Regulation of the cross-bridge transition from a weakly to strongly bound state in skinned rabbit muscle fibers
Regnier, M.; Morris, C.; Homsher, E.
American Journal of Physiology 269(6 Pt 1): C1532-C1539
1995
ISSN/ISBN: 0002-9513 PMID: 8572183 Document Number: 444051
The regulation of crossbridge transition from weakly attached to force-bearing states was studied at 10 degree C in skinned muscle fibers by measuring the rate of force development after a quick release-restretch cycle (k-tr), the rate of force decline (k-P-i) after photogeneration of P-i from caged P-i, and stiffness in the presence and absence of an inhibitor of strong cross-bridge formation, 2,3-butanedione monoxime (BDM). Both BDM and P-i suppressed force more than stiffness. However, reduction of Ca-2+ suppressed force and stiffness in a parallel fashion. Both k-tr and k-P-i were reversibly reduced (by 30-35%) in 3 mM BDM, but both were increased by increasing P-i concentration. Reduction of Ca-2+ concentration to match the force seen in 3 mM BDM had no effect on k-P-i but decreased k-tr 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.