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Skov M, Ruijs TQ, Grønnebæk TS, Skals M, Riisager A, Winther JB, Dybdahl KLT, Findsen A, Morgen JJ, Huus N, Broch-Lips M, Nielsen OB, de Cuba CMKE, Heuberger JAAC, de Kam ML, Tannemaat M, Verschuuren JJGM, Knutsen LJS, Kelly NM, Jensen KG, Arnold WD, Burghes AH, Olesen C, Bold J, Petersen TK, Quiroz JA, Hutchison J, Chin ER, Groeneveld GJ, Pedersen TH. The ClC-1 chloride channel inhibitor NMD670 improves skeletal muscle function in rat models and patients with myasthenia gravis. Sci Transl Med 2024; 16:eadk9109. [PMID: 38507469 DOI: 10.1126/scitranslmed.adk9109] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2023] [Accepted: 02/23/2024] [Indexed: 03/22/2024]
Abstract
Myasthenia gravis (MG) is a neuromuscular disease that results in compromised transmission of electrical signals at the neuromuscular junction (NMJ) from motor neurons to skeletal muscle fibers. As a result, patients with MG have reduced skeletal muscle function and present with symptoms of severe muscle weakness and fatigue. ClC-1 is a skeletal muscle specific chloride (Cl-) ion channel that plays important roles in regulating neuromuscular transmission and muscle fiber excitability during intense exercise. Here, we show that partial inhibition of ClC-1 with an orally bioavailable small molecule (NMD670) can restore muscle function in rat models of MG and in patients with MG. In severely affected MG rats, ClC-1 inhibition enhanced neuromuscular transmission, restored muscle function, and improved mobility after both single and prolonged administrations of NMD670. On this basis, NMD670 was progressed through nonclinical safety pharmacology and toxicology studies, leading to approval for testing in clinical studies. After successfully completing phase 1 single ascending dose in healthy volunteers, NMD670 was tested in patients with MG in a randomized, placebo-controlled, single-dose, three-way crossover clinical trial. The clinical trial evaluated safety, pharmacokinetics, and pharmacodynamics of NMD670 in 12 patients with mild MG. NMD670 had a favorable safety profile and led to clinically relevant improvements in the quantitative myasthenia gravis (QMG) total score. This translational study spanning from single muscle fiber recordings to patients provides proof of mechanism for ClC-1 inhibition as a potential therapeutic approach in MG and supports further development of NMD670.
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Affiliation(s)
- Martin Skov
- NMD Pharma A/S, Palle Juul-Jensens Boulevard 82, 8200 Aarhus N, Denmark
| | - Titia Q Ruijs
- Centre for Human Drug Research, 2333 CL Leiden, Netherlands
- Leiden University Medical Centre, 2333 ZA Leiden, Netherlands
| | | | - Marianne Skals
- NMD Pharma A/S, Palle Juul-Jensens Boulevard 82, 8200 Aarhus N, Denmark
| | - Anders Riisager
- NMD Pharma A/S, Palle Juul-Jensens Boulevard 82, 8200 Aarhus N, Denmark
| | | | | | - Anders Findsen
- NMD Pharma A/S, Palle Juul-Jensens Boulevard 82, 8200 Aarhus N, Denmark
| | - Jeanette J Morgen
- NMD Pharma A/S, Palle Juul-Jensens Boulevard 82, 8200 Aarhus N, Denmark
| | - Nete Huus
- NMD Pharma A/S, Palle Juul-Jensens Boulevard 82, 8200 Aarhus N, Denmark
| | - Martin Broch-Lips
- NMD Pharma A/S, Palle Juul-Jensens Boulevard 82, 8200 Aarhus N, Denmark
| | - Ole B Nielsen
- NMD Pharma A/S, Palle Juul-Jensens Boulevard 82, 8200 Aarhus N, Denmark
- Department of Biomedicine, Aarhus University, Ole Worms Alle 4, 8000 Aarhus C, Denmark
| | - Catherine M K E de Cuba
- Centre for Human Drug Research, 2333 CL Leiden, Netherlands
- Leiden University Medical Centre, 2333 ZA Leiden, Netherlands
| | | | | | | | | | - Lars J S Knutsen
- NMD Pharma A/S, Palle Juul-Jensens Boulevard 82, 8200 Aarhus N, Denmark
| | - Nicholas M Kelly
- NMD Pharma A/S, Palle Juul-Jensens Boulevard 82, 8200 Aarhus N, Denmark
| | - Klaus G Jensen
- NMD Pharma A/S, Palle Juul-Jensens Boulevard 82, 8200 Aarhus N, Denmark
| | - William D Arnold
- NextGen Precision Health, University of Missouri, 1030 Hitt St, Columbia, MO 65212, USA
| | - Arthur H Burghes
- Department of Biological Chemistry and Pharmacology, Ohio State University Wexner Medical Center, 1060 Carmack Road, Columbus, OH 43210, USA
- Department of Neurology, Neuromuscular Division, Ohio State University Wexner Medical Center, 395 W. 12(th) Ave, Columbus, OH 43210, USA
