Differential properties of two charge components in frog skeletal muscle.

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Abstract
Charge movement in frog twitch muscle fibers bathed in a moderately hypertonic solution (containing 350 mM-sucrose), it showed a main component (Q.beta.) and a secondary hump (Q.gamma.). Assuming that Q.beta. decays with a single exponential and Q.gamma. follows the time course of a symmetrical bell, a mathematical model was developed to separate Q.gamma. from Q.beta.. The activation curves of Q.beta. and Q.gamma. can be individually fitted by the 2-state model of Schneider and Chandler. The voltage distribution of Q.gamma. is approximately twice as steep as that of Q.beta. and the maximum moveable amount of Q.beta. about 4 times that of Q.gamma.. The decay rate constant of Q.beta., expressed as a function of potential, follows the familiar U-shaped curve whereas the reciprocal of the time-to-peak of Q.gamma. rises linearly with increasing potentials. Application of the mathematical dissection technique to Qon values in solutions of varying concentrations of tetracaine yielded the dose dependence of the suppression of Q.gamma. by tetracaine. Q.gamma. inactivates more steeply than Q.beta. as the holding potential is made less negative. Each of the steady-state inactivation curves of Q.beta. and Q.gamma. forms a mirror image with the respective activation curve. Q.gamma. might be more directly involved than Q.beta. in triggering Ca release and activating contraction.