Regulation of the cross-bridge transition from a weakly to strongly bound state in skinned rabbit muscle fibers.
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.
Regnier
M
M
Department of Physiology, School of Medicine, University of California at Los Angeles 90024, USA.
Morris
C
C
Homsher
E
E
D000199:Actins / Q000502:physiology*; D000818:Animals; D001696:Biomechanical Phenomena; D002118:Calcium / Q000494:pharmacology; D003931:Diacetyl / Q000031:analogs & derivatives / Q000494:pharmacology; D005260:Female; D006652:Histological Techniques; D009119:Muscle Contraction / Q000187:drug effects; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000502:physiology*; D009218:Myosins / Q000502:physiology*; D009994:Osmolar Concentration; D010710:Phosphates / Q000494:pharmacology; D011817:Rabbits
D000199:Actins; D010710:Phosphates; C004717:diacetylmonoxime; D009218:Myosins; D003931:Diacetyl; D002118:Calcium