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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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2
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Cairns SP. Potassium effects on skeletal muscle contraction: are potassium-metabolic interactions required for fatigue? Eur J Appl Physiol 2023; 123:2341-2343. [PMID: 37728786 DOI: 10.1007/s00421-023-05313-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2023] [Accepted: 08/24/2023] [Indexed: 09/21/2023]
Affiliation(s)
- Simeon P Cairns
- SPRINZ, School of Sport and Recreation, Auckland University of Technology, Auckland, New Zealand.
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3
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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: 4] [Impact Index Per Article: 4.0] [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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4
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Leijding C, Viken I, Bruton JD, Andersson DC, Cheng AJ, Westerblad H. Increased tetanic calcium in early fatigue of mammalian muscle fibers is accompanied by accelerated force development despite a decreased force. FASEB J 2023; 37:e22978. [PMID: 37191967 DOI: 10.1096/fj.202300401r] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2023] [Revised: 04/18/2023] [Accepted: 05/05/2023] [Indexed: 05/17/2023]
Abstract
During the initial phase of fatigue induced by repeated contractions in fast-twitch muscle fibers, tetanic force decreases despite increasing tetanic free cytosolic [Ca2+ ] ([Ca2+ ]cyt ). Here, we hypothesized that the increase in tetanic [Ca2+ ]cyt nevertheless has positive effects on force in early fatigue. Experiments on enzymatically isolated mouse flexor digitorum brevis (FDB) fibers showed that an increase in tetanic [Ca2+ ]cyt during ten 350 ms contractions required trains of electrical pulses to be elicited at short intervals (≤2 s) and at high frequencies (≥70 Hz). Mechanically dissected mouse FDB fibers showed greater decrease in tetanic force when the stimulation frequency during contractions was gradually reduced to prevent the increase in tetanic [Ca2+ ]cyt . Novel analyses of data from previous studies revealed an increased rate of force development in the tenth fatiguing contraction in mouse FDB fibers, as well as in rat FDB and human intercostal fibers. Mouse FDB fibers deficient in creatine kinase showed no increase in tetanic [Ca2+ ]cyt and slowed force development in the tenth contraction; after injection of creatine kinase to enable phosphocreatine breakdown, these fibers showed an increase in tetanic [Ca2+ ]cyt and accelerated force development. Mouse FDB fibers exposed to ten short contractions (43 ms) produced at short intervals (142 ms) showed increased tetanic [Ca2+ ]cyt accompanied by a marked (~16%) increase in the developed force. In conclusion, the increase in tetanic [Ca2+ ]cyt in early fatigue is accompanied by accelerated force development, which under some circumstances can counteract the decline in physical performance caused by the concomitant decrease in maximum force.
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Affiliation(s)
- Cecilia Leijding
- Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden
| | - Ida Viken
- Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden
| | - Joseph D Bruton
- Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden
| | - Daniel C Andersson
- Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden
- Heart, Vascular and Neurology Theme, Cardiology Unit, Karolinska University Hospital, Stockholm, Sweden
| | - Arthur J Cheng
- Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden
| | - Håkan Westerblad
- Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden
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5
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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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6
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Cairns SP, Leader JP, Higgins A, Renaud JM. The peak force - resting membrane potential relationships of mouse fast- and slow-twitch muscle. Am J Physiol Cell Physiol 2022; 322:C1151-C1165. [PMID: 35385328 DOI: 10.1152/ajpcell.00401.2021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We endeavored to understand the factors determining the peak force‑resting membrane potential (EM) relationships of isolated slow-twitch soleus and fast-twitch extensor digitorum longus (EDL) muscles from mice (25oC), especially in relation to fatigue. Inter-relationships between intracellular K+‑activity (aK+i), extracellular K+‑concentration ([K+]o), resting EM, action potentials and force were studied. The large resting EM variation was mainly due to the variability of aK+i. Action potential overshoot‑resting EM relationships determined at 4 and 8-10mM[K+]o following short (<5min) and prolonged (>50min) depolarization periods revealed a constant overshoot from ‑90 to ‑70mV providing a safety margin. Overshoot decline with depolarization beyond ‑70mV was less following short than prolonged depolarization. Inexcitable fibers occurred only with prolonged depolarization. The overshoot decline during action potential trains (2‑s) exceeded that during short depolarizations. Concomitant lower extracellular [Na+] and raised [K+]o depressed the overshoot in an additive manner and peak force in a synergistic manner. Raised [K+]o-induced force loss was exacerbated with transverse wire versus parallel plate stimulation in soleus, implicating action potential propagation failure in the surface membrane. Increasing stimulus pulse parameters restored tetanic force at 9‑10mM[K+]o in soleus, but not EDL, indicative of action potential failure within trains. The peak tetanic force‑resting EM relationships (determined using resting EM from deeper rather than surface fibers) were dynamic and show pronounced force depression over ‑69 to ‑60mV in both muscle-types, implicating that such depolarization contributes to fatigue. The K+-Na+-interaction shifted this relationship towards less depolarized potentials suggesting that the combined ionic effect is physiologically important during fatigue.
