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Yin W, Yang C, Liu D, Cha S, Cai L, Ye G, Song X, Zhang J, Qiu X. Mussel shell-derived pro-regenerative scaffold with conductive porous multi-scale-patterned microenvironment for spinal cord injury repair. Biomed Mater 2024; 19:035041. [PMID: 38626779 DOI: 10.1088/1748-605x/ad3f63] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2023] [Accepted: 04/16/2024] [Indexed: 05/01/2024]
Abstract
It is well-established that multi-scale porous scaffolds can guide axonal growth and facilitate functional restoration after spinal cord injury (SCI). In this study, we developed a novel mussel shell-inspired conductive scaffold for SCI repair with ease of production, multi-scale porous structure, high flexibility, and excellent biocompatibility. By utilizing the reducing properties of polydopamine, non-conductive graphene oxide (GO) was converted into conductive reduced graphene oxide (rGO) and crosslinkedin situwithin the mussel shells.In vitroexperiments confirmed that this multi-scale porous Shell@PDA-GO could serve as structural cues for enhancing cell adhesion, differentiation, and maturation, as well as promoting the electrophysiological development of hippocampal neurons. After transplantation at the injury sites, the Shell@PDA-GO provided a pro-regenerative microenvironment, promoting endogenous neurogenesis, triggering neovascularization, and relieving glial fibrosis formation. Interestingly, the Shell@PDA-GO could induce the release of endogenous growth factors (NGF and NT-3), resulting in the complete regeneration of nerve fibers at 12 weeks. This work provides a feasible strategy for the exploration of conductive multi-scale patterned scaffold to repair SCI.
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Affiliation(s)
- Wenming Yin
- Guangdong Provincial Key Laboratory of Construction and Detection in Tissue Engineering, School of Basic Medical Sciences, Southern Medical University, Guangzhou, Guangdong 510515, People's Republic of China
| | - Chang Yang
- Guangdong Provincial Key Laboratory of Construction and Detection in Tissue Engineering, School of Basic Medical Sciences, Southern Medical University, Guangzhou, Guangdong 510515, People's Republic of China
- Central Laboratory, The Fifth Affiliated Hospital, Southern Medical University, Guangzhou, Guangdong 510910, People's Republic of China
| | - Dan Liu
- Guangdong Provincial Key Laboratory of Construction and Detection in Tissue Engineering, School of Basic Medical Sciences, Southern Medical University, Guangzhou, Guangdong 510515, People's Republic of China
| | - Shuhan Cha
- Department of Anatomy, Neuroscience Laboratory for Cognitive and Developmental Disorders, Medical College of Jinan University, Guangzhou 510630, People's Republic of China
| | - Liu Cai
- Guangdong Provincial Key Laboratory of Construction and Detection in Tissue Engineering, School of Basic Medical Sciences, Southern Medical University, Guangzhou, Guangdong 510515, People's Republic of China
| | - Genlan Ye
- Central Laboratory, The Fifth Affiliated Hospital, Southern Medical University, Guangzhou, Guangdong 510910, People's Republic of China
| | - Xiaoping Song
- Central Laboratory, The Fifth Affiliated Hospital, Southern Medical University, Guangzhou, Guangdong 510910, People's Republic of China
| | - Jifeng Zhang
- Department of Anatomy, Neuroscience Laboratory for Cognitive and Developmental Disorders, Medical College of Jinan University, Guangzhou 510630, People's Republic of China
| | - Xiaozhong Qiu
- Guangdong Provincial Key Laboratory of Construction and Detection in Tissue Engineering, School of Basic Medical Sciences, Southern Medical University, Guangzhou, Guangdong 510515, People's Republic of China
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2
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Quantification of the calcium signaling deficit in muscles devoid of triadin. PLoS One 2022; 17:e0264146. [PMID: 35213584 PMCID: PMC8880904 DOI: 10.1371/journal.pone.0264146] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2021] [Accepted: 02/03/2022] [Indexed: 11/24/2022] Open
Abstract
Triadin, a protein of the sarcoplasmic reticulum (SR) of striated muscles, anchors the calcium-storing protein calsequestrin to calcium release RyR channels at the junction with t-tubules, and modulates these channels by conformational effects. Triadin ablation induces structural SR changes and alters the expression of other proteins. Here we quantify alterations of calcium signaling in single skeletal myofibers of constitutive triadin-null mice. We find higher resting cytosolic and lower SR-luminal [Ca2+], 40% lower calsequestrin expression, and more CaV1.1, RyR1 and SERCA1. Despite the increased CaV1.1, the mobile intramembrane charge was reduced by ~20% in Triadin-null fibers. The initial peak of calcium release flux by pulse depolarization was minimally altered in the null fibers (revealing an increase in peak calcium permeability). The “hump” phase that followed, attributable to calcium detaching from calsequestrin, was 25% lower, a smaller change than expected from the reduced calsequestrin content and calcium saturation. The exponential decay rate of calcium transients was 25% higher, consistent with the higher SERCA1 content. Recovery of calcium flux after a depleting depolarization was faster in triadin-null myofibers, consistent with the increased uptake rate and lower SR calsequestrin content. In sum, the triadin knockout determines an increased RyR1 channel openness, which depletes the SR, a substantial loss of calsequestrin and gains in other couplon proteins. Powerful functional compensations ensue: activation of SOCE that increases [Ca2+]cyto; increased SERCA1 activity, which limits the decrease in [Ca2+]SR and a restoration of SR calcium storage of unknown substrate. Together, they effectively limit the functional loss in skeletal muscles.
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Melzer W. ECC meets CEU-New focus on the backdoor for calcium ions in skeletal muscle cells. J Gen Physiol 2020; 152:152046. [PMID: 32851409 PMCID: PMC7537343 DOI: 10.1085/jgp.202012679] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
In this issue, Michelucci et al. report the existence of specific sites acting as Ca2+ entry units (CEUs) in fast skeletal muscle of mice lacking calsequestrin (CASQ1), the major Ca2+ binding protein of the SR. The CEU provides constitutive and store-operated Ca2+ entry (SOCE) and resistance to force decline resulting from SR Ca2+ depletion during repetitive muscle activity.
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Affiliation(s)
- Werner Melzer
- Institute of Applied Physiology, Ulm University, Ulm, Germany
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4
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Fodor J, Al-Gaadi D, Czirják T, Oláh T, Dienes B, Csernoch L, Szentesi P. Improved Calcium Homeostasis and Force by Selenium Treatment and Training in Aged Mouse Skeletal Muscle. Sci Rep 2020; 10:1707. [PMID: 32015413 PMCID: PMC6997352 DOI: 10.1038/s41598-020-58500-x] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2019] [Accepted: 01/10/2020] [Indexed: 12/13/2022] Open
Abstract
During aging reduction in muscle mass (sarcopenia) and decrease in physical activity lead to partial loss of muscle force and increased fatigability. Deficiency in the essential trace element selenium might augment these symptoms as it can cause muscle pain, fatigue, and proximal weakness. Average voluntary daily running, maximal twitch and tetanic force, and calcium release from the sarcoplasmic reticulum (SR) decreased while reactive oxygen species (ROS) production associated with tetanic contractions increased in aged – 22-month-old – as compared to young – 4-month-old – mice. These changes were accompanied by a decline in the ryanodine receptor type 1 (RyR1) and Selenoprotein N content and the increased amount of a degraded RyR1. Both lifelong training and selenium supplementation, but not the presence of an increased muscle mass at young age, were able to compensate for the reduction in muscle force and SR calcium release with age. Selenium supplementation was also able to significantly enhance the Selenoprotein N levels in aged mice. Our results describe, for the first time, the beneficial effects of selenium supplementation on calcium release from the SR and muscle force in old age while point out that increased muscle mass does not improve physical performance with aging.
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Affiliation(s)
- János Fodor
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Dána Al-Gaadi
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary.,Doctoral School of Molecular Medicine, University of Debrecen, Debrecen, Hungary
| | - Tamás Czirják
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary.,Doctoral School of Molecular Medicine, University of Debrecen, Debrecen, Hungary
| | - Tamás Oláh
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Beatrix Dienes
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - László Csernoch
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Péter Szentesi
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary.
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Allard B. Measurement of intracellular ion activity in skeletal muscle fibers: Four microelectrodes or no deal. J Gen Physiol 2019; 151:1160-1162. [PMID: 31471451 PMCID: PMC6785731 DOI: 10.1085/jgp.201912425] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
Abstract
Allard reviews a new powerful method allowing measurement of intracellular ion activity in isolated skeletal muscle fibers.