| | - Claus Olesen
- NMD Pharma A/S, Palle Juul-Jensens Boulevard 82, 8200 Aarhus N, Denmark
- Department of Biomedicine, Aarhus University, Ole Worms Alle 4, 8000 Aarhus C, Denmark
| | - Jane Bold
- NMD Pharma A/S, Palle Juul-Jensens Boulevard 82, 8200 Aarhus N, Denmark
| | - Thomas K Petersen
- NMD Pharma A/S, Palle Juul-Jensens Boulevard 82, 8200 Aarhus N, Denmark
| | - Jorge A Quiroz
- NMD Pharma A/S, Palle Juul-Jensens Boulevard 82, 8200 Aarhus N, Denmark
| | - John Hutchison
- NMD Pharma A/S, Palle Juul-Jensens Boulevard 82, 8200 Aarhus N, Denmark
| | - Eva R Chin
- NMD Pharma A/S, Palle Juul-Jensens Boulevard 82, 8200 Aarhus N, Denmark
| | - Geert J Groeneveld
- Centre for Human Drug Research, 2333 CL Leiden, Netherlands
- Leiden University Medical Centre, 2333 ZA Leiden, Netherlands
| | - Thomas H Pedersen
- NMD Pharma A/S, Palle Juul-Jensens Boulevard 82, 8200 Aarhus N, Denmark
- Department of Biomedicine, Aarhus University, Ole Worms Alle 4, 8000 Aarhus C, Denmark
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Cairns SP, Renaud JM. The potassium-glycogen interaction on force and excitability in mouse skeletal muscle: implications for fatigue. J Physiol 2023; 601:5669-5687. [PMID: 37934587 DOI: 10.1113/jp285129] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2023] [Accepted: 10/17/2023] [Indexed: 11/08/2023] Open
Abstract
A reduced muscle glycogen content and potassium (K+ ) disturbances across muscle membranes occur concomitantly during repeated intense exercise and together may contribute to skeletal muscle fatigue. Therefore, we examined whether raised extracellular K+ concentration ([K+ ]o ) (4 to 11 mM) interacts with lowered glycogen to reduce force production. Isometric contractions were evoked in isolated mouse soleus muscles (37°C) using direct supramaximal field stimulation. (1) Glycogen declined markedly in non-fatigued muscle with >2 h exposure in glucose-free physiological saline compared with control solutions (11 mM glucose), i.e. to <45% control. (2) Severe glycogen depletion was associated with increased 5'-AMP-activated protein kinase activity, indicative of metabolic stress. (3) The decline of peak tetanic force at 11 mM [K+ ]o was exacerbated from 67% initial at normal glycogen to 22% initial at lowered glycogen. This was due to a higher percentage of inexcitable fibres (71% vs. 43%), yet without greater sarcolemmal depolarisation or smaller amplitude action potentials. (4) Returning glucose while at 11 mM [K+ ]o increased both glycogen and force. (5) Exposure to 4 mM [K+ ]o glucose-free solutions (15 min) did not increase fatiguability during repeated tetani; however, after recovery there was a greater force decline at 11 mM [K+ ]o at lower than normal glycogen. (6) An important exponential relationship was established between relative peak tetanic force at 11 mM [K+ ]o and muscle glycogen content. These findings provide direct evidence of a synergistic interaction between raised [K+ ]o and lowered muscle glycogen as the latter shifts the peak tetanic force-resting EM relationship towards more negative resting EM due to lowered sarcolemmal excitability, which hence may contribute to muscle fatigue. KEY POINTS: Diminished muscle glycogen levels and raised extracellular potassium concentrations ([K+ ]o ) occur simultaneously during intense exercise and together may contribute to muscle fatigue. Prolonged exposure of isolated non-fatigued soleus muscles of mice to glucose-free physiological saline solutions markedly lowered muscle glycogen levels, as does fatigue then recovery in glucose-free solutions. For both approaches, the subsequent decline of maximal force at 11 mM [K+ ]o , which mimics interstitial [K+ ] levels during intense exercise, was exacerbated at lowered compared with normal glycogen. This was mainly due to many more muscle fibres becoming inexcitable. We established an important relationship that provides evidence of a synergistic interaction between raised [K+ ]o and lowered glycogen content to reduce force production. This paper indicates that partially lowered muscle glycogen (and/or metabolic stress) together with elevated interstitial [K+ ] interactively lowers muscle force, and hence may diminish performance especially during repeated high-intensity exercise.
