Myosin light chain 2 modulates calcium-sensitive cross-bridge transitions in vertebrate skeletal muscle.
We investigated the mechanism of the Ca2+ sensitivity of cross-bridge transitions that limit the rate of force development in vertebrate skeletal muscle. The rate of force development increases with Ca2+ concentration in the physiological range. We show here that at low concentrations of Ca2+ the rate of force development increases after partial extraction of the 20-kD light chain 2 subunit of myosin, whereas reconstitution with light chain 2 fully restores native sensitivity to Ca2+ in skinned single skeletal fibers. Furthermore, elevated free Mg2+ concentration reduces Ca2+ sensitivity, an effect that is reversed by extraction of the light chain but not by disruption of thin-filament activation by partial removal of troponin C, the Ca2+ binding protein of the thin filament. Our findings indicate that the Ca2+ sensitivity of the rate of force development in vertebrate skeletal muscle is mediated in part by the light chain 2 subunit of the myosin cross-bridge.
Metzger
J M
JM
Department of Physiology, School of Medicine, University of Wisconsin, Madison 53706.
Moss
R L
RL
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D003285:Contractile Proteins / Q000302:isolation & purification; D005260:Female; D066298:In Vitro Techniques; D007700:Kinetics; D009119:Muscle Contraction / Q000187:drug effects; D009124:Muscle Proteins / Q000302:isolation & purification; D009132:Muscles / Q000502:physiology*; D009218:Myosins / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012518:Sarcomeres / Q000187:drug effects / Q000502:physiology*; D013997:Time Factors; D014336:Troponin / Q000302:isolation & purification / Q000378:metabolism; D019209:Troponin C
D003285:Contractile Proteins; D009124:Muscle Proteins; D014336:Troponin; D019209:Troponin C; D009218:Myosins; D002118:Calcium