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Affiliation(s)
- Bruno Allard
- Institut NeuroMyoGène, Université Claude Bernard Lyon 1, Université de Lyon, Centre National de la Recherche Scientifique Unité Mixte de Recherche 5310, Institut National de la Santé et de la Recherche Médicale Unité 1217, Lyon, France
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6
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Melzer W. No voltage change at skeletal muscle SR membrane during Ca 2+ release-just Mermaids on acid. J Gen Physiol 2018; 150:1055-1058. [PMID: 29970411 PMCID: PMC6080887 DOI: 10.1085/jgp.201812084] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Melzer highlights new work confirming that the sarcoplasmic reticulum transmembrane voltage changes little during Ca2+ release Calcium ions control multiple physiological functions by binding to extracellular and intracellular targets. One of the best-studied Ca2+-dependent functions is contraction of smooth and striated muscle tissue, which results from Ca2+ ligation to calmodulin and troponin C, respectively. Ca2+ signaling typically involves flux of the ion across membranes via specifically gated channel proteins. Because calcium ions are charged, they possess the ability to generate changes in the respective transmembrane voltage. Ca2+-dependent voltage alterations of the surface membrane are easily measured using microelectrodes. A well-known example is the characteristic plateau phase of the action potential in cardiac ventricular cells that results from the opening of voltage-gated L-type Ca2+ channels. Ca2+ ions are also released from intracellular storage compartments in many cells, but these membranes are not accessible to direct voltage recording with microelectrodes. In muscle, for example, release of Ca2+ from the sarcoplasmic reticulum (SR) to the myoplasm constitutes a flux that is considerably larger than the entry flux from the extracellular space. Whether this flux is accompanied by a voltage change across the SR membrane is an obvious question of mechanistic importance and has been the subject of many investigations. Because the tiny spaces enclosed by the SR membrane are inaccessible to microelectrodes, alternative methods have to be applied. In a study by Sanchez et al. (2018. J. Gen. Physiol.https://doi.org/10.1085/jgp.201812035) in this issue, modern confocal light microscopy and genetically encoded voltage probes targeted to the SR were applied in a new approach to search for changes in the membrane potential of the SR during Ca2+ release.
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Affiliation(s)
- Werner Melzer
- Institut für Angewandte Physiologie, Universität Ulm, Ulm, Germany
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7
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Zullo A, Textor M, Elischer P, Mall S, Alt A, Klingler W, Melzer W. Voltage modulates halothane-triggered Ca 2+ release in malignant hyperthermia-susceptible muscle. J Gen Physiol 2017; 150:111-125. [PMID: 29247050 PMCID: PMC5749113 DOI: 10.1085/jgp.201711864] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2017] [Accepted: 11/16/2017] [Indexed: 12/20/2022] Open
Abstract
Malignant hyperthermia can result from mutations in the ryanodine receptor that favor anesthetic-induced Ca2+ release. Zullo et al. find that membrane potential modulates the effect of the volatile anesthetic halothane on skeletal muscle ryanodine receptors possessing the Y524S mutation. Malignant hyperthermia (MH) is a fatal hypermetabolic state that may occur during general anesthesia in susceptible individuals. It is often caused by mutations in the ryanodine receptor RyR1 that favor drug-induced release of Ca2+ from the sarcoplasmic reticulum. Here, knowing that membrane depolarization triggers Ca2+ release in normal muscle function, we study the cross-influence of membrane potential and anesthetic drugs on Ca2+ release. We used short single muscle fibers of knock-in mice heterozygous for the RyR1 mutation Y524S combined with microfluorimetry to measure intracellular Ca2+ signals. Halothane, a volatile anesthetic used in contracture testing for MH susceptibility, was equilibrated with the solution superfusing the cells by means of a vaporizer system. In the range 0.2 to 3%, the drug causes significantly larger elevations of free myoplasmic [Ca2+] in mutant (YS) compared with wild-type (WT) fibers. Action potential–induced Ca2+ signals exhibit a slowing of their time course of relaxation that can be attributed to a component of delayed Ca2+ release turnoff. In further experiments, we applied halothane to single fibers that were voltage-clamped using two intracellular microelectrodes and studied the effect of small (10-mV) deviations from the holding potential (−80 mV). Untreated WT fibers show essentially no changes in [Ca2+], whereas the Ca2+ level of YS fibers increases and decreases on depolarization and hyperpolarization, respectively. The drug causes a significant enhancement of this response. Depolarizing pulses reveal a substantial negative shift in the voltage dependence of activation of Ca2+ release. This behavior likely results from the allosteric coupling between RyR1 and its transverse tubular voltage sensor. We conclude that the binding of halothane to RyR1 alters the voltage dependence of Ca2+ release in MH-susceptible muscle fibers such that the resting membrane potential becomes a decisive factor for the efficiency of the drug to trigger Ca2+ release.
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Affiliation(s)
- Alberto Zullo
- Institute of Applied Physiology, Ulm University, Ulm, Germany.,CEINGE - Biotecnologie Avanzate, Napoli, Italy.,Department of Sciences and Technologies, University of Sannio, Benevento, Italy
| | - Martin Textor
- Institute of Applied Physiology, Ulm University, Ulm, Germany
| | | | - Stefan Mall
- Institute of Applied Physiology, Ulm University, Ulm, Germany
| | - Andreas Alt
- Institute of Legal Medicine, Ulm University, Ulm, Germany
| | - Werner Klingler
- Department of Neuroanaesthesiology, Ulm University, Günzburg, Germany.,Queensland University of Technology, Brisbane, Australia
| | - Werner Melzer
- Institute of Applied Physiology, Ulm University, Ulm, Germany
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8
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The Ca 2+ influx through the mammalian skeletal muscle dihydropyridine receptor is irrelevant for muscle performance. Nat Commun 2017; 8:475. [PMID: 28883413 PMCID: PMC5589907 DOI: 10.1038/s41467-017-00629-x] [Citation(s) in RCA: 57] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2016] [Accepted: 07/14/2017] [Indexed: 01/01/2023] Open
Abstract
Skeletal muscle excitation-contraction (EC) coupling is initiated by sarcolemmal depolarization, which is translated into a conformational change of the dihydropyridine receptor (DHPR), which in turn activates sarcoplasmic reticulum (SR) Ca2+ release to trigger muscle contraction. During EC coupling, the mammalian DHPR embraces functional duality, as voltage sensor and L-type Ca2+ channel. Although its unique role as voltage sensor for conformational EC coupling is firmly established, the conventional function as Ca2+ channel is still enigmatic. Here we show that Ca2+ influx via DHPR is not necessary for muscle performance by generating a knock-in mouse where DHPR-mediated Ca2+ influx is eliminated. Homozygous knock-in mice display SR Ca2+ release, locomotor activity, motor coordination, muscle strength and susceptibility to fatigue comparable to wild-type controls, without any compensatory regulation of multiple key proteins of the EC coupling machinery and Ca2+ homeostasis. These findings support the hypothesis that the DHPR-mediated Ca2+ influx in mammalian skeletal muscle is an evolutionary remnant.In mammalian skeletal muscle, the DHPR functions as a voltage sensor to trigger muscle contraction and as a Ca2+ channel. Here the authors show that mice where Ca2+ influx through the DHPR is eliminated display no difference in skeletal muscle function, suggesting that the Ca2+ influx through this channel is vestigial.