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Affiliation(s)
- Simeon P Cairns
- SPRINZ, School of Sport and Recreation, Faculty of Health and Environmental Sciences, Auckland University of Technology, New Zealand
- Health and Rehabilitation Research Institute, Faculty of Health and Environmental Sciences, Auckland University of Technology, New Zealand
| | - Jean-Marc Renaud
- Department of Cellular and Molecular Medicine, Neuromuscular Research Center, University of Ottawa, Ottawa, Ontario, Canada
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Renaud JM, Ørtenblad N, McKenna MJ, Overgaard K. Exercise and fatigue: integrating the role of K +, Na + and Cl - in the regulation of sarcolemmal excitability of skeletal muscle. Eur J Appl Physiol 2023; 123:2345-2378. [PMID: 37584745 PMCID: PMC10615939 DOI: 10.1007/s00421-023-05270-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2023] [Accepted: 06/29/2023] [Indexed: 08/17/2023]
Abstract
Perturbations in K+ have long been considered a key factor in skeletal muscle fatigue. However, the exercise-induced changes in K+ intra-to-extracellular gradient is by itself insufficiently large to be a major cause for the force decrease during fatigue unless combined to other ion gradient changes such as for Na+. Whilst several studies described K+-induced force depression at high extracellular [K+] ([K+]e), others reported that small increases in [K+]e induced potentiation during submaximal activation frequencies, a finding that has mostly been ignored. There is evidence for decreased Cl- ClC-1 channel activity at muscle activity onset, which may limit K+-induced force depression, and large increases in ClC-1 channel activity during metabolic stress that may enhance K+ induced force depression. The ATP-sensitive K+ channel (KATP channel) is also activated during metabolic stress to lower sarcolemmal excitability. Taking into account all these findings, we propose a revised concept in which K+ has two physiological roles: (1) K+-induced potentiation and (2) K+-induced force depression. During low-moderate intensity muscle contractions, the K+-induced force depression associated with increased [K+]e is prevented by concomitant decreased ClC-1 channel activity, allowing K+-induced potentiation of sub-maximal tetanic contractions to dominate, thereby optimizing muscle performance. When ATP demand exceeds supply, creating metabolic stress, both KATP and ClC-1 channels are activated. KATP channels contribute to force reductions by lowering sarcolemmal generation of action potentials, whilst ClC-1 channel enhances the force-depressing effects of K+, thereby triggering fatigue. The ultimate function of these changes is to preserve the remaining ATP to prevent damaging ATP depletion.
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Affiliation(s)
- Jean-Marc Renaud
- Faculty of Medicine, Department of Cellular and Molecular Medicine, University of Ottawa, 451 Smyth Rd., Ottawa, ON, K1H 8M5, Canada.
