The effects of temperature, local anaesthetics, pH, divalent cations, and group-specific reagents on repriming and repolarization-induced contractures in frog skeletal muscle

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Abstract
Contractures appear during repolarization of frog toe muscles in media containing perchlorate in place of chloride. These contractures were suppressed or delayed by certain procedures which retard the repriming of K contractures, i.e., by sufficient reduction in temperature or by alkaline pH in solutions lacking divalent cations. They also were greatly reduced without interference with repriming after treatment with a reagent which selectively modifies free amino groups. In the presence of appropriate concentrations of procaine, repriming was markedly impaired with only a small reduction in the amplitude of repolarization-induced contractures. Small contractures were produced during repolarization in chloride solutions in the presence of 10 mM procaine at pH 8.0. None of these procedures affected the changes produced by perchlorate solutions in the potential dependence and the time course of K contractures. The results support the view that activation and inactivation of contraction following depolarization are separate potential dependent processes. Tension appears to develop during repolarization when the reversal of inactivation occurs before the reversal of activation is completed, both steps being necessary to recover the reprimed resting state.