Proposed mechanism for dual regulation of cross-bridge turn-over in vertebrate muscle.
The studies on intact fibers of the frog and fast-twitch skinned fibers of the Syrian hamster suggest the presence of intermediate low-force (weak) and high-force (strong) attachments in the cross-bridge cycle. Our results suggest that the weak and strong attachments may be separately regulated by independent calcium switches. The switch for weak bridges operates by calcium or decreasing ionic strength, such that in low ionic strength in skinned fibers the bridges form even in the virtual absence of TnC and calcium. The weak to strong transition appears to require Ca in both low and high ionic strengths. The Ca action effecting this transition may be mediated also by TnC and/or may involve the myosin moiety. Thus, the possibility is raised that Ca may act at two separate steps in the cross-bridge mechanism under physiological conditions.
Babu
A
A
Department of Medicine, Albert Einstein College of Medicine, Bronx, New York 10461.
Gulati
J
J
D000199:Actins / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D006224:Cricetinae; D066298:In Vitro Techniques; D008647:Mesocricetus; D008954:Models, Biological; D009119:Muscle Contraction; D009132:Muscles / Q000502:physiology*; D009218:Myosins / Q000502:physiology*; D011898:Ranidae; D014336:Troponin / Q000502:physiology; D019209:Troponin C
D000199:Actins; D014336:Troponin; D019209:Troponin C; D009218:Myosins; D002118:Calcium