Abstract: Using patch clamp whole cell recording techiques, we examined the effects of IQ23, a benzyl-isoquinoline derivative with antiarrhythmic activities, on the action potential (AP) and potassium currents in single guinea pig ventricular myocytes. The results showed that IQ23 at 10, 30and 100 μmol·L^-1 slowed the repolarization in AP dose-dependently. The APD90 were prolonged by15%, 28% and 31% respectively. This effect did not depend on the extracellular Ca²⁺. In voltage clamp mode, IQ23 effectively blocked both the components of the delayed rectifier potassium current (Ik), i.e., Iks and Ikr. At concentrations of 30 and 100 μmol·L^-1, IQ23 suppressed Iks by 21% and 26% and suppressed Ikr by 67% and 86% respectively. But even at 100 μmol·L^-1, IQ23 had little effect onthe inward rectifier potassium current (Ikl). It is concluded: (1) IQ23 can dose-dependently prolong APD in the ventriculas myocytes of guinea pig, the effect does not depend on the extracellular Ca²⁺; (2) IQ23 blocks both Iks and Ikr in the ventricular myocytes without obvious specificities between them.

Key words: IQ13, Antiarrhythmic drug, Patch clamp technic, Action potential, Potassiumchannel, Ventricular myocyte, Guinea pig