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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, Auckland, New Zealand.,Health and Rehabilitation Research Institute, Faculty of Health and Environmental Sciences, Auckland University of Technology, Auckland, New Zealand.,Department of Physiology, School of Medicine, University of Auckland, Auckland, New Zealand
| | - John P Leader
- Department of Physiology, University of Otago, Dunedin, New Zealand.,Department of Medicine, University of Otago, Dunedin, New Zealand
| | - Amanda Higgins
- Department of Cellular and Molecular Medicine, Neuromuscular Research Center, University of Ottawa, Ottawa, Canada
| | - Jean-Marc Renaud
- Department of Cellular and Molecular Medicine, Neuromuscular Research Center, University of Ottawa, Ottawa, Canada
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7
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Morris CE, Wheeler JJ, Joos B. The Donnan-dominated resting state of skeletal muscle fibers contributes to resilience and longevity in dystrophic fibers. J Gen Physiol 2022; 154:212743. [PMID: 34731883 PMCID: PMC8570295 DOI: 10.1085/jgp.202112914] [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: 03/17/2021] [Accepted: 09/30/2021] [Indexed: 11/28/2022] Open
Abstract
Duchenne muscular dystrophy (DMD) is an X-linked dystrophin-minus muscle-wasting disease. Ion homeostasis in skeletal muscle fibers underperforms as DMD progresses. But though DMD renders these excitable cells intolerant of exertion, sodium overloaded, depolarized, and spontaneously contractile, they can survive for several decades. We show computationally that underpinning this longevity is a strikingly frugal, robust Pump-Leak/Donnan (P-L/D) ion homeostatic process. Unlike neurons, which operate with a costly “Pump-Leak–dominated” ion homeostatic steady state, skeletal muscle fibers operate with a low-cost “Donnan-dominated” ion homeostatic steady state that combines a large chloride permeability with an exceptionally small sodium permeability. Simultaneously, this combination keeps fiber excitability low and minimizes pump expenditures. As mechanically active, long-lived multinucleate cells, skeletal muscle fibers have evolved to handle overexertion, sarcolemmal tears, ischemic bouts, etc.; the frugality of their Donnan dominated steady state lets them maintain the outsized pump reserves that make them resilient during these inevitable transient emergencies. Here, P-L/D model variants challenged with DMD-type insult/injury (low pump-strength, overstimulation, leaky Nav and cation channels) show how chronic “nonosmotic” sodium overload (observed in DMD patients) develops. Profoundly severe DMD ion homeostatic insult/injury causes spontaneous firing (and, consequently, unwanted excitation–contraction coupling) that elicits cytotoxic swelling. Therefore, boosting operational pump-strength and/or diminishing sodium and cation channel leaks should help extend DMD fiber longevity.
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Affiliation(s)
- Catherine E Morris
- Neuroscience, Ottawa Hospital Research Institute, Ottawa, Canada.,Center for Neural Dynamics, University of Ottawa, Ottawa, Canada
| | | | - Béla Joos
- Center for Neural Dynamics, University of Ottawa, Ottawa, Canada.,Department of Physics, University of Ottawa, Ottawa, Canada
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8
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Rodriguez B, Jost K, Larsen LH, Tankisi H, Z'Graggen WJ. Leg pain in neuropathic postural tachycardia syndrome is associated with altered muscle membrane properties. Clin Auton Res 2021; 31:719-727. [PMID: 34674068 PMCID: PMC8629901 DOI: 10.1007/s10286-021-00830-5] [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: 07/19/2021] [Accepted: 10/07/2021] [Indexed: 11/29/2022]
Abstract
Purpose In neuropathic postural tachycardia syndrome, peripheral sympathetic dysfunction leads to excessive venous blood pooling during orthostasis. Up to 84% of patients report leg pain and weakness in the upright position. To explore possible pathophysiological processes underlying these symptoms, the present study examined muscle excitability depending on body position in patients with neuropathic postural tachycardia syndrome and healthy subjects. Methods In ten patients with neuropathic postural tachycardia syndrome and ten healthy subjects, muscle excitability measurements were performed repeatedly: in the supine position, during 10 min of head-up tilt and during 6 min thereafter. Additionally, lower leg circumference was measured and subjective leg pain levels were assessed. Results In patients with neuropathic postural tachycardia syndrome, muscle excitability was increased in the supine position, decreased progressively during tilt, continued to decrease after being returned to the supine position, and did not completely recover to baseline values after 6 min of supine rest. The reduction in muscle excitability during tilt was paralleled by an increase in lower leg circumference as well as leg pain levels. No such changes were observed in healthy subjects. Conclusions This study provides evidence for the occurrence of orthostatic changes in muscle excitability in patients with neuropathic postural tachycardia syndrome and that these may be associated with inadequate perfusion of the lower extremities. Insufficient perfusion as a consequence of blood stasis may cause misery perfusion of the muscles, which could explain the occurrence of orthostatic leg pain in neuropathic postural tachycardia syndrome.
