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Xu J, Liao C, Yin CC, Li G, Zhu Y, Sun F. In situ structural insights into the excitation-contraction coupling mechanism of skeletal muscle. SCIENCE ADVANCES 2024; 10:eadl1126. [PMID: 38507485 PMCID: PMC10954225 DOI: 10.1126/sciadv.adl1126] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/28/2023] [Accepted: 02/12/2024] [Indexed: 03/22/2024]
Abstract
Excitation-contraction coupling (ECC) is a fundamental mechanism in control of skeletal muscle contraction and occurs at triad junctions, where dihydropyridine receptors (DHPRs) on transverse tubules sense excitation signals and then cause calcium release from the sarcoplasmic reticulum via coupling to type 1 ryanodine receptors (RyR1s), inducing the subsequent contraction of muscle filaments. However, the molecular mechanism remains unclear due to the lack of structural details. Here, we explored the architecture of triad junction by cryo-electron tomography, solved the in situ structure of RyR1 in complex with FKBP12 and calmodulin with the resolution of 16.7 Angstrom, and found the intact RyR1-DHPR supercomplex. RyR1s arrange into two rows on the terminal cisternae membrane by forming right-hand corner-to-corner contacts, and tetrads of DHPRs bind to RyR1s in an alternating manner, forming another two rows on the transverse tubule membrane. This unique arrangement is important for synergistic calcium release and provides direct evidence of physical coupling in ECC.
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Affiliation(s)
- Jiashu Xu
- Key Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Chenyi Liao
- Laboratory of Molecular Modeling and Design, State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
| | - Chang-Cheng Yin
- Department of Biophysics, The Health Science Center, Peking University, Beijing 100191, China
- Electron Microscopy Analysis Laboratory, The Health Science Center, Peking University, Beijing 100191, China
- Center for Protein Science, Peking University, Beijing 100871, China
| | - Guohui Li
- Laboratory of Molecular Modeling and Design, State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
| | - Yun Zhu
- Key Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
| | - Fei Sun
- Key Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
- University of Chinese Academy of Sciences, Beijing 100049, China
- Center for Biological Imaging, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
- Bioland Laboratory (Guangzhou Regenerative Medicine and Health Guangdong Laboratory), Guangzhou, Guangdong, 510005, China
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2
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Bibollet H, Kramer A, Bannister RA, Hernández-Ochoa EO. Advances in Ca V1.1 gating: New insights into permeation and voltage-sensing mechanisms. Channels (Austin) 2023; 17:2167569. [PMID: 36642864 PMCID: PMC9851209 DOI: 10.1080/19336950.2023.2167569] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2022] [Accepted: 01/09/2023] [Indexed: 01/17/2023] Open
Abstract
The CaV1.1 voltage-gated Ca2+ channel carries L-type Ca2+ current and is the voltage-sensor for excitation-contraction (EC) coupling in skeletal muscle. Significant breakthroughs in the EC coupling field have often been close on the heels of technological advancement. In particular, CaV1.1 was the first voltage-gated Ca2+ channel to be cloned, the first ion channel to have its gating current measured and the first ion channel to have an effectively null animal model. Though these innovations have provided invaluable information regarding how CaV1.1 detects changes in membrane potential and transmits intra- and inter-molecular signals which cause opening of the channel pore and support Ca2+ release from the sarcoplasmic reticulum remain elusive. Here, we review current perspectives on this topic including the recent application of functional site-directed fluorometry.
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Affiliation(s)
- Hugo Bibollet
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, MD, USA
| | - Audra Kramer
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, MD, USA
| | - Roger A. Bannister
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, MD, USA
- Department of Pathology, University of Maryland School of Medicine, Baltimore, MD, USA
| | - Erick O. Hernández-Ochoa
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, MD, USA
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3
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Iyer KA, Barnakov V, Samsó M. Three-dimensional perspective on ryanodine receptor mutations causing skeletal and cardiac muscle-related diseases. Curr Opin Pharmacol 2023; 68:102327. [PMID: 36516687 PMCID: PMC9908851 DOI: 10.1016/j.coph.2022.102327] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2022] [Revised: 10/18/2022] [Accepted: 11/12/2022] [Indexed: 12/14/2022]
Abstract
Mutations in RyR alter the cell's Ca2+ homeostasis and can cause serious health problems for which few effective therapies are available. Until recently, there was little structural context for the hundreds of mutations linked to muscular disorders reported for this large channel. Growing knowledge of the three-dimensional structure of RyR starts to illustrate the fine control of Ca2+ release. Current efforts directed towards understanding how disease mutations impinge in such processes will be crucial for future design of novel therapies. In this review article we discuss the up-to-date information about mutations according to their role in the 3D structure, and classified them to provide context from a structural perspective.
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Affiliation(s)
- Kavita A Iyer
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, VA, USA
| | - Vadim Barnakov
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, VA, USA
| | - Montserrat Samsó
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, VA, USA.
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4
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Kittelberger JM, Franzini-Armstrong C, Boncompagni S. Ca2+ entry units in a superfast fish muscle. Front Physiol 2022; 13:1036594. [DOI: 10.3389/fphys.2022.1036594] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2022] [Accepted: 10/13/2022] [Indexed: 11/13/2022] Open
Abstract
Over the past two decades, mounting evidence has demonstrated that a mechanism known as store-operated Ca2+ entry (SOCE) plays a crucial role in sustaining skeletal muscle contractility by facilitating Ca2+ influx from the extracellular space during sarcoplasmic reticulum (SR) Ca2+ depletion. We recently demonstrated that, in exercised fast-twitch muscle from mice, the incidence of Ca2+ entry units (CEUs), newly described intracellular junctions between dead-end longitudinal transverse tubular (T-tubule) extensions and stacks of sarcoplasmic reticulum (SR) flat cisternae, strictly correlate with both the capability of fibers to maintain contractions during fatigue and enhanced Ca2+ influx via SOCE. Here, we tested the broader relevance of this result across vertebrates by searching for the presence of CEUs in the vocal muscles of a teleost fish adapted for extended, high-frequency activity. Specifically, we examined active vs. inactive superfast sonic muscles of plainfin midshipman (Porichthys notatus). Interestingly, muscles from actively humming territorial males had a much higher incidence of CEU SR stacks relative to territorial males that were not actively vocalizing, strengthening the concept that assembly of these structures is dynamic and use-dependent, as recently described in exercised muscles from mice. Our results support the hypothesis that CEUs represent a conserved mechanism, across vertebrates, for enabling high levels of repetitive muscle activity, and also provide new insights into the adaptive mechanisms underlying the unique properties of superfast midshipman sonic muscles.
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5
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Dixon RE, Navedo MF, Binder MD, Santana LF. Mechanisms and Physiological Implications of Cooperative Gating of Ion Channels Clusters. Physiol Rev 2021; 102:1159-1210. [PMID: 34927454 DOI: 10.1152/physrev.00022.2021] [Citation(s) in RCA: 33] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Ion channels play a central role in the regulation of nearly every cellular process. Dating back to the classic 1952 Hodgkin-Huxley model of the generation of the action potential, ion channels have always been thought of as independent agents. A myriad of recent experimental findings exploiting advances in electrophysiology, structural biology, and imaging techniques, however, have posed a serious challenge to this long-held axiom as several classes of ion channels appear to open and close in a coordinated, cooperative manner. Ion channel cooperativity ranges from variable-sized oligomeric cooperative gating in voltage-gated, dihydropyridine-sensitive Cav1.2 and Cav1.3 channels to obligatory dimeric assembly and gating of voltage-gated Nav1.5 channels. Potassium channels, transient receptor potential channels, hyperpolarization cyclic nucleotide-activated channels, ryanodine receptors (RyRs), and inositol trisphosphate receptors (IP3Rs) have also been shown to gate cooperatively. The implications of cooperative gating of these ion channels range from fine tuning excitation-contraction coupling in muscle cells to regulating cardiac function and vascular tone, to modulation of action potential and conduction velocity in neurons and cardiac cells, and to control of pace-making activity in the heart. In this review, we discuss the mechanisms leading to cooperative gating of ion channels, their physiological consequences and how alterations in cooperative gating of ion channels may induce a range of clinically significant pathologies.
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Affiliation(s)
- Rose Ellen Dixon
- Department of Physiology and Membrane Biology, University of California, Davis, CA, United States
| | - Manuel F Navedo
- Department of Pharmacology, University of California, Davis, CA, United States
| | - Marc D Binder
- Department of Physiology and Biophysics, University of Washington, Seattle, WA, United States
| | - L Fernando Santana
- Department of Physiology and Membrane Biology, University of California, Davis, CA, United States
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6
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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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7
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Yin L, Zahradnikova A, Rizzetto R, Boncompagni S, Rabesahala de Meritens C, Zhang Y, Joanne P, Marqués-Sulé E, Aguilar-Sánchez Y, Fernández-Tenorio M, Villejoubert O, Li L, Wang YY, Mateo P, Nicolas V, Gerbaud P, Lai FA, Perrier R, Álvarez JL, Niggli E, Valdivia HH, Valdivia CR, Ramos-Franco J, Zorio E, Zissimopoulos S, Protasi F, Benitah JP, Gómez AM. Impaired Binding to Junctophilin-2 and Nanostructural Alteration in CPVT Mutation. Circ Res 2021; 129:e35-e52. [PMID: 34111951 DOI: 10.1161/circresaha.121.319094] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
[Figure: see text].