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9
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Hernández-Ochoa EO, Vanegas C, Iyer SR, Lovering RM, Schneider MF. Alternating bipolar field stimulation identifies muscle fibers with defective excitability but maintained local Ca(2+) signals and contraction. Skelet Muscle 2016; 6:6. [PMID: 26855765 PMCID: PMC4743112 DOI: 10.1186/s13395-016-0076-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2015] [Accepted: 01/05/2016] [Indexed: 11/25/2022] Open
Abstract
Background Most cultured enzymatically dissociated adult myofibers exhibit spatially uniform (UNI) contractile responses and Ca2+ transients over the entire myofiber in response to electric field stimuli of either polarity applied via bipolar electrodes. However, some myofibers only exhibit contraction and Ca2+ transients at alternating (ALT) ends in response to alternating polarity field stimulation. Here, we present for the first time the methodology for identification of ALT myofibers in primary cultures and isolated muscles, as well as a study of their electrophysiological properties. Results We used high-speed confocal microscopic Ca2+ imaging, electric field stimulation, microelectrode recordings, immunostaining, and confocal microscopy to characterize the properties of action potential-induced Ca2+ transients, contractility, resting membrane potential, and staining of T-tubule voltage-gated Na+ channel distribution applied to cultured adult myofibers. Here, we show for the first time, with high temporal and spatial resolution, that normal control myofibers with UNI responses can be converted to ALT response myofibers by TTX addition or by removal of Na+ from the bathing medium, with reappearance of the UNI response on return of Na+. Our results suggest disrupted excitability as the cause of ALT behavior and indicate that the ALT response is due to local depolarization-induced Ca2+ release, whereas the UNI response is triggered by action potential propagation over the entire myofiber. Consistent with this interpretation, local depolarizing monopolar stimuli give uniform (propagated) responses in UNI myofibers, but only local responses at the electrode in ALT myofibers. The ALT responses in electrically inexcitable myofibers are consistent with expectations of current spread between bipolar stimulating electrodes, entering (hyperpolarizing) one end of a myofiber and leaving (depolarizing) the other end of the myofiber. ALT responses were also detected in some myofibers within intact isolated whole muscles from wild-type and MDX mice, demonstrating that ALT responses can be present before enzymatic dissociation. Conclusions We suggest that checking for ALT myofiber responsiveness by looking at the end of a myofiber during alternating polarity stimuli provides a test for compromised excitability of myofibers, and could be used to identify inexcitable, damaged or diseased myofibers by ALT behavior in healthy and diseased muscle. Electronic supplementary material The online version of this article (doi:10.1186/s13395-016-0076-8) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Erick O Hernández-Ochoa
- Department of Biochemistry and Molecular Biology, School of Medicine, University of Maryland, Baltimore, 108 N. Greene Street, Baltimore, MD 21201 USA
| | - Camilo Vanegas
- Department of Biochemistry and Molecular Biology, School of Medicine, University of Maryland, Baltimore, 108 N. Greene Street, Baltimore, MD 21201 USA
| | - Shama R Iyer
- Department of Orthopaedics, University of Maryland School of Medicine, Baltimore, MD 21201 USA
| | - Richard M Lovering
- Department of Orthopaedics, University of Maryland School of Medicine, Baltimore, MD 21201 USA
| | - Martin F Schneider
- Department of Biochemistry and Molecular Biology, School of Medicine, University of Maryland, Baltimore, 108 N. Greene Street, Baltimore, MD 21201 USA
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10
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Braubach P, Orynbayev M, Andronache Z, Hering T, Landwehrmeyer GB, Lindenberg KS, Melzer W. Altered Ca(2+) signaling in skeletal muscle fibers of the R6/2 mouse, a model of Huntington's disease. ACTA ACUST UNITED AC 2015; 144:393-413. [PMID: 25348412 PMCID: PMC4210430 DOI: 10.1085/jgp.201411255] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Huntington's disease (HD) is caused by an expanded CAG trinucleotide repeat within the gene encoding the protein huntingtin. The resulting elongated glutamine (poly-Q) sequence of mutant huntingtin (mhtt) affects both central neurons and skeletal muscle. Recent reports suggest that ryanodine receptor-based Ca(2+) signaling, which is crucial for skeletal muscle excitation-contraction coupling (ECC), is changed by mhtt in HD neurons. Consequently, we searched for alterations of ECC in muscle fibers of the R6/2 mouse, a mouse model of HD. We performed fluorometric recordings of action potentials (APs) and cellular Ca(2+) transients on intact isolated toe muscle fibers (musculi interossei), and measured L-type Ca(2+) inward currents on internally dialyzed fibers under voltage-clamp conditions. Both APs and AP-triggered Ca(2+) transients showed slower kinetics in R6/2 fibers than in fibers from wild-type mice. Ca(2+) removal from the myoplasm and Ca(2+) release flux from the sarcoplasmic reticulum were characterized using a Ca(2+) binding and transport model, which indicated a significant reduction in slow Ca(2+) removal activity and Ca(2+) release flux both after APs and under voltage-clamp conditions. In addition, the voltage-clamp experiments showed a highly significant decrease in L-type Ca(2+) channel conductance. These results indicate profound changes of Ca(2+) turnover in skeletal muscle of R6/2 mice and suggest that these changes may be associated with muscle pathology in HD.
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Affiliation(s)
- Peter Braubach
- Institute of Applied Physiology and Department of Neurology, Ulm University, D-89081 Ulm, Germany
| | - Murat Orynbayev
- Institute of Applied Physiology and Department of Neurology, Ulm University, D-89081 Ulm, Germany
| | - Zoita Andronache
- Institute of Applied Physiology and Department of Neurology, Ulm University, D-89081 Ulm, Germany
| | - Tanja Hering
- Institute of Applied Physiology and Department of Neurology, Ulm University, D-89081 Ulm, Germany Institute of Applied Physiology and Department of Neurology, Ulm University, D-89081 Ulm, Germany
| | | | - Katrin S Lindenberg
- Institute of Applied Physiology and Department of Neurology, Ulm University, D-89081 Ulm, Germany
| | - Werner Melzer
- Institute of Applied Physiology and Department of Neurology, Ulm University, D-89081 Ulm, Germany
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11
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Robin G, Allard B. Major contribution of sarcoplasmic reticulum Ca(2+) depletion during long-lasting activation of skeletal muscle. ACTA ACUST UNITED AC 2014; 141:557-65. [PMID: 23630339 PMCID: PMC3639577 DOI: 10.1085/jgp.201310957] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Depolarization of skeletal muscle fibers induces sarcoplasmic reticulum (SR) Ca2+ release and contraction that progressively decline while depolarization is maintained. Voltage-dependent inactivation of SR Ca2+ release channels and SR Ca2+ depletion are the two processes proposed to explain the decline of SR Ca2+ release during long-lasting depolarizations. However, the relative contribution of these processes, especially under physiological conditions of activation, is not clearly established. Using Fura-2 and Fluo-5N to monitor cytosolic and SR Ca2+ changes, respectively, in voltage-controlled mouse muscle fibers, we show that 2-min conditioning depolarizations reduce voltage-activated cytosolic Ca2+ signals with a V1/2 of −53 mV but also induce SR Ca2+ depletion that decreased the releasable pool of Ca2+ with the same voltage sensitivity. In contrast, measurement of SR Ca2+ changes indicated that SR Ca2+ release channels were inactivated after SR had been depleted and in response to much higher depolarizations with a V1/2 of −13 mV. In response to trains of action potentials, cytosolic Ca2+ signals decayed with time, whereas SR Ca2+ changes remained stable over 1-min stimulation, demonstrating that SR Ca2+ depletion is exclusively responsible for the decline of SR Ca2+ release under physiological conditions of excitation. These results suggest that previous studies using steady-state inactivation protocols to investigate the voltage dependence of Ca2+ release inactivation in fact probed the voltage dependence of SR Ca2+ depletion, and that SR Ca2+ depletion is the only process that leads to Ca2+ release decline during continuous stimulation of skeletal muscle.
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Affiliation(s)
- Gaëlle Robin
- Centre National de la Recherche Scientifique UMR 5534, Centre de Génétique et de Physiologie Moléculaires et Cellulaires, Université Lyon 1, 69622 Villeurbanne, France
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12
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Melzer W. Skeletal muscle fibers: Inactivated or depleted after long depolarizations? ACTA ACUST UNITED AC 2014; 141:517-20. [PMID: 23630336 PMCID: PMC3639573 DOI: 10.1085/jgp.201310997] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- Werner Melzer
- Institute of Applied Physiology, Ulm University, D-89081 Ulm, Germany.
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13
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DiFranco M, Quinonez M, Vergara JL. The delayed rectifier potassium conductance in the sarcolemma and the transverse tubular system membranes of mammalian skeletal muscle fibers. ACTA ACUST UNITED AC 2012; 140:109-37. [PMID: 22851675 PMCID: PMC3409102 DOI: 10.1085/jgp.201210802] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
A two-microelectrode voltage clamp and optical measurements of membrane potential changes at the transverse tubular system (TTS) were used to characterize delayed rectifier K currents (IK(V)) in murine muscle fibers stained with the potentiometric dye di-8-ANEPPS. In intact fibers, IK(V) displays the canonical hallmarks of K(V) channels: voltage-dependent delayed activation and decay in time. The voltage dependence of the peak conductance (gK(V)) was only accounted for by double Boltzmann fits, suggesting at least two channel contributions to IK(V). Osmotically treated fibers showed significant disconnection of the TTS and displayed smaller IK(V), but with similar voltage dependence and time decays to intact fibers. This suggests that inactivation may be responsible for most of the decay in IK(V) records. A two-channel model that faithfully simulates IK(V) records in osmotically treated fibers comprises a low threshold and steeply voltage-dependent channel (channel A), which contributes ∼31% of gK(V), and a more abundant high threshold channel (channel B), with shallower voltage dependence. Significant expression of the IK(V)1.4 and IK(V)3.4 channels was demonstrated by immunoblotting. Rectangular depolarizing pulses elicited step-like di-8-ANEPPS transients in intact fibers rendered electrically passive. In contrast, activation of IK(V) resulted in time- and voltage-dependent attenuations in optical transients that coincided in time with the peaks of IK(V) records. Normalized peak attenuations showed the same voltage dependence as peak IK(V) plots. A radial cable model including channels A and B and K diffusion in the TTS was used to simulate IK(V) and average TTS voltage changes. Model predictions and experimental data were compared to determine what fraction of gK(V) in the TTS accounted simultaneously for the electrical and optical data. Best predictions suggest that K(V) channels are approximately equally distributed in the sarcolemma and TTS membranes; under these conditions, >70% of IK(V) arises from the TTS.
