title: Myosin light chain phosphorylation and contractile performance of human skeletal muscle.
abstract: Twitch tension and maximal unloaded velocity of human knee extensor muscles were studied under conditions of low phosphate content of the phosphorylatable light chains (P-light chains) of myosin and elevated phosphate content, following a 10-s maximal voluntary isometric contraction (MVC). After the MVC, twitch tension was significantly potentiated, with greater potentiation observed at a shorter muscle length (p less than 0.05). The MVC was associated with at least a twofold increase in phosphate content of the fast (LC2F) and two slow (LC2S and LC2S') P-light chains, but this increase was unrelated to muscle length. No significant differences in knee extension velocity were observed between conditions where P-light chains had low or elevated phosphate content. Positive but nonsignificant correlations were noted between the extent of twitch potentiation and phosphate content of individual P-light chains as well as the percentage of type II muscle fibres in vastus lateralis muscle. No significant relationships were determined for myosin light chain kinase activity and either P-light chain phosphorylation or type II fibre percentage. These data suggest that, unlike other mammalian fast muscles, P-light chain phosphorylation of mixed human muscles is not strongly associated with altered contractile performance.
authors: Department of Kinesiology, University of Waterloo, Ont., Canada.
authors: D S
authors: DS
authors: Stuart
authors: M D
authors: MD
authors: Lingley
authors: R W
authors: RW
authors: Grange
authors: M E
authors: ME
authors: Houston
mesh_terms: D000293:Adolescent; D000328:Adult; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D007537:Isometric Contraction; D008297:Male; D009119:Muscle Contraction; D009132:Muscles / Q000378:metabolism*; D009219:Myosin-Light-Chain Kinase / Q000378:metabolism; D009218:Myosins / Q000378:metabolism*; D010766:Phosphorylation
chemical_list: D009219:Myosin-Light-Chain Kinase; D009218:Myosins