Contraction transients of skinned muscle fibers: effects of calcium and ionic strength.

Abstract

Ca and ionic strength modify the force developed by skinned frog muscle fibers. To determine how these parameters affect the cross-bridge contraction mechanism, the isotonic velocity transients following step changes in load were studied in solutions in which Ca concentration and ionic strength were varied. Analysis of the motion showed that Ca has no effect on either the null time or the amplitude of the transients. In contrast, the transient amplitude was increased in high ionic strength and was suppressed in low ionic strength. These results are consistent with the idea that Ca affects force in skeletal muscle by modulating the number of force generators in a simple switchlike on-off manner and that the steady force of a given Ca level is proportional to cross-bridge number. The effect of ionic strength on force is associated with changes in the kinetic properties of the cross-bridge mechanism.