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Bolaños P, Calderón JC. Excitation-contraction coupling in mammalian skeletal muscle: Blending old and last-decade research. Front Physiol 2022; 13:989796. [PMID: 36117698 PMCID: PMC9478590 DOI: 10.3389/fphys.2022.989796] [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: 07/08/2022] [Accepted: 08/08/2022] [Indexed: 11/13/2022] Open
Abstract
The excitation–contraction coupling (ECC) in skeletal muscle refers to the Ca2+-mediated link between the membrane excitation and the mechanical contraction. The initiation and propagation of an action potential through the membranous system of the sarcolemma and the tubular network lead to the activation of the Ca2+-release units (CRU): tightly coupled dihydropyridine and ryanodine (RyR) receptors. The RyR gating allows a rapid, massive, and highly regulated release of Ca2+ from the sarcoplasmic reticulum (SR). The release from triadic places generates a sarcomeric gradient of Ca2+ concentrations ([Ca2+]) depending on the distance of a subcellular region from the CRU. Upon release, the diffusing Ca2+ has multiple fates: binds to troponin C thus activating the contractile machinery, binds to classical sarcoplasmic Ca2+ buffers such as parvalbumin, adenosine triphosphate and, experimentally, fluorescent dyes, enters the mitochondria and the SR, or is recycled through the Na+/Ca2+ exchanger and store-operated Ca2+ entry (SOCE) mechanisms. To commemorate the 7th decade after being coined, we comprehensively and critically reviewed “old”, historical landmarks and well-established concepts, and blended them with recent advances to have a complete, quantitative-focused landscape of the ECC. We discuss the: 1) elucidation of the CRU structures at near-atomic resolution and its implications for functional coupling; 2) reliable quantification of peak sarcoplasmic [Ca2+] using fast, low affinity Ca2+ dyes and the relative contributions of the Ca2+-binding mechanisms to the whole concert of Ca2+ fluxes inside the fibre; 3) articulation of this novel quantitative information with the unveiled structural details of the molecular machinery involved in mitochondrial Ca2+ handing to understand how and how much Ca2+ enters the mitochondria; 4) presence of the SOCE machinery and its different modes of activation, which awaits understanding of its magnitude and relevance in situ; 5) pharmacology of the ECC, and 6) emerging topics such as the use and potential applications of super-resolution and induced pluripotent stem cells (iPSC) in ECC. Blending the old with the new works better!
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Affiliation(s)
- Pura Bolaños
- Laboratory of Cellular Physiology, Centre of Biophysics and Biochemistry, Venezuelan Institute for Scientific Research (IVIC), Caracas, Venezuela
| | - Juan C. Calderón
- Physiology and Biochemistry Research Group-PHYSIS, Faculty of Medicine, University of Antioquia, Medellín, Colombia
- *Correspondence: Juan C. Calderón,
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2
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Hostrup M, Cairns SP, Bangsbo J. Muscle Ionic Shifts During Exercise: Implications for Fatigue and Exercise Performance. Compr Physiol 2021; 11:1895-1959. [PMID: 34190344 DOI: 10.1002/cphy.c190024] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Exercise causes major shifts in multiple ions (e.g., K+ , Na+ , H+ , lactate- , Ca2+ , and Cl- ) during muscle activity that contributes to development of muscle fatigue. Sarcolemmal processes can be impaired by the trans-sarcolemmal rundown of ion gradients for K+ , Na+ , and Ca2+ during fatiguing exercise, while changes in gradients for Cl- and Cl- conductance may exert either protective or detrimental effects on fatigue. Myocellular H+ accumulation may also contribute to fatigue development by lowering glycolytic rate and has been shown to act synergistically with inorganic phosphate (Pi) to compromise cross-bridge function. In addition, sarcoplasmic reticulum Ca2+ release function is severely affected by fatiguing exercise. Skeletal muscle has a multitude of ion transport systems that counter exercise-related ionic shifts of which the Na+ /K+ -ATPase is of major importance. Metabolic perturbations occurring during exercise can exacerbate trans-sarcolemmal ionic shifts, in particular for K+ and Cl- , respectively via metabolic regulation of the ATP-sensitive K+ channel (KATP ) and the chloride channel isoform 1 (ClC-1). Ion transport systems are highly adaptable to exercise training resulting in an enhanced ability to counter ionic disturbances to delay fatigue and improve exercise performance. In this article, we discuss (i) the ionic shifts occurring during exercise, (ii) the role of ion transport systems in skeletal muscle for ionic regulation, (iii) how ionic disturbances affect sarcolemmal processes and muscle fatigue, (iv) how metabolic perturbations exacerbate ionic shifts during exercise, and (v) how pharmacological manipulation and exercise training regulate ion transport systems to influence exercise performance in humans. © 2021 American Physiological Society. Compr Physiol 11:1895-1959, 2021.
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Affiliation(s)
- Morten Hostrup
- Section of Integrative Physiology, Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark
| | - Simeon Peter Cairns
- SPRINZ, School of Sport and Recreation, Auckland University of Technology, Auckland, New Zealand.,Health and Rehabilitation Research Institute, Auckland University of Technology, Auckland, New Zealand
| | - Jens Bangsbo
- Section of Integrative Physiology, Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark
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3
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Son J, Rymer WZ. Longer electromechanical delay in paretic triceps surae muscles during voluntary isometric plantarflexion torque generation in chronic hemispheric stroke survivors. J Electromyogr Kinesiol 2020; 56:102475. [PMID: 33242750 DOI: 10.1016/j.jelekin.2020.102475] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2020] [Revised: 08/16/2020] [Accepted: 09/17/2020] [Indexed: 11/28/2022] Open
Abstract
Electromechanical delay (EMD) is the time delay between the onset of muscle activity and the onset of force/joint torque. This delay appears to be linked to muscular contraction efficiency. However, to our knowledge, limited evidence is available regarding the magnitude of the EMD in stroke-impaired muscles. Accordingly, this study aims to quantify the EMD in both paretic and non-paretic triceps surae muscles of chronic hemispheric stroke survivors, and to investigate whether the EMD is related to voluntary force-generating capacity in this muscle group. Nine male chronic stroke survivors were asked to perform isometric plantarflexion contractions at different force levels and at different ankle joint angles ranging from maximum plantarflexion to maximum dorsiflexion. The surface electromyograms were recorded from triceps surae muscles. The longest EMD among triceps surae muscles was chosen as the EMD for each side. Our results revealed that the EMD in paretic muscles was significantly longer than in non-paretic muscles. Moreover, both paretic and non-paretic muscles showed a negative correlation between the EMD and maximum torque-generating capacity. In addition, there was a strong positive relationship between the EMD and shear wave speed in paretic muscles as well as a negative relationship between the EMD and passive ankle joint range of motion. These findings imply that the EMD may be a useful biomarker, in part, associated with contractile and material properties in stroke-impaired muscles.