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Affiliation(s)
- Marino DiFranco
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
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14
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Figueroa L, Shkryl VM, Zhou J, Manno C, Momotake A, Brum G, Blatter LA, Ellis-Davies GCR, Ríos E. Synthetic localized calcium transients directly probe signalling mechanisms in skeletal muscle. J Physiol 2012; 590:1389-411. [PMID: 22310315 DOI: 10.1113/jphysiol.2011.225854] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The contribution of Ca2+-induced Ca2+ release (CICR) to trigger muscle contraction is controversial. It was studied on isolated muscle fibres using synthetic localized increases in Ca2+ concentration, SLICs, generated by two-photon photorelease from nitrodibenzofuran (NDBF)-EGTA just outside the permeabilized plasma membrane. SLICs provided a way to increase cytosolic [Ca2+] rapidly and reversibly, up to 8 μM, levels similar to those reached during physiological activity. They improve over previous paradigms in rate of rise, locality and reproducibility. Use of NDBF-EGTA allowed for the separate modification of resting [Ca2+], trigger [Ca2+] and resting [Mg2+]. In frog muscle, SLICs elicited propagated responses that had the characteristics of CICR. The threshold [Ca2+] for triggering a response was 0.5 μM or less. As this value is much lower than concentrations prevailing near channels during normal activity, the result supports participation of CICR in the physiological control of contraction in amphibian muscle. As SLICs were applied outside cells, the primary stimulus was Ca2+, rather than the radiation or subproducts of photorelease. Therefore the responses qualify as ‘classic' CICR. By contrast, mouse muscle fibres did not respond unless channel-opening drugs were present at substantial concentrations, an observation contrary to the physiological involvement of CICR in mammalian excitation–contraction coupling. In mouse muscle, the propagating wave had a substantially lower release flux, which together with a much higher threshold justified the absence of response when drugs were not present. The differences in flux and threshold may be ascribed to the absence of ryanodine receptor 3 (RyR3) isoforms in adult mammalian muscle.
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Affiliation(s)
- Lourdes Figueroa
- Section of Cellular Signaling, Department of Molecular Biophysics and Physiology, Rush University School of Medicine, 1750 W. Harrison St, Suite 1279JS, Chicago, IL 60612, USA
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15
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Hernández-Ochoa EO, Schneider MF. Voltage clamp methods for the study of membrane currents and SR Ca(2+) release in adult skeletal muscle fibres. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2012; 108:98-118. [PMID: 22306655 DOI: 10.1016/j.pbiomolbio.2012.01.001] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/07/2011] [Revised: 01/14/2012] [Accepted: 01/17/2012] [Indexed: 01/03/2023]
Abstract
Skeletal muscle excitation-contraction (E-C)(1) coupling is a process composed of multiple sequential stages, by which an action potential triggers sarcoplasmic reticulum (SR)(2) Ca(2+) release and subsequent contractile activation. The various steps in the E-C coupling process in skeletal muscle can be studied using different techniques. The simultaneous recordings of sarcolemmal electrical signals and the accompanying elevation in myoplasmic Ca(2+), due to depolarization-initiated SR Ca(2+) release in skeletal muscle fibres, have been useful to obtain a better understanding of muscle function. In studying the origin and mechanism of voltage dependency of E-C coupling a variety of different techniques have been used to control the voltage in adult skeletal fibres. Pioneering work in muscles isolated from amphibians or crustaceans used microelectrodes or 'high resistance gap' techniques to manipulate the voltage in the muscle fibres. The development of the patch clamp technique and its variant, the whole-cell clamp configuration that facilitates the manipulation of the intracellular environment, allowed the use of the voltage clamp techniques in different cell types, including skeletal muscle fibres. The aim of this article is to present an historical perspective of the voltage clamp methods used to study skeletal muscle E-C coupling as well as to describe the current status of using the whole-cell patch clamp technique in studies in which the electrical and Ca(2+) signalling properties of mouse skeletal muscle membranes are being investigated.
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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 St., Baltimore, MD 21201, USA.
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16
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Wang ZM, Tang S, Messi ML, Yang JJ, Delbono O. Residual sarcoplasmic reticulum Ca2+ concentration after Ca2+ release in skeletal myofibers from young adult and old mice. Pflugers Arch 2012; 463:615-24. [PMID: 22249494 DOI: 10.1007/s00424-012-1073-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2011] [Revised: 12/31/2011] [Accepted: 01/02/2012] [Indexed: 10/14/2022]
Abstract
Contrasting information suggests either almost complete depletion of sarcoplasmic reticulum (SR) Ca(2+) or significant residual Ca(2+) concentration after prolonged depolarization of the skeletal muscle fiber. The primary obstacle to resolving this controversy is the lack of genetically encoded Ca(2+) indicators targeted to the SR that exhibit low-Ca(2+) affinity, a fast biosensor: Ca(2+) off-rate reaction, and can be expressed in myofibers from adult and older adult mammalian species. This work used the recently designed low-affinity Ca(2+) sensor (Kd = 1.66 mM in the myofiber) CatchER (calcium sensor for detecting high concentrations in the ER) targeted to the SR, to investigate whether prolonged skeletal muscle fiber depolarization significantly alters residual SR Ca(2+) with aging. We found CatchER a proper tool to investigate SR Ca(2+) depletion in young adult and older adult mice, consistently tracking SR luminal Ca(2+) release in response to brief and repetitive stimulation. We evoked SR Ca(2+) release in whole-cell voltage-clamped flexor digitorum brevis muscle fibers from young and old FVB mice and tested the maximal SR Ca(2+) release by directly activating the ryanodine receptor (RyR1) with 4-chloro-m-cresol in the same myofibers. Here, we report for the first time that the Ca(2+) remaining in the SR after prolonged depolarization (2 s) in myofibers from aging (~220 μM) was larger than young (~132 μM) mice. These experiments indicate that SR Ca(2+) is far from fully depleted under physiological conditions throughout life, and support the concept of excitation-contraction uncoupling in functional senescent myofibers.
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Affiliation(s)
- Zhong-Min Wang
- Department of Internal Medicine, Section on Gerontology and Geriatric Medicine, Wake Forest University School of Medicine, 1 Medical Center Boulevard, Winston-Salem, NC, 27157, USA
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17
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Sztretye M, Yi J, Figueroa L, Zhou J, Royer L, Allen P, Brum G, Ríos E. Measurement of RyR permeability reveals a role of calsequestrin in termination of SR Ca(2+) release in skeletal muscle. ACTA ACUST UNITED AC 2012; 138:231-47. [PMID: 21788611 PMCID: PMC3149434 DOI: 10.1085/jgp.201010592] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The mechanisms that terminate Ca2+ release from the sarcoplasmic reticulum are not fully understood. D4cpv-Casq1 (Sztretye et al. 2011. J. Gen. Physiol. doi:10.1085/jgp.201010591) was used in mouse skeletal muscle cells under voltage clamp to measure free Ca2+ concentration inside the sarcoplasmic reticulum (SR), [Ca2+]SR, simultaneously with that in the cytosol, [Ca2+]c, during the response to long-lasting depolarization of the plasma membrane. The ratio of Ca2+ release flux (derived from [Ca2+]c(t)) over the gradient that drives it (essentially equal to [Ca2+]SR) provided directly, for the first time, a dynamic measure of the permeability to Ca2+ of the releasing SR membrane. During maximal depolarization, flux rapidly rises to a peak and then decays. Before 0.5 s, [Ca2+]SR stabilized at ∼35% of its resting level; depletion was therefore incomplete. By 0.4 s of depolarization, the measured permeability decayed to ∼10% of maximum, indicating ryanodine receptor channel closure. Inactivation of the t tubule voltage sensor was immeasurably small by this time and thus not a significant factor in channel closure. In cells of mice null for Casq1, permeability did not decrease in the same way, indicating that calsequestrin (Casq) is essential in the mechanism of channel closure and termination of Ca2+ release. The absence of this mechanism explains why the total amount of calcium releasable by depolarization is not greatly reduced in Casq-null muscle (Royer et al. 2010. J. Gen. Physiol. doi:10.1085/jgp.201010454). When the fast buffer BAPTA was introduced in the cytosol, release flux became more intense, and the SR emptied earlier. The consequent reduction in permeability accelerated as well, reaching comparable decay at earlier times but comparable levels of depletion. This observation indicates that [Ca2+]SR, sensed by Casq and transmitted to the channels presumably via connecting proteins, is determinant to cause the closure that terminates Ca2+ release.