| | - Niels Ørtenblad
- Department of Sports Science and Clinical Biomechanics, University of Southern Denmark, Odense, Denmark
| | - Michael J McKenna
- Institute for Health and Sport, Victoria University, Melbourne, VIC, 8001, Australia
- College of Physical Education, Southwest University, Chongqing, China
- College of Sport Science, Zhuhai College of Science and Technology, Zhuhai, China
| | - Kristian Overgaard
- Exercise Biology, Department of Public Health, Aarhus University, Aarhus, Denmark
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Wang J, Rindom E, Groennebaek T, Sieljacks P, Jakobsgaard JE, Farup J, Vissing K, Pedersen TH, de Paoli FV. Six weeks of high-load resistance and low-load blood flow restricted training increase Na/K-ATPase sub-units α2 and β1 equally, but does not alter ClC-1 abundance in untrained human skeletal muscle. J Muscle Res Cell Motil 2023; 44:25-36. [PMID: 37014477 DOI: 10.1007/s10974-023-09644-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2022] [Accepted: 02/08/2023] [Indexed: 04/05/2023]
Abstract
Contractile function of skeletal muscle relies on the ability of muscle fibers to trigger and propagate action potentials (APs). These electrical signals are created by transmembrane ion transport through ion channels and membrane transporter systems. In this regard, the Cl- ion channel 1 (ClC-1) and the Na+/K--ATPase (NKA) are central for maintaining ion homeostasis across the sarcolemma during intense contractile activity. Therefore, this randomized controlled trial aimed to investigate the changes in ClC-1 and specific NKA subunit isoform expression in response to six weeks (18 training sessions) of high-load resistance exercise (HLRE) and low-load blood flow restricted resistance exercise (BFRRE), respectively. HLRE was conducted as 4 sets of 12 repetitions of knee extensions performed at 70% of 1 repetition maximum (RM), while BFRRE was conducted as 4 sets of knee extensions at 30% of 1RM performed to volitional fatigue. Furthermore, the potential associations between protein expression and contractile performance were investigated. We show that muscle ClC-1 abundance was not affected by either exercise modality, whereas NKA subunit isoforms [Formula: see text]2 and [Formula: see text]1 increased equally by appx. 80-90% with BFRRE (p < 0.05) and 70-80% with HLRE (p < 0.05). No differential impact between exercise modalities was observed. At baseline, ClC-1 protein expression correlated inversely with dynamic knee extensor strength (r=-0.365, p = 0.04), whereas no correlation was observed between NKA subunit content and contractile performance at baseline. However, training-induced changes in NKA [Formula: see text]2 subunit (r = 0.603, p < 0.01) and [Formula: see text]1 subunit (r = 0.453, p < 0.05) correlated with exercise-induced changes in maximal voluntary contraction. These results suggest that the initial adaptation to resistance-based exercise does not involve changes in ClC-1 abundance in untrained skeletal muscle, and that increased content of NKA subunits may facilitate increases in maximal force production.
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Affiliation(s)
- Jakob Wang
- Section for Sport Science, Department of Public Health, Aarhus University, Aarhus, Denmark
| | - Emil Rindom
- Department of Zoophysiology, Aarhus University, Aarhus, Denmark
| | - Thomas Groennebaek
- Section for Sport Science, Department of Public Health, Aarhus University, Aarhus, Denmark
| | - Peter Sieljacks
- Section for Sport Science, Department of Public Health, Aarhus University, Aarhus, Denmark
| | | | - Jean Farup
- Department of Biomedicine - Physiology, Aarhus University, Ole Worms Allé, Building 1163, Aarhus C, DK-8000, Denmark
- Steno Diabetes Center Aarhus, Aarhus, Denmark
| | - Kristian Vissing
- Section for Sport Science, Department of Public Health, Aarhus University, Aarhus, Denmark
| | - Thomas Holm Pedersen
- Department of Biomedicine - Physiology, Aarhus University, Ole Worms Allé, Building 1163, Aarhus C, DK-8000, Denmark
| | - Frank Vincenzo de Paoli
- Department of Biomedicine - Physiology, Aarhus University, Ole Worms Allé, Building 1163, Aarhus C, DK-8000, Denmark.
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Wang X, Nawaz M, DuPont C, Myers JH, Burke SR, Bannister RA, Foy BD, Voss AA, Rich MM. The role of action potential changes in depolarization-induced failure of excitation contraction coupling in mouse skeletal muscle. eLife 2022; 11:71588. [PMID: 34985413 PMCID: PMC8730720 DOI: 10.7554/elife.71588] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2021] [Accepted: 12/24/2021] [Indexed: 12/24/2022] Open
Abstract
Excitation-contraction coupling (ECC) is the process by which electrical excitation of muscle is converted into force generation. Depolarization of skeletal muscle resting potential contributes to failure of ECC in diseases such as periodic paralysis, intensive care unit acquired weakness and possibly fatigue of muscle during vigorous exercise. When extracellular K+ is raised to depolarize the resting potential, failure of ECC occurs suddenly, over a narrow range of resting potentials. Simultaneous imaging of Ca2+ transients and recording of action potentials (APs) demonstrated failure to generate Ca2+ transients when APs peaked at potentials more negative than -30mV. An AP property that closely correlated with failure of the Ca2+ transient was the integral of AP voltage with respect to time. Simultaneous recording of Ca2+ transients and APs with electrodes separated by 1.6mm revealed AP conduction fails when APs peak below -21mV. We hypothesize propagation of APs and generation of Ca2+ transients are governed by distinct AP properties: AP conduction is governed by AP peak, whereas Ca2+ release from the sarcoplasmic reticulum is governed by AP integral. The reason distinct AP properties may govern distinct steps of ECC is the kinetics of the ion channels involved. Na channels, which govern propagation, have rapid kinetics and are insensitive to AP width (and thus AP integral) whereas Ca2+ release is governed by gating charge movement of Cav1.1 channels, which have slower kinetics such that Ca2+ release is sensitive to AP integral. The quantitative relationships established between resting potential, AP properties, AP conduction and Ca2+ transients provide the foundation for future studies of failure of ECC induced by depolarization of the resting potential.
