High-frequency fatigue in rat skeletal muscle: role of extracellular ion concentrations.
High-frequency fatigue (HFF), the decline of force during continuous tetanic stimulation (lasting 4-40 s), was studied in isolated bundles of rat skeletal muscle fibers. HFF was slower in slow-twitch soleus fibers than in fast-twitch red or white sternomastoid fibers; denervation accelerated fatigue in soleus. Maximal 200-mmol/L potassium contractures of normal amplitude were induced in fatigued fibers, suggesting that crossbridge cycling and the voltage activation of excitation-contraction coupling could still occur maximally, but that activation by action potentials was impaired. An increase in [Na+]o slowed HFF, while a small increase in [K+]o or reduction in [Cl(-)]o accelerated HFF. Increasing the tetanic stimulation frequency exacerbated fatigue. Recovery from HFF proceeded rapidly since force increased markedly within a few seconds when stimulation ceased. These results support the hypothesis that a redistribution of Na+, K+, and Cl- across the transverse tubular membranes during repeated action potential activity induces fatigue by reducing the amplitude and conduction of action potentials.
Cairns
S P
SP
Muscle Research Group, John Curtin School of Medical Research, Australian National University, Canberra.
Dulhunty
A F
AF
D000818:Animals; D002712:Chlorides / Q000378:metabolism; D003714:Denervation; D005110:Extracellular Space / Q000378:metabolism*; D017136:Ion Transport; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000187:drug effects / Q000502:physiology*; D018656:Muscle Fibers, Fast-Twitch / Q000378:metabolism; D018657:Muscle Fibers, Slow-Twitch / Q000378:metabolism; D018482:Muscle, Skeletal / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism; D013997:Time Factors
D002712:Chlorides; D012964:Sodium; D011188:Potassium