. 2. At 0.5Hz, 30 microM TBQ induced a marked negative inotropic effect in both species (-57% in the rabbit and -68% in the rat) and decreased the rate of rise and fall of twitch tension. In parallel, SR Ca2+ content (assessed by rapid cooling contractures) was depressed in the rabbit by 42%. The force-frequency relationship (positive for the rabbit and negative for the rat) was significantly attenuated. In the rabbit, this alteration was shown to rely on insufficient SR Ca2+ reloading with increasing frequencies. 3. Exposure of TBQ-treated preparations to 8 mM extracellular Ca2+ or 5 microM isoprenaline were effective in reloading the SR with Ca2+ whereas 20 mM caffeine emptied this compartment. 4. In the rabbit ventricle, increase in stimulation frequency shortened control twitch time course by decreasing both the time to peak tension (TTP) and the time to half relaxation (t1/2). TBQ did not differentially affect the pattern for t1/2 but significantly attenuated the frequency-induced decrease of TTP. 5. In rabbit ventricular muscle, the action potential duration increased between 0.5 and 3 Hz whether or not TBQ was present. However, TBQ induced a small but significant additional action potential shortening. 6. TBQ decreased twitch tension in the rat ventricle between 0.5 and 3 Hz but the negative staircase was not differentially affected by the SR Ca2+ pump inhibitor. In control conditions and in the presence of 30 microM TBQ, t1/2 was frequency-independent but TBQ consistently increased this parameter (by approximately 29%). 7. These data argue in favour of a specific and partial inhibition of the SR Ca2+ pump by 30 microM TBQ in the rabbit and rat ventricle and emphasise the importance of SR Ca2+ uptake in the force-frequency phenomenon.
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Affiliation(s)
- S Baudet
- Laboratoire de Physiologie et Pharmacologie Cellulaire et Moléculaire, Hôpital G. R. Laënnec, Nantes, France
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