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Affiliation(s)
- Jongsang Son
- Shirley Ryan AbilityLab (formerly the Rehabilitation Institute of Chicago), Chicago, IL, United States; Department of Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States.
| | - William Zev Rymer
- Shirley Ryan AbilityLab (formerly the Rehabilitation Institute of Chicago), Chicago, IL, United States; Department of Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States
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4
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Rall JA. A perfect confluence of physiology and morphology: discovery of the transverse tubular system and inward spread of activation in skeletal muscle. ADVANCES IN PHYSIOLOGY EDUCATION 2020; 44:402-413. [PMID: 32697151 DOI: 10.1152/advan.00091.2020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
By early 1954, there existed a plausible model of muscle contraction called the sliding filament model. In addition, the nature of muscle excitation was understood. Surprisingly, the link between the membrane excitation and contraction was entirely unknown. This dilemma has been called the time-distance paradox. The path to discovery of the missing link between excitation and contraction was a rocky one involving the simultaneous but independent development of physiological and morphological studies. From the viewpoint of physiology, significant events included the most thrilling moment of a scientific life, confirmation of a hypothesis that was wrong, a major surprise and shock, a result not expected from evolutionary relationships, and disappointment and confusion before clarity. From the viewpoint of morphology, there was the exciting beginning and rapid development of biological electron microscopy, heroic experiments, the importance of sample preparative procedures, and discovery of clues from the old light microscopic literature. However, it was the confluence of physiology and morphology that brought clarity and a major advance in understanding, leading to the discovery of the transverse tubular system and inward spread of activation in skeletal muscle.
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Affiliation(s)
- Jack A Rall
- Department of Physiology and Cell Biology, College of Medicine, Ohio State University, Columbus, Ohio
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5
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RyR1-targeted drug discovery pipeline integrating FRET-based high-throughput screening and human myofiber dynamic Ca 2+ assays. Sci Rep 2020; 10:1791. [PMID: 32019969 PMCID: PMC7000700 DOI: 10.1038/s41598-020-58461-1] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2019] [Accepted: 01/13/2020] [Indexed: 11/18/2022] Open
Abstract
Elevated cytoplasmic [Ca2+] is characteristic in severe skeletal and cardiac myopathies, diabetes, and neurodegeneration, and partly results from increased Ca2+ leak from sarcoplasmic reticulum stores via dysregulated ryanodine receptor (RyR) channels. Consequently, RyR is recognized as a high-value target for drug discovery to treat such pathologies. Using a FRET-based high-throughput screening assay that we previously reported, we identified small-molecule compounds that modulate the skeletal muscle channel isoform (RyR1) interaction with calmodulin and FK506 binding protein 12.6. Two such compounds, chloroxine and myricetin, increase FRET and inhibit [3H]ryanodine binding to RyR1 at nanomolar Ca2+. Both compounds also decrease RyR1 Ca2+ leak in human skinned skeletal muscle fibers. Furthermore, we identified compound concentrations that reduced leak by > 50% but only slightly affected Ca2+ release in excitation-contraction coupling, which is essential for normal muscle contraction. This report demonstrates a pipeline that effectively filters small-molecule RyR1 modulators towards clinical relevance.
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Azimi I, Stevenson RJ, Zhang X, Meizoso-Huesca A, Xin P, Johnson M, Flanagan JU, Chalmers SB, Yoast RE, Kapure JS, Ross BP, Vetter I, Ashton MR, Launikonis BS, Denny WA, Trebak M, Monteith GR. A new selective pharmacological enhancer of the Orai1 Ca 2+ channel reveals roles for Orai1 in smooth and skeletal muscle functions. ACS Pharmacol Transl Sci 2020; 3:135-147. [PMID: 32190822 DOI: 10.1021/acsptsci.9b00081] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Store operated calcium (Ca2+) entry is an important homeostatic mechanism in cells, whereby the release of Ca2+ from intracellular endoplasmic reticulum stores triggers the activation of a Ca2+ influx pathway. Mediated by Orai1, this Ca2+ influx has specific and essential roles in biological processes as diverse as lactation to immunity. Although pharmacological inhibitors of this Ca2+ influx mechanism have helped to define the role of store operated Ca2+ entry in many cellular events, the lack of isoform specific modulators and activators of Orai1 has limited our full understanding of these processes. Here we report the identification and synthesis of an Orai1 activity enhancer that concurrently potentiated Orai1 Ca2+ -dependent inactivation (CDI). This unique enhancer of Orai1 had only a modest effect on Orai3 with weak inhibitory effects at high concentrations in intact MCF-7 breast cancer cells. The Orai1 enhancer heightened vascular smooth muscle cell migration induced by platelet-derived growth factor and the unique store operated Ca2+ entry pathway present in skeletal muscle cells. These studies show that IA65 is an exemplar for the translation and development of Orai isoform selective agents. The ability of IA65 to activate CDI demonstrates that agents can be developed that can enhance Orai1-mediated Ca2+ influx but avoid the cytotoxicity associated with sustained Orai1 activation. IA65 and/or future analogues with similar Orai1 and CDI activating properties could be fine tuners of physiological processes important in specific disease states, such as cellular migration and immune cell function.