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Affiliation(s)
- Belén Rodriguez
- Department of Neurosurgery, Inselspital, Bern University Hospital, Bern, Switzerland
| | - Karin Jost
- Department of Neurology, Inselspital, Bern University Hospital, Bern, Switzerland
| | - Lotte Hardbo Larsen
- Department of Clinical Neurophysiology, Aarhus University Hospital, Aarhus, Denmark
| | - Hatice Tankisi
- Department of Clinical Neurophysiology, Aarhus University Hospital, Aarhus, Denmark
| | - Werner J Z'Graggen
- Department of Neurosurgery, Inselspital, Bern University Hospital, Bern, Switzerland. .,Department of Neurology, Inselspital, Bern University Hospital, Bern, Switzerland.
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9
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Stephenson DG. ClC-1 Cl - channels as modulators of signal transmission at neuromuscular junction. Acta Physiol (Oxf) 2021; 233:e13718. [PMID: 34273251 DOI: 10.1111/apha.13718] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- D. George Stephenson
- Department of Physiology, Anatomy and Microbiology School of Life Science La Trobe University Bundoora VIC Australia
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10
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Mohr M, Fatouros IG, Jamurtas AZ, Draganidis D, Thomassen M, Ørntoft C, Ermidis G, Loules G, Batsilas D, Poulios A, Papanikolaou K, Randers MB, Krustrup P, Nybo L. Skeletal muscle phenotype and game performance in elite women football players. Scand J Med Sci Sports 2021; 32 Suppl 1:39-53. [PMID: 34427373 DOI: 10.1111/sms.14022] [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: 03/23/2021] [Accepted: 07/13/2021] [Indexed: 11/29/2022]
Abstract
We combined game activity analyses with skeletal muscle phenotypes and comprehensive physiological testing to elucidate factors of importance for physical performance in elite women's football. GPS-data from an experimental game, sprint and endurance testing, and muscle tissue analysis of metabolic enzyme activity, protein expression and fiber type composition were completed for international top-level women players (n = 20; age; 23 ± 4 yrs, height; 166 ± 10 cm, weight; 60 ± 8 kg; VO2max ; 51 ± 6 ml/min/kg). Muscle monocarboxylate transporter 4 (MCT4) protein expression explained 46% of the variance in total game distance, while the ability to maintain high-intensity running (HIR) during the final 15 min of the game correlated to myosin heavy chain 1 (MHCI) and Na+ -K+ ATPase β1, FXYD1 (phospholemman) and superoxide dismutase 2 (SOD2) protein expression (range: r = 0.51-0.71; all p < 0.05). Total HIR distance correlated with (MHCIIa) protein expression (r = 0.51; p < 0.05), while muscle Na+ /H+ exchanger 1 (NHE1) protein explained 36% of the variance in game sprint distance (p < 0.05). Total game accelerations (actions >4 m/s2 ) correlated with platelet endothelial cell adhesion molecule (PECAM-1) protein expression (r = 0.51; p < 0.05), while concentric knee flexor strength explained 42-62% of the variance in intense decelerations (>4 m/s2 ). In conclusion, for elite women players' game endurance performance and resistance to end-game fatigue were affected by monocarboxylate transporter expression and myosin heavy chain profile. HIR was also correlated to ion transporter expression and muscle antioxidative capacity. Finally, the importance of functional strength and measures of muscle vascularization in relation to total game decelerations and accelerations, respectively, illustrates the complex physiological demands in elite women's football.