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Affiliation(s)
- Monika Sztretye
- Section of Cellular Signaling, Department of Molecular Biophysics and Physiology, Rush University, Chicago, IL 60612, USA
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18
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DiFranco M, Tran P, Quiñonez M, Vergara JL. Functional expression of transgenic 1sDHPR channels in adult mammalian skeletal muscle fibres. J Physiol 2011; 589:1421-42. [PMID: 21262876 DOI: 10.1113/jphysiol.2010.202804] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
We investigated the effects of the overexpression of two enhanced green fluorescent protein (EGFP)-tagged α1sDHPR variants on Ca2+ currents (ICa), charge movements (Q) and SR Ca2+ release of muscle fibres isolated from adult mice. Flexor digitorum brevis (FDB)muscles were transfected by in vivo electroporation with plasmids encoding for EGFP-α1sDHPR-wt and EGFP-α1sDHPR-T935Y (an isradipine-insensitive mutant). Two-photon laser scanning microscopy (TPLSM) was used to study the subcellular localization of transgenic proteins, while ICa, Q and Ca2+ release were studied electrophysiologically and optically under voltage-clamp conditions. TPLSM images demonstrated that most of the transgenic α1sDHPR was correctly targeted to the transverse tubular system (TTS). Immunoblotting analysis of crude extracts of transfected fibres demonstrated the synthesis of bona fide transgenic EGFP-α1sDHPR-wt in quantities comparable to that of native α1sDHPR. Though expression of both transgenic variants of the alpha subunit of the dihydropyridine receptor (α1sDHPR) resulted in ∼50% increase in Q, they surprisingly had no effect on the maximal Ca2+ conductance (gCa) nor the SR Ca2+ release. Nonetheless, fibres expressing EGFP-α1sDHPR-T935Y exhibited up to 70% isradipine-insensitive ICa (ICa-ins) with a right-shifted voltage dependence compared to that in control fibres. Interestingly, Qand SRCa2+ release also displayed right-shifted voltage dependence in fibres expressing EGFP-α1sDHPR-T935Y. In contrast, the midpoints of the voltage dependence of gCa, Q and Ca2+ release were not different from those in control fibres and in fibres expressing EGFP-α1sDHPR-wt. Overall, our results suggest that transgenic α1sDHPRs are correctly trafficked and inserted in the TTS membrane, and that a substantial fraction of the mworks as conductive Ca2+ channels capable of physiologically controlling the release of Ca2+ from the SR. A plausible corollary of this work is that the expression of transgenic variants of the α1sDHPR leads to the replacement of native channels interacting with the ryanodine receptor 1 (RyR1), thus demonstrating the feasibility of molecular remodelling of the triads in adult skeletal muscle fibres.
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Affiliation(s)
- Marino DiFranco
- Department of Physiology, David Geffen School of Medicine, UCLA, 10833 Le Conte Avenue, Los Angeles, CA 90095-1751, USA
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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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20
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Royer L, Sztretye M, Manno C, Pouvreau S, Zhou J, Knollmann BC, Protasi F, Allen PD, Ríos E. Paradoxical buffering of calcium by calsequestrin demonstrated for the calcium store of skeletal muscle. J Gen Physiol 2010; 136:325-38. [PMID: 20713548 PMCID: PMC2931149 DOI: 10.1085/jgp.201010454] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2010] [Accepted: 07/22/2010] [Indexed: 11/20/2022] Open
Abstract
Contractile activation in striated muscles requires a Ca(2+) reservoir of large capacity inside the sarcoplasmic reticulum (SR), presumably the protein calsequestrin. The buffering power of calsequestrin in vitro has a paradoxical dependence on [Ca(2+)] that should be valuable for function. Here, we demonstrate that this dependence is present in living cells. Ca(2+) signals elicited by membrane depolarization under voltage clamp were compared in single skeletal fibers of wild-type (WT) and double (d) Casq-null mice, which lack both calsequestrin isoforms. In nulls, Ca(2+) release started normally, but the store depleted much more rapidly than in the WT. This deficit was reflected in the evolution of SR evacuability, E, which is directly proportional to SR Ca(2+) permeability and inversely to its Ca(2+) buffering power, B. In WT mice E starts low and increases progressively as the SR is depleted. In dCasq-nulls, E started high and decreased upon Ca(2+) depletion. An elevated E in nulls is consistent with the decrease in B expected upon deletion of calsequestrin. The different value and time course of E in cells without calsequestrin indicate that the normal evolution of E reflects loss of B upon SR Ca(2+) depletion. Decrement of B upon SR depletion was supported further. When SR calcium was reduced by exposure to low extracellular [Ca(2+)], release kinetics in the WT became similar to that in the dCasq-null. E became much higher, similar to that of null cells. These results indicate that calsequestrin not only stores Ca(2+), but also varies its affinity in ways that progressively increase the ability of the store to deliver Ca(2+) as it becomes depleted, a novel feedback mechanism of potentially valuable functional implications. The study revealed a surprisingly modest loss of Ca(2+) storage capacity in null cells, which may reflect concurrent changes, rather than detract from the physiological importance of calsequestrin.
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Affiliation(s)
- Leandro Royer
- Section of Cellular Signaling, Department of Molecular Biophysics and Physiology, Rush University, Chicago, IL 60612
| | - Monika Sztretye
- Section of Cellular Signaling, Department of Molecular Biophysics and Physiology, Rush University, Chicago, IL 60612
| | - Carlo Manno
- Section of Cellular Signaling, Department of Molecular Biophysics and Physiology, Rush University, Chicago, IL 60612
| | - Sandrine Pouvreau
- Section of Cellular Signaling, Department of Molecular Biophysics and Physiology, Rush University, Chicago, IL 60612
| | - Jingsong Zhou
- Section of Cellular Signaling, Department of Molecular Biophysics and Physiology, Rush University, Chicago, IL 60612
| | - Bjorn C. Knollmann
- Department of Medicine and Pharmacology, Vanderbilt University, Nashville, TN 37240
| | - Feliciano Protasi
- Centro Scienze dell’Invecchiamento, Università G. d’Annunzio, 66100 Chieti, Italy
| | - Paul D. Allen
- Department of Anesthesia, Perioperative and Pain Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA 02115
| | - Eduardo Ríos
- Section of Cellular Signaling, Department of Molecular Biophysics and Physiology, Rush University, Chicago, IL 60612
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Baylor SM, Hollingworth S. Calcium indicators and calcium signalling in skeletal muscle fibres during excitation-contraction coupling. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2010; 105:162-79. [PMID: 20599552 DOI: 10.1016/j.pbiomolbio.2010.06.001] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/12/2010] [Accepted: 06/14/2010] [Indexed: 11/25/2022]
Abstract
During excitation-contraction coupling in skeletal muscle, calcium ions are released into the myoplasm by the sarcoplasmic reticulum (SR) in response to depolarization of the fibre's exterior membranes. Ca(2+) then diffuses to the thin filaments, where Ca(2+) binds to the Ca(2+) regulatory sites on troponin to activate muscle contraction. Quantitative studies of these events in intact muscle preparations have relied heavily on Ca(2+)-indicator dyes to measure the change in the spatially-averaged myoplasmic free Ca(2+) concentration (Δ[Ca(2+)]) that results from the release of SR Ca(2+). In normal fibres stimulated by an action potential, Δ[Ca(2+)] is large and brief, requiring that an accurate measurement of Δ[Ca(2+)] be made with a low-affinity rapidly-responding indicator. Some low-affinity Ca(2+) indicators monitor Δ[Ca(2+)] much more accurately than others, however, as reviewed here in measurements in frog twitch fibres with sixteen low-affinity indicators. This article also examines measurements and simulations of Δ[Ca(2+)] in mouse fast-twitch fibres. The simulations use a multi-compartment model of the sarcomere that takes into account Ca(2+)'s release from the SR, its diffusion and binding within the myoplasm, and its re-sequestration by the SR Ca(2+) pump. The simulations are quantitatively consistent with the measurements and appear to provide a satisfactory picture of the underlying Ca(2+) movements.
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Affiliation(s)
- Stephen M Baylor
- Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6085, USA.
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22
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Ruggiu AA, Bannwarth M, Johnsson K. Fura-2FF-based calcium indicator for protein labeling. Org Biomol Chem 2010; 8:3398-401. [PMID: 20556282 DOI: 10.1039/c000158a] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We describe the synthesis and fluorescence properties of a Fura-2FF-based fluorescent Ca(2+) indicator that can be covalently linked to SNAP-tag fusion proteins and retains its Ca(2+) sensing ability after coupling to protein.
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Affiliation(s)
- Agostina A Ruggiu
- Laboratory of Protein Engineering, Institute of Chemical Sciences and Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015, Lausanne, Switzerland
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23
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Hollingworth S, Gee KR, Baylor SM. Low-affinity Ca2+ indicators compared in measurements of skeletal muscle Ca2+ transients. Biophys J 2009; 97:1864-72. [PMID: 19804716 DOI: 10.1016/j.bpj.2009.07.021] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2009] [Revised: 06/25/2009] [Accepted: 07/13/2009] [Indexed: 12/01/2022] Open
Abstract
The low-affinity fluorescent Ca(2+) indicators OGB-5N, Fluo-5N, fura-5N, Rhod-5N, and Mag-fluo-4 were evaluated for their ability to accurately track the kinetics of the spatially averaged free Ca(2+) transient (Delta[Ca(2+)]) in skeletal muscle. Frog single fibers were injected with one of the above indicators and, usually, furaptra (previously shown to rapidly track Delta[Ca(2+)]). In response to an action potential, the full duration at half-maximum of the indicator's fluorescence change (DeltaF) was found to be larger with OGB-5N, Fluo-5N, fura-5N, and Rhod-5N than with furaptra; thus, these indicators do not track Delta[Ca(2+)] with kinetic fidelity. In contrast, the DeltaF time course of Mag-fluo-4 was identical to furaptra's; thus, Mag-fluo-4 also yields reliable kinetic information about Delta[Ca(2+)]. Mag-fluo-4's DeltaF has a larger signal/noise ratio than furaptra's (for similar indicator concentrations), and should thus be more useful for tracking Delta[Ca(2+)] in small cell volumes. However, because the resting fluorescence of Mag-fluo-4 probably arises largely from indicator that is bound with Mg(2+), the amplitude of the Mag-fluo-4 signal, and its calibration in Delta[Ca(2+)] units, is likely to be more sensitive to variations in [Mg(2+)] than furaptra's.