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Affiliation(s)
- Iman Azimi
- Division of Pharmacy, College of Health and Medicine, University of Tasmania, Hobart, Tasmania 7001, Australia
| | - Ralph J Stevenson
- Auckland Cancer Society Research Centre, School of Medical Sciences, The University of Auckland, Auckland, 1142, New Zealand
| | - Xuexin Zhang
- Department of Cellular and Molecular Physiology, and Pennsylvania State Cancer Institute. The Pennsylvania State University College of Medicine, Hershey, PA, 17033, USA
| | - Aldo Meizoso-Huesca
- School of Biomedical Sciences, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Ping Xin
- Department of Cellular and Molecular Physiology, and Pennsylvania State Cancer Institute. The Pennsylvania State University College of Medicine, Hershey, PA, 17033, USA
| | - Martin Johnson
- Department of Cellular and Molecular Physiology, and Pennsylvania State Cancer Institute. The Pennsylvania State University College of Medicine, Hershey, PA, 17033, USA
| | - Jack U Flanagan
- Auckland Cancer Society Research Centre, School of Medical Sciences, The University of Auckland, Auckland, 1142, New Zealand
| | - Silke B Chalmers
- School of Pharmacy, The University of Queensland, Brisbane 4072, Queensland, Australia
| | - Ryan E Yoast
- Department of Cellular and Molecular Physiology, and Pennsylvania State Cancer Institute. The Pennsylvania State University College of Medicine, Hershey, PA, 17033, USA
| | - Jeevak S Kapure
- School of Pharmacy, The University of Queensland, Brisbane 4072, Queensland, Australia
| | - Benjamin P Ross
- School of Pharmacy, The University of Queensland, Brisbane 4072, Queensland, Australia
| | - Irina Vetter
- School of Pharmacy, The University of Queensland, Brisbane 4072, Queensland, Australia.,IMB Centre for Pain Research, Institute for Molecular Bioscience, University of Queensland, Brisbane, Queensland, 4072, Australia
| | - Mark R Ashton
- UniQuest Pty Ltd, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Bradley S Launikonis
- School of Biomedical Sciences, The University of Queensland, Brisbane, QLD 4072, Australia
| | - William A Denny
- Auckland Cancer Society Research Centre, School of Medical Sciences, The University of Auckland, Auckland, 1142, New Zealand
| | - Mohamed Trebak
- Department of Cellular and Molecular Physiology, and Pennsylvania State Cancer Institute. The Pennsylvania State University College of Medicine, Hershey, PA, 17033, USA
| | - Gregory R Monteith
- School of Pharmacy, The University of Queensland, Brisbane 4072, Queensland, Australia.,Mater Research Institute, Translational Research Institute, The University of Queensland, Brisbane 4102, Queensland, Australia
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Banks Q, Pratt SJP, Iyer SR, Lovering RM, Hernández-Ochoa EO, Schneider MF. Optical Recording of Action Potential Initiation and Propagation in Mouse Skeletal Muscle Fibers. Biophys J 2018; 115:2127-2140. [PMID: 30448039 PMCID: PMC6289662 DOI: 10.1016/j.bpj.2018.10.026] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2018] [Revised: 10/18/2018] [Accepted: 10/24/2018] [Indexed: 01/29/2023] Open
Abstract
Skeletal muscle fibers have been used to examine a variety of cellular functions and pathologies. Among other parameters, skeletal muscle action potential (AP) propagation has been measured to assess the integrity and function of skeletal muscle. In this work, we utilize 1-(3-sulfonatopropyl)-4[β[2-(Di-n-octylamino)-6-naphtyl]vinyl]pyridinium betaine, a potentiometric dye, and mag-fluo-4, a low-affinity intracellular Ca2+indicator, to noninvasively and reliably measure AP conduction velocity in skeletal muscle. We used remote extracellular bipolar electrodes to generate an alternating polarity electric field that initiates an AP at either end of the fiber. Using enzymatically dissociated flexor digitorum brevis (FDB) fibers and high-speed line scans, we determine the conduction velocity to be ∼0.4 m/s. We applied these methodologies to FDB fibers under elevated extracellular potassium conditions and confirmed that the conduction velocity is significantly reduced in elevated [K+]o. Because our recorded velocities for FDB fibers were much slower than previously reported for other muscle groups, we compared the conduction velocity in FDB fibers to that of extensor digitorum longus (EDL) fibers and measured a significantly faster velocity in EDL fibers than FDB fibers. As a basis for this difference in conduction velocity, we found a similarly higher level of expression of Na+ channels in EDL than in FDB fibers. In addition to measuring the conduction velocity, we can also measure the passive electrotonic potentials elicited by pulses by applying tetrodotoxin and have constructed a circuit model of a skeletal muscle fiber to predict passive polarization of the fiber by the field stimuli. Our predictions from the model fiber closely resemble the recordings acquired from in vitro assays. With these techniques, we can examine how various pathologies and mutations affect skeletal muscle AP propagation. Our work demonstrates the utility of using 1-(3-sulfonatopropyl)-4[β[2-(Di-n-octylamino)-6-naphtyl]vinyl]pyridinium betaine or mag-fluo-4 to noninvasively measure AP initiation and conduction.
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Affiliation(s)
- Quinton Banks
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, Maryland
| | - Stephen Joseph Paul Pratt
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, Maryland
| | - Shama Rajan Iyer
- Department of Orthopedics, University of Maryland School of Medicine, Baltimore, Maryland
| | | | - Erick Omar Hernández-Ochoa
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, Maryland
| | - Martin Frederick Schneider
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, Maryland.
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8
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Lamb GD, Stephenson DG. Measurement of force and calcium release using mechanically skinned fibers from mammalian skeletal muscle. J Appl Physiol (1985) 2018; 125:1105-1127. [DOI: 10.1152/japplphysiol.00445.2018] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The mechanically skinned (or “peeled”) skeletal muscle fiber technique is a highly versatile procedure that allows controlled examination of each of the steps in the excitation-contraction (EC)-coupling sequence in skeletal muscle fibers, starting with excitation/depolarization of the transverse tubular (T)-system through to Ca2+ release from sarcoplasmic reticulum (SR) and finally force development by the contractile apparatus. It can also show the overall response of the whole EC-coupling sequence together, such as in twitch and tetanic force responses. A major advantage over intact muscle fiber preparations is that it is possible to set and rapidly manipulate the “intracellular” conditions, allowing examination of the effects of key variables (e.g., intracellular pH, ATP levels, redox state, etc.) on each individual step in EC coupling. This Cores of Reproducibility in Physiology (CORP) article describes the rationale, procedures, and experimental details of the various ways in which the mechanically skinned fiber technique is used in our laboratory to examine the physiological mechanisms controlling Ca2+ release and contraction in skeletal muscle fibers and the aberrations and dysfunction occurring with exercise and disease.
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Affiliation(s)
- Graham D. Lamb
- Department of Physiology, Anatomy, and Microbiology, School of Life Sciences, La Trobe University, Melbourne, Victoria, Australia
| | - D. George Stephenson
- Department of Physiology, Anatomy, and Microbiology, School of Life Sciences, La Trobe University, Melbourne, Victoria, Australia
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9
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Launikonis BS, Cully TR, Csernoch L, Stephenson DG. NHE- and diffusion-dependent proton fluxes across the tubular system membranes of fast-twitch muscle fibers of the rat. J Gen Physiol 2017; 150:95-110. [PMID: 29229646 PMCID: PMC5749115 DOI: 10.1085/jgp.201711891] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2017] [Accepted: 11/01/2017] [Indexed: 11/20/2022] Open
Abstract
The regulation of pH across the t-system membrane of skeletal muscle fibers is poorly understood. Using a sealed tubule preparation, Launikonis et al. reveal Na+/H+ exchange activity and characterize the properties of the diffusional and NHE proton fluxes across the t-system. The complex membrane structure of the tubular system (t-system) in skeletal muscle fibers is open to the extracellular environment, which prevents measurements of H+ movement across its interface with the cytoplasm by conventional methods. Consequently, little is known about the t-system’s role in the regulation of cytoplasmic pH, which is different from extracellular pH. Here we describe a novel approach to measure H+-flux measurements across the t-system of fast-twitch fibers under different conditions. The approach involves loading the t-system of intact rat fast-twitch fibers with a strong pH buffer (20 mM HEPES) and pH-sensitive fluorescent probe (10 mM HPTS) before the t-system is sealed off. The pH changes in the t-system are then tracked by confocal microscopy after rapid changes in cytoplasmic ionic conditions. T-system sealing is achieved by removing the sarcolemma by microdissection (mechanical skinning), which causes the tubules to pinch off and seal tight. After this procedure, the t-system repolarizes to physiological levels and can be electrically stimulated when placed in K+-based solutions of cytosolic-like ionic composition. Using this approach, we show that the t-system of fast-twitch skeletal fibers displays amiloride-sensitive Na+/H+ exchange (NHE), which decreases markedly at alkaline cytosolic pH and has properties similar to that in mammalian cardiac myocytes. We observed mean values for NHE density and proton permeability coefficient of 339 pmol/m2 of t-system membrane and 158 µm/s, respectively. We conclude that the cytosolic pH in intact resting muscle can be quantitatively explained with respect to extracellular pH by assuming that these values apply to the t-system membrane and the sarcolemma.
