Interfilament spacing, Ca2+ sensitivity, and Ca2+ binding in skinned bovine cardiac muscle.
The length-dependence of myofilament Ca2+ sensitivity in cardiac muscle appears to be a function of length-dependent variation in the lateral separation of actin and myosin filaments. The goal of this study was to determine how force, Ca2+ sensitivity, and Ca2+ binding to troponin C are correlated in skinned bovine ventricular muscle bundles set at sarcomere length 1.9 microm and subjected to varying degrees of osmotic compression with Dextran T-500. With 5, 10, and 15% Dextran T-500 the muscle diameter was reduced by 13, 21, and 25%, respectively. Addition of 5% Dextran T-500 caused increases in developed force, Ca2+ sensitivity, and in the affinity of Ca2+ for the regulatory binding site on troponin C. All of these parameters were reversed back toward control levels with 10% Dextran T-500. With 15% Dextran T-500 all parameters were decreased to below control levels. These data indicate that (1) there is an optimal filament separation at which both Ca2+ sensitivity and Ca2+ binding are maximized, and (2) Ca2+-troponin C affinity is linked to changes in Ca2+ sensitivity rather than to changes in interfilament spacing.
Wang
Y
Y
Department of Cell Biology and Physiology, University of Pittsburgh, School of Medicine, PA 15261, USA.
Fuchs
F
F
D000199:Actins / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D002417:Cattle; D003911:Dextrans; D066298:In Vitro Techniques; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000502:physiology*; D009200:Myocardial Contraction / Q000502:physiology*; D009206:Myocardium / Q000166:cytology*; D009218:Myosins / Q000378:metabolism; D009997:Osmotic Pressure; D010952:Plasma Substitutes; D012518:Sarcomeres / Q000502:physiology; D019209:Troponin C / Q000378:metabolism
D000199:Actins; D003911:Dextrans; D010952:Plasma Substitutes; D019209:Troponin C; D009218:Myosins; D002118:Calcium