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Affiliation(s)
- Magni Mohr
- Department of Sports Science and Clinical Biomechanics, SDU Sport and Health Sciences Cluster (SHSC), University of Southern Denmark, Odense, Denmark.,Centre of Health Science, Faculty of Health, University of the Faroe Islands, Tórshavn, Faroe Islands
| | - Ioannis G Fatouros
- Department of Physical Education and Sport Sciences, University of Thessaly, Trikala, Greece
| | - Athanasios Z Jamurtas
- Department of Physical Education and Sport Sciences, University of Thessaly, Trikala, Greece.,Department of Nutrition and Dietetics, University of Thessaly, Trikala, Greece
| | - Dimitrios Draganidis
- Department of Physical Education and Sport Sciences, University of Thessaly, Trikala, Greece
| | - Martin Thomassen
- Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark
| | - Christina Ørntoft
- Department of Sports Science and Clinical Biomechanics, SDU Sport and Health Sciences Cluster (SHSC), University of Southern Denmark, Odense, Denmark
| | - Georgios Ermidis
- Department of Sports Science and Clinical Biomechanics, SDU Sport and Health Sciences Cluster (SHSC), University of Southern Denmark, Odense, Denmark.,Department of Movement Sciences and Wellbeing, University of Naples Parthenope, Naples, Italy
| | - Georgios Loules
- Department of Physical Education and Sport Sciences, University of Thessaly, Trikala, Greece
| | - Dimitrios Batsilas
- Department of Physical Education and Sport Sciences, University of Thessaly, Trikala, Greece
| | - Athanasios Poulios
- Department of Physical Education and Sport Sciences, University of Thessaly, Trikala, Greece
| | | | - Morten B Randers
- Department of Sports Science and Clinical Biomechanics, SDU Sport and Health Sciences Cluster (SHSC), University of Southern Denmark, Odense, Denmark.,School of Sport Sciences, Faculty of Health Sciences, UiT The Arctic University of Norway, Tromsø, Norway
| | - Peter Krustrup
- Department of Sports Science and Clinical Biomechanics, SDU Sport and Health Sciences Cluster (SHSC), University of Southern Denmark, Odense, Denmark.,Sport and Health Sciences, University of Exeter, Exeter, UK.,Shanghai University of Sport, Shanghai, China.,Danish Institute for Advanced Study (DIAS), University of Southern Denmark, Odense, Denmark
| | - Lars Nybo
- Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark
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11
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Hochstrasser A, Rodriguez B, Söll N, Bostock H, Z'Graggen WJ. Effect of intermittent high-frequency stimulation on muscle velocity recovery cycle recordings. J Neurophysiol 2021; 126:736-742. [PMID: 34288792 DOI: 10.1152/jn.00213.2021] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The technique of multifiber muscle velocity recovery cycle recordings was developed as a diagnostic tool to assess muscle membrane potential changes and ion channel function in vivo. This study was undertaken to assess the impact of intermittent high-frequency stimulation on muscle velocity recovery cycle components and to study whether the changes can be modified by endurance training. We recorded muscle velocity recovery cycles with 1 and 2 conditioning stimuli in the left tibialis anterior muscle in 15 healthy subjects during intermittent 37-Hz stimulation and analyzed its effects on the different phases of supernormality. Recordings were conducted before and after 2-wk endurance training. Training effect was assessed by measuring the difference in endurance time, peak force, and limb circumference. Muscle velocity recovery cycle recordings during intermittent high-frequency stimulation were successfully recorded in 12 subjects. Supernormality for interstimulus intervals shorter than 15 ms (early supernormality) was maximally reduced at the beginning of repetitive stimulation and recovered during stimulation. Supernormality for interstimulus intervals between 50 and 150 ms (late supernormality) showed a delayed decrease and stayed significantly reduced after high-frequency stimulation. Training had no significant effect on any of the measured parameters, but we found that training induced changes in peak force correlated positively with baseline changes of early supernormality. Our results support the hypothesis that early supernormality represents membrane potential, which depolarizes in the beginning of high-frequency stimulation. Late supernormality probably reflects transverse tubular function and shows progressive changes during high-frequency stimulation with delayed normalization.NEW & NOTEWORTHY A conditioning impulse in human muscle fibers induces a prolonged phase of increased velocity (also called supernormality) with two phases related to an early and late afterpotential. We investigated the effects of intermittent 37-Hz stimulation on muscle fiber supernormality and found that the early and late phases of supernormality changed differently, and that the late phase may reflect the ionic interactions responsible for the counter-regulation of muscle fatigue.
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Affiliation(s)
- Annie Hochstrasser
- Department of Neurology, Inselspital, Bern University Hospital and University of Bern, Bern, Switzerland
| | - Belén Rodriguez
- Department of Neurosurgery, Inselspital, Bern University Hospital and University of Bern, Bern, Switzerland
| | - Nicole Söll
- Department of Neurosurgery, Inselspital, Bern University Hospital and University of Bern, Bern, Switzerland
| | - Hugh Bostock
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology, London, United Kingdom
| | - Werner J Z'Graggen
- Department of Neurology, Inselspital, Bern University Hospital and University of Bern, Bern, Switzerland.,Department of Neurosurgery, Inselspital, Bern University Hospital and University of Bern, Bern, Switzerland
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12
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Senneff S, Lowery MM. Effects of extracellular potassium on calcium handling and force generation in a model of excitation-contraction coupling in skeletal muscle. J Theor Biol 2021; 519:110656. [PMID: 33667541 DOI: 10.1016/j.jtbi.2021.110656] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2020] [Revised: 11/03/2020] [Accepted: 02/22/2021] [Indexed: 10/22/2022]
Abstract
It is well-established that extracellular potassium (Ko+) accumulation reduces muscle fiber excitability, however the effects of Ko+ on the excitation-contraction coupling (ECC) pathway are less understood. In vivo and in vitro studies following fatiguing stimulation protocols are limited in their ability to capture the effects of Ko+ on force production in combination with other simultaneously changing factors. To address this, a computational model of ECC for slow and fast twitch muscle is presented to explore the relative contributions of excitability-induced and metabolic-induced changes in force generation in response to increasing [Formula: see text] . The model incorporates mechanisms previously unexplored in modelling studies, including the effects of extracellular calcium on excitability, calcium-dependent inhibition of calcium release, ATP-dependent ionic pumping, and the contribution of ATP hydrolysis to intracellular phosphate accumulation rate. The model was able to capture the frequency-dependent biphasic Force- [Formula: see text] response observed experimentally. Force potentiation for moderately elevated [Formula: see text] was driven by increased action potential duration, myoplasmic calcium potentiation, and phosphate accumulation rate, while attenuation of force at higher [Formula: see text] was due to action potential failure resulting in reduced calcium release. These results suggest that altered calcium release and phosphate accumulation work together with elevated Ko+ to affect force during sustained contractions.