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Affiliation(s)
- Bradley S Launikonis
- School of Biomedical Sciences, The University of Queensland, Brisbane, QLD, Australia
| | - Tanya R Cully
- School of Biomedical Sciences, The University of Queensland, Brisbane, QLD, Australia
| | - Laszlo Csernoch
- Department of Physiology, University of Debrecen, Debrecen, Hungary
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Abstract
Malignant hyperthermia (MH) is a clinical syndrome of skeletal muscle that presents as a hypermetabolic response to volatile anesthetic gases, where susceptible persons may develop lethally high body temperatures. Genetic predisposition mainly arises from mutations on the skeletal muscle ryanodine receptor (RyR). Dantrolene is administered to alleviate MH symptoms, but its mechanism of action and its influence on the Ca2+ transients elicited by MH triggers are unknown. Here, we show that Ca2+ release in the absence of Mg2+ is unaffected by the presence of dantrolene but that dantrolene becomes increasingly effective as cytoplasmic-free [Mg2+] (free [Mg2+]cyto) passes mM levels. Furthermore, we found in human muscle susceptible to MH that dantrolene was ineffective at reducing halothane-induced repetitive Ca2+ waves in the presence of resting levels of free [Mg2+]cyto (1 mM). However, an increase of free [Mg2+]cyto to 1.5 mM could increase the period between Ca2+ waves. These results reconcile previous contradictory reports in muscle fibers and isolated RyRs, where Mg2+ is present or absent, respectively, and define the mechanism of action of dantrolene is to increase the Mg2+ affinity of the RyR (or "stabilize" the resting state of the channel) and suggest that the accumulation of the metabolite Mg2+ from MgATP hydrolysis is required to make dantrolene administration effective in arresting an MH episode.
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Bakker AJ, Cully TR, Wingate CD, Barclay CJ, Launikonis BS. Doublet stimulation increases Ca 2+ binding to troponin C to ensure rapid force development in skeletal muscle. J Gen Physiol 2017; 149:323-334. [PMID: 28209802 PMCID: PMC5339514 DOI: 10.1085/jgp.201611727] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2016] [Revised: 01/08/2017] [Accepted: 01/09/2017] [Indexed: 01/24/2023] Open
Abstract
Fast-twitch skeletal muscle fibers are often exposed to motor neuron double discharges (≥200 Hz), which markedly increase both the rate of contraction and the magnitude of the resulting force responses. However, the mechanism responsible for these effects is poorly understood, likely because of technical limitations in previous studies. In this study, we measured cytosolic Ca2+ during doublet activation using the low-affinity indicator Mag-Fluo-4 at high temporal resolution and modeled the effects of doublet stimulation on sarcoplasmic reticulum (SR) Ca2+ release, binding of Ca2+ to cytosolic buffers, and force enhancement in fast-twitch fibers. Single isolated fibers respond to doublet pulses with two clear Ca2+ spikes, at doublet frequencies up to 1 KHz. A 200-Hz doublet at the start of a tetanic stimulation train (70 Hz) decreases the drop in free Ca2+ between the first three Ca2+ spikes of the transient, maintaining a higher overall free Ca2+ level during first 20-30 ms of the response. Doublet stimulation also increased the rate of force development in isolated fast-twitch muscles. We also modeled SR Ca2+ release rates during doublet stimulation and showed that Ca2+-dependent inactivation of ryanodine receptor activity is rapid, occurring ≤1ms after initial release. Furthermore, we modeled Ca2+ binding to the main intracellular Ca2+ buffers of troponin C (TnC), parvalbumin, and the SR Ca2+ pump during Ca2+ release and found that the main effect of the second response in the doublet is to more rapidly increase the occupation of the second Ca2+-binding site on TnC (TnC2), resulting in earlier activation of force. We conclude that doublet stimulation maintains high cytosolic Ca2+ levels for longer in the early phase of the Ca2+ response, resulting in faster saturation of TnC2 with Ca2+, faster initiation of cross-bridge cycling, and more rapid force development.
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Affiliation(s)
- Anthony J Bakker
- School of Anatomy, Physiology, and Human Biology, University of Western Australia, Perth, WA 6009, Australia
| | - Tanya R Cully
- School of Biomedical Sciences, University of Queensland, Brisbane, QLD 4072, Australia
| | - Catherine D Wingate
- School of Anatomy, Physiology, and Human Biology, University of Western Australia, Perth, WA 6009, Australia
| | - Christopher J Barclay
- School of Allied Health Sciences, Griffith University, Gold Coast, QLD 4222, Australia
| | - Bradley S Launikonis
- School of Biomedical Sciences, University of Queensland, Brisbane, QLD 4072, Australia
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12
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Esposito F, Cè E, Rampichini S, Monti E, Limonta E, Fossati B, Meola G. Electromechanical delays during a fatiguing exercise and recovery in patients with myotonic dystrophy type 1. Eur J Appl Physiol 2017; 117:551-566. [PMID: 28194519 DOI: 10.1007/s00421-017-3558-4] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2016] [Accepted: 01/24/2017] [Indexed: 01/08/2023]
Abstract
PURPOSE The partitioning of the electromechanical delay by an electromyographic (EMG), mechanomyographic (MMG) and force combined approach can provide further insight into the electrochemical and mechanical processes involved with skeletal muscle contraction and relaxation. The aim of the study was to monitor by this combined approach the changes in delays' electrochemical and mechanical components throughout a fatiguing task and during recovery in patients with myotonic dystrophy type 1 (DM1), who present at the skeletal muscle level fibres rearrangement, muscle weakness and myotonia, especially in the distal muscles. METHODS After assessing maximum voluntary contraction (MVC), 14 male patients with DM1 and 14 healthy controls (HC) performed a fatiguing exercise at 50% MVC until exhaustion. EMG, MMG, and force signals were recorded from tibialis anterior and vastus lateralis muscles. The electromechanical delay during contraction (DelayTOT) and relaxation (R-DelayTOT) components, EMG and MMG root mean square (RMS) and mean frequency (MF) were calculated off-line. RESULTS The fatiguing exercise duration was similar in both groups. In patients with DM1, delays components were significantly longer compared to HC, especially in the distal muscle during relaxation. Delays components recovered quickly from the fatiguing exercise in HC than in patients with DM1 in both muscles. CONCLUSIONS The alterations in delays observed in DM1 during the fatiguing exercise may indicate that also the lengthening of the electrochemical and mechanical processes during contraction and relaxation could play a role in explaining exercise intolerance in this pathology.