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Affiliation(s)
- Liheng Yin
- Signaling and Cardiovascular Pathophysiology - UMR-S 1180, Inserm, Université Paris-Saclay 92296 Châtenay-Malabry, France (L.Y., A.Z., R.R., P.J., E.M.-S., O.V., L.L., Y.Y.W., P.M., P.G., R.P., J.L.A., J.-P.B., A.M.G.)
| | - Alexandra Zahradnikova
- Signaling and Cardiovascular Pathophysiology - UMR-S 1180, Inserm, Université Paris-Saclay 92296 Châtenay-Malabry, France (L.Y., A.Z., R.R., P.J., E.M.-S., O.V., L.L., Y.Y.W., P.M., P.G., R.P., J.L.A., J.-P.B., A.M.G.)
| | - Riccardo Rizzetto
- Signaling and Cardiovascular Pathophysiology - UMR-S 1180, Inserm, Université Paris-Saclay 92296 Châtenay-Malabry, France (L.Y., A.Z., R.R., P.J., E.M.-S., O.V., L.L., Y.Y.W., P.M., P.G., R.P., J.L.A., J.-P.B., A.M.G.)
| | - Simona Boncompagni
- CAST, Department of Neuroscience, Imaging and Clinical Sciences (DNICS), Medicine and Ageing Sciences (DMSI), University Gabriele d'Annunzio, Chieti, Italy (S.B., F.P.)
| | | | - Yadan Zhang
- Swansea University Medical School, Institute of Life Science, Swansea, SA2 8PP, UK (C.R.d.M., Y.Z., S.Z.)
| | - Pierre Joanne
- Signaling and Cardiovascular Pathophysiology - UMR-S 1180, Inserm, Université Paris-Saclay 92296 Châtenay-Malabry, France (L.Y., A.Z., R.R., P.J., E.M.-S., O.V., L.L., Y.Y.W., P.M., P.G., R.P., J.L.A., J.-P.B., A.M.G.)
| | - Elena Marqués-Sulé
- Signaling and Cardiovascular Pathophysiology - UMR-S 1180, Inserm, Université Paris-Saclay 92296 Châtenay-Malabry, France (L.Y., A.Z., R.R., P.J., E.M.-S., O.V., L.L., Y.Y.W., P.M., P.G., R.P., J.L.A., J.-P.B., A.M.G.).,Physiotherapy, University of Valencia, Valencia, Spain (E.M.-S.)
| | - Yuriana Aguilar-Sánchez
- Physiology and Biophysics, Rush University Medical Center, Chicago, IL, USA (Y.A.-S., J.R.-F.)
| | | | - Olivier Villejoubert
- Signaling and Cardiovascular Pathophysiology - UMR-S 1180, Inserm, Université Paris-Saclay 92296 Châtenay-Malabry, France (L.Y., A.Z., R.R., P.J., E.M.-S., O.V., L.L., Y.Y.W., P.M., P.G., R.P., J.L.A., J.-P.B., A.M.G.)
| | - Linwei Li
- Signaling and Cardiovascular Pathophysiology - UMR-S 1180, Inserm, Université Paris-Saclay 92296 Châtenay-Malabry, France (L.Y., A.Z., R.R., P.J., E.M.-S., O.V., L.L., Y.Y.W., P.M., P.G., R.P., J.L.A., J.-P.B., A.M.G.)
| | - Yue Yi Wang
- Signaling and Cardiovascular Pathophysiology - UMR-S 1180, Inserm, Université Paris-Saclay 92296 Châtenay-Malabry, France (L.Y., A.Z., R.R., P.J., E.M.-S., O.V., L.L., Y.Y.W., P.M., P.G., R.P., J.L.A., J.-P.B., A.M.G.)
| | - Philippe Mateo
- Signaling and Cardiovascular Pathophysiology - UMR-S 1180, Inserm, Université Paris-Saclay 92296 Châtenay-Malabry, France (L.Y., A.Z., R.R., P.J., E.M.-S., O.V., L.L., Y.Y.W., P.M., P.G., R.P., J.L.A., J.-P.B., A.M.G.)
| | | | - Pascale Gerbaud
- Signaling and Cardiovascular Pathophysiology - UMR-S 1180, Inserm, Université Paris-Saclay 92296 Châtenay-Malabry, France (L.Y., A.Z., R.R., P.J., E.M.-S., O.V., L.L., Y.Y.W., P.M., P.G., R.P., J.L.A., J.-P.B., A.M.G.)
| | - F Anthony Lai
- College of Medicine, Biomedical & Pharmaceutical Research Unit, QU Health, & Biomedical Research Centre, Qatar University, Doha, Qatar (F.A.L.)
| | | | - Julio L Álvarez
- Signaling and Cardiovascular Pathophysiology - UMR-S 1180, Inserm, Université Paris-Saclay 92296 Châtenay-Malabry, France (L.Y., A.Z., R.R., P.J., E.M.-S., O.V., L.L., Y.Y.W., P.M., P.G., R.P., J.L.A., J.-P.B., A.M.G.).,Institute of Cardiology, Havana, Cuba (J.L.A.)
| | - Ernst Niggli
- Physiology, University of Bern, Bern, Switzerland (M.F.-T., E.N.)
| | - Héctor H Valdivia
- Medicine and Cardiovascular Research Center, University of Wisconsin-Madison School of Medicine and Public Health, Madison, Wisconsin (H.H.V., C.R.V.)
| | - Carmen R Valdivia
- Medicine and Cardiovascular Research Center, University of Wisconsin-Madison School of Medicine and Public Health, Madison, Wisconsin (H.H.V., C.R.V.)
| | - Josefina Ramos-Franco
- Physiology and Biophysics, Rush University Medical Center, Chicago, IL, USA (Y.A.-S., J.R.-F.)
| | - Esther Zorio
- Cardiology Department and Unidad de Cardiopatías Familiares, Muerte Súbita y Mecanismos de Enfermedad (CaFaMuSMe), Hospital Universitario y Politécnico La Fe and Instituto de Investigación Sanitaria La Fe, Valencia, Spain (E.Z.).,Center for Biomedical Network Research on Cardiovascular diseases (CIBERCV), Madrid, Spain (E.Z.)
| | - Spyros Zissimopoulos
- Swansea University Medical School, Institute of Life Science, Swansea, SA2 8PP, UK (C.R.d.M., Y.Z., S.Z.)
| | - Feliciano Protasi
- CAST, Department of Neuroscience, Imaging and Clinical Sciences (DNICS), Medicine and Ageing Sciences (DMSI), University Gabriele d'Annunzio, Chieti, Italy (S.B., F.P.)
| | - Jean-Pierre Benitah
- Signaling and Cardiovascular Pathophysiology - UMR-S 1180, Inserm, Université Paris-Saclay 92296 Châtenay-Malabry, France (L.Y., A.Z., R.R., P.J., E.M.-S., O.V., L.L., Y.Y.W., P.M., P.G., R.P., J.L.A., J.-P.B., A.M.G.)
| | - Ana M Gómez
- Signaling and Cardiovascular Pathophysiology - UMR-S 1180, Inserm, Université Paris-Saclay 92296 Châtenay-Malabry, France (L.Y., A.Z., R.R., P.J., E.M.-S., O.V., L.L., Y.Y.W., P.M., P.G., R.P., J.L.A., J.-P.B., A.M.G.)
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8
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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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9
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Gong D, Yan N, Ledford HA. Structural Basis for the Modulation of Ryanodine Receptors. Trends Biochem Sci 2020; 46:489-501. [PMID: 33353849 DOI: 10.1016/j.tibs.2020.11.009] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2020] [Revised: 11/16/2020] [Accepted: 11/20/2020] [Indexed: 12/11/2022]
Abstract
Historically, ryanodine receptors (RyRs) have presented unique challenges for high-resolution structural determination despite long-standing interest in their role in excitation-contraction coupling. Owing to their large size (nearly 2.2 MDa), high-resolution structures remained elusive until the advent of cryogenic electron microscopy (cryo-EM) techniques. In recent years, structures for both RyR1 and RyR2 have been solved at near-atomic resolution. Furthermore, recent reports have delved into their more complex structural associations with key modulators - proteins such as the dihydropyridine receptor (DHPR), FKBP12/12.6, and calmodulin (CaM), as well as ions and small molecules including Ca2+, ATP, caffeine, and PCB95. This review addresses the modulation of RyR1 and RyR2, in addition to the impact of such discoveries on intracellular Ca2+ dynamics and biophysical properties.
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Affiliation(s)
- Deshun Gong
- Zhejiang Provincial Laboratory of Life Sciences and Biomedicine, Key Laboratory of Structural Biology of Zhejiang Province/Key Laboratory of Growth Regulation and Transformation Research of Zhejiang Province, School of Life Sciences, Westlake University, Hangzhou 310024, Zhejiang, China; Institute of Biology, Westlake Institute for Advanced Study, Hangzhou 310024, Zhejiang Province, China.
| | - Nieng Yan
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA.
| | - Hannah A Ledford
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA.
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10
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Rusu MC, Nicolescu MI, Jianu AM, Mănoiu VS, Ilie AC, Dincă D. The ultrastructural anatomy of the nuclear envelope in the masseter muscle indicates its role in the metabolism of the intracellular Ca +. Ann Anat 2019; 224:117-123. [PMID: 31117003 DOI: 10.1016/j.aanat.2019.05.006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2018] [Revised: 04/05/2019] [Accepted: 05/06/2019] [Indexed: 11/16/2022]
Abstract
Specific ultrastructural anatomy of masticatory muscles is commonly referred to a general pattern assigned to striated muscles. Junctional feet consisting of calcium channels of the sarcoplasmic reticulum (i.e. the ryanodine receptors, RyRs) physically connected to the calcium channels of the t-tubules build triads within striated muscles. Functional RyRs were demonstrated in the nuclear envelopes of pancreas and of a skeletal muscle derived cell line, but not in muscle in situ. It was hypothesized that ryanodine receptors (RyRs) could also exist in the nuclear envelope in the masseter muscle, thus aiming at studying this by transmission electron microscopy. There were identified paired and consistent subsarcolemmal clusters of mitochondria, appearing as outpockets of the muscle fibers, usually flanking an endomysial microvessel. It was observed on grazing longitudinal cuts that the I-band-limited mitochondria were not strictly located in a single intermyofibrillar space but continued transversally over the I-band to the next intermyofibrillar space. It appeared that the I-band-limited transverse mitochondria participate with the column-forming mitochondria in building a rather incomplete mitochondrial reticulum of the masseter muscle. Subsarcolemmal nuclei presented nuclear envelope-associated RyRs. Moreover, t-tubules were contacting the nuclear envelope and they were seemingly filled from the perinuclear space. This could suggest that nucleoplasmic calcium could contribute to balance the cytosolic concentration via pre-built anatomical routes: (i) indirectly, via the RyRs of the nuclear envelope and (ii) directly via the communication of t-tubules and sarcoplasmic reticulum through the perinuclear space.
