Abstract

Microelectrode techniques were used to study the effects of procaine amide (PA), 10 to 90 µg/ml, on electrophysiologic properties of canine Purkinje fibers (PF) and ventricular muscle perfused with Tyrode's solution containing 2.5, 4.0 or 5.5 mM KCl. Automaticity of spontaneously beating PF decreased within 40 minutes of perfusion with [PF] = 10 µg/ml; this was the only consistent electrophysiologic change at [PA]<30 µg/ml. After 30 minutes of perfusion with [PA] = 30 µg/ml, action potential amplitude and maximal slope of phase 0 decreased, and conduction throughout the ventricular conducting system was slowed, especially that in ventricular muscle. The voltage-time course of repolarization was altered in such a way that action potentials dissimilar in duration, recorded from sites proximal to, distal to and at the area of maximum action potential duration became similar. Simultaneously action potential duration measured to full repolarization and effective refractory periods were prolonged. Changes were most prominent at [K⁺]₀ = 2.5 and least apparent at [K⁺]₀ = 5.5 mM. At [PA] = 90 µg/ml the aforementioned changes were accentuated.