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- Title
Exercise and fatigue: integrating the role of K<sup>+</sup>, Na<sup>+</sup> and Cl<sup>−</sup> in the regulation of sarcolemmal excitability of skeletal muscle.
- Authors
Renaud, Jean-Marc; Ørtenblad, Niels; McKenna, Michael J.; Overgaard, Kristian
- 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.
- Subjects
SKELETAL muscle; SUPPLY &; demand; ACTION potentials; MUSCLE fatigue; MUSCLE contraction
- Publication
European Journal of Applied Physiology, 2023, Vol 123, Issue 11, p2345
- ISSN
1439-6319
- Publication type
Article
- DOI
10.1007/s00421-023-05270-9