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Affiliation(s)
- M C Rusu
- Division of Anatomy, Faculty of Dental Medicine, "Carol Davila" University of Medicine and Pharmacy, Bucharest, Romania.
| | - M I Nicolescu
- Division of Histology, Faculty of Dental Medicine, "Carol Davila" University of Medicine and Pharmacy, Bucharest, Romania; "Victor Babeș" National Institute of Pathology, Bucharest, Romania
| | - A M Jianu
- Division of Anatomy, Faculty of Medicine, "Victor Babeş" University of Medicine and Pharmacy, Timişoara, Romania
| | - V S Mănoiu
- Department of Cellular and Molecular Biology, National Institute of Research and Development for Biological Sciences, Bucharest, Romania
| | - A C Ilie
- Division of Anatomy, Faculty of Medicine, "Victor Babeş" University of Medicine and Pharmacy, Timişoara, Romania
| | - D Dincă
- Department II of Surgical Clinical Divisions, Faculty of Medicine, "Ovidius" University, Constanţa, Romania
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11
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Ríos E, Gillespie D, Franzini-Armstrong C. The binding interactions that maintain excitation-contraction coupling junctions in skeletal muscle. J Gen Physiol 2019; 151:593-605. [PMID: 30728215 PMCID: PMC6445584 DOI: 10.1085/jgp.201812268] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2018] [Accepted: 01/02/2019] [Indexed: 12/03/2022] Open
Abstract
Calcium for contraction of skeletal muscles is released via tetrameric ryanodine receptor (RYR1) channels of the sarcoplasmic reticulum (SR), which are assembled in ordered arrays called couplons at junctions where the SR abuts T tubules or plasmalemma. Voltage-gated Ca2+ (CaV1.1) channels, found in tubules or plasmalemma, form symmetric complexes called CaV tetrads that associate with and activate underlying RYR tetramers during membrane depolarization by conveying a conformational change. Intriguingly, CaV tetrads regularly skip every other RYR tetramer within the array; therefore, the RYRs underlying tetrads (named V), but not the voltage sensor-lacking (C) RYRs, should be activated by depolarization. Here we hypothesize that the checkerboard association is maintained solely by reversible binary interactions between CaVs and RYRs and test this hypothesis using a quantitative model of the energies that govern CaV1.1-RYR1 binding, which are assumed to depend on number and location of bound CaVs. A Monte Carlo simulation generates large statistical samples and distributions of state variables that can be compared with quantitative features in freeze-fracture images of couplons from various sources. This analysis reveals two necessary model features: (1) the energy of a tetramer must have wells at low and high occupation by CaVs, so that CaVs positively cooperate in binding RYR (an allosteric effect), and (2) a large energy penalty results when two CaVs bind simultaneously to adjacent RYR protomers in adjacent tetramers (a steric clash). Under the hypothesis, V and C channels will eventually reverse roles. Role reversal justifies the presence of sensor-lacking C channels, as a structural and functional reserve for control of muscle contraction.
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Affiliation(s)
- Eduardo Ríos
- Section of Cellular Signaling, Department of Physiology and Biophysics, Rush University, Chicago, IL
| | - Dirk Gillespie
- Section of Cellular Signaling, Department of Physiology and Biophysics, Rush University, Chicago, IL
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12
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Hernández-Ochoa EO, Schneider MF. Voltage sensing mechanism in skeletal muscle excitation-contraction coupling: coming of age or midlife crisis? Skelet Muscle 2018; 8:22. [PMID: 30025545 PMCID: PMC6053751 DOI: 10.1186/s13395-018-0167-9] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2018] [Accepted: 06/26/2018] [Indexed: 11/10/2022] Open
Abstract
The process by which muscle fiber electrical depolarization is linked to activation of muscle contraction is known as excitation-contraction coupling (ECC). Our understanding of ECC has increased enormously since the early scientific descriptions of the phenomenon of electrical activation of muscle contraction by Galvani that date back to the end of the eighteenth century. Major advances in electrical and optical measurements, including muscle fiber voltage clamp to reveal membrane electrical properties, in conjunction with the development of electron microscopy to unveil structural details provided an elegant view of ECC in skeletal muscle during the last century. This surge of knowledge on structural and biophysical aspects of the skeletal muscle was followed by breakthroughs in biochemistry and molecular biology, which allowed for the isolation, purification, and DNA sequencing of the muscle fiber membrane calcium channel/transverse tubule (TT) membrane voltage sensor (Cav1.1) for ECC and of the muscle ryanodine receptor/sarcoplasmic reticulum Ca2+ release channel (RyR1), two essential players of ECC in skeletal muscle. In regard to the process of voltage sensing for controlling calcium release, numerous studies support the concept that the TT Cav1.1 channel is the voltage sensor for ECC, as well as also being a Ca2+ channel in the TT membrane. In this review, we present early and recent findings that support and define the role of Cav1.1 as a voltage sensor for ECC.
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Affiliation(s)
- Erick O. Hernández-Ochoa
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, 108 N. Greene Street, Baltimore, MD 21201 USA
| | - Martin F. Schneider
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, 108 N. Greene Street, Baltimore, MD 21201 USA
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13
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Abstract
During the complex series of events leading to muscle contraction, the initial electric signal coming from motor neurons is transformed into an increase in calcium concentration that triggers sliding of myofibrils. This process, referred to as excitation-contraction coupling, is reliant upon the calcium-release complex, which is restricted spatially to a sub-compartment of muscle cells ("the triad") and regulated precisely. Any dysfunction in the calcium-release complex leads to muscle impairment and myopathy. Various causes can lead to alterations in excitation-contraction coupling and to muscle diseases. The latter are reviewed and classified into four categories: (i) mutation in a protein of the calcium-release complex; (ii) alteration in triad structure; (iii) modification of regulation of channels; (iv) modification in calcium stores within the muscle. Current knowledge of the pathophysiologic mechanisms in each category is described and discussed.
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Affiliation(s)
- Isabelle Marty
- University Grenoble Alpes, Grenoble Institut des Neurosciences, GIN, F-38000 Grenoble, France.,INSERM, U1216, F-38000 Grenoble, France
| | - Julien Fauré
- University Grenoble Alpes, Grenoble Institut des Neurosciences, GIN, F-38000 Grenoble, France.,INSERM, U1216, F-38000 Grenoble, France.,CHU de Grenoble, F-38000 Grenoble, France
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14
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Franzini-Armstrong C. The relationship between form and function throughout the history of excitation-contraction coupling. J Gen Physiol 2018; 150:189-210. [PMID: 29317466 PMCID: PMC5806676 DOI: 10.1085/jgp.201711889] [Citation(s) in RCA: 46] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Franzini-Armstrong reviews the development of the excitation–contraction coupling field over time. The concept of excitation–contraction coupling is almost as old as Journal of General Physiology. It was understood as early as the 1940s that a series of stereotyped events is responsible for the rapid contraction response of muscle fibers to an initial electrical event at the surface. These early developments, now lost in what seems to be the far past for most young investigators, have provided an endless source of experimental approaches. In this Milestone in Physiology, I describe in detail the experiments and concepts that introduced and established the field of excitation–contraction coupling in skeletal muscle. More recent advances are presented in an abbreviated form, as readers are likely to be familiar with recent work in the field.
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Affiliation(s)
- Clara Franzini-Armstrong
- Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA
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15
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Samsó M. A guide to the 3D structure of the ryanodine receptor type 1 by cryoEM. Protein Sci 2016; 26:52-68. [PMID: 27671094 DOI: 10.1002/pro.3052] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2016] [Revised: 09/21/2016] [Accepted: 09/22/2016] [Indexed: 01/04/2023]
Abstract
Signal transduction by the ryanodine receptor (RyR) is essential in many excitable cells including all striated contractile cells and some types of neurons. While its transmembrane domain is a classic tetrameric, six-transmembrane cation channel, the cytoplasmic domain is uniquely large and complex, hosting a multiplicity of specialized domains. The overall outline and substructure readily recognizable by electron microscopy make RyR a geometrically well-behaved specimen. Hence, for the last two decades, the 3D structural study of the RyR has tracked closely the technological advances in electron microscopy, cryo-electron microscopy (cryoEM), and computerized 3D reconstruction. This review summarizes the progress in the structural determination of RyR by cryoEM and, bearing in mind the leap in resolution provided by the recent implementation of direct electron detection, analyzes the first near-atomic structures of RyR. These reveal a complex orchestration of domains controlling the channel's function, and help to understand how this could break down as a consequence of disease-causing mutations.
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Affiliation(s)
- Montserrat Samsó
- Department of Physiology and Biophysics, Virginia Commonwealth University, Richmond, Virginia
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16
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Carlo C, Pura B, Magaly R, Marino D. Differential effects of contractile potentiators on action potential-induced Ca 2+ transients of frog and mouse skeletal muscle fibres. J Muscle Res Cell Motil 2016; 37:169-180. [PMID: 27590123 DOI: 10.1007/s10974-016-9455-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2016] [Accepted: 08/22/2016] [Indexed: 10/21/2022]
Abstract
Muscle fibres, isolated from frog tibialis anterior and mouse flexor digitorum brevis (FDB) were loaded with the fast dye MagFluo-4 to study the effects of potentiators caffeine, nitrate, Zn2+ and perchlorate on Ca2+ transients elicited by single action potentials. Overall, the potentiators doubled the transients amplitude and prolonged by about 1.5-fold their decay time. In contrast, as shown here for the first time, nitrate and Zn2+, but not caffeine, activated a late, secondary component of the transient rising phase of frog but not mouse, fibres. The rise time was increased from 1.9 ms in normal solution (NR) to 3.3 ms (nitrate) and 4.4 ms (Zn2+). In NR, a single exponential, fitted the rising phase of calcium transients of frog (τ1 = 0.47 ms) and mouse (τ1 = 0.28 ms). In nitrate and Zn2+ only frog transients showed a secondary exponential component, τ2 = 0.72 ms (nitrate) and 0.94 ms, (Zn2+). We suggest that nitrate and Zn2+ activate a late slower component of the ΔF/F signals of frog but not of mouse fibres, possibly promoting Ca2+ induced Ca2+ release at level of the RyR3, that in frog muscle fibres are localized in the para-junctional region of the triads and are absent in mouse FDB muscle fibres.
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Affiliation(s)
- Caputo Carlo
- Laboratorio de Fisiología Celular, Centro de Biofísica y Bioquímica, Instituto Venezolano de Investigaciones Científicas, IVIC, Apartado 21827, Caracas, 1020, Venezuela.
| | - Bolaños Pura
- Laboratorio de Fisiología Celular, Centro de Biofísica y Bioquímica, Instituto Venezolano de Investigaciones Científicas, IVIC, Apartado 21827, Caracas, 1020, Venezuela
| | - Ramos Magaly
- Laboratorio de Fisiología Celular, Centro de Biofísica y Bioquímica, Instituto Venezolano de Investigaciones Científicas, IVIC, Apartado 21827, Caracas, 1020, Venezuela
| | - DiFranco Marino
- Department of Physiology, David Geffen School of Medicine, UCLA, Los Angeles, CF, USA
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17
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Hernández-Ochoa EO, Pratt SJP, Lovering RM, Schneider MF. Critical Role of Intracellular RyR1 Calcium Release Channels in Skeletal Muscle Function and Disease. Front Physiol 2016; 6:420. [PMID: 26793121 PMCID: PMC4709859 DOI: 10.3389/fphys.2015.00420] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2015] [Accepted: 12/21/2015] [Indexed: 01/25/2023] Open
Abstract
The skeletal muscle Ca2+ release channel, also known as ryanodine receptor type 1 (RyR1), is the largest ion channel protein known and is crucial for effective skeletal muscle contractile activation. RyR1 function is controlled by Cav1.1, a voltage gated Ca2+ channel that works mainly as a voltage sensor for RyR1 activity during skeletal muscle contraction and is also fine-tuned by Ca2+, several intracellular compounds (e.g., ATP), and modulatory proteins (e.g., calmodulin). Dominant and recessive mutations in RyR1, as well as acquired channel alterations, are the underlying cause of various skeletal muscle diseases. The aim of this mini review is to summarize several current aspects of RyR1 function, structure, regulation, and to describe the most common diseases caused by hereditary or acquired RyR1 malfunction.
