The temperature dependence of ionic influences on contractile function in frog twitch muscle.

Abstract

Alterations in the ionic composition of the medium produce striking changes in the potential-dependent contractile responses of skeletal muscles. This study was undertaken to examine the temperature dependence of some of these effects. The suppression of maximal K contractures of frog toe muscles in media lacking divalent cations was largely overcome by a sufficient increase in temperature. The restoration of K contractures by perchlorate in the absence of divalent cations was prevented by a sufficient decrease in temperature. The effect of perchlorate was to shift the temperature dependence of these contractures toward lower temperatures. The reduction in the amplitude of maximal K contractures in the absence of divalent cations was less marked after pretreatment with a reagent (trinitrobenzenesulfonate) that selectively modifies free amino groups, although the temperature dependence of these contractures was unchanged. The reduction in the amplitude of K contractures in the presence of an organic anion (hexanoate) was partially antagonized both by an increase in temperature or by a decrease in temperature, effects that resemble those observed in solutions in which the divalent cation concentration was reduced. In chloride solutions, the relation between [K]0 and K contractures was shifted toward lower [K]0 by an increase in temperature, whereas in perchlorate solutions increased temperature produced a shift in the opposite direction. The shift in this relation toward lower [K]0 at reduced temperature, and the accelerated time course of K contractures with an increase in temperature were similar in perchlorate and in chloride solutions. Thermodynamic analysis by Arrhenius plots indicated that the influence of divalent cations and perchlorate anions on K contractures may be the result of their effects on hydrational factors.