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Affiliation(s)
- Xueyong Wang
- Wright State University, Department of Neuroscience, Cell Biology, and Physiology, Dayton, United States
| | - Murad Nawaz
- Wright State University, Department of Neuroscience, Cell Biology, and Physiology, Dayton, United States
| | - Chris DuPont
- Wright State University, Department of Neuroscience, Cell Biology, and Physiology, Dayton, United States
| | - Jessica H Myers
- Wright State University, Department of Neuroscience, Cell Biology, and Physiology, Dayton, United States
| | - Steve Ra Burke
- Wright State University, Department of Biological Sciences, Dayton, United States
| | - Roger A Bannister
- University of Maryland School of Medicine, Departments of Pathology/Biochemistry & Molecular Biology, Baltimore, United States
| | - Brent D Foy
- Wright State University, Department of Physics, Dayton, United States
| | - Andrew A Voss
- Wright State University, Department of Biological Sciences, Dayton, United States
| | - Mark M Rich
- Wright State University, Department of Neuroscience, Cell Biology, and Physiology, Dayton, United States
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Leermakers PA, Skov M, Riisager A, Nielsen OB, Pedersen TH. Alterations in fast-twitch muscle membrane conductance regulation do not explain decreased muscle function of SOD1 G93A rats. Muscle Nerve 2021; 64:755-764. [PMID: 34486134 DOI: 10.1002/mus.27413] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2021] [Revised: 08/29/2021] [Accepted: 08/31/2021] [Indexed: 11/06/2022]
Abstract
INTRODUCTION/AIMS Both neuromuscular junction (NMJ) dysfunction and altered electrophysiological properties of muscle fibers have been reported in amyotrophic lateral sclerosis (ALS) patients. ALS-related preclinical studies typically use rodent SOD1G93A overexpression models, but translation to the human disease has been challenged. The present work explored NMJ function and cellular electrophysiological properties of muscles fibers in SOD1G93A overexpression rats. METHODS Longitudinal studies of compound muscle action potentials (CMAPs) were performed in SOD1G93A rats. Cellular studies were performed to evaluate electrophysiological properties of muscle fibers, including the resting membrane conductance (Gm ) and its regulation during prolonged action potential (AP) firing. RESULTS SOD1G93A rats showed a substantial loss of gastrocnemius CMAP amplitude (35.8 mV, P < .001) and a minor increase in CMAP decrement (8.5%, P = .002) at 25 weeks. In addition, SOD1G93A EDL muscle fibers showed a lower baseline Gm (wild-type, 1325 μS/cm2 ; SOD1G93A , 1137 μS/cm2 ; P < .001) and minor alterations in Gm regulation during repeated firing of APs as compared with wild-type rats. DISCUSSION The current data suggest that loss of CMAP amplitude is largely explained by defects in either lower motor neuron or skeletal muscle with only minor indications of a role for neuromuscular transmission defects in SOD1G93A rats. Electrophysiological properties of muscle fibers were not markedly affected, and an elevated Gm , as has been reported in motor neuron disease (MND) patients, was not replicated in SOD1G93A muscles. Collectively, the neuromuscular pathology of SOD1G93A rats appears to differ from that of ALS/MND patients with respect to neuromuscular transmission defects and electrophysiological properties of muscle fibers.
