Effects of isocorydine on action potentials in isolated canine Purkinje fibers and ventricular muscles.

Standard microelectrode techniques were used to study the effects of isocorydine (Isoc) on potential characteristics of canine cardiac Purkinje fibers (PF) and ventricular myocardium (VM) in vitro. In PF, the action potential durations (APD), APD50, and APD90, were prolonged at 3 mumol.L-1 but shortened at 30 mumol.L-1 by Isoc. The action potential amplitude (APA) and the maximal upstroke velocity (Vmax) were decreased at 100 mumol.L-1. In VM, the action potential characteristics were changed by Isoc at above 30 mumol.L-1. APD50 was shortened by APD90 was prolonged. Vmax were decreased at 30 mumol.L-1. The effective refractory period (ERP) was prolonged by Isoc in PF and VM. The results suggest that Isoc may interfere with K+, Na+, and Ca2+ currents in myocardiac cell membrane at different concentrations.