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Affiliation(s)
- Erick O Hernández-Ochoa
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine Baltimore, MD, USA
| | - Stephen J P Pratt
- Department of Orthopaedics, University of Maryland School of Medicine Baltimore, MD, USA
| | - Richard M Lovering
- Department of Orthopaedics, University of Maryland School of Medicine Baltimore, MD, USA
| | - Martin F Schneider
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine Baltimore, MD, USA
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18
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Wagenknecht T, Hsieh C, Marko M. Skeletal Muscle Triad Junction Ultrastructure by Focused-Ion-Beam Milling of Muscle and Cryo-Electron Tomography. Eur J Transl Myol 2015; 25:4823. [PMID: 26913145 PMCID: PMC4748973 DOI: 10.4081/ejtm.2015.4823] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2014] [Revised: 01/09/2015] [Accepted: 01/15/2015] [Indexed: 11/23/2022] Open
Abstract
Cryo-electron tomography (cryo-ET) has emerged as perhaps the only practical technique for revealing nanometer-level three-dimensional structural details of subcellular macromolecular complexes in their native context, inside the cell. As currently practiced, the specimen should be 0.1-0.2 microns in thickness to achieve optimal resolution. Thus, application of cryo-ET to intact frozen (vitreous) tissues, such as skeletal muscle, requires that they be sectioned. Cryo-ultramicrotomy is notoriously difficult and artifact-prone when applied to frozen cells and tissue, but a new technique, focused ion beam milling (cryo-FIB), shows great promise for “thinning” frozen biological specimens. Here we describe our initial results in applying cryo-FIB and cryo-ET to triad junctions of skeletal muscle.
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Affiliation(s)
- Terence Wagenknecht
- New York State Department of Health, Wadsworth Cente, Empire State Plaza, Albany, NY, USA.,Department of Biomedical Sciences, School of Public Health, University at Albany, Albany, NY, USA
| | - Chyongere Hsieh
- New York State Department of Health, Wadsworth Cente, Empire State Plaza, Albany, NY, USA
| | - Michael Marko
- New York State Department of Health, Wadsworth Cente, Empire State Plaza, Albany, NY, USA
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19
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Hollingworth S, Baylor SM. Comparison of myoplasmic calcium movements during excitation-contraction coupling in frog twitch and mouse fast-twitch muscle fibers. J Gen Physiol 2013; 141:567-83. [PMID: 23630340 PMCID: PMC3639574 DOI: 10.1085/jgp.201310961] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2013] [Accepted: 03/25/2013] [Indexed: 01/26/2023] Open
Abstract
Single twitch fibers from frog leg muscles were isolated by dissection and micro-injected with furaptra, a rapidly responding fluorescent Ca(2+) indicator. Indicator resting fluorescence (FR) and the change evoked by an action potential (ΔF) were measured at long sarcomere length (16°C); ΔF/FR was scaled to units of ΔfCaD, the change in fraction of the indicator in the Ca(2+)-bound form. ΔfCaD was simulated with a multicompartment model of the underlying myoplasmic Ca(2+) movements, and the results were compared with previous measurements and analyses in mouse fast-twitch fibers. In frog fibers, sarcoplasmic reticulum (SR) Ca(2+) release evoked by an action potential appears to be the sum of two components. The time course of the first component is similar to that of the entire Ca(2+) release waveform in mouse fibers, whereas that of the second component is severalfold slower; the fractional release amounts are ~0.8 (first component) and ~0.2 (second component). Similar results were obtained in frog simulations with a modified model that permitted competition between Mg(2+) and Ca(2+) for occupancy of the regulatory sites on troponin. An anatomical basis for two release components in frog fibers is the presence of both junctional and parajunctional SR Ca(2+) release channels (ryanodine receptors [RyRs]), whereas mouse fibers (usually) have only junctional RyRs. Also, frog fibers have two RyR isoforms, RyRα and RyRβ, whereas the mouse fibers (usually) have only one, RyR1. Our simulations suggest that the second release component in frog fibers functions to supply extra Ca(2+) to activate troponin, which, in mouse fibers, is not needed because of the more favorable location of their triadic junctions (near the middle of the thin filament). We speculate that, in general, parajunctional RyRs permit increased myofilament activation in fibers whose triadic junctions are located at the z-line.
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Affiliation(s)
- Stephen Hollingworth
- Department of Physiology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA 19104, USA
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20
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Baylor SM, Hollingworth S. Intracellular calcium movements during excitation-contraction coupling in mammalian slow-twitch and fast-twitch muscle fibers. ACTA ACUST UNITED AC 2012; 139:261-72. [PMID: 22450485 PMCID: PMC3315149 DOI: 10.1085/jgp.201210773] [Citation(s) in RCA: 80] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
In skeletal muscle fibers, action potentials elicit contractions by releasing calcium ions (Ca2+) from the sarcoplasmic reticulum. Experiments on individual mouse muscle fibers micro-injected with a rapidly responding fluorescent Ca2+ indicator dye reveal that the amount of Ca2+ released is three- to fourfold larger in fast-twitch fibers than in slow-twitch fibers, and the proportion of the released Ca2+ that binds to troponin to activate contraction is substantially smaller.
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Affiliation(s)
- Stephen M Baylor
- Department of Physiology, University of Pennsylvania, Philadelphia, PA 19104, USA
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21
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Contribution of anti-ryanodine receptor antibody to impairment of excitation–contraction coupling in myasthenia gravis. Clin Neurophysiol 2012; 123:1242-7. [DOI: 10.1016/j.clinph.2011.10.038] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2011] [Revised: 09/01/2011] [Accepted: 10/02/2011] [Indexed: 11/21/2022]
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22
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Imai T, Tsuda E, Hozuki T, Yamauchi R, Saitoh M, Hisahara S, Yoshikawa H, Motomura M, Kawamata J, Shimohama S. Early effect of tacrolimus in improving excitation-contraction coupling in myasthenia gravis. Clin Neurophysiol 2012; 123:1886-90. [PMID: 22386321 DOI: 10.1016/j.clinph.2012.01.017] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2011] [Revised: 12/27/2011] [Accepted: 01/27/2012] [Indexed: 12/31/2022]
Abstract
OBJECTIVES Tacrolimus (FK506) is a macrolide T-cell immunomodulator used to treat myasthenia gravis (MG). Besides immunosuppression, tacrolimus has been reported to have the potential to increase muscle strength by enhancing ryanodine receptor (RyR) function. However, few attempts have been made to demonstrate the early effect of tacrolimus as an RyR enhancer in clinical investigation. METHODS In 20 MG patients, masseteric compound muscle action potential (CMAP) and mandibular movement-related potentials (MRPs) were recorded simultaneously after stimulating the trigeminal motor nerve with a needle electrode. The excitation-contraction (E-C) coupling time (ECCT) was calculated by the latency difference between CMAP and MRP. Bite force was measured using a pressure-sensitive sheet. Serial assessments of % decrement in masseteric repetitive nerve stimulation (RNS), ECCT and bite force were performed before and within 4 weeks of tacrolimus (3 mg day(-1)) treatment. The median (mean, range) interval of assessment was 2 (2.4, 1-4) weeks. We also measured serum antibodies against RyR, acetylcholine receptor and muscle-specific receptor tyrosine kinase. RESULTS Bite force increased after tacrolimus treatment accompanying clinical improvement assessed by Myasthenia Gravis Foundation of America classification, but the bite force difference did not reach statistical significance. Wilcoxon matched-pairs signed-ranks test detected a significant ECCT shortening in 12 patients assessed after 1-2 weeks of tacrolimus treatment as well as in eight patients assessed after 3-4 weeks. In contrast, masseteric CMAP and % decrement showed no significant changes after short-term tacrolimus treatment. CONCLUSIONS Tacrolimus induces ECCT shortening accompanying clinical improvement despite no improvement in % decrement within 2 weeks. SIGNIFICANCE This early effect of tacrolimus may imply a pharmacological enhancement of RyR function to improve E-C coupling in MG.
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Affiliation(s)
- Tomihiro Imai
- Department of Neurology, Sapporo Medical University School of Medicine, Sapporo, Japan.
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Huang CLH, Pedersen TH, Fraser JA. Reciprocal dihydropyridine and ryanodine receptor interactions in skeletal muscle activation. J Muscle Res Cell Motil 2011; 32:171-202. [PMID: 21993921 DOI: 10.1007/s10974-011-9262-9] [Citation(s) in RCA: 110] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2011] [Accepted: 09/12/2011] [Indexed: 11/25/2022]
Abstract
Dihydropyridine (DHPR) and ryanodine receptors (RyRs) are central to transduction of transverse (T) tubular membrane depolarisation initiated by surface action potentials into release of sarcoplasmic reticular (SR) Ca2+ in skeletal muscle excitation-contraction coupling. Electronmicroscopic methods demonstrate an orderly positioning of such tubular DHPRs relative to RyRs in the SR at triad junctions where their membranes come into close proximity. Biochemical and genetic studies associated expression of specific, DHPR and RyR, isoforms with the particular excitation-contraction coupling processes and related elementary Ca2+ release events found respectively in skeletal and cardiac muscle. Physiological studies of intramembrane charge movements potentially related to voltage triggering of Ca2+ release demonstrated a particular qγ charging species identifiable with DHPRs through its T-tubular localization, pharmacological properties, and steep voltage-dependence paralleling Ca2+ release. Its nonlinear kinetics implicated highly co-operative conformational events in its transitions in response to voltage change. The effects of DHPR and RyR agonists and antagonists upon this intramembrane charge in turn implicated reciprocal rather than merely unidirectional DHPR-RyR interactions in these complex reactions. Thus, following membrane potential depolarization, an orthograde qγ-DHPR-RyR signaling likely initiates conformational alterations in the RyR with which it makes contact. The latter changes could then retrogradely promote further qγ-DHPR transitions through reciprocal co-operative allosteric interactions between receptors. These would relieve the resting constraints on both further, delayed, nonlinear qγ-DHPR charge transfers and on RyR-mediated Ca2+ release. They would also explain the more rapid charging and recovery qγ transients following larger depolarizations and membrane potential repolarization to the resting level.
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Affiliation(s)
- Christopher L-H Huang
- Physiological Laboratory, Department of Biochemistry, University of Cambridge, Cambridge, CB2 3EG, UK.