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Affiliation(s)
| | - Martin Skov
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
| | - Anders Riisager
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
| | - Ole B Nielsen
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
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7
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Clerx M, Mirams GR, Rogers AJ, Narayan SM, Giles WR. Immediate and Delayed Response of Simulated Human Atrial Myocytes to Clinically-Relevant Hypokalemia. Front Physiol 2021; 12:651162. [PMID: 34122128 PMCID: PMC8188899 DOI: 10.3389/fphys.2021.651162] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2021] [Accepted: 03/22/2021] [Indexed: 12/18/2022] Open
Abstract
Although plasma electrolyte levels are quickly and precisely regulated in the mammalian cardiovascular system, even small transient changes in K+, Na+, Ca2+, and/or Mg2+ can significantly alter physiological responses in the heart, blood vessels, and intrinsic (intracardiac) autonomic nervous system. We have used mathematical models of the human atrial action potential (AP) to explore the electrophysiological mechanisms that underlie changes in resting potential (Vr) and the AP following decreases in plasma K+, [K+]o, that were selected to mimic clinical hypokalemia. Such changes may be associated with arrhythmias and are commonly encountered in patients (i) in therapy for hypertension and heart failure; (ii) undergoing renal dialysis; (iii) with any disease with acid-base imbalance; or (iv) post-operatively. Our study emphasizes clinically-relevant hypokalemic conditions, corresponding to [K+]o reductions of approximately 1.5 mM from the normal value of 4 to 4.5 mM. We show how the resulting electrophysiological responses in human atrial myocytes progress within two distinct time frames: (i) Immediately after [K+]o is reduced, the K+-sensing mechanism of the background inward rectifier current (IK1) responds. Specifically, its highly non-linear current-voltage relationship changes significantly as judged by the voltage dependence of its region of outward current. This rapidly alters, and sometimes even depolarizes, Vr and can also markedly prolong the final repolarization phase of the AP, thus modulating excitability and refractoriness. (ii) A second much slower electrophysiological response (developing 5-10 minutes after [K+]o is reduced) results from alterations in the intracellular electrolyte balance. A progressive shift in intracellular [Na+]i causes a change in the outward electrogenic current generated by the Na+/K+ pump, thereby modifying Vr and AP repolarization and changing the human atrial electrophysiological substrate. In this study, these two effects were investigated quantitatively, using seven published models of the human atrial AP. This highlighted the important role of IK1 rectification when analyzing both the mechanisms by which [K+]o regulates Vr and how the AP waveform may contribute to "trigger" mechanisms within the proarrhythmic substrate. Our simulations complement and extend previous studies aimed at understanding key factors by which decreases in [K+]o can produce effects that are known to promote atrial arrhythmias in human hearts.
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Affiliation(s)
- Michael Clerx
- Centre for Mathematical Medicine and Biology, School of Mathematical Sciences, University of Nottingham, Nottingham, United Kingdom
| | - Gary R Mirams
- Centre for Mathematical Medicine and Biology, School of Mathematical Sciences, University of Nottingham, Nottingham, United Kingdom
| | - Albert J Rogers
- Department of Medicine and Cardiovascular Institute, Stanford University, Stanford, CA, United States
| | - Sanjiv M Narayan
- Department of Medicine and Cardiovascular Institute, Stanford University, Stanford, CA, United States
| | - Wayne R Giles
- Department of Physiology and Pharmacology, University of Calgary, Calgary, AB, Canada
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Leermakers PA, Dybdahl KLT, Husted KS, Riisager A, de Paoli FV, Pinós T, Vissing J, Krag TOB, Pedersen TH. Depletion of ATP Limits Membrane Excitability of Skeletal Muscle by Increasing Both ClC1-Open Probability and Membrane Conductance. Front Neurol 2020; 11:541. [PMID: 32655483 PMCID: PMC7325937 DOI: 10.3389/fneur.2020.00541] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2020] [Accepted: 05/14/2020] [Indexed: 12/20/2022] Open
Abstract
Activation of skeletal muscle contractions require that action potentials can be excited and propagated along the muscle fibers. Recent studies have revealed that muscle fiber excitability is regulated during repeated firing of action potentials by cellular signaling systems that control the function of ion channel that determine the resting membrane conductance (Gm). In fast-twitch muscle, prolonged firing of action potentials triggers a marked increase in Gm, reducing muscle fiber excitability and causing action potential failure. Both ClC-1 and KATP ion channels contribute to this Gm rise, but the exact molecular regulation underlying their activation remains unclear. Studies in expression systems have revealed that ClC-1 is able to bind adenosine nucleotides, and that low adenosine nucleotide levels result in ClC-1 activation. In three series of experiments, this study aimed to explore whether ClC-1 is also regulated by adenosine nucleotides in native skeletal muscle fibers, and whether the adenosine nucleotide sensitivity of ClC-1 could explain the rise in Gm muscle fibers during prolonged action potential firing. First, whole cell patch clamping of mouse muscle fibers demonstrated that ClC-1 activation shifted in the hyperpolarized direction when clamping pipette solution contained 0 mM ATP compared with 5 mM ATP. Second, three-electrode Gm measurement during muscle fiber stimulation showed that glycolysis inhibition, with 2-deoxy-glucose or iodoacetate, resulted in an accelerated and rapid >400% Gm rise during short periods of repeated action potential firing in both fast-twitch and slow-twitch rat, and in human muscle fibers. Moreover, ClC-1 inhibition with 9-anthracenecarboxylic acid resulted in either an absence or blunted Gm rise during action potential firing in human muscle fibers. Third, Gm measurement during repeated action potential firing in muscle fibers from a murine McArdle disease model suggest that the rise in Gm was accelerated in a subset of fibers. Together, these results are compatible with ClC-1 function being regulated by the level of adenosine nucleotides in native tissue, and that the channel operates as a sensor of skeletal muscle metabolic state, limiting muscle excitability when energy status is low.