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Affiliation(s)
- Sageanne Senneff
- School of Electrical and Electronic Engineering, University College Dublin, Belfield, Dublin 4, Ireland.
| | - Madeleine M Lowery
- School of Electrical and Electronic Engineering, University College Dublin, Belfield, Dublin 4, Ireland
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13
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Lindinger MI, Cairns SP. Regulation of muscle potassium: exercise performance, fatigue and health implications. Eur J Appl Physiol 2021; 121:721-748. [PMID: 33392745 DOI: 10.1007/s00421-020-04546-8] [Citation(s) in RCA: 29] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2020] [Accepted: 10/29/2020] [Indexed: 12/30/2022]
Abstract
This review integrates from the single muscle fibre to exercising human the current understanding of the role of skeletal muscle for whole-body potassium (K+) regulation, and specifically the regulation of skeletal muscle [K+]. We describe the K+ transport proteins in skeletal muscle and how they contribute to, or modulate, K+ disturbances during exercise. Muscle and plasma K+ balance are markedly altered during and after high-intensity dynamic exercise (including sports), static contractions and ischaemia, which have implications for skeletal and cardiac muscle contractile performance. Moderate elevations of plasma and interstitial [K+] during exercise have beneficial effects on multiple physiological systems. Severe reductions of the trans-sarcolemmal K+ gradient likely contributes to muscle and whole-body fatigue, i.e. impaired exercise performance. Chronic or acute changes of arterial plasma [K+] (hyperkalaemia or hypokalaemia) have dangerous health implications for cardiac function. The current mechanisms to explain how raised extracellular [K+] impairs cardiac and skeletal muscle function are discussed, along with the latest cell physiology research explaining how calcium, β-adrenergic agonists, insulin or glucose act as clinical treatments for hyperkalaemia to protect the heart and skeletal muscle in vivo. Finally, whether these agents can also modulate K+-induced muscle fatigue are evaluated.
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Affiliation(s)
- Michael I Lindinger
- Research and Development, The Nutraceutical Alliance, Burlington, ON, L7N 2Z9, Canada
| | - Simeon P Cairns
- SPRINZ, School of Sport and Recreation, Faculty of Health and Environmental Sciences, Auckland University of Technology, Auckland, 1020, New Zealand.
- Health and Rehabilitation Research Institute, Faculty of Health and Environmental Sciences, Auckland University of Technology, Auckland, 1020, New Zealand.
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14
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Conte E, Fonzino A, Cibelli A, De Benedictis V, Imbrici P, Nicchia GP, Pierno S, Camerino GM. Changes in Expression and Cellular Localization of Rat Skeletal Muscle ClC-1 Chloride Channel in Relation to Age, Myofiber Phenotype and PKC Modulation. Front Pharmacol 2020; 11:714. [PMID: 32499703 PMCID: PMC7243361 DOI: 10.3389/fphar.2020.00714] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2019] [Accepted: 04/30/2020] [Indexed: 12/16/2022] Open
Abstract
The ClC-1 chloride channel 1 is important for muscle function as it stabilizes resting membrane potential and helps to repolarize the membrane after action potentials. We investigated the contribution of ClC-1 to adaptation of skeletal muscles to needs induced by the different stages of life. We analyzed the ClC-1 gene and protein expression as well as mRNA levels of protein kinase C (PKC) alpha and theta involved in ClC-1 modulation, in soleus (SOL) and extensor digitorum longus (EDL) muscles of rats in all stage of life. The cellular localization of ClC-1 in relation to age was also investigated. Our data show that during muscle development ClC-1 expression differs according to phenotype. In fast-twitch EDL muscles ClC-1 expression increased 10-fold starting at 7 days up to 8 months of life. Conversely, in slow-twitch SOL muscles ClC-1 expression remained constant until 33 days of life and subsequently increased fivefold to reach the adult value. Aging induced a downregulation of gene and protein ClC-1 expression in both muscle types analyzed. The mRNA of PKC-theta revealed the same trend as ClC-1 except in old age, whereas the mRNA of PKC-alpha increased only after 2 months of age. Also, we found that the ClC-1 is localized in both membrane and cytoplasm, in fibers of 12-day-old rats, becoming perfectly localized on the membrane in 2-month-old rats. This study could represent a point of comparison helpful for the identification of accurate pharmacological strategies for all the pathological situations in which ClC-1 protein is altered.