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Loy RE, Orynbayev M, Xu L, Andronache Z, Apostol S, Zvaritch E, MacLennan DH, Meissner G, Melzer W, Dirksen RT. Muscle weakness in Ryr1I4895T/WT knock-in mice as a result of reduced ryanodine receptor Ca2+ ion permeation and release from the sarcoplasmic reticulum. ACTA ACUST UNITED AC 2010; 137:43-57. [PMID: 21149547 PMCID: PMC3010056 DOI: 10.1085/jgp.201010523] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The type 1 isoform of the ryanodine receptor (RYR1) is the Ca(2+) release channel of the sarcoplasmic reticulum (SR) that is activated during skeletal muscle excitation-contraction (EC) coupling. Mutations in the RYR1 gene cause several rare inherited skeletal muscle disorders, including malignant hyperthermia and central core disease (CCD). The human RYR1(I4898T) mutation is one of the most common CCD mutations. To elucidate the mechanism by which RYR1 function is altered by this mutation, we characterized in vivo muscle strength, EC coupling, SR Ca(2+) content, and RYR1 Ca(2+) release channel function using adult heterozygous Ryr1(I4895T/+) knock-in mice (IT/+). Compared with age-matched wild-type (WT) mice, IT/+ mice exhibited significantly reduced upper body and grip strength. In spite of normal total SR Ca(2+) content, both electrically evoked and 4-chloro-m-cresol-induced Ca(2+) release were significantly reduced and slowed in single intact flexor digitorum brevis fibers isolated from 4-6-mo-old IT/+ mice. The sensitivity of the SR Ca(2+) release mechanism to activation was not enhanced in fibers of IT/+ mice. Single-channel measurements of purified recombinant channels incorporated in planar lipid bilayers revealed that Ca(2+) permeation was abolished for homotetrameric IT channels and significantly reduced for heterotetrameric WT:IT channels. Collectively, these findings indicate that in vivo muscle weakness observed in IT/+ knock-in mice arises from a reduction in the magnitude and rate of RYR1 Ca(2+) release during EC coupling that results from the mutation producing a dominant-negative suppression of RYR1 channel Ca(2+) ion permeation.
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Affiliation(s)
- Ryan E Loy
- Department of Pharmacology and Physiology, University of Rochester, Rochester, NY 14642, USA
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25
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Lanner JT, Georgiou DK, Joshi AD, Hamilton SL. Ryanodine receptors: structure, expression, molecular details, and function in calcium release. Cold Spring Harb Perspect Biol 2010; 2:a003996. [PMID: 20961976 DOI: 10.1101/cshperspect.a003996] [Citation(s) in RCA: 537] [Impact Index Per Article: 38.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Ryanodine receptors (RyRs) are located in the sarcoplasmic/endoplasmic reticulum membrane and are responsible for the release of Ca(2+) from intracellular stores during excitation-contraction coupling in both cardiac and skeletal muscle. RyRs are the largest known ion channels (> 2MDa) and exist as three mammalian isoforms (RyR 1-3), all of which are homotetrameric proteins that interact with and are regulated by phosphorylation, redox modifications, and a variety of small proteins and ions. Most RyR channel modulators interact with the large cytoplasmic domain whereas the carboxy-terminal portion of the protein forms the ion-conducting pore. Mutations in RyR2 are associated with human disorders such as catecholaminergic polymorphic ventricular tachycardia whereas mutations in RyR1 underlie diseases such as central core disease and malignant hyperthermia. This chapter examines the current concepts of the structure, function and regulation of RyRs and assesses the current state of understanding of their roles in associated disorders.
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Affiliation(s)
- Johanna T Lanner
- Baylor College of Medicine, Department of Molecular Physiology and Biophysics, Houston, Texas 77030,USA
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26
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Grabner M, Dayal A. Crosstalk via the Sarcoplasmic Gap: The DHPR-RyR Interaction. CURRENT TOPICS IN MEMBRANES 2010; 66:115-38. [PMID: 22353478 DOI: 10.1016/s1063-5823(10)66006-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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27
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Is high concentration of parvalbumin a requirement for superfast relaxation? J Muscle Res Cell Motil 2009; 30:57-65. [PMID: 19387850 DOI: 10.1007/s10974-009-9175-z] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2009] [Accepted: 03/21/2009] [Indexed: 10/20/2022]
Abstract
It is generally thought that the rapid relaxation of fast muscles is facilitated by the Ca(2+) binding protein parvalbumin (Parv). Indeed superfast swimbladder (SWB) muscle of toadfish contains the largest concentration of this protein ever observed (up to 1.5 mM). At 15 degrees C toadfish perform a 100 Hz call, 400 ms in duration, followed by a long (5-15 s) intercall interval. It has been proposed that Parv helps sequester the Ca(2+) during the call, and then Ca(2+) unbinds and is pumped back into the sarcoplasmic reticulum during the long intercall interval. Midshipman (Porichthys notatus) is another fish which calls at a high frequency; 80-100 Hz at a temperature of 12-15 degrees C. However, unlike toadfish, midshipman call with a 100% duty cycle. Without an intercall interval, Parv would seem of little use as it would become saturated early in calling. Here we show that the midshipman SWB has only about 1/8th of the Parv in toadfish. Moreover, total Parv content in calling male midshipman SWB was not different from that in the non-calling female and the much slower locomotory muscles. These data suggest that Parv does not play a large role in the calling of midshipman, which is accomplished without a high concentration of this protein. Native gel-electrophoresis also revealed presence of three major (PA-I, PA-II and PA-III) and two minor (PA-Ia and PA-IIIa, <5% of total content) Parv isoforms in adult toadfish SWB. Midshipman SWB contained about equal amounts of PA-I and PA-II and also a small (approximately 10%) amount of PA-III. By amino acid composition, toadfish PA-Ia and PA-I isoforms were different from PA-II and PA-III isoforms (by 24 and 14 residues, respectively).
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Rigoard P, Bauche S, Buffenoir K, Giot JP, Faure JP, Scepi M, Richer JP, Lapierre F, Wager M. Le support anatomique de la contraction musculaire. Neurochirurgie 2009; 55 Suppl 1:S69-82. [DOI: 10.1016/j.neuchi.2008.05.006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2008] [Accepted: 05/09/2008] [Indexed: 11/24/2022]
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An Ryr1I4895T mutation abolishes Ca2+ release channel function and delays development in homozygous offspring of a mutant mouse line. Proc Natl Acad Sci U S A 2007; 104:18537-42. [PMID: 18003898 DOI: 10.1073/pnas.0709312104] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
A heterozygous Ile4898 to Thr (I4898T) mutation in the human type 1 ryanodine receptor/Ca(2+) release channel (RyR1) leads to a severe form of central core disease. We created a mouse line in which the corresponding Ryr1(I4895T) mutation was introduced by using a "knockin" protocol. The heterozygote does not exhibit an overt disease phenotype, but homozygous (IT/IT) mice are paralyzed and die perinatally, apparently because of asphyxia. Histological analysis shows that IT/IT mice have greatly reduced and amorphous skeletal muscle. Myotubes are small, nuclei remain central, myofibrils are disarranged, and no cross striation is obvious. Many areas indicate probable degeneration, with shortened myotubes containing central stacks of pyknotic nuclei. Other manifestations of a delay in completion of late stages of embryogenesis include growth retardation and marked delay in ossification, dermatogenesis, and cardiovascular development. Electron microscopy of IT/IT muscle demonstrates appropriate targeting and positioning of RyR1 at triad junctions and a normal organization of dihydropyridine receptor (DHPR) complexes into RyR1-associated tetrads. Functional studies carried out in cultured IT/IT myotubes show that ligand-induced and DHPR-activated RyR1 Ca(2+) release is absent, although retrograde enhancement of DHPR Ca(2+) conductance is retained. IT/IT mice, in which RyR1-mediated Ca(2+) release is abolished without altering the formation of the junctional DHPR-RyR1 macromolecular complex, provide a valuable model for elucidation of the role of RyR1-mediated Ca(2+) signaling in mammalian embryogenesis.
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Nakata M, Kuwabara S, Kawaguchi N, Takahashi H, Misawa S, Kanai K, Tamura N, Sawai S, Motomura M, Shiraishi H, Takamori M, Maruta T, Yoshikawa H, Hattori T. Is excitation–contraction coupling impaired in myasthenia gravis? Clin Neurophysiol 2007; 118:1144-8. [PMID: 17307394 DOI: 10.1016/j.clinph.2007.01.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2006] [Revised: 12/09/2006] [Accepted: 01/02/2007] [Indexed: 11/25/2022]
Abstract
OBJECTIVE To investigate whether excitation-contraction (E-C) coupling of muscle is impaired in patients with myasthenia gravis (MG). METHODS In 51 patients with generalized MG and 35 normal subjects, compound muscle action potentials (CMAPs) of the abductor pollicis brevis, and movement-related potentials using an accelerometer placed at the thumb tip were simultaneously recorded after median nerve stimulation at the wrist. The E-C coupling time (ECCT) was estimated by a latency difference between CMAP and movement-related potential. Antibodies against acetylcholine receptor (AChR), ryanodine receptor (RyR), and muscle specific receptor tyrosine kinase (MuSK) were measured by immunoassays. RESULTS The mean ECCT was significantly longer in patients with MG (mean+/-SEM; 2.79+/-0.1 ms; p=0.002) than in normal controls (2.52+/-0.1 ms). Among MG patients, the mean ECCT was longer for patients with thymoma than for those without it (P=0.04), and was shorter for patients treated with FK506 (an immunosuppressant and also an enhancer of RyR related Ca(2+) release) than for those not receiving this treatment (p=0.04). ECCT had no significant correlation with anti-AChR, anti-RyR, or anti-MuSK antibodies. CONCLUSIONS In MG, E-C coupling appears to be impaired, particularly in patients with thymoma, and FK506 possibly facilitates E-C coupling. SIGNIFICANCE The functional implication of impaired E-C coupling is not established, but it may contribute to muscle weakness in patients with MG.
