AJP - Cell Physiology, Vol 269, Issue 6 C1532-C1539, Copyright © 1995 by American Physiological Society

ARTICLES

Regulation of the cross-bridge transition from a weakly to strongly bound state in skinned rabbit muscle fibers

M. Regnier, C. Morris and E. Homsher
Department of Physiology, School of Medicine, University of California at Los Angeles 90024, USA.

The regulation of cross-bridge transition from weakly attached to force-bearing states was studied at 10 degrees C in skinned muscle fibers by measuring the rate of force development after a quick release-restretch cycle (ktr), the rate of force decline (kPi) after photogeneration of Pi from caged Pi, and stiffness in the presence and absence of an inhibitor of strong cross-bridge formation, 2,3-butanedione monoxime (BDM). Both BDM and Pi suppressed force more than stiffness. However, reduction of Ca2+ suppressed force and stiffness in a parallel fashion. Both ktr and kPi were reversibly reduced (by 30-35%) in 3 mM BDM, but both were increased by increasing Pi concentration. Reduction of Ca2+ concentration to match the force seen in 3 mM BDM had no effect on kPi but decreased ktr by 85%. These results are inconsistent with cross-bridge models undergoing the transition from a weakly bound to a force-generating state in a single step but are consistent with a model having two steps, one of which is controlled by pCa.

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