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Affiliation(s)
- Elena Conte
- Department of Pharmacy-Drug Sciences, University of Bari "Aldo Moro", Bari, Italy
| | - Adriano Fonzino
- Department of Pharmacy-Drug Sciences, University of Bari "Aldo Moro", Bari, Italy
| | - Antonio Cibelli
- Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari "Aldo Moro", Bari, Italy
| | - Vito De Benedictis
- Department of Pharmacy-Drug Sciences, University of Bari "Aldo Moro", Bari, Italy
| | - Paola Imbrici
- Department of Pharmacy-Drug Sciences, University of Bari "Aldo Moro", Bari, Italy
| | - Grazia Paola Nicchia
- Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari "Aldo Moro", Bari, Italy
| | - Sabata Pierno
- Department of Pharmacy-Drug Sciences, University of Bari "Aldo Moro", Bari, Italy
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15
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Altamura C, Desaphy JF, Conte D, De Luca A, Imbrici P. Skeletal muscle ClC-1 chloride channels in health and diseases. Pflugers Arch 2020; 472:961-975. [PMID: 32361781 DOI: 10.1007/s00424-020-02376-3] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2020] [Revised: 03/18/2020] [Accepted: 03/31/2020] [Indexed: 12/14/2022]
Abstract
In 1970, the study of the pathomechanisms underlying myotonia in muscle fibers isolated from myotonic goats highlighted the importance of chloride conductance for skeletal muscle function; 20 years later, the human ClC-1 chloride channel has been cloned; last year, the crystal structure of human protein has been solved. Over the years, the efforts of many researchers led to significant advances in acknowledging the role of ClC-1 in skeletal muscle physiology and the mechanisms through which ClC-1 dysfunctions lead to impaired muscle function. The wide spectrum of pathophysiological conditions associated with modification of ClC-1 activity, either as the primary cause, such as in myotonia congenita, or as a secondary adaptive mechanism in other neuromuscular diseases, supports the idea that ClC-1 is relevant to preserve not only for skeletal muscle excitability, but also for skeletal muscle adaptation to physiological or harmful events. Improving this understanding could open promising avenues toward the development of selective and safe drugs targeting ClC-1, with the aim to restore normal muscle function. This review summarizes the most relevant research on ClC-1 channel physiology, associated diseases, and pharmacology.
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Affiliation(s)
- Concetta Altamura
- Department of Biomedical Sciences and Human Oncology, School of Medicine, University of Bari "Aldo Moro", Bari, Italy
| | - Jean-Francois Desaphy
- Department of Biomedical Sciences and Human Oncology, School of Medicine, University of Bari "Aldo Moro", Bari, Italy
| | - Diana Conte
- Department of Pharmacy-Drug Sciences, University of Bari "Aldo Moro", Bari, Italy
| | - Annamaria De Luca
- Department of Pharmacy-Drug Sciences, University of Bari "Aldo Moro", Bari, Italy
| | - Paola Imbrici
- Department of Pharmacy-Drug Sciences, University of Bari "Aldo Moro", Bari, Italy.
