Electrophysiological observations on the digitalis-potassium interaction in canine Purkinje fibers.

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Abstract
We studied the effects of elevating potassium concentration on the membrane potential of Purkinje cells exposed to toxic concentrations of acetylstrophanthidin or ouabain. Conventional intracellular microelectrode techniques were employed. Rapid elevation of [K+]o from 2.7 to 5.4 mEq/liter resulted in an initial increase (more negative) in membrane potential of cells demonstrating ouabain-induced phase 4 depolarization. The increase in maximal diastolic potential occurred initially without suppression of phase 4 depolarization. In cells rendered inexcitable by ouabain or acetylstrophanthidin, elevation of [K+]o consistently increased membrane potential and restored excitability. In four experiments automaticity was initiated within 2 minutes after the increase in [K]o. Although automaticity reappeared, as maximal diastolic potential increased, the automatic rate slowed and then pacemaker activity was suppressed. Studies with 3H-ouabain showed that the increase in membrane potential paralleled K+-induced release of 3H-ouabain from Purkinje cells. These studies suggest that elevation of [K+]o reverses digitalis toxic manifestations in canine Purkinje fibers by causing release of cardiac glycosides bound to the membrane. The observed increase in membrane potential of ouabain-treated Purkinje fibers that occurred after [K+]o elevation was considered to be mediated in part by restoration of the Na pump and by electrogenic pumping.