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Affiliation(s)
- Fabio Esposito
- Department of Biomedical Sciences for Health (SCIBIS), Università degli Studi di Milano, Via G. Colombo 71, 20133, Milan, Italy. .,IRCCS Fondazione don Gnocchi, Centro di Medicina dello Sport, via Capecelatro 66, 20148, Milan, Italy.
| | - Emiliano Cè
- Department of Biomedical Sciences for Health (SCIBIS), Università degli Studi di Milano, Via G. Colombo 71, 20133, Milan, Italy
| | - Susanna Rampichini
- Department of Biomedical Sciences for Health (SCIBIS), Università degli Studi di Milano, Via G. Colombo 71, 20133, Milan, Italy
| | - Elena Monti
- Department of Biomedical Sciences for Health (SCIBIS), Università degli Studi di Milano, Via G. Colombo 71, 20133, Milan, Italy
| | - Eloisa Limonta
- Department of Biomedical Sciences for Health (SCIBIS), Università degli Studi di Milano, Via G. Colombo 71, 20133, Milan, Italy
| | - Barbara Fossati
- IRCCS Policlinico San Donato, Piazza Malan 2, 20097, San Donato Milanese (MI), Italy
| | - Giovanni Meola
- Department of Biomedical Sciences for Health (SCIBIS), Università degli Studi di Milano, Via G. Colombo 71, 20133, Milan, Italy.,IRCCS Policlinico San Donato, Piazza Malan 2, 20097, San Donato Milanese (MI), Italy
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Cully TR, Murphy RM, Roberts L, Raastad T, Fassett RG, Coombes JS, Jayasinghe I, Launikonis BS. Human skeletal muscle plasmalemma alters its structure to change its Ca 2+-handling following heavy-load resistance exercise. Nat Commun 2017; 8:14266. [PMID: 28193999 PMCID: PMC5316829 DOI: 10.1038/ncomms14266] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2016] [Accepted: 12/08/2016] [Indexed: 01/30/2023] Open
Abstract
High-force eccentric exercise results in sustained increases in cytoplasmic Ca2+ levels ([Ca2+]cyto), which can cause damage to the muscle. Here we report that a heavy-load strength training bout greatly alters the structure of the membrane network inside the fibres, the tubular (t-) system, causing the loss of its predominantly transverse organization and an increase in vacuolation of its longitudinal tubules across adjacent sarcomeres. The transverse tubules and vacuoles displayed distinct Ca2+-handling properties. Both t-system components could take up Ca2+ from the cytoplasm but only transverse tubules supported store-operated Ca2+ entry. The retention of significant amounts of Ca2+ within vacuoles provides an effective mechanism to reduce the total content of Ca2+ within the fibre cytoplasm. We propose this ability can reduce or limit resistance exercise-induced, Ca2+-dependent damage to the fibre by the reduction of [Ca2+]cyto to help maintain fibre viability during the period associated with delayed onset muscle soreness.
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Affiliation(s)
- Tanya R. Cully
- School of Biomedical Sciences, The University of Queensland,
Brisbane, Queensland
4072, Australia
| | - Robyn M. Murphy
- Department of Biochemistry & Genetics, La Trobe Institute for
Molecular Science, La Trobe University, Melbourne, Victoria
3086, Australia
| | - Llion Roberts
- School of Human Movement and Nutritional Sciences, The University of
Queensland, Brisbane, Queensland
4072, Australia
- Centre of Excellence for Applied Sport Science Research, Queensland
Academy of Sport, Brisbane, Queensland
4111, Australia
| | - Truls Raastad
- Norwegian School of Sport Sciences, Oslo
N-0806, Norway
| | - Robert G. Fassett
- School of Human Movement and Nutritional Sciences, The University of
Queensland, Brisbane, Queensland
4072, Australia
| | - Jeff S. Coombes
- School of Human Movement and Nutritional Sciences, The University of
Queensland, Brisbane, Queensland
4072, Australia
| | - Izzy Jayasinghe
- School of Biomedical Sciences, The University of Queensland,
Brisbane, Queensland
4072, Australia
- School of Biomedical Sciences, University of Leeds,
Leeds
LS2 9JT, UK
| | - Bradley S. Launikonis
- School of Biomedical Sciences, The University of Queensland,
Brisbane, Queensland
4072, Australia
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14
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Hernández-Ochoa EO, Banks Q, Schneider MF. Acute Elevated Glucose Promotes Abnormal Action Potential-Induced Ca 2+ Transients in Cultured Skeletal Muscle Fibers. J Diabetes Res 2017; 2017:1509048. [PMID: 28835899 PMCID: PMC5557004 DOI: 10.1155/2017/1509048] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/19/2017] [Revised: 06/01/2017] [Accepted: 06/22/2017] [Indexed: 12/13/2022] Open
Abstract
A common comorbidity of diabetes is skeletal muscle dysfunction, which leads to compromised physical function. Previous studies of diabetes in skeletal muscle have shown alterations in excitation-contraction coupling (ECC)-the sequential link between action potentials (AP), intracellular Ca2+ release, and the contractile machinery. Yet, little is known about the impact of acute elevated glucose on the temporal properties of AP-induced Ca2+ transients and ionic underlying mechanisms that lead to muscle dysfunction. Here, we used high-speed confocal Ca2+ imaging to investigate the temporal properties of AP-induced Ca2+ transients, an intermediate step of ECC, using an acute in cellulo model of uncontrolled hyperglycemia (25 mM, 48 h.). Control and elevated glucose-exposed muscle fibers cultured for five days displayed four distinct patterns of AP-induced Ca2+ transients (phasic, biphasic, phasic-delayed, and phasic-slow decay); most control muscle fibers show phasic AP-induced Ca2+ transients, while most fibers exposed to elevated D-glucose displayed biphasic Ca2+ transients upon single field stimulation. We hypothesize that these changes in the temporal profile of the AP-induced Ca2+ transients are due to changes in the intrinsic excitable properties of the muscle fibers. We propose that these changes accompany early stages of diabetic myopathy.