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Affiliation(s)
- Miho Nakata
- Department of Neurology, Graduate School of Medicine, Chiba University, 1-8-1, Inohana, Chuo-ku, Chiba 260-8670, Japan
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Usher-Smith JA, Fraser JA, Huang CLH, Skepper JN. Alterations in triad ultrastructure following repetitive stimulation and intracellular changes associated with exercise in amphibian skeletal muscle. J Muscle Res Cell Motil 2007; 28:19-28. [PMID: 17333488 PMCID: PMC3714558 DOI: 10.1007/s10974-007-9100-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2006] [Accepted: 01/05/2007] [Indexed: 11/06/2022]
Abstract
This study used Rana temporaria sartorius muscles to examine the effect of fatiguing electrical stimulation on the gap between the T-tubular and sarcoplasmic reticular membranes (T-SR distance) and the T-tubule diameter and compared this with corresponding effects on resting fibres exposed to a range of extracellular conditions that each replicate one of the major changes associated with muscular activity: membrane depolarisation, isotonic volume increase, acidification and intracellular lactate accumulation. Following each treatment, muscles were immersed in isotonic fixative solution and processed for transmission electron microscopy (TEM). Mean T-SR distances were estimated from orthogonal intercepts to provide estimates of diffusion distances between T and SR membranes and T-tubule diameter was estimated by measuring its shortest axis in the sampled J-SR complexes. Measurements from muscles fatigued by low frequency intermittent stimulation showed significant (P << 0.05) reversible increases in both T-SR distance and T-tubule diameter from 15.97 ± 0.37 nm to 20.15 ± 0.56 nm and from 15.44 ± 0.60 nm to 22.26 ± 0.84 nm (n = 40, 30) respectively. Exposure to increasing concentrations of extracellular [K+] in the absence of Cl− to produce membrane depolarisation without accompanying cell swelling reduced T-SR distance and increased T-tubule diameter, whilst comparable increases in [K+]e in the presence of Cl− suggested that isotonic cell swelling has the opposite effect. Acidification alone, produced by NH4Cl addition and withdrawal, also decreased T-SR distance and T-tubule diameter. A similar reduction in T-SR distance occurred following exposure to extracellular Na-lactate where such acidification was accompanied by elevations of intracellular lactate, but these conditions produced a significant swelling of T-tubules attributable to movement of lactate from the cell into the T-tubules. This study thus confirms previous reports of significant increases in T-SR distance and T-tubule diameter following stimulation. However, of membrane depolarisation, isotonic cell swelling, intracellular acidification and lactate accumulation, only isotonic cell swelling increases T-SR distance whilst membrane depolarisation and intracellular lactate likely contribute to the observed increases in T-tubule diameter.
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Affiliation(s)
- Juliet A Usher-Smith
- Physiological Laboratory, Department of Physiology, Development and Neuroscience, University of Cambridge, Downing Street, Cambridge CB2 3EG, UK.
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Yang SN, Berggren PO. The role of voltage-gated calcium channels in pancreatic beta-cell physiology and pathophysiology. Endocr Rev 2006; 27:621-76. [PMID: 16868246 DOI: 10.1210/er.2005-0888] [Citation(s) in RCA: 175] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Voltage-gated calcium (CaV) channels are ubiquitously expressed in various cell types throughout the body. In principle, the molecular identity, biophysical profile, and pharmacological property of CaV channels are independent of the cell type where they reside, whereas these channels execute unique functions in different cell types, such as muscle contraction, neurotransmitter release, and hormone secretion. At least six CaValpha1 subunits, including CaV1.2, CaV1.3, CaV2.1, CaV2.2, CaV2.3, and CaV3.1, have been identified in pancreatic beta-cells. These pore-forming subunits complex with certain auxiliary subunits to conduct L-, P/Q-, N-, R-, and T-type CaV currents, respectively. beta-Cell CaV channels take center stage in insulin secretion and play an important role in beta-cell physiology and pathophysiology. CaV3 channels become expressed in diabetes-prone mouse beta-cells. Point mutation in the human CaV1.2 gene results in excessive insulin secretion. Trinucleotide expansion in the human CaV1.3 and CaV2.1 gene is revealed in a subgroup of patients with type 2 diabetes. beta-Cell CaV channels are regulated by a wide range of mechanisms, either shared by other cell types or specific to beta-cells, to always guarantee a satisfactory concentration of Ca2+. Inappropriate regulation of beta-cell CaV channels causes beta-cell dysfunction and even death manifested in both type 1 and type 2 diabetes. This review summarizes current knowledge of CaV channels in beta-cell physiology and pathophysiology.
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Affiliation(s)
- Shao-Nian Yang
- The Rolf Luft Research Center for Diabetes and Endocrinology L1:03, Karolinska University Hospital Solna, SE-171 76 Stockholm, Sweden.
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Di Biase V, Franzini-Armstrong C. Evolution of skeletal type e-c coupling: a novel means of controlling calcium delivery. ACTA ACUST UNITED AC 2005; 171:695-704. [PMID: 16286507 PMCID: PMC2171569 DOI: 10.1083/jcb.200503077] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The functional separation between skeletal and cardiac muscles, which occurs at the threshold between vertebrates and invertebrates, involves the evolution of separate contractile and control proteins for the two types of striated muscles, as well as separate mechanisms of contractile activation. The functional link between electrical excitation of the surface membrane and activation of the contractile material (known as excitation–contraction [e–c] coupling) requires the interaction between a voltage sensor in the surface membrane, the dihydropyridine receptor (DHPR), and a calcium release channel in the sarcoplasmic reticulum, the ryanodine receptor (RyR). Skeletal and cardiac muscles have different isoforms of the two proteins and present two structurally and functionally distinct modes of interaction. We use structural clues to trace the evolution of the dichotomy from a single, generic type of e–c coupling to a diversified system involving a novel mechanism for skeletal muscle activation. Our results show that a significant structural transition marks the protochordate to the Craniate evolutionary step, with the appearance of skeletal muscle–specific RyR and DHPR isoforms.
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Affiliation(s)
- Valentina Di Biase
- Department of Cell and Developmental Biology, University of Pennsylvania, Philadelphia, PA 19104.
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Abstract
Ca(2+) sparks monitor transient local releases of Ca(2+) from the sarcoplasmic reticulum (SR) into the myoplasm. The release takes place through ryanodine receptors (RYRs), the Ca(2+)-release channels of the SR. In intact fibers from frog skeletal muscle, the temporal and spatial properties of voltage-activated Ca(2+) sparks are well simulated by a model that assumes that the Ca(2+) flux underlying a spark is 2.5 pA (units of Ca(2+) current) for 4.6 ms (18 degrees C). This flux amplitude suggests that 1-5 active RYRs participate in the generation of a typical voltage-activated spark under physiological conditions. A major goal of future experiments is to estimate this number more precisely and, if it is two or more, to investigate the communication mechanism that allows multiple RYRs to be co-activated in a rapid but self-limited fashion.
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Affiliation(s)
- Stephen M Baylor
- Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, 19104-6085, USA.
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Notsu E, Matsuno A. An ultrastructural and biochemical study of foot structure in "catch" smooth muscle cells of a clam. Cell Struct Funct 2004; 29:43-8. [PMID: 15342964 DOI: 10.1247/csf.29.43] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The foot structure of molluscan (clam) catch muscle cells was studied from the structural and biochemical standpoints. In vertebrate cross striated muscle cells, foot structures are situated in the interspaces between T-tubules and sarcoplasmic reticula (SRs). By contrast, T-tubules were not observed in clam catch muscle cells, but foot structures were ultrastructurally identified in the interspaces between the SRs and cell membranes. We isolated the SR fraction from muscle cells which contained vesicles with SRs and cell membranes. Foot structures were also observed in the SR fraction by thin sectioning. The size and shape of the foot structure in both intact muscle cells and the SR fractions appeared to be slightly smaller than those of vertebrates. However, the molecular weight of the foot structures (foot proteins) as determined by SDS-PAGE (450 kD) was similar to ryanodine receptors (RyRs) which were reported previously in cross striated muscle cells from pecten and vertebrates. The protein showing the 450 kD band reacted to an anti-ryanodine receptor by Western blotting. These findings are discussed in comparison with previous studies of foot structures and RyRs of vertebrates and invertebrates.
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Affiliation(s)
- Eiji Notsu
- Department of Biological Science, Faculty of Life and Environmental Sciences, Shimane University, Matsue 690-0823, Japan
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Paolini C, Fessenden JD, Pessah IN, Franzini-Armstrong C. Evidence for conformational coupling between two calcium channels. Proc Natl Acad Sci U S A 2004; 101:12748-52. [PMID: 15310845 PMCID: PMC515124 DOI: 10.1073/pnas.0404836101] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Ryanodine receptor 1 (RyR1, the sarcoplasmic reticulum Ca(2+) release channel) and alpha(1S)dihydropyridine receptor (DHPR, the surface membrane voltage sensor) of skeletal muscle belong to separate membrane systems but are functionally and structurally linked. Four alpha(1S)DHPRs associated with the four identical subunits of a RyR form a tetrad. We treated skeletal muscle cell lines with ryanodine, at concentrations that block RyRs, and determined whether this treatment affects the distance between DHPRs in the tetrad. We find a substantial ( approximately 2-nm) shift in the alpha(1S)DHPR positions, indicating that ryanodine induces large conformational changes in the RyR1 cytoplasmic domain and that the alpha(1S)DHPR-RyR complex acts as a unit.
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Affiliation(s)
- C Paolini
- Department of Cell and Developmental Biology, University of Pennsylvania, Philadelphia, PA 19104-6058, USA
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Martin CA, Petousi N, Chawla S, Hockaday AR, Burgess AJ, Fraser JA, Huang CLH, Skepper JN. The effect of extracellular tonicity on the anatomy of triad complexes in amphibian skeletal muscle. J Muscle Res Cell Motil 2004; 24:407-15. [PMID: 14677643 DOI: 10.1023/a:1027356410698] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Ultrastructural features of tubular-sarcoplasmic (T-SR) triad junctions and measures of cell volume following graded increases of extracellular tonicity were compared under physiological conditions recently shown to produce spontaneous release of intracellularly stored Ca2+ in fully polarized amphibian skeletal muscle fibres. The fibres were fixed using solutions of equivalent tonicities prior to processing for electron microscopy. The resulting anatomical sections demonstrated a partially reversible cell shrinkage corresponding to substantial increases in intracellular solute or ionic strength graded with extracellular tonicity. Serial thin sections through triad structures confirmed the presence of geometrically close but anatomically isolated transverse (T-) tubular and sarcoplasmic reticular (SR) membranes contrary to earlier suggestions for the development of luminal continuities between these structures in hypertonic solutions. They also quantitatively demonstrated accompanying decreases in T-SR distances, increased numbers of sections that showed closely apposed T and SR membranes, tubular luminal swelling and reductions in luminal volume of the junctional SR, all correlated with the imposed increases in extracellular osmolarity. Fully polarized fibres correspondingly showed elementary Ca(2+)-release events ('sparks', in 100 mM-sucrose-Ringer solution), sustained Ca2+ elevations and propagated Ca2+ waves (> or = 350-500 mM sucrose) following exposure to physiological Ringer solutions of successively greater tonicities. These were absent in hypotonic, isotonic or less strongly hypertonic (approximately 50 mM sucrose-Ringer) solutions. Yet exposure to hypotonic solutions also disrupted T-SR junctional anatomy. It increased the tubular diameters and T-SR distances and reduced their area of potential contact. The spontaneous release of intracellularly stored Ca2+ thus appears more closely to correlate with the expected changes in intracellular solute strength or a reduction in absolute T-SR distance rather than disruption of an optimal anatomical relationship between T and SR membranes taking place with either increases or decreases in extracellular tonicity.