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Affiliation(s)
| | | | | | - Anders Riisager
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
| | | | - Tomàs Pinós
- Mitochondrial and Neuromuscular Disorders Unit, Vall d'Hebron Institut de Recerca, Universitat Autònoma de Barcelona, Barcelona, Spain.,Centro de Investigación Biomédica en Red de Enfermedades Raras (CIBERER), Madrid, Spain
| | - John Vissing
- Department of Neurology, Rigshospitalet, Copenhagen Neuromuscular Center, University of Copenhagen, Copenhagen, Denmark
| | - Thomas Oliver Brøgger Krag
- Department of Neurology, Rigshospitalet, Copenhagen Neuromuscular Center, University of Copenhagen, Copenhagen, Denmark
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9
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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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Bækgaard Nielsen O, de Paoli FV, Riisager A, Pedersen TH. Chloride Channels Take Center Stage in Acute Regulation of Excitability in Skeletal Muscle: Implications for Fatigue. Physiology (Bethesda) 2017; 32:425-434. [DOI: 10.1152/physiol.00006.2015] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2015] [Revised: 07/14/2017] [Accepted: 08/02/2017] [Indexed: 01/28/2023] Open
Abstract
Initiation and propagation of action potentials in muscle fibers is a key element in the transmission of activating motor input from the central nervous system to their contractile apparatus, and maintenance of excitability is therefore paramount for their endurance during work. Here, we review current knowledge about the acute regulation of ClC-1 channels in active muscles and its importance for muscle excitability, function, and fatigue.
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Affiliation(s)
| | | | - Anders Riisager
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
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Pedersen TH, Riisager A, de Paoli FV, Chen TY, Nielsen OB. Role of physiological ClC-1 Cl- ion channel regulation for the excitability and function of working skeletal muscle. ACTA ACUST UNITED AC 2016; 147:291-308. [PMID: 27022190 PMCID: PMC4810071 DOI: 10.1085/jgp.201611582] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2016] [Accepted: 03/07/2016] [Indexed: 12/13/2022]
Abstract
Electrical membrane properties of skeletal muscle fibers have been thoroughly studied over the last five to six decades. This has shown that muscle fibers from a wide range of species, including fish, amphibians, reptiles, birds, and mammals, are all characterized by high resting membrane permeability for Cl− ions. Thus, in resting human muscle, ClC-1 Cl− ion channels account for ∼80% of the membrane conductance, and because active Cl− transport is limited in muscle fibers, the equilibrium potential for Cl− lies close to the resting membrane potential. These conditions—high membrane conductance and passive distribution—enable ClC-1 to conduct membrane current that inhibits muscle excitability. This depressing effect of ClC-1 current on muscle excitability has mostly been associated with skeletal muscle hyperexcitability in myotonia congenita, which arises from loss-of-function mutations in the CLCN1 gene. However, given that ClC-1 must be drastically inhibited (∼80%) before myotonia develops, more recent studies have explored whether acute and more subtle ClC-1 regulation contributes to controlling the excitability of working muscle. Methods were developed to measure ClC-1 function with subsecond temporal resolution in action potential firing muscle fibers. These and other techniques have revealed that ClC-1 function is controlled by multiple cellular signals during muscle activity. Thus, onset of muscle activity triggers ClC-1 inhibition via protein kinase C, intracellular acidosis, and lactate ions. This inhibition is important for preserving excitability of working muscle in the face of activity-induced elevation of extracellular K+ and accumulating inactivation of voltage-gated sodium channels. Furthermore, during prolonged activity, a marked ClC-1 activation can develop that compromises muscle excitability. Data from ClC-1 expression systems suggest that this ClC-1 activation may arise from loss of regulation by adenosine nucleotides and/or oxidation. The present review summarizes the current knowledge of the physiological factors that control ClC-1 function in active muscle.