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16
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Jeng CJ, Fu SJ, You CY, Peng YJ, Hsiao CT, Chen TY, Tang CY. Defective Gating and Proteostasis of Human ClC-1 Chloride Channel: Molecular Pathophysiology of Myotonia Congenita. Front Neurol 2020; 11:76. [PMID: 32117034 PMCID: PMC7026490 DOI: 10.3389/fneur.2020.00076] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2019] [Accepted: 01/22/2020] [Indexed: 01/17/2023] Open
Abstract
The voltage-dependent ClC-1 chloride channel, whose open probability increases with membrane potential depolarization, belongs to the superfamily of CLC channels/transporters. ClC-1 is almost exclusively expressed in skeletal muscles and is essential for stabilizing the excitability of muscle membranes. Elucidation of the molecular structures of human ClC-1 and several CLC homologs provides important insight to the gating and ion permeation mechanisms of this chloride channel. Mutations in the human CLCN1 gene, which encodes the ClC-1 channel, are associated with a hereditary skeletal muscle disease, myotonia congenita. Most disease-causing CLCN1 mutations lead to loss-of-function phenotypes in the ClC-1 channel and thus increase membrane excitability in skeletal muscles, consequently manifesting as delayed relaxations following voluntary muscle contractions in myotonic subjects. The inheritance pattern of myotonia congenita can be autosomal dominant (Thomsen type) or recessive (Becker type). To date over 200 myotonia-associated ClC-1 mutations have been identified, which are scattered throughout the entire protein sequence. The dominant inheritance pattern of some myotonia mutations may be explained by a dominant-negative effect on ClC-1 channel gating. For many other myotonia mutations, however, no clear relationship can be established between the inheritance pattern and the location of the mutation in the ClC-1 protein. Emerging evidence indicates that the effects of some mutations may entail impaired ClC-1 protein homeostasis (proteostasis). Proteostasis of membrane proteins comprises of biogenesis at the endoplasmic reticulum (ER), trafficking to the surface membrane, and protein turn-over at the plasma membrane. Maintenance of proteostasis requires the coordination of a wide variety of different molecular chaperones and protein quality control factors. A number of regulatory molecules have recently been shown to contribute to post-translational modifications of ClC-1 and play critical roles in the ER quality control, membrane trafficking, and peripheral quality control of this chloride channel. Further illumination of the mechanisms of ClC-1 proteostasis network will enhance our understanding of the molecular pathophysiology of myotonia congenita, and may also bring to light novel therapeutic targets for skeletal muscle dysfunction caused by myotonia and other pathological conditions.
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Affiliation(s)
- Chung-Jiuan Jeng
- Institute of Anatomy and Cell Biology, School of Medicine, National Yang-Ming University, Taipei, Taiwan.,Brain Research Center, National Yang-Ming University, Taipei, Taiwan
| | - Ssu-Ju Fu
- Institute of Anatomy and Cell Biology, School of Medicine, National Yang-Ming University, Taipei, Taiwan.,Department of Physiology, College of Medicine, National Taiwan University, Taipei, Taiwan
| | - Chia-Ying You
- Department of Physiology, College of Medicine, National Taiwan University, Taipei, Taiwan
| | - Yi-Jheng Peng
- Department of Physiology, College of Medicine, National Taiwan University, Taipei, Taiwan
| | - Cheng-Tsung Hsiao
- Department of Physiology, College of Medicine, National Taiwan University, Taipei, Taiwan.,Department of Neurology, Taipei Veterans General Hospital, Taipei, Taiwan
| | - Tsung-Yu Chen
- Center for Neuroscience, University of California, Davis, Davis, CA, United States
| | - Chih-Yung Tang
- Department of Physiology, College of Medicine, National Taiwan University, Taipei, Taiwan.,College of Medicine, Graduate Institute of Brain and Mind Sciences, National Taiwan University, Taipei, Taiwan
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17
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Metzger S, Dupont C, Voss AA, Rich MM. Central Role of Subthreshold Currents in Myotonia. Ann Neurol 2019; 87:175-183. [PMID: 31725924 DOI: 10.1002/ana.25646] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2019] [Revised: 11/12/2019] [Accepted: 11/12/2019] [Indexed: 01/11/2023]
Abstract
It is generally thought that muscle excitability is almost exclusively controlled by currents responsible for generation of action potentials. We propose that smaller ion channel currents that contribute to setting the resting potential and to subthreshold fluctuations in membrane potential can also modulate excitability in important ways. These channels open at voltages more negative than the action potential threshold and are thus termed subthreshold currents. As subthreshold currents are orders of magnitude smaller than the currents responsible for the action potential, they are hard to identify and easily overlooked. Discovery of their importance in regulation of excitability opens new avenues for improved therapy for muscle channelopathies and diseases of the neuromuscular junction. ANN NEUROL 2020;87:175-183.
