Electrophysiology of cardiac myocytes of Aplysia brasiliana

Abstract

The electrical properties of Aplysia brasiliana myogenic heart were evaluated. Two distinct types of action potentials (APs) were recorded from intact hearts, an AP with a slow rising phase followed by a slow repolarizing phase and an AP with a ‘fast’ depolarizing phase followed by a plateau. Although these two APs differ in their rates of depolarization (2.2=0.3 Vys), both APs were abolished by the addition of Co2q, Mn2q and nifedipine or by omitting Ca2q from the external solution. These data suggest that a Ca2q inward current is responsible for the generation of both types of APs. Two outward currents activated at y40 mV membrane potential were prominent in isolated cardiac myocytes: a fast activating, fast inactivating outward current similar to the A-type Kq current and a slow activating outward current with kinetics similar to the delayed rectifier Kq current were recorded under voltage clamp conditions. Based on the effects of 4-AP and TEA on the electrical properties of ventricular myocytes, we suggest that the fast kinetic outward current substantially attenuates the peak values of the APs and that the slow activating outward current is involved on membrane repolarization.