Role of calcium and cross bridges in determining rate of force development in frog muscle fibers.
The influence of Ca2+ and force-generating cross bridges on the kinetics of force development was examined in skinned frog muscle fibers activated by photolytic release of Ca2+ from caged Ca2+ at 10 degrees C. Isometric force development was fit by a double exponential equation with rates of 44.4 s-1 (kc1) and 6.1 s-1 (kc2); kc1 was not significantly different from the rate of force development observed in intact fibers. Maximum activation by caged Ca2+ from preexisting submaximal force produced rates of contraction similar to those observed with maximum activation from zero force. Decreasing the Ca2+ level to an extent that resulted in 50% of maximum force development produced an approximately sevenfold decrease in kc1 and no change in kc2. Partial extraction of troponin C reduced kc1 only slightly (by 16%), whereas decreasing the number of force-generating cross bridges by vanadate did not decrease kc1. Neither treatment altered kc2. Thus the rate of force development increases dramatically with increases in Ca2+ level.
Wahr
P A
PA
Department of Physiology, Ohio State University, Columbus 43210, USA.
Rall
J A
JA
D000085:Acetates; D000818:Animals; D002118:Calcium / Q000502:physiology*; D002614:Chelating Agents; D004533:Egtazic Acid / Q000031:analogs & derivatives; D005029:Ethylenediamines; D007537:Isometric Contraction / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D010782:Photolysis; D011896:Rana temporaria; D019209:Troponin C / Q000502:physiology
D000085:Acetates; D002614:Chelating Agents; D005029:Ethylenediamines; D019209:Troponin C; C052456:nitr 7; C057014:DM-nitrophen; D004533:Egtazic Acid; D002118:Calcium