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Affiliation(s)
- Sabrina Metzger
- Department of Neuroscience, Cell Biology, and Physiology, Wright State University, Dayton, OH
| | - Chris Dupont
- Department of Neuroscience, Cell Biology, and Physiology, Wright State University, Dayton, OH
| | - Andrew A Voss
- Department of Biology, Wright State University, Dayton, OH
| | - Mark M Rich
- Department of Neuroscience, Cell Biology, and Physiology, Wright State University, Dayton, OH
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18
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Pedersen KK, Nielsen OB, Overgaard K. Contractile benefits of doublet-initiated low-frequency stimulation in rat extensor digitorum longus muscle exposed to high extracellular [K +] or fatiguing contractions. Am J Physiol Cell Physiol 2019; 317:C39-C47. [PMID: 30969780 DOI: 10.1152/ajpcell.00519.2018] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
During dynamic contractions, high-frequency muscle activation is needed to achieve optimal power. This must be balanced against an increased excitation-induced accumulation of extracellular K+, which can reduce excitability and ultimately may prevent adequate responses to high-frequency activation. Mean activation frequencies in vivo are often low (subtetanic), but activation patterns contain bursts of high (supratetanic) frequencies known as doublets, which enhance dynamic contraction in rested muscles at normal extracellular K+ concentration ([K+]o). Here, we examine how dynamic contractions in fast-twitch fibers stimulated by high frequency/doublets are affected during exposure to 11 mM [K+]o and during fatigue. Dynamic contractions were elicited by electrical stimulation in isolated rat extensor digitorum longus muscles incubated at 4 or 11 mM K+. When stimulation frequency was maintained constant, an increase from 150 to 300 Hz enhanced maximal power (Pmax), maximal velocity (Vmax), and rate of force development (RFD) at 4 mM K+ but only Vmax at 11 mM K+. With the use of subtetanic frequency trains (50 Hz) with or without an initiating doublet (300 Hz), the addition of a doublet increased maximal force, Pmax, Vmax, and RFD at both 4 and 11 mM K+. Furthermore, a work-matched fatiguing protocol was performed comparing a doublet-initiated subtetanic train (DT) of 60 Hz with a constant-frequency train (CFT) of 71 Hz during 100 dynamic contractions. We found that DT produced higher power, velocity, and RFD than CFT throughout the fatiguing protocol. The results indicate that doublets enhance dynamic contraction in fast-twitch muscles stimulated at subtetanic frequency during both normal and fatiguing conditions.
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Affiliation(s)
| | - Ole Bækgaard Nielsen
- Department of Public Health, Aarhus University , Aarhus , Denmark.,Department of Biomedicine, Aarhus University , Aarhus , Denmark
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19
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Thomassen M, Hostrup M, Murphy RM, Cromer BA, Skovgaard C, Gunnarsson TP, Christensen PM, Bangsbo J. Abundance of ClC-1 chloride channel in human skeletal muscle: fiber type specific differences and effect of training. J Appl Physiol (1985) 2018; 125:470-478. [DOI: 10.1152/japplphysiol.01042.2017] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Cl− channel protein 1 (ClC-1) may be important for excitability and contractility in skeletal muscle, but ClC-1 abundance has not been examined in human muscle. The aim of the present study was to examine ClC-1 abundance in human skeletal muscle, including fiber type specific differences and the effect of exercise training. A commercially available antibody was tested with positive and negative control tissue, and it recognized specifically ClC-1 in the range from 100 to 150 kDa. Abundance of ClC-1 was 38% higher ( P < 0.01) in fast twitch Type IIa muscle fibers than in slow twitch Type I. Muscle ClC-1 abundance did not change with 4 wk of training consisting of 30 min cycling at 85% of maximal heart rate (HRmax) and 3 × 30-s all out sprints or during a 7-wk training period with 10–12 × 30 s uphill cycling and 4–5 × ~4 min cycling at 90%–95% of HRmax. ClC-1 abundance correlated negatively ( P < 0.01) with maximal oxygen consumption ( r = –0.552) and incremental exercise performance ( r = –0.546). In addition, trained cyclists had lower ( P < 0.01) ClC-1 abundance than lesser trained individuals. The present observations indicate that a low abundance of muscle ClC-1 may be beneficial for exercise performance, but the role of abundance and regulation of ClC-1 in skeletal muscle of humans with respect to exercise performance and trainability need to be elucidated. NEW & NOTEWORTHY Abundance of the Cl− channel protein 1 (ClC-1) chloride channel may be important for excitability and contractility in human skeletal muscle and may therefore have implications for fatigue development. In this study, we confirmed ClC-1 specificity for a commercially available antibody, and this study is first to our knowledge to determine ClC-1 protein abundance in human muscle by Western blotting. We observed that abundance of ClC-1 was higher in fast compared with slow twitch fibers and lower in trained individuals than in recreationally active.
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Affiliation(s)
- Martin Thomassen
- Section of Integrative Physiology, Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark
| | - Morten Hostrup
- Section of Integrative Physiology, Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark
| | - Robyn M. Murphy
- Department of Biochemistry & Genetics, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Victoria, Australia
| | - Brett A. Cromer
- Department of Chemistry and Biotechnology, Swinburne University, Melbourne, Victoria, Australia
| | - Casper Skovgaard
- Section of Integrative Physiology, Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark
| | - Thomas P. Gunnarsson
- Section of Integrative Physiology, Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark
| | - Peter M. Christensen
- Section of Integrative Physiology, Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark
| | - Jens Bangsbo
- Section of Integrative Physiology, Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark
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20
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Sieck GC. Physiology in Perspective: Physiology Provides Insight into Health. Physiology (Bethesda) 2017; 32:408-409. [PMID: 29021360 DOI: 10.1152/physiol.00024.2017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2017] [Accepted: 09/12/2017] [Indexed: 11/22/2022] Open
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