MUSCULAR CONTRACTION AS REGULATED BY THE ACTION POTENTIAL.

Lowering the mechanical threshold and, independently, prolonging the duration of the action potential cause an increased rate of tension development, as well as potentiation of the twitch, of frog skeletal muscle. The alterations of the two different features of function of the action potential modify excitation-contraction coupling in essentially identical fashion (probably by increasing the liberation of free Ca(2+) into the myoplasm), and this results in early intensification as well as later prolongation of the active state.