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Affiliation(s)
- Erick O. Hernández-Ochoa
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, MD 21201, USA
- *Erick O. Hernández-Ochoa:
| | - Quinton Banks
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, MD 21201, USA
| | - Martin F. Schneider
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, MD 21201, USA
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15
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Cè E, Rampichini S, Monti E, Venturelli M, Limonta E, Esposito F. Changes in the electromechanical delay components during a fatiguing stimulation in human skeletal muscle: an EMG, MMG and force combined approach. Eur J Appl Physiol 2016; 117:95-107. [PMID: 27858153 DOI: 10.1007/s00421-016-3502-z] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2016] [Accepted: 11/09/2016] [Indexed: 11/29/2022]
Abstract
PURPOSE Peripheral fatigue involves electrochemical and mechanical mechanisms. An electromyographic, mechanomyographic and force combined approach may permit a kinetic evaluation of the changes at the synaptic, skeletal muscle fiber, and muscle-tendon unit level during a fatiguing stimulation. METHODS Surface electromyogram, mechanomyogram, force and stimulation current were detected from the gastrocnemius medialis muscle in twenty male participants during a fatiguing stimulation (twelve blocks of 35 Hz stimulations, duty cycle 9 s on/1 s off, duration 120 s). The total electromechanical delay and its three components (between stimulation current and electromyogram, synaptic component; between electromyogram and mechanomyogram signal onset, muscle fiber electrochemical component, and between mechanomyogram and force signal onset, mechanical component) were calculated. Interday reliability and sensitivity were determined. RESULTS After fatigue, peak force decreased by 48% (P < 0.05) and the total electromechanical delay and its synaptic, electrochemical and mechanical components lengthened from 25.8 ± 0.9, 1.47 ± 0.04, 11.2 ± 0.6, and 13.1 ± 1.3 ms to 29.0 ± 1.6, 1.56 ± 0.05, 12.4 ± 0.9, and 17.2 ± 0.6 ms, respectively (P < 0.05). During fatigue, the total electromechanical delay and the mechanical component increased significantly after the 40th second, and then remained stable. The synaptic and electrochemical components lengthened significantly after the 20th and 30th second, respectively. Interday reliability was high to very high, with an adequate level of sensitivity. CONCLUSIONS The kinetic evaluation of the delays during the fatiguing stimulation highlighted different onsets and kinetics, with the events at synaptic level being the first to reveal a significant elongation, followed by those at the intra-fiber level. The mechanical events, which were the most affected by fatigue, were the last to lengthen.
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Affiliation(s)
- Emiliano Cè
- Department of Biomedical Sciences for Health (SCIBIS), Università degli Studi di Milano, Via G. Colombo 71, 20133, Milan, Italy.
| | - Susanna Rampichini
- Department of Biomedical Sciences for Health (SCIBIS), Università degli Studi di Milano, Via G. Colombo 71, 20133, Milan, Italy
| | - Elena Monti
- Department of Biomedical Sciences for Health (SCIBIS), Università degli Studi di Milano, Via G. Colombo 71, 20133, Milan, Italy
| | - Massimo Venturelli
- Department of Biomedical Sciences for Health (SCIBIS), Università degli Studi di Milano, Via G. Colombo 71, 20133, Milan, Italy
| | - Eloisa Limonta
- Department of Biomedical Sciences for Health (SCIBIS), Università degli Studi di Milano, Via G. Colombo 71, 20133, Milan, Italy
| | - Fabio Esposito
- Department of Biomedical Sciences for Health (SCIBIS), Università degli Studi di Milano, Via G. Colombo 71, 20133, Milan, Italy
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16
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Jayasinghe ID, Clowsley AH, Munro M, Hou Y, Crossman DJ, Soeller C. Revealing T-Tubules in Striated Muscle with New Optical Super-Resolution Microscopy Techniquess. Eur J Transl Myol 2014; 25:4747. [PMID: 26913143 PMCID: PMC4748971 DOI: 10.4081/ejtm.2015.4747] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2014] [Accepted: 12/18/2014] [Indexed: 01/03/2023] Open
Abstract
The t-tubular system plays a central role in the synchronisation of calcium signalling and excitation-contraction coupling in most striated muscle cells. Light microscopy has been used for imaging t-tubules for well over 100 years and together with electron microscopy (EM), has revealed the three-dimensional complexities of the t-system topology within cardiomyocytes and skeletal muscle fibres from a range of species. The emerging super-resolution single molecule localisation microscopy (SMLM) techniques are offering a near 10-fold improvement over the resolution of conventional fluorescence light microscopy methods, with the ability to spectrally resolve nanometre scale distributions of multiple molecular targets. In conjunction with the next generation of electron microscopy, SMLM has allowed the visualisation and quantification of intricate t-tubule morphologies within large areas of muscle cells at an unprecedented level of detail. In this paper, we review recent advancements in the t-tubule structural biology with the utility of various microscopy techniques. We outline the technical considerations in adapting SMLM to study t-tubules and its potential to further our understanding of the molecular processes that underlie the sub-micron scale structural alterations observed in a range of muscle pathologies.
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Affiliation(s)
| | | | - Michelle Munro
- Department of Physiology, The University of Auckland , New Zealand
| | - Yufeng Hou
- Department of Physiology, The University of Auckland , New Zealand
| | - David J Crossman
- Department of Physiology, The University of Auckland , New Zealand
| | - Christian Soeller
- Biomedical Physics, University of Exeter, UK, New Zealand; Biomedical Physics, University of Exeter, UK, New Zealand
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17
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Cully TR, Edwards JN, Launikonis BS. Activation and propagation of Ca2+ release from inside the sarcoplasmic reticulum network of mammalian skeletal muscle. J Physiol 2014; 592:3727-46. [PMID: 24973406 DOI: 10.1113/jphysiol.2014.274274] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Skeletal muscle fibres are large and highly elongated cells specialized for producing the force required for posture and movement. The process of controlling the production of force within the muscle, known as excitation-contraction coupling, requires virtually simultaneous release of large amounts of Ca(2+) from the sarcoplasmic reticulum (SR) at the level of every sarcomere within the muscle fibre. Here we imaged Ca(2+) movements within the SR, tubular (t-) system and in the cytoplasm to observe that the SR of skeletal muscle is a connected network capable of allowing diffusion of Ca(2+) within its lumen to promote the propagation of Ca(2+) release throughout the fibre under conditions where inhibition of SR ryanodine receptors (RyRs) was reduced. Reduction of cytoplasmic [Mg(2+)] ([Mg(2+)]cyto) induced a leak of Ca(2+) through RyRs, causing a reduction in SR Ca(2+) buffering power argued to be due to a breakdown of SR calsequestrin polymers, leading to a local elevation of [Ca(2+)]SR. The local rise in [Ca(2+)]SR, an intra-SR Ca(2+) transient, induced a local diffusely rising [Ca(2+)]cyto. A prolonged Ca(2+) wave lasting tens of seconds or more was generated from these events. Ca(2+) waves were dependent on the diffusion of Ca(2+) within the lumen of the SR and ended as [Ca(2+)]SR dropped to low levels to inactivate RyRs. Inactivation of RyRs allowed re-accumulation of [Ca(2+)]SR and the activation of secondary Ca(2+) waves in the persistent presence of low [Mg(2+)]cyto if the threshold [Ca(2+)]SR for RyR opening could be reached. Secondary Ca(2+) waves occurred without an abrupt reduction in SR Ca(2+) buffering power. Ca(2+) release and wave propagation occurred in the absence of Ca(2+)-induced Ca(2+) release. These observations are consistent with the activation of Ca(2+) release through RyRs of lowered cytoplasmic inhibition by [Ca(2+)]SR or store overload-induced Ca(2+) release. Restitution of SR Ca(2+) buffering power to its initially high value required imposing normal resting ionic conditions in the cytoplasm, which re-imposed the normal resting inhibition on the RyRs, allowing [Ca(2+)]SR to return to endogenous levels without activation of store overload-induced Ca(2+) release. These results are discussed in the context of how pathophysiological Ca(2+) release such as that occurring in malignant hyperthermia can be generated.
