Myosin phosphorylation, twitch potentiation, and fatigue in human skeletal muscle.
Twitch tension and phosphate incorporation into the phosphorylatable light chains (P-light chains) of myosin were studied during a 10-min recovery period following a 10- or 60-s maximal voluntary isometric contraction (MVC) in 18 subjects. Analysis of muscle biopsy samples obtained before, immediately after, 1 min, and 10 min following the 10-s MVC revealed that the 10-s MVC produced a modest but transient metabolic displacement from rest, a 35% decrease in phosphocreatine, and a threefold elevation in lactate concentration. Immediately after the 60-s MVC, ATP was decreased by 20%, phosphocreatine decreased by 84%, and lactate was elevated by 15-fold. Lactate remained elevated over the 10-min recovery period. Twitch force was maximally potentiated following the 10-s MVC and declined to rest by 10 min of recovery. Twitch force was 0.66 of rest value immediately after the 60-s MVC, then increased over the next 4 min to reach a potentiated value 21% greater than rest, before declining. Significant phosphate incorporation into P-light chains was observed immediately after both contractions, but dephosphorylation to rest values at the end of recovery was only noted for the 60-s condition. These results demonstrate an inconsistent relationship between twitch tension enhancement and P-light chain phosphorylation in the in vivo human model.
Houston
M E
ME
Department of Kinesiology, University of Waterloo, Ont., Canada.
Grange
R W
RW
D000255:Adenosine Triphosphate / Q000378:metabolism; D000328:Adult; D004558:Electric Stimulation; D005260:Female; D006003:Glycogen / Q000378:metabolism; D006801:Humans; D007537:Isometric Contraction; D007773:Lactates / Q000378:metabolism; D008297:Male; D009119:Muscle Contraction; D009132:Muscles / Q000378:metabolism / Q000502:physiology*; D009218:Myosins / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism; D010725:Phosphocreatine / Q000378:metabolism; D010766:Phosphorylation
D007773:Lactates; D010710:Phosphates; D010725:Phosphocreatine; D000255:Adenosine Triphosphate; D006003:Glycogen; D009218:Myosins