Effects of potassium on frog skeletal muscle in a chloride-deficient medium

¹ Department of Pharmacology, School of Medicine, University of Washington, Seattle, Washington

Muscle fibers give prolonged action potentials with a characteristic plateau in a medium in which chloride has been replaced by anions which do not carry charge across the membrane. Repolarization is aperiodic or oscillatory with negative damping. Duration of the plateau and growth of oscillations are potassium sensitive and independent of changes in resting potential. In the absence of external K, spontaneous spikes are fired off until the membrane potential becomes set at the plateau level or oscillates in the region thereof. Fibers remain depolarized indefinitely until K is added. A fiber may have two modes of oscillation, one associated-with deviations from the resting state, the other with a depolarized steady state. Both forms of oscillations belong to excitable systems but their voltage dependence differs. Lithium can substitute for sodium in the prolonged response.