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Affiliation(s)
| | - Anders Riisager
- Department of Biomedicine, Aarhus University, 8000 Aarhus C, Denmark
| | | | - Tsung-Yu Chen
- Center for Neuroscience and Department of Neurology, University of California, Davis, Davis, CA 95618 Center for Neuroscience and Department of Neurology, University of California, Davis, Davis, CA 95618
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Riisager A, de Paoli FV, Yu WP, Pedersen TH, Chen TY, Nielsen OB. Protein kinase C-dependent regulation of ClC-1 channels in active human muscle and its effect on fast and slow gating. J Physiol 2016; 594:3391-406. [PMID: 26857341 DOI: 10.1113/jp271556] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2015] [Accepted: 01/26/2016] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Regulation of ion channel function during repeated firing of action potentials is commonly observed in excitable cells. Recently it was shown that muscle activity is associated with rapid, protein kinase C (PKC)-dependent ClC-1 Cl(-) channel inhibition in rodent muscle. While this PKC-dependent ClC-1 inhibition during muscle activity was shown to be important for the maintenance of contractile endurance in rat muscle it is unknown whether a similar regulation exists in human muscle. Also, the molecular mechanisms underlying the observed PKC-dependent ClC-1 inhibition are unclear. Here we present the first demonstration of ClC-1 inhibition in active human muscle fibres, and we determine the changes in ClC-1 gating that underlie the PKC-dependent ClC-1 inhibition in active muscle using human ClC-1 expressed in Xenopus oocytes. This activity-induced ClC-1 inhibition is suggested to represent a mechanism by which human muscle fibres maintain their excitability during sustained activity. ABSTRACT Repeated firing of action potentials (APs) is known to trigger rapid, protein kinase C (PKC)-dependent inhibition of ClC-1 Cl(-) ion channels in rodent muscle and this inhibition is important for contractile endurance. It is currently unknown whether similar regulation exists in human muscle, and the molecular mechanisms underlying PKC-dependent ClC-1 inhibition are unclear. This study first determined whether PKC-dependent ClC-1 inhibition exists in active human muscle, and second, it clarified how PKC alters the gating of human ClC-1 expressed in Xenopus oocytes. In human abdominal and intercostal muscles, repeated AP firing was associated with 30-60% reduction of ClC-1 function, which could be completely prevented by PKC inhibition (1 μm GF109203X). The role of the PKC-dependent ClC-1 inhibition was evaluated from rheobase currents before and after firing 1000 APs: while rheobase current was well maintained after activity under control conditions it rose dramatically if PKC-dependent ClC-1 inhibition had been prevented with the inhibitor. This demonstrates that the ClC-1 inhibition is important for maintenance of excitability in active human muscle fibres. Oocyte experiments showed that PKC activation lowered the overall open probability of ClC-1 in the voltage range relevant for AP initiation in muscle fibres. More detailed analysis of this reduction showed that PKC mostly affected the slow gate of ClC-1. Indeed, there was no effect of PKC activation in C277S mutated ClC-1 in which the slow gate is effectively locked open. It is concluded that regulation of excitability of active human muscle fibres relies on PKC-dependent ClC-1 inhibition via a gating mechanism.
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Affiliation(s)
- Anders Riisager
- Department of Biomedicine, Aarhus University, Ole Worms Allé 4, 8000, Aarhus C, Denmark.,Centre for Neuroscience and Department of Neurology, University of California, Davis, CA, 95618, USA
| | - Frank Vincenzo de Paoli
- Department of Biomedicine, Aarhus University, Ole Worms Allé 4, 8000, Aarhus C, Denmark.,Department of Cardiothoracic and Vascular Surgery, Aarhus University Hospital, Palle Juul-Jensens Boulevard 99, 8200, Aarhus N, Denmark
| | - Wei-Ping Yu
- Centre for Neuroscience and Department of Neurology, University of California, Davis, CA, 95618, USA
| | - Thomas Holm Pedersen
- Department of Biomedicine, Aarhus University, Ole Worms Allé 4, 8000, Aarhus C, Denmark
| | - Tsung-Yu Chen
- Centre for Neuroscience and Department of Neurology, University of California, Davis, CA, 95618, USA
| | - Ole Baekgaard Nielsen
- Department of Biomedicine, Aarhus University, Ole Worms Allé 4, 8000, Aarhus C, Denmark
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