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Affiliation(s)
- Stephen Hollingworth
- Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, USA
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24
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Eisner DA, Trafford AW. What is the purpose of the large sarcolemmal calcium flux on each heartbeat? Am J Physiol Heart Circ Physiol 2009; 297:H493-4. [PMID: 19525376 DOI: 10.1152/ajpheart.00423.2009] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In cardiac muscle, although most of the calcium that activates contraction comes from the sarcoplasmic reticulum (SR), a significant fraction (up to 30%, depending on the species) enters from outside the cell and is then pumped out at the end of systole. Although some of this calcium influx is required to trigger calcium release from the SR, the bulk serves to reload the cell (and thence the SR) with calcium to replace the calcium that is pumped out of the cell. An alternative strategy would be for the heart to have a much smaller calcium influx balancing a smaller efflux. We demonstrate that this would result in a slowing of inotropic responses due to changes of SR calcium content. We conclude that the large sarcolemmal calcium fluxes facilitate rapid changes of contractility.
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Affiliation(s)
- D A Eisner
- Unit of Cardiac Physiology, University of Manchester, Manchester, United Kingdom.
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25
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A retrograde signal from RyR1 alters DHP receptor inactivation and limits window Ca2+ release in muscle fibers of Y522S RyR1 knock-in mice. Proc Natl Acad Sci U S A 2009; 106:4531-6. [PMID: 19246389 DOI: 10.1073/pnas.0812661106] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Malignant hyperthermia (MH) is a life-threatening hypermetabolic condition caused by dysfunctional Ca(2+) homeostasis in skeletal muscle, which primarily originates from genetic alterations in the Ca(2+) release channel (ryanodine receptor, RyR1) of the sarcoplasmic reticulum (SR). Owing to its physical interaction with the dihydropyridine receptor (DHPR), RyR1 is controlled by the electrical potential across the transverse tubular (TT) membrane. The DHPR exhibits both voltage-dependent activation and inactivation. Here we determined the impact of an MH mutation in RyR1 (Y522S) on these processes in adult muscle fibers isolated from heterozygous RyR1(Y522S)-knock-in mice. The voltage dependence of DHPR-triggered Ca(2+) release flux was left-shifted by approximately 8 mV. As a consequence, the voltage window for steady-state Ca(2+) release extended to more negative holding potentials in muscle fibers of the RyR1(Y522S)-mice. A rise in temperature from 20 degrees to 30 degrees C caused a further shift to more negative potentials of this window (by approximately 20 mV). The activation of the DHPR-mediated Ca(2+) current was minimally changed by the mutation. However, surprisingly, the voltage dependence of steady-state inactivation of DHPR-mediated calcium conductance and release were also shifted by approximately 10 mV to more negative potentials, indicating a retrograde action of the RyR1 mutation on DHPR inactivation that limits window Ca(2+) release. This effect serves as a compensatory response to the lowered voltage threshold for Ca(2+) release caused by the Y522S mutation and represents a novel mechanism to counteract excessive Ca(2+) leak and store depletion in MH-susceptible muscle.
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26
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Paredes RM, Etzler JC, Watts LT, Zheng W, Lechleiter JD. Chemical calcium indicators. Methods 2008; 46:143-51. [PMID: 18929663 DOI: 10.1016/j.ymeth.2008.09.025] [Citation(s) in RCA: 397] [Impact Index Per Article: 24.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2008] [Accepted: 09/12/2008] [Indexed: 11/24/2022] Open
Abstract
Our understanding of the underlying mechanisms of Ca2+ signaling as well as our appreciation for its ubiquitous role in cellular processes has been rapidly advanced, in large part, due to the development of fluorescent Ca2+ indicators. In this chapter, we discuss some of the most common chemical Ca2+ indicators that are widely used for the investigation of intracellular Ca2+ signaling. Advantages, limitations and relevant procedures will be presented for each dye including their spectral qualities, dissociation constants, chemical forms, loading methods and equipment for optimal imaging. Chemical indicators now available allow for intracellular Ca2+ detection over a very large range (<50 nM to >50 microM). High affinity indicators can be used to quantify Ca2+ levels in the cytosol while lower affinity indicators can be optimized for measuring Ca2+ in subcellular compartments with higher concentrations. Indicators can be classified into either single wavelength or ratiometric dyes. Both classes require specific lasers, filters, and/or detection methods that are dependent upon their spectral properties and both classes have advantages and limitations. Single wavelength indicators are generally very bright and optimal for Ca2+ detection when more than one fluorophore is being imaged. Ratiometric indicators can be calibrated very precisely and they minimize the most common problems associated with chemical Ca2+ indicators including uneven dye loading, leakage, photobleaching, and changes in cell volume. Recent technical advances that permit in vivo Ca2+ measurements will also be discussed.
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Affiliation(s)
- R Madelaine Paredes
- Department of Cellular and Structural Biology, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229, USA
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27
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Payne AM, Jimenez-Moreno R, Wang ZM, Messi ML, Delbono O. Role of Ca2+, membrane excitability, and Ca2+ stores in failing muscle contraction with aging. Exp Gerontol 2008; 44:261-73. [PMID: 18948183 DOI: 10.1016/j.exger.2008.09.013] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2008] [Revised: 09/18/2008] [Accepted: 09/21/2008] [Indexed: 10/21/2022]
Abstract
Excitation-contraction (EC) coupling in a population of skeletal muscle fibers of aged mice becomes dependent on the presence of external Ca(2+) ions (Payne, A.M., Zheng, Z., Gonzalez, E., Wang, Z.M., Messi, M.L., Delbono, O., 2004b. External Ca(2+)-dependent excitation - contraction coupling in a population of aging mouse skeletal muscle fibers. J. Physiol. 560, 137-155.). However, the mechanism(s) underlying this process remain unknown. In this work, we examined the role of (1) extracellular Ca(2+); (2) voltage-induced influx of external Ca(2+) ions; (3) sarcoplasmic reticulum (SR) Ca(2+) depletion during repeated contractions; (4) store-operated Ca(2+) entry (SOCE); (5) SR ultrastructure; (6) SR subdomain localization of the ryanodine receptor; and (7) sarcolemmal excitability in muscle force decline with aging. These experiments show that external Ca(2+), but not Ca(2+) influx, is needed to maintain force upon repetitive fiber electrical stimulation. Decline in fiber force is associated with depressed SR Ca(2+) release. SR Ca(2+) depletion, SOCE, and the putative segregated Ca(2+) release store do not play a significant role in external Ca(2+)-dependent contraction. More importantly, a significant number of action potentials fail in senescent mouse muscle fibers subjected to a stimulation frequency. These results indicate that failure to generate action potentials accounts for decreased intracellular Ca(2+) mobilization and tetanic force in aging muscle exposed to a Ca(2+)-free medium.
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Affiliation(s)
- Anthony Michael Payne
- Department of Physiology and Pharmacology, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA
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Royer L, Pouvreau S, Ríos E. Evolution and modulation of intracellular calcium release during long-lasting, depleting depolarization in mouse muscle. J Physiol 2008; 586:4609-29. [PMID: 18687715 PMCID: PMC2614033 DOI: 10.1113/jphysiol.2008.157990] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2008] [Accepted: 08/06/2008] [Indexed: 01/21/2023] Open
Abstract
Intracellular calcium signals regulate multiple cellular functions. They depend on release of Ca(2+) from cellular stores into the cytosol, a process that in many types of cells appears to be tightly controlled by changes in [Ca(2+)] within the store. In contrast with cardiac muscle, where depletion of Ca(2+) in the sarcoplasmic reticulum is a crucial determinant of termination of Ca(2+) release, in skeletal muscle there is no agreement regarding the sign, or even the existence of an effect of SR Ca(2+) level on Ca(2+) release. To address this issue we measured Ca(2+) transients in mouse flexor digitorum brevis (FDB) skeletal muscle fibres under voltage clamp, using confocal microscopy and the Ca(2+) monitor rhod-2. The evolution of Ca(2+) release flux was quantified during long-lasting depolarizations that reduced severely the Ca(2+) content of the SR. As in all previous determinations in mammals and non-mammals, release flux consisted of an early peak, relaxing to a lower level from which it continued to decay more slowly. Decay of flux in this second stage, which has been attributed largely to depletion of SR Ca(2+), was studied in detail. A simple depletion mechanism without change in release permeability predicts an exponential decay with time. In contrast, flux decreased non-exponentially, to a finite, measurable level that could be maintained for the longest pulses applied (1.8 s). An algorithm on the flux record allowed us to define a quantitative index, the normalized flux rate of change (NFRC), which was shown to be proportional to the ratio of release permeability P and inversely proportional to Ca(2+) buffering power B of the SR, thus quantifying the 'evacuability' or ability of the SR to empty its content. When P and B were constant, flux then decayed exponentially, and NFRC was equal to the exponential rate constant. Instead, in most cases NFRC increased during the pulse, from a minimum reached immediately after the early peak in flux, to a time between 200 and 250 ms, when the index was no longer defined. NFRC increased by 111% on average (in 27 images from 18 cells), reaching 300% in some cases. The increase may reflect an increase in P, a decrease in B, or both. On experimental and theoretical grounds, both changes are to be expected upon SR depletion. A variable evacuability helps maintain a constant Ca(2+) output under conditions of diminishing store Ca(2+) load.