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Affiliation(s)
- Claire A Martin
- Physiological Laboratory, University of Cambridge, Downing Street, Cambridge CB2 3EG, United Kingdom
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Connaughton MA. Sound generation in the searobin (Prionotus carolinus), a fish with alternate sonic muscle contraction. ACTA ACUST UNITED AC 2004; 207:1643-54. [PMID: 15073197 DOI: 10.1242/jeb.00928] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The Northern searobin (Prionotus carolinus) contracts its paired sonic muscles alternately rather than simultaneously during sound production. This study describes this phenomenon and examines its effect on sound production by recording sound and EMGs during voluntary and electrically stimulated calls. Sounds produced by a single twitch resulted in a two-part sound representing contraction and relaxation sounds. The relaxation sound of one twitch coincides with the contraction sound of the next twitch of that muscle. Maximum amplitude of evoked sounds occurs between 100 Hz and 140 Hz, approximately half the fundamental frequency of a voluntarily calling fish. The muscle is capable of following electrical stimulation at frequencies of up to 360 Hz. Rapid damping and response over a wide frequency range indicate that the swimbladder is a highly damped, broadly tuned resonator. A consequence of alternate contraction is a 3.3 dB loss in acoustic pressure due to the contraction of a single sonic muscle at a time. This decrease in amplitude is offset by a doubling of fundamental frequency and a constructive interaction between the sides of the bladder, resulting in increased amplitude of each unilaterally produced sound. The alternate contraction of the bilateral sonic muscles represents a novel solution to the inherent trade-off between speed and force of contraction in rapidly contracting sonic muscles.
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Affiliation(s)
- Martin A Connaughton
- Washington College, Department of Biology, 300 Washington Ave, Chestertown, MD 21620, USA.
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Modesto T, Canário AVM. Hormonal control of swimbladder sonic muscle dimorphism in the Lusitanian toadfish Halobatrachus didactylus. J Exp Biol 2003; 206:3467-77. [PMID: 12939377 DOI: 10.1242/jeb.00581] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The swimbladder and associated sonic muscle of the Lusitanian toadfish Halobatrachus didactylus increase in size throughout life and are, respectively, 25% and 30% larger in type I (nest-holder) males than females, which may generate sexual differences in sound production. Sexual dimorphism in swimbladder is also evident in the morphological features of sonic muscle fibers. During the breeding season, type I males have smaller myofibril contracting zones surrounded by larger sarcoplasm areas compared with females, possibly an adaptation to speed and fatigue resistance for the production of long mating calls. Type II (floater) males show characteristics that are intermediate, but statistically not significantly different, between type I males and females. Six weeks after castration and androgen (testosterone and 11-ketotestosterone) replacement in type I and type II males there were no alterations either in swimbladder mass or fiber morphology. However, 17beta-estradiol induced a significant decrease in swimbladder mass and sarcoplasm area/myofibril area ratio. Six months after castration there was a clear reduction in the seasonal swimbladder hypertrophy in males and induction of sonic fiber morphological characteristics that resemble those occurring in females (low sarcoplasm area/myofibril area ratio). These results suggest that testicular factors are required to initiate sonic muscle hypertrophy and type I sonic fiber phenotype in H. didactylus, but a specific involvement of androgens has not been completely clarified.
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Affiliation(s)
- Teresa Modesto
- Centro de Ciências do Mar, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal.
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Lewis MK, Nahirney PC, Chen V, Adhikari BB, Wright J, Reedy MK, Bass AH, Wang K. Concentric intermediate filament lattice links to specialized Z-band junctional complexes in sonic muscle fibers of the type I male midshipman fish. J Struct Biol 2003; 143:56-71. [PMID: 12892726 DOI: 10.1016/s1047-8477(03)00121-7] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Type I male midshipman fish produce high-frequency hums for prolonged durations using sonic muscle fibers, each of which contains a hollow tube of radially oriented thin and flat myofibrils that display extraordinarily wide ( approximately 1.2 microm) Z bands. We have revealed an elaborate cytoskeletal network of desmin filaments associated with the contractile cylinder that form interconnected concentric ring structures in the core and periphery at the level of the Z bands. Stretch and release of single fibers revealed reversible length changes in the elastic desmin lattice. This lattice is linked to Z bands via novel intracellular desmosome-like junctional complexes that collectively form a ring, termed the "Z corset," around the periphery and within the core of the cylinder. The junctional complex consists of regularly spaced parallel approximately 900-nm-long cytoskeletal rods, or "Z bars," interconnected with slender (3-4 nm) plectin-positive filaments. Z bars are linked to the Z band by plectin filaments and on the opposite side to a dense mesh of desmin filaments. Adjacent Z bands are linked by slender filaments that appear to suspend sarcotubules. We propose that the highly reinforced elastic desmin cytoskeleton and the unique Z band junctions are structural adaptations that enable the muscles' high-frequency and high-endurance activity.
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Affiliation(s)
- Michael K Lewis
- Muscle Proteomics and Nanotechnology Section, Laboratory of Muscle Biology, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, DHHS, Bethesda, MD 20892, USA
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Hu XF, Chen KY, Xia R, Xu YH, Sun JL, Hu J, Zhu PH. Modulation of the interactions of isolated ryanodine receptors of rabbit skeletal muscle by Na+ and K+. Biochemistry 2003; 42:5515-21. [PMID: 12731894 DOI: 10.1021/bi034016o] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Ryanodine receptors (RyRs) of skeletal muscle, as calcium release channels, have been found to form semicrystalline arrays in the membrane of sarcoplasmic reticulum. Recently, both experimental observations and theoretical simulations suggested cooperative coupling within interlocking RyRs. To better understand the interactions between RyRs and their modulation, the aggregation and dissociation of isolated RyRs in aqueous medium containing various Na(+) and K(+) concentrations were investigated using photon correlation spectroscopy (PCS) and atomic force microscopy (AFM). RyRs aggregated readily at low salt concentrations. However, a different behavior was observed in the presence of Na(+) or K(+). Detectable aggregates were formed in 5 microg/mL RyR sample when the concentration of Na(+) and K(+) was reduced from 1 M to below 0.28 and 0.23 M, respectively. The dissociation of RyR aggregates was also examined when raising the salt concentration. While aggregates formed in 0.15 M NaCl medium could reverse almost completely, those formed in 0.15 M KCl medium only dissolved partly. When keeping the total salt concentration at 0.15 M, the aggregation and dissociation of RyRs were seen to evidently depend on the relative concentration of Na(+) and K(+). The interaction between RyRs was strengthened with increasing Na(+)/K(+) ratios in the mixed medium. Accompanying this, a decrease of [(3)H]ryanodine binding occurred. The results obtained with PCS and AFM provide further evidence for the interaction between RyRs and suggest the importance of Na(+), K(+), and their relative composition in modulating the interaction and cooperation between RyRs in vivo.
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Affiliation(s)
- Xiao-Fang Hu
- Bio-X Life Science Research Center, Shanghai Jiao Tong University, 1954 Hua-Shan Road, Shanghai 200030, China
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Abstract
BACKGROUND CONTEXT Calcium influx into cells is responsible for initiating the "final pathway" to cell death in neuronal tissue after traumatic or hypoxic injury. The specific pathways in this cascade are myriad and the importance each one plays is controversial. It is clear, though, that blocking individual pathways confers protection to these tissues. PURPOSE In the present study we examined the role of Cyclosporin A (CsA), FK-506 and rapamycin in modulating the effects of Ca(2+) influx through their interactions with immunophilins and specifically the end result of calcineurin modulation. METHODS Dorsal columns were isolated from the spinal cord of adult rats and injured by exposure to hypoxic conditions for 60 minutes. The samples were monitored electrophysiologically in an in vitro recording chamber (maintained at 37 C degrees ) during injury, and the compound action potential (CAP) was monitored with glass microelectrodes. The dorsal column was exposed to hypoxic Ringers solution alone or with the different immunosuppressants and compared with baseline readings. Functional recovery of the dorsal column was then assessed by recovery of the CAP. RESULTS The mean CAP decreased to about 20% of baseline control levels during hypoxia and returned 53.8+/-7.6% of baseline (p<.05) after reoxygenation. CsA, an immunosuppressant known to inhibit calcineurin, promoted a significantly greater recovery of CAP amplitude to 76.8+/-5.2% and 72.1+/-13.2% of control (p<.05) after hypoxic injury and reoxygenation of dorsal column white matter when applied at concentrations of 1 microM and 10 microM, respectively. FK-506, which also inhibits calcineurin, was applied at a concentration of 0.1 microM, and promoted CAP amplitude recovery to 82.6+/-5.0% of control after hypoxic injury and reoxygenation of dorsal column white matter. The addition of rapamycin (1 microM), which binds to the same immunophilin as FK-506, to the FK-506 (0.1 microM) solution during hypoxic injury showed recovery of CAP amplitudes to only 56.9+/-6.7% of control. Electron microscopy revealed remarkable protection of axons and prevention of organelle disruption in segments treated with CsA and FK-506 during hypoxia when compared with hypoxic controls. CONCLUSION In conclusion, both CsA and FK-506 confer in vitro protection to dorsal columns during hypoxic injury at physiological temperatures, and rapamycin blocks the protective effect of FK-506. Thus, calcineurin may play an important role in the physiology of neuronal injury.
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Affiliation(s)
- Lloyd W Mobley
- Section of Neurosurgery, Department of Surgery, 982035 University of Nebraska Medical Center, Omaha, NE 68198-2035, USA
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Takekura H, Franzini-Armstrong C. The structure of Ca(2+) release units in arthropod body muscle indicates an indirect mechanism for excitation-contraction coupling. Biophys J 2002; 83:2742-53. [PMID: 12414707 PMCID: PMC1302359 DOI: 10.1016/s0006-3495(02)75284-3] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
The relative disposition of ryanodine receptors (RyRs) and L-type Ca(2+) channels was examined in body muscles from three arthropods. In all muscles the disposition of ryanodine receptors in the junctional gap between apposed SR and T tubule elements is highly ordered. By contrast, the junctional membrane of the T tubule is occupied by distinctive large particles that are clustered within the small junctional domain, but show no order in their arrangement. We propose that the large particles of the junctional T tubules represent L-type Ca(2+) channels involved in excitation-contraction (e-c) coupling, based on their similarity in size and location with the L-type Ca(2+) channels or dihydropyridine receptors (DHPRs) of skeletal and cardiac muscle. The random arrangement of DHPRs in arthropod body muscles indicates that there is no close link between them and RyRs. This matches the architecture of vertebrate cardiac muscle and is in keeping with the similarity in e-c coupling mechanisms in cardiac and invertebrate striated muscles.