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Affiliation(s)
- Tanya R Cully
- School of Biomedical Sciences, The University of Queensland, Brisbane, QLD, 4072, Australia
| | - Joshua N Edwards
- School of Biomedical Sciences, The University of Queensland, Brisbane, QLD, 4072, Australia
| | - Bradley S Launikonis
- School of Biomedical Sciences, The University of Queensland, Brisbane, QLD, 4072, Australia
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18
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Calderón JC, Bolaños P, Caputo C. The excitation-contraction coupling mechanism in skeletal muscle. Biophys Rev 2014; 6:133-160. [PMID: 28509964 PMCID: PMC5425715 DOI: 10.1007/s12551-013-0135-x] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2013] [Accepted: 12/06/2013] [Indexed: 12/27/2022] Open
Abstract
First coined by Alexander Sandow in 1952, the term excitation-contraction coupling (ECC) describes the rapid communication between electrical events occurring in the plasma membrane of skeletal muscle fibres and Ca2+ release from the SR, which leads to contraction. The sequence of events in twitch skeletal muscle involves: (1) initiation and propagation of an action potential along the plasma membrane, (2) spread of the potential throughout the transverse tubule system (T-tubule system), (3) dihydropyridine receptors (DHPR)-mediated detection of changes in membrane potential, (4) allosteric interaction between DHPR and sarcoplasmic reticulum (SR) ryanodine receptors (RyR), (5) release of Ca2+ from the SR and transient increase of Ca2+ concentration in the myoplasm, (6) activation of the myoplasmic Ca2+ buffering system and the contractile apparatus, followed by (7) Ca2+ disappearance from the myoplasm mediated mainly by its reuptake by the SR through the SR Ca2+ adenosine triphosphatase (SERCA), and under several conditions movement to the mitochondria and extrusion by the Na+/Ca2+ exchanger (NCX). In this text, we review the basics of ECC in skeletal muscle and the techniques used to study it. Moreover, we highlight some recent advances and point out gaps in knowledge on particular issues related to ECC such as (1) DHPR-RyR molecular interaction, (2) differences regarding fibre types, (3) its alteration during muscle fatigue, (4) the role of mitochondria and store-operated Ca2+ entry in the general ECC sequence, (5) contractile potentiators, and (6) Ca2+ sparks.
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Affiliation(s)
- Juan C Calderón
- Physiology and Biochemistry Research Group-Physis, Department of Physiology and Biochemistry, Faculty of Medicine, University of Antioquia UdeA, Calle 70 No 52-21, Medellín, Colombia.
- Laboratory of Cellular Physiology, Centre of Biophysics and Biochemistry, Venezuelan Institute for Scientific Research (IVIC), Caracas, Venezuela.
- Departamento de Fisiología y Bioquímica, Grupo de Investigación en Fisiología y Bioquímica-Physis, Facultad de Medicina, Universidad de Antioquia, Calle 70 No 52-21, Medellín, Colombia.
| | - Pura Bolaños
- Laboratory of Cellular Physiology, Centre of Biophysics and Biochemistry, Venezuelan Institute for Scientific Research (IVIC), Caracas, Venezuela
| | - Carlo Caputo
- Laboratory of Cellular Physiology, Centre of Biophysics and Biochemistry, Venezuelan Institute for Scientific Research (IVIC), Caracas, Venezuela
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19
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Rampichini S, Cè E, Limonta E, Esposito F. Effects of fatigue on the electromechanical delay components in gastrocnemius medialis muscle. Eur J Appl Physiol 2013; 114:639-51. [PMID: 24362940 DOI: 10.1007/s00421-013-2790-9] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2013] [Accepted: 12/03/2013] [Indexed: 12/19/2022]
Abstract
PURPOSE Under electrically evoked contractions, the time interval between the onset of the stimulation pulse (Stim) and the beginning of force (F) development can be partitioned (Delay(TOT)), by an electromyographic (EMG), mechanomyographic (MMG) and F combined approach, into three components each containing different parts of the electrochemical and mechanical processes underlying neuromuscular activation and contraction. The aim of the study was to evaluate inter- and intra-operator reliability of the measurements and to assess the effects of fatigue on the different Delay(TOT) components. METHODS Sixteen participants underwent two sets of tetanic stimulations of the gastrocnemius medialis muscle, with 10 min of rest in between. After a fatiguing protocol of 120 s, tetanic stimulations were replicated. The same protocol was repeated on a different day. Stim, EMG, MMG and F signals were recorded during contraction. Delay(TOT) and its three components (between Stim and EMG, Δt Stim-EMG; between EMG and MMG, Δt EMG-MMG and between MMG and F, Δt MMG-F) were calculated. RESULTS Before fatigue, Delay(TOT), Δt Stim-EMG, Δt EMG-MMG and Δt MMG-F lasted 27.5 ± 0.9, 1.4 ± 0.1, 9.2 ± 0.5 and 16.8 ± 0.7 ms, respectively. Fatigue lengthened Delay(TOT), Δt Stim-EMG, Δt EMG-MMG and Δt MMG-F by 18, 7, 16 and 22 %, respectively. Δt Stim-EMG, Δt EMG-MMG and Δt MMG-F contributed to Delay(TOT) lengthening by 2, 27 and 71 %, respectively. Reliability was always from high to very high. CONCLUSIONS The combined approach allowed a reliable calculation of the three contributors to Delay(TOT). The effects of fatigue on each Delay(TOT) component could be precisely assessed.
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Affiliation(s)
- Susanna Rampichini
- Department of Biomedical Sciences for Health, University of Milan, Via G. Colombo 71, 20133, Milan, Italy
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20
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Jayasinghe I, Launikonis BS. Three-dimensional reconstruction and analysis of the tubular system of vertebrate skeletal muscle. J Cell Sci 2013; 126:4048-58. [PMID: 23813954 DOI: 10.1242/jcs.131565] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/01/2024] Open
Abstract
Skeletal muscle fibres are very large and elongated. In response to excitation there must be a rapid and uniform release of Ca(2+) throughout for contraction. To ensure a uniform spread of excitation throughout the fibre to all the Ca(2+) release sites, the muscle internalizes the plasma membrane, to form the tubular (t-) system. Hence the t-system forms a complex and dense network throughout the fibre that is responsible for excitation-contraction coupling and other signalling mechanisms. However, we currently do not have a very detailed view of this membrane network because of limitations in previously used imaging techniques to visualize it. In this study we serially imaged fluorescent dye trapped in the t-system of fibres from rat and toad muscle using the confocal microscope, and deconvolved and reconstructed these images to produce the first three-dimensional reconstructions of large volumes of the vertebrate t-system. These images showed complex arrangements of tubules that have not been described previously and also allowed the association of the t-system with cellular organelles to be visualized. There was a high density of tubules close to the nuclear envelope because of the close and parallel alignment of the long axes of the myofibrils and the nuclei. Furthermore local fluorescence intensity variations from sub-resolution tubules were converted to tubule diameters. Mean diameters of tubules were 85.9±6.6 and 91.2±8.2 nm, from rat and toad muscle under isotonic conditions, respectively. Under osmotic stress the distribution of tubular diameters shifted significantly in toad muscle only, with change specifically occurring in the transverse but not longitudinal tubules.