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Affiliation(s)
- Leandro Royer
- Department of Molecular Biophysics & Physiology, Section of Cellular Signalling, Rush University School of Medicine, Chicago, IL 60612, USA
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Dystrophic skeletal muscle fibers display alterations at the level of calcium microdomains. Proc Natl Acad Sci U S A 2008; 105:14698-703. [PMID: 18787128 DOI: 10.1073/pnas.0802217105] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The spatiotemporal properties of the Ca(2+)-release process in skeletal muscle fibers from normal and mdx fibers were determined using the confocal-spot detection technique. The Ca(2+) indicator OGB-5N was used to record action potential-evoked fluorescence signals at consecutive locations separated by 200 nm along multiple sarcomeres of FDB fibers loaded with 10- and 30-mM EGTA. Three-dimensional reconstructions of fluorescence transients demonstrated the existence of microdomains of increased fluorescence around the Ca(2+)-release sites in both mouse strains. The Ca(2+) microdomains in mdx fibers were regularly spaced along the fiber axis, displaying a distribution similar to that seen in normal fibers. Nevertheless, both preparations differed in that in 10-mM EGTA Ca(2+) microdomains had smaller amplitudes and were wider in mdx fibers than in controls. In addition, Ca(2+)-dependent fluorescence transients recorded at selected locations within the sarcomere of mdx muscle fibers were not only smaller, but also slower than their counterparts in normal fibers. Notably, differences in the spatial features of the Ca(2+) microdomains recorded in mdx and normal fibers, but not in the amplitude and kinetics of the Ca(2+) transients, were eliminated in 30-mM EGTA. Our results consistently demonstrate that Ca(2+)-release flux calculated from release sites in mdx fibers is uniformly impaired with respect to those normal fibers. The Ca(2+)-release reduction is consistent with that previously measured using global detection techniques.
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Jiménez-Moreno R, Wang ZM, Gerring RC, Delbono O. Sarcoplasmic reticulum Ca2+ release declines in muscle fibers from aging mice. Biophys J 2008; 94:3178-88. [PMID: 18178643 PMCID: PMC2275691 DOI: 10.1529/biophysj.107.118786] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2007] [Accepted: 12/03/2007] [Indexed: 11/18/2022] Open
Abstract
This study hypothesized that decline in sarcoplasmic reticulum (SR) Ca(2+) release and maximal SR-releasable Ca(2+) contributes to decreased specific force with aging. To test it, we recorded electrically evoked maximal isometric specific force followed by 4-chloro-m-cresol (4-CmC)-evoked maximal contracture force in single intact fibers from the mouse flexor digitorum brevis muscle. Significant differences in tetanic, but not in 4-CmC-evoked, contracture forces were recorded in fibers from aging mice as compared to younger mice. Peak intracellular Ca(2+) in response to 4-CmC did not differ significantly. SR Ca(2+) release was recorded in whole-cell patch-clamped fibers in the linescan mode of confocal microscopy using a low-affinity Ca(2+) indicator (Oregon green bapta-5N) with high-intracellular ethylene glycol-bis(alpha-aminoethyl ether)-N,N,N'N'-tetraacetic acid (20 mM). Maximal SR Ca(2+) release, but not voltage dependence, was significantly changed in fibers from old compared to young mice. Increasing the duration of fiber depolarization did not increase the maximal rate of SR Ca(2+) release in fibers from old compared to young mice. Voltage-dependent inactivation of SR Ca(2+) release did not differ significantly between fibers from young and old mice. These findings indicate that alterations in excitation-contraction coupling, but not in maximal SR-releasable Ca(2+), account for the age-dependent decline in intracellular Ca(2+) mobilization and specific force.
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Affiliation(s)
- Ramón Jiménez-Moreno
- Department of Physiology and Pharmacology, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157, USA
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The auxiliary subunit gamma 1 of the skeletal muscle L-type Ca2+ channel is an endogenous Ca2+ antagonist. Proc Natl Acad Sci U S A 2007; 104:17885-90. [PMID: 17978188 DOI: 10.1073/pnas.0704340104] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Ca2+ channels play crucial roles in cellular signal transduction and are important targets of pharmacological agents. They are also associated with auxiliary subunits exhibiting functions that are still incompletely resolved. Skeletal muscle L-type Ca2+ channels (dihydropyridine receptors, DHPRs) are specialized for the remote voltage control of type 1 ryanodine receptors (RyR1) to release stored Ca2+. The skeletal muscle-specific gamma subunit of the DHPR (gamma 1) down-modulates availability by altering its steady state voltage dependence. The effect resembles the action of certain Ca2+ antagonistic drugs that are thought to stabilize inactivated states of the DHPR. In the present study we investigated the cross influence of gamma 1 and Ca2+ antagonists by using wild-type (gamma+/+) and gamma 1 knockout (gamma-/-) mice. We studied voltage-dependent gating of both L-type Ca2+ current and Ca2+ release and the allosteric modulation of drug binding. We found that 10 microM diltiazem, a benzothiazepine drug, more than compensated for the reduction in high-affinity binding of the dihydropyridine agent isradipine caused by gamma 1 elimination; 5 muM devapamil [(-)D888], a phenylalkylamine Ca2+ antagonist, approximately reversed the right-shifted voltage dependence of availability and the accelerated recovery kinetics of Ca2+ current and Ca2+ release. Moreover, the presence of gamma 1 altered the effect of D888 on availability and strongly enhanced its impact on recovery kinetics demonstrating that gamma 1 and the drug do not act independently of each other. We propose that the gamma 1 subunit of the DHPR functions as an endogenous Ca2+ antagonist whose task may be to minimize Ca2+ entry and Ca2+ release under stress-induced conditions favoring plasmalemma depolarization.
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Caputo C, Bolaños P. Effect of mitochondria poisoning by FCCP on Ca2+ signaling in mouse skeletal muscle fibers. Pflugers Arch 2007; 455:733-43. [PMID: 17676335 DOI: 10.1007/s00424-007-0317-0] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2007] [Revised: 06/26/2007] [Accepted: 06/27/2007] [Indexed: 10/23/2022]
Abstract
We have studied the effects of mitochondria poisoning by carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone (FCCP) on Ca(2+) signaling in enzymatically dissociated mouse flexor digitorum brevis (FDB) muscle fibers. We used Fura-2AM to measure resting [Ca(2+)](i) and MagFluo-4AM to measure Ca(2+) transients. Exposure to FCCP (2 microM, 2 min) caused a continuous increase in [Ca(2+)](i) at a rate of 0.60 nM/s and a drastic reduction of electrically elicited Ca(2+) transients without much effect on their decay phase. Half of the maximal effect occurred at [Ca(2+)](i) = 220 nM. This effect was partially reversible after long recuperation and was not diminished by Tiron, a reactive oxygen species (ROS) scavenger. FCCP had no effects on fiber excitability as shown by the generation of action potentials. 4CmC, an agonist of ryanodine receptors, induced a massive Ca(2+) release. FCCP diminished the rate but not the amount of Ca(2+) released, indicating that depletion of Ca(2+) stores did not cause the decrease in Ca(2+) transient amplitude. Ca(2+) transient amplitude could also be diminished, but to a lesser degree, by increases in [Ca(2+)](i) induced by repetitive stimulation of fibers treated with ciclopiazonic acid. This suggests an important role for Ca(2+) in the FCCP effect on transient amplitude.
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MESH Headings
- 1,2-Dihydroxybenzene-3,5-Disulfonic Acid Disodium Salt/pharmacology
- Action Potentials
- Animals
- Calcium Signaling/drug effects
- Calcium-Transporting ATPases/antagonists & inhibitors
- Calcium-Transporting ATPases/metabolism
- Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone/toxicity
- Cresols/pharmacology
- Enzyme Inhibitors/pharmacology
- Fluorescent Dyes
- Free Radical Scavengers/pharmacology
- Fura-2/analogs & derivatives
- Indoles/pharmacology
- Kinetics
- Mice
- Microscopy, Fluorescence/methods
- Mitochondria, Muscle/drug effects
- Mitochondria, Muscle/metabolism
- Muscle Fibers, Fast-Twitch/drug effects
- Muscle Fibers, Fast-Twitch/enzymology
- Muscle Fibers, Fast-Twitch/metabolism
- Muscle, Skeletal/drug effects
- Muscle, Skeletal/enzymology
- Muscle, Skeletal/metabolism
- Ryanodine Receptor Calcium Release Channel/metabolism
- Uncoupling Agents/toxicity
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Affiliation(s)
- Carlo Caputo
- Laboratorio de Fisiología Celular, Centro de Biofísica y Bioquímica, Instituto Venezolano de Investigaciones Cientificas, Apartado 21827, Caracas 1020A, Venezuela.