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Affiliation(s)
- Hiroaki Takekura
- Department of Physiological Sciences, National Institute of Fitness and Sports, Kanoya, Kagoshima 891-23, Japan
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Connaughton MA, Fine ML, Taylor MH. Weakfish sonic muscle: influence of size, temperature and season. J Exp Biol 2002; 205:2183-8. [PMID: 12110652 DOI: 10.1242/jeb.205.15.2183] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARYThe influence of temperature, size and season on the sounds produced by the sonic muscles of the weakfish Cynoscion regalis are categorized and used to formulate a hypothesis about the mechanism of sound generation by the sonic muscle and swimbladder. Sounds produced by male weakfish occur at the time and location of spawning and have been observed in courtship in captivity. Each call includes a series of 6-10 sound pulses, and each pulse expresses a damped, 2-3 cycle acoustic waveform generated by single simultaneous twitches of the bilateral sonic muscles. The sonic muscles triple in mass during the spawning season, and this hypertrophy is initiated by rising testosterone levels that trigger increases in myofibrillar and sarcoplasmic cross-sectional area of sonic muscle fibers. In response to increasing temperature, sound pressure level (SPL), dominant frequency and repetition rate increase, and pulse duration decreases. Likewise, SPL and pulse duration increase and dominant frequency decreases with fish size. Changes in acoustic parameters with fish size suggest the possibility that drumming sounds act as an `honest' signal of male fitness during courtship. These parameters also correlate with seasonally increasing sonic muscle mass. We hypothesize that sonic muscle twitch duration rather than the resonant frequency of the swimbladder determines dominant frequency. The brief (3.5 ms), rapidly decaying acoustic pulses reflect a low-Q, broadly tuned resonator, suggesting that dominant frequency is determined by the forced response of the swimbladder to sonic muscle contractions. The changing dominant frequency with temperature in fish of the same size further suggests that frequency is not determined by the natural frequency of the bladder because temperature is unlikely to affect resonance. Finally, dominant frequency correlates with pulse duration (reflecting muscle twitch duration),and the inverse of the period of the second cycle of acoustic energy approximates the recorded frequency. This paper demonstrates for the first time that the dominant frequency of a fish sound produced by a single muscle twitch is apparently determined by the velocity of the muscle twitch rather than the natural frequency of the swimbladder.
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Affiliation(s)
- M A Connaughton
- Washington College, Department of Biology, 300 Washington Avenue, Chestertown, MD 21620, USA.
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Caputo C. Calcium release in skeletal muscle: from K+ contractures to Ca2+ sparks. J Muscle Res Cell Motil 2002; 22:485-504. [PMID: 12038583 DOI: 10.1023/a:1015062914947] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- C Caputo
- Labortorio Biofísica del Músculo, Centro de Biofísica y Bioquímica, Instituto Venezolano de Investigaciones Científicas, IVIC, Caracas, Venezuela.
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Felder E, Franzini-Armstrong C. Type 3 ryanodine receptors of skeletal muscle are segregated in a parajunctional position. Proc Natl Acad Sci U S A 2002; 99:1695-700. [PMID: 11818557 PMCID: PMC122253 DOI: 10.1073/pnas.032657599] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
A key event in skeletal muscle activation is the rapid release of Ca(2+) from the sarcoplasmic reticulum (SR), the Ca(2+) storage organelle in the muscle cell. The surface membrane/transverse tubules and the SR form functional units (calcium release units containing one or two couplons or junctions), where the voltage-sensing dihydropyridine receptor of the surface membrane interacts with the SR Ca(2+) release channel [ryanodine receptor (RyR)] and depolarization of the cell membrane is converted into Ca(2+) release from the SR. Although RyR1 is the most important isoform in skeletal muscle, some muscles also express high levels of RyR3, an isoform with a wide tissue distribution. The cytoplasmic domains of RyRs are visible in the electron microscope as periodically disposed feet. We find that, in muscles containing only RyR1, feet are exclusively located over the junctional SR surface facing the surface membrane/transverse tubule. In muscles containing RyR1 as well as RyR3, additional feet are located in lateral parajunctional regions immediately adjacent to junctional SR. Biochemical content of RyR3 and content of parajunctional feet are highly correlated in different muscles and the disposition of parajunctional versus junctional feet are notably different. On the basis of these two observations, we postulate that RyR3s are restricted to the parajunctional region, and thus their activation must be indirect and derivative during excitation-contraction coupling.
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Affiliation(s)
- Edward Felder
- Department of Cell and Developmental Biology, University of Pennsylvania, Philadelphia, PA 19104-6058, USA.
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Chawla S, Skepper JN, Hockaday AR, Huang CL. Calcium waves induced by hypertonic solutions in intact frog skeletal muscle fibres. J Physiol 2001; 536:351-9. [PMID: 11600671 PMCID: PMC2278869 DOI: 10.1111/j.1469-7793.2001.0351c.xd] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
1. Regenerative Ca2+ waves and oscillations indicative of calcium-induced calcium release (CICR) activity were induced in fully polarized, fluo-3-loaded, intact frog skeletal muscle fibres by exposure to hypertonic Ringer solutions. 2. The calcium waves persisted in fibres exposed to EGTA-containing solutions, during sustained depolarization of the membrane potential or following treatment with the dihydropyridine receptor (DHPR)-blocker nifedipine. 3. The waves were blocked by the ryanodine receptor (RyR)-specific agents ryanodine and tetracaine, and potentiated by caffeine. 4. In addition to these pharmacological properties, the amplitudes, frequency and velocity of such hypertonicity-induced waves closely resembled those of Ca2+ waves previously described in dyspedic skeletal myocytes expressing the cardiac RyR-2. 5. Quantitative transmission and freeze-fracture electronmicroscopy demonstrated a reversible cell shrinkage, transverse (T)-tubular luminal swelling and decreased T-sarcoplasmic reticular (SR) junctional gaps in fibres maintained in and then fixed using hypertonic solutions. 6. The findings are consistent with a hypothesis in which RyR-Ca2+ release channels can be partially liberated from their normal control by T-tubular DHPR-voltage sensors in hypertonic solutions, thereby permitting CICR to operate even in such fully polarized skeletal muscle fibres.
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Affiliation(s)
- S Chawla
- Physiological Laboratory, Department of Anatomy, University of Cambridge, Cambridge CB2 3EG, UK
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Lorenzon NM, Grabner M, Suda N, Beam KG. Structure and targeting of RyR1: implications from fusion of green fluorescent protein at the amino-terminal. Arch Biochem Biophys 2001; 388:13-7. [PMID: 11361129 DOI: 10.1006/abbi.2000.2263] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In skeletal muscle, an anterograde signal from the dihydropyridine receptor (DHPR) to the ryanodine receptor (RyR1) is required for excitation-contraction (EC) coupling and a retrograde signal from RyR1 to the DHPR regulates the magnitude of the calcium current carried by the DHPR. As a tool for studying biosynthesis and targeting, we constructed a cDNA encoding green fluorescent protein (GFP) fused to the amino terminal of RyR1 and expressed it in dyspedic myotubes. The GFP-RyR1 was present in a restricted domain near the nucleus injected with cDNA and was fully functional, which places constraints on the location of the amino terminal in the folded structure of RyR1.
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Affiliation(s)
- N M Lorenzon
- Department of Anatomy and Neurobiology, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins 80523, USA
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Skeie GO, Lunde PK, Sejersted OM, Mygland A, Aarli JA, Gilhus NE. Autoimmunity against the ryanodine receptor in myasthenia gravis. ACTA PHYSIOLOGICA SCANDINAVICA 2001; 171:379-84. [PMID: 11412151 DOI: 10.1046/j.1365-201x.2001.00841.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Some myasthenia gravis (MG) patients have antibodies against skeletal muscle antigens in addition to the acetylcholine receptor (AChR). A major antigen for these antibodies is the Ca2+ release channel of the sarcoplasmic reticulum the ryanodine receptor (RyR). These antibodies are found mainly in MG patients with a thymoma MG and correlate with severe MG symptoms. The antibodies recognize a region near the N-terminus on the RyR, which seems to be of importance for RyR regulation. The antibodies cause allosteric inhibition of RyR function in vitro, inhibiting Ca2+ release from sarcoplasmic reticulum.
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Affiliation(s)
- G O Skeie
- Department of Neurology, University of Bergen, Bergen, Norway
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Protasi F, Takekura H, Wang Y, Chen SR, Meissner G, Allen PD, Franzini-Armstrong C. RYR1 and RYR3 have different roles in the assembly of calcium release units of skeletal muscle. Biophys J 2000; 79:2494-508. [PMID: 11053125 PMCID: PMC1301133 DOI: 10.1016/s0006-3495(00)76491-5] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Calcium release units (CRUs) are junctions between the sarcoplasmic reticulum (SR) and exterior membranes that mediates excitation contraction (e-c) coupling in muscle cells. In skeletal muscle CRUs contain two isoforms of the sarcoplasmic reticulum Ca(2+)release channel: ryanodine receptors type 1 and type 3 (RyR1 and RyR3). 1B5s are a mouse skeletal muscle cell line that carries a null mutation for RyR1 and does not express either RyR1 or RyR3. These cells develop dyspedic SR/exterior membrane junctions (i.e., dyspedic calcium release units, dCRUs) that contain dihydropyridine receptors (DHPRs) and triadin, two essential components of CRUs, but no RyRs (or feet). Lack of RyRs in turn affects the disposition of DHPRs, which is normally dictated by a linkage to RyR subunits. In the dCRUs of 1B5 cells, DHPRs are neither grouped into tetrads nor aligned in two orthogonal directions. We have explored the structural role of RyR3 in the assembly of CRUs in 1B5 cells independently expressing either RyR1 or RyR3. Either isoform colocalizes with DHPRs and triadin at the cell periphery. Electron microscopy shows that expression of either isoform results in CRUs containing arrays of feet, indicating the ability of both isoforms to be targeted to dCRUs and to assemble in ordered arrays in the absence of the other. However, a significant difference between RyR1- and RyR3-rescued junctions is revealed by freeze fracture. While cells transfected with RyR1 show restoration of DHPR tetrads and DHPR orthogonal alignment indicative of a link to RyRs, those transfected with RyR3 do not. This indicates that RyR3 fails to link to DHPRs in a specific manner. This morphological evidence supports the hypothesis that activation of RyR3 in skeletal muscle cells must be indirect and provides the basis for failure of e-c coupling in muscle cells containing RyR3 but lacking RyR1 (see the accompanying report, ).
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Affiliation(s)
- F Protasi
- Department of Anesthesia Research, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA.
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