Physiological significance of myosin phosphorylation in skeletal muscle.
Each S-1 or head portion of the myosin molecule in skeletal muscle contains a subunit known as the regulatory or phosphorylatable light chain (P-LC). Phosphorylation of the P-LC is mediated by the second messenger Ca2+ and takes place when the muscle fibre is activated. In smooth muscle, phosphorylation of the P-LC is the principal mechanism that initiates contraction, but in skeletal muscle myosin P-LC phosphorylation is not required for contraction and a definitive role has not been established. It has been proposed that P-LC phosphorylation modulates the intrinsic nature of actin-myosin interactions, leading to force potentiation under suboptimal activation conditions. An example of this is posttetanic potentiation. This paper describes a P-LC phosphorylation induced mechanism for force enhancement during isometric contraction. In addition, it summarizes recent data revealing that P-LC phosphorylation is associated with enhanced work output of fast-twitch muscle during shortening and lengthening contractions.
Grange
R W
RW
Department of Kinesiology, Faculty of Applied Health Sciences, University of Waterloo, Ontario.
Vandenboom
R
R
Houston
M E
ME
D000199:Actins / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000502:physiology*; D004526:Efficiency; D004734:Energy Metabolism; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D051379:Mice; D015879:Myosin Subfragments / Q000502:physiology*; D009219:Myosin-Light-Chain Kinase / Q000502:physiology*; D010766:Phosphorylation; D011817:Rabbits; D051381:Rats; D015290:Second Messenger Systems / Q000502:physiology*
D000199:Actins; D015879:Myosin Subfragments; D009219:Myosin-Light-Chain Kinase; D002118:Calcium