APStracts 3:0408C, 1996.

Role of calcium and crossbridges in determining rate of force development in frog muscle fibers. Wahr, Philip A., and Jack A. Rall. Department of Physiology, The Ohio State University, Columbus, OH 43210, USA

APStracts 3:0408C, 1996.

The influence of Ca2+ and force generating crossbridges 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 pre-existing 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 7-fold decrease in kc1 and no change in kc2. Partial extraction of troponin C only reduced kc1 slightly (by 16%) whereas decreasing the number of force generating crossbridges by vanadate did not decrease kc1. Neither treatment altered kc2. Thus the rate of force development increases dramatically with increases in Ca2+ level.

Received 5 August 1996; accepted in final form 5 December 1996.
APS Manuscript Number C441-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996