Role of Calcium and Crossbridges in Modulation of Rates of Force Development and Relaxation in Skinned Muscle Fibers

  • Jack A. Rall
  • Philip A. Wahr
Part of the Advances in Experimental Medicine and Biology book series (AEMB, volume 453)


The influence of Ca2+ and force generating crossbridges on the kinetics of force development and relaxation was examined in skinned muscle fibers activated by photolytic release of Ca2+ from a caged calcium or inactivated by photolytic uptake of Ca2+ by a caged Ca2+ chelator. In frog fibers at 10°C, decreasing the Ca2+ released from caged calcium to an extent that resulted in 50% of maximum force development produced an approximate seven-fold decrease in the rate of contraction. In contrast decreasing the number of force generating crossbridges by partial extraction of troponin C (TnC) or addition of vanadate caused only minor changes in contraction rate. Thus the rate of force development decreases dramatically with decreases in the Ca2+ level which suggests that a step in the crossbridge cycle may be Ca2+ dependent. The kinetics of relaxation induced by photolysis of diazo-2 was: a) slowed by stabilization of the sarcomeres by repeated releases and re-stretches during contraction and b) accelerated when the amplitude of force development was decreased by decreasing the [Ca2+] which induced a steady contraction. The half time of relaxation decreased by approximately two- to three-fold, when 50% of maximum force was developed. One interpretation of these results is that decreasing the number of force generating crossbridges may speed relaxation by inducing a decreased affinity of TnC for Ca2+ and thus accelerating the Ca2+ dissociation rate from TnC and thereby increasing relaxation rate.


Force Development Thin Filament Partial Extraction Relaxing Solution Intact Fiber 
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Copyright information

© Plenum Press, New York 1998

Authors and Affiliations

  • Jack A. Rall
    • 1
  • Philip A. Wahr
    • 2
  1. 1.Department of PhysiologyOhio State UniversityColumbusUSA
  2. 2.Department of PhysiologyUniversity of MichiganUSA

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