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Pouvreau S, Royer L, Yi J, Brum G, Meissner G, Ríos E, Zhou J. Ca(2+) sparks operated by membrane depolarization require isoform 3 ryanodine receptor channels in skeletal muscle. Proc Natl Acad Sci U S A 2007; 104:5235-40. [PMID: 17360329 PMCID: PMC1829292 DOI: 10.1073/pnas.0700748104] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Stimuli are translated to intracellular calcium signals via opening of inositol trisphosphate receptor and ryanodine receptor (RyR) channels of the sarcoplasmic reticulum or endoplasmic reticulum. In cardiac and skeletal muscle of amphibians the stimulus is depolarization of the transverse tubular membrane, transduced by voltage sensors at tubular-sarcoplasmic reticulum junctions, and the unit signal is the Ca(2+) spark, caused by concerted opening of multiple RyR channels. Mammalian muscles instead lose postnatally the ability to produce sparks, and they also lose RyR3, an isoform abundant in spark-producing skeletal muscles. What does it take for cells to respond to membrane depolarization with Ca(2+) sparks? To answer this question we made skeletal muscles of adult mice expressing exogenous RyR3, demonstrated as immunoreactivity at triad junctions. These muscles showed abundant sparks upon depolarization. Sparks produced thusly were found to amplify the response to depolarization in a manner characteristic of Ca(2+)-induced Ca(2+) release processes. The amplification was particularly effective in responses to brief depolarizations, as in action potentials. We also induced expression of exogenous RyR1 or yellow fluorescent protein-tagged RyR1 in muscles of adult mice. In these, tag fluorescence was present at triad junctions. RyR1-transfected muscle lacked voltage-operated sparks. Therefore, the voltage-operated sparks phenotype is specific to the RyR3 isoform. Because RyR3 does not contact voltage sensors, their opening was probably activated by Ca(2+), secondarily to Ca(2+) release through junctional RyR1. Physiologically voltage-controlled Ca(2+) sparks thus require a voltage sensor, a master junctional RyR1 channel that provides trigger Ca(2+), and a slave parajunctional RyR3 cohort.
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Affiliation(s)
- Sandrine Pouvreau
- *Section of Cellular Signaling, Department of Molecular Biophysics and Physiology, Rush University, 1750 West Harrison Street, Suite 1279JS, Chicago, IL 60612
| | - Leandro Royer
- *Section of Cellular Signaling, Department of Molecular Biophysics and Physiology, Rush University, 1750 West Harrison Street, Suite 1279JS, Chicago, IL 60612
| | - Jianxun Yi
- *Section of Cellular Signaling, Department of Molecular Biophysics and Physiology, Rush University, 1750 West Harrison Street, Suite 1279JS, Chicago, IL 60612
| | - Gustavo Brum
- Departamento de Biofísica, Facultad de Medicina, Universidad de la República, Avenida General Flores 2125, Montevideo, Uruguay; and
| | - Gerhard Meissner
- Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, NC 27599-7260
| | - Eduardo Ríos
- *Section of Cellular Signaling, Department of Molecular Biophysics and Physiology, Rush University, 1750 West Harrison Street, Suite 1279JS, Chicago, IL 60612
- To whom correspondence may be addressed. E-mail: or
| | - Jingsong Zhou
- *Section of Cellular Signaling, Department of Molecular Biophysics and Physiology, Rush University, 1750 West Harrison Street, Suite 1279JS, Chicago, IL 60612
- To whom correspondence may be addressed. E-mail: or
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Allard B, Couchoux H, Pouvreau S, Jacquemond V. Sarcoplasmic reticulum Ca2+ release and depletion fail to affect sarcolemmal ion channel activity in mouse skeletal muscle. J Physiol 2006; 575:69-81. [PMID: 16777939 PMCID: PMC1819412 DOI: 10.1113/jphysiol.2006.112367] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Revised: 04/27/2006] [Accepted: 06/15/2006] [Indexed: 11/08/2022] Open
Abstract
In skeletal muscle, sarcoplasmic reticulum (SR) Ca2+ depletion is suspected to trigger a calcium entry across the plasma membrane and recent studies also suggest that the opening of channels spontaneously active at rest and possibly involved in Duchenne dystrophy may be regulated by SR Ca2+ depletion. Here we simultaneously used the cell-attached and whole-cell voltage-clamp techniques as well as intracellular Ca2+ measurements on single isolated mouse skeletal muscle fibres to unravel any possible change in membrane conductance that would depend upon SR Ca2+ release and/or SR Ca2+ depletion. Delayed rectifier K+ single channel activity was routinely detected during whole-cell depolarizing pulses. In addition the activity of channels carrying unitary inward currents of approximately 1.5 pA at -80 mV was detected in 17 out of 127 and in 21 out of 59 patches in control and mdx dystrophic fibres, respectively. In both populations of fibres, large whole-cell depolarizing pulses did not reproducibly increase this channel activity. This was also true when, repeated application of the whole-cell pulses led to exhaustion of the Ca2+ transient. SR Ca2+ depletion produced by the SR Ca2+ pump inhibitor cyclopiazonic acid (CPA) also failed to induce any increase in the resting whole-cell conductance and in the inward single channel activity. Overall results indicate that voltage-activated SR Ca2+ release and/or SR Ca2+ depletion are not sufficient to activate the opening of channels carrying inward currents at negative voltages and challenge the physiological relevance of a store-operated membrane conductance in adult skeletal muscle.
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Affiliation(s)
- Bruno Allard
- Physiologie Intégrative, Cellulaire et Moléculaire, UMR CNRS 5123, Université C. Bernard Lyon I, 43 bd du 11 Novembre 1918, 69622 Villeurbanne cedex, France
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35
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Melzer W, Andronache Z, Ursu D. Functional roles of the gamma subunit of the skeletal muscle DHP-receptor. J Muscle Res Cell Motil 2006; 27:307-14. [PMID: 16897572 DOI: 10.1007/s10974-006-9093-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2006] [Accepted: 07/12/2006] [Indexed: 10/24/2022]
Abstract
In excitation-contraction coupling (EC coupling) of skeletal muscle, large and rapid changes of the myoplasmic Ca2+ concentration mediate the activation and termination of force. The L-type Ca2+ channel (dihydropyridine receptor, DHP receptor) is a central component of the EC coupling process. Its predominant role is to provide the Ca2+ release channels of the sarcoplasmic reticulum (SR) with the sensitivity to cell membrane voltage. The DHP receptor consists of five different proteins (alpha1S, beta1, gamma1, delta and alpha2) whose tasks and functional characteristics are still incompletely understood. This short review summarizes progress made in studying the physiology of the gamma1 subunit, a membrane polypeptide that is highly specific for skeletal muscle. The focus is on recent results obtained from muscle of gamma1-deficient mice.
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Affiliation(s)
- Werner Melzer
- Department of Applied Physiology, University of Ulm, Albert-Einstein-Allee 11, D-89069, Ulm, Germany.
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Gouadon E, Schuhmeier RP, Ursu D, Anderson AA, Treves S, Zorzato F, Lehmann-Horn F, Melzer W. A possible role of the junctional face protein JP-45 in modulating Ca2+ release in skeletal muscle. J Physiol 2006; 572:269-80. [PMID: 16423849 PMCID: PMC1779648 DOI: 10.1113/jphysiol.2005.104406] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
We investigated the functional role of JP-45, a recently discovered protein of the junctional face membrane (JFM) of skeletal muscle. For this purpose, we expressed JP-45 C-terminally tagged with the fluorescent protein DsRed2 by nuclear microinjection in myotubes derived from the C2C12 skeletal muscle cell line and performed whole-cell voltage-clamp experiments. We recorded in parallel cell membrane currents and Ca(2+) signals using fura-2 during step depolarization. It was found that properties of the voltage-activated Ca(2+) current were not significantly changed in JP-45-DsRed2-expressing C2C12 myotubes whereas the amplitude of depolarization-induced Ca(2+) transient was decreased compared to control myotubes expressing only DsRed2. Converting Ca(2+) transients to Ca(2+) input flux using a model fit approach to quantify Ca(2+) removal, the change could be attributed to an alteration in voltage-activated Ca(2+) permeability rather than to altered removal properties or a lower Ca(2+) content of the sarcoplasmic reticulum (SR). Determining non-linear capacitive currents revealed a reduction of Ca(2+) permeability per voltage-sensor charge. The results may be explained by a modulatory effect of JP-45 related to its reported in vitro interaction with the dihydropyridine receptor and the SR Ca(2+) binding protein calsequestrin (CSQ).
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Affiliation(s)
- E Gouadon
- University of Ulm, Department of Applied Physiology, Albert-Einstein-Allee 11, D-89069 Ulm, Germany
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