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Affiliation(s)
- Izzy Jayasinghe
- School of Biomedical Science, The University of Queensland, Brisbane, QLD 4072, Australia
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21
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Jayasinghe I, Lo H, Morgan G, Baddeley D, Parton R, Soeller C, Launikonis B. Examination of the subsarcolemmal tubular system of mammalian skeletal muscle fibers. Biophys J 2013; 104:L19-21. [PMID: 23746530 PMCID: PMC3672866 DOI: 10.1016/j.bpj.2013.04.029] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2012] [Revised: 04/02/2013] [Accepted: 04/16/2013] [Indexed: 11/26/2022] Open
Abstract
A subsarcolemmal tubular system network (SSTN) has been detected in skeletal muscle fibers by confocal imaging after the removal of the sarcolemma. Here we confirm the existence and resolve the fine architecture and the localization of the SSTN at an unprecedented level of detail by examining extracellularly applied tubular system markers in skeletal muscle fiber preparations with a combination of three imaging modalities: confocal fluorescence microscopy, direct stochastic optical reconstruction microscopy, and tomographic electron microscopy. Three-dimensional reconstructions showed that the SSTN was a dense two-dimensional network within the subsarcolemmal space around the fiber, running ~500-600 nm underneath and parallel to the sarcolemma. The SSTN is composed of tubules ~95 nm in width with ~60% of the tubules directed transversely and >30% directed longitudinally. The deeper regular transverse tubules located at each A-I boundary of the sarcomeres branched from the SSTN, indicating individual transverse tubules that form triads are continuous with, but do not directly contact the sarcolemma. This suggests that the SSTN plays an important role in affecting the exchange of deeper tubule lumina with the extracellular space.
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Affiliation(s)
- Izzy Jayasinghe
- School of Biomedical Sciences, Faculty of Science, The University of Queensland, Brisbane, Australia
| | - Harriet P. Lo
- School of Molecular and Microbial Sciences, The University of Queensland, Brisbane, Australia
| | - Garry P. Morgan
- Institute for Molecular Bioscience and Centre for Microscopy and Microanalysis, The University of Queensland, Brisbane, Australia
| | - David Baddeley
- School of Medical Sciences, Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand
- Department of Cell Biology, Yale University, New Haven
| | - Robert G. Parton
- School of Molecular and Microbial Sciences, The University of Queensland, Brisbane, Australia
| | - Christian Soeller
- School of Medical Sciences, Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand
- School of Physics, The University of Exeter, United Kingdom
| | - Bradley S. Launikonis
- School of Biomedical Sciences, Faculty of Science, The University of Queensland, Brisbane, Australia
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22
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Kohl T, Westphal V, Hell SW, Lehnart SE. Superresolution microscopy in heart - cardiac nanoscopy. J Mol Cell Cardiol 2012; 58:13-21. [PMID: 23219451 DOI: 10.1016/j.yjmcc.2012.11.016] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/30/2012] [Revised: 11/03/2012] [Accepted: 11/24/2012] [Indexed: 12/23/2022]
Abstract
Detailed understanding of the adaptive nature of cardiac cells in health and disease requires investigation of proteins and membranes in their native physiological environment, ideally by noninvasive optical methods. However, conventional light microscopy does not resolve the spatial characteristics of small fluorescently labeled protein or membrane structures in cells. Due to diffraction limiting resolution to half the wavelength of light, adjacent fluorescent molecules spaced at less than ~250 nm are not separately visualized. This fundamental problem has lead to a rapidly growing area of research, superresolution fluorescence microscopy, also called nanoscopy. We discuss pioneering applications of superresolution microscopy relevant to the heart, emphasizing different nanoscopy strategies toward new insight in cardiac cell biology. Here, we focus on molecular and structural readouts from subcellular nanodomains and organelles related to Ca(2+) signaling during excitation-contraction (EC) coupling, including live cell imaging strategies. Based on existing data and superresolution techniques, we suggest that an important future aim will be subcellular in situ structure-function analysis with nanometric resolving power in organotypic cells.
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Affiliation(s)
- Tobias Kohl
- Heart Research Center Goettingen, University Medicine Goettingen, Germany
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23
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Hernández-Ochoa EO, Robison P, Contreras M, Shen T, Zhao Z, Schneider MF. Elevated extracellular glucose and uncontrolled type 1 diabetes enhance NFAT5 signaling and disrupt the transverse tubular network in mouse skeletal muscle. Exp Biol Med (Maywood) 2012; 237:1068-83. [PMID: 22966145 DOI: 10.1258/ebm.2012.012052] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The transcription factor nuclear factor of activated T-cells 5 (NFAT5) is a key protector from hypertonic stress in the kidney, but its role in skeletal muscle is unexamined. Here, we evaluate the effects of glucose hypertonicity and hyperglycemia on endogenous NFAT5 activity, transverse tubular system morphology and Ca(2+) signaling in adult murine skeletal muscle fibers. We found that exposure to elevated glucose (25-50 mmol/L) increased NFAT5 expression and nuclear translocation, and NFAT-driven transcriptional activity. These effects were insensitive to the inhibition of calcineurin A, but sensitive to both p38α mitogen-activated protein kinases and phosphoinositide 3-kinase-related kinase inhibition. Fibers exposed to elevated glucose exhibited disrupted transverse tubular morphology, characterized by swollen transverse tubules and an increase in longitudinal connections between adjacent transverse tubules. Ca(2+) transients elicited by a single, brief electric field stimuli were increased in amplitude in fibers challenged by elevated glucose. Muscle fibers from type 1 diabetic mice exhibited increased NFAT5 expression and transverse tubule disruptions, but no differences in electrically evoked Ca(2+) transients. Our results suggest the hypothesis that these changes in skeletal muscle could play a role in the pathophysiology of acute and severe hyperglycemic episodes commonly observed in uncontrolled diabetes.
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Affiliation(s)
- Erick O Hernández-Ochoa
- Department of Biochemistry and Molecular Biology, University of Maryland, School of Medicine, Baltimore, MD 21201, USA.
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