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EFFECTS OF VERAPAMIL ON ELECTROPHYSIOLOGIC PROPERTIES OF CANINE CARDIAC PURKINJE FIBERS

1974; American Society for Pharmacology and Experimental Therapeutics; Volume: 189; Issue: 2 Linguagem: Inglês

10.1016/s0022-3565(25)29845-7

1521-0103

Michael R. Rosen, Joseph P. Ilvento, Henry Gelband, Charles Merker,

Cardiac Arrhythmias and Treatments

Standard microelectrode techniques were used to determine the effects of verapamil, 2 x 10 -7 to 1 x 10 -5 M, on the electrophysiologic properties of isolated canine cardiac Purkinje fibers. Verapamil, -6 M, had no effect on the Purkinje fiber action potential (AP). Verapamil, 2 x 10 -6 M, altered repolarization primarily by enhancing phase 1 and increasing the slope of phase 2. Verapamil, ≥6 x 10 -6 M, had more pronounced effects on AP repolarization and decreased amplitude, resting membrane potential, maximum rate of rise of phase 0 and membrane responsiveness as well. The ratio of AP duration to effective refractory period was unchanged by verapamil. Conduction velocity was slowed only by verapamil, ≥6 x 10 -6 M. The effects of verapamil on phase 4 depolarization and automaticity induced by low potassium perfusates and/or ouabain, 2 x 10 -7 M, and on ouabain-induced low amplitude potentials were studied as well. Verapamil, 2 x 10 -6 M, suppressed automaticity and low amplitude potentials. Verapamil effects on the AP and phase 4 were partly reversible by increasing perfusate calcium concentration. These studies suggest that verapamil acts via mechanisms differing from other antiarrhythmics. The effective refractory period and conduction are not modified by lower verapamil concentrations and the AP, other than repolarization, is not altered. Verapamil does suppress automaticity and low amplitude potentials and may suppress arrhythmias initiated by calcium-induced slow responses.