Regulation of crossbridge transition from weakly to strongly bound
states in skinned rabbit psoas muscle fibers.
Regnier, M., C. Morris, and E. Homsher.
Department of Physiology, School of Medicine, University of
California at Los Angeles, Los Angeles, California 90024
APStracts 2:0253C, 1995.
The regulation of crossbridge 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) following
photogeneration of Pi from caged-Pi, and stiffness in the presence
and absence of an inhibitor of strong crossbridge formation,
butanedione monoxime (BDM). Both BDM and Pi suppressed force more
than stiffness. However, reduction of Ca&2 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]. Reduction of [Ca2&] to match the force seen in 3
mM BDM had no effect on kPi but decreased ktr by 85%. These results
are inconsistent with crossbridge 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.
Received 3 August 1994; accepted in final form 9 June 1995
APS Manuscript Number C0456-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 18 July 1995.