Effects of N-acetylprocainamide and sotalol on ion currents in isolated guinea-pig ventricular myocytes

The effects of N-acetylprocainamide (NAPA) and sotalol on membrane current systems of guinea-pig ventricular myocytes were examined and compared with those of quinidine using patch-clamp techniques. All of the drugs prolonged the action potential duration (i.e. Class III effect) in isolated guinea-pig papillary muscles. In isolated ventricular cells, NAPA (300 μM) and sotalol (100 μM) produced a decrease in the delayed outward potassium current (I K) concomitantly with a slight decrease in the calcium current (I Ca), which was similar to quinidine (10 μM). NAPA also slightly depressed the inward rectifier potassium current (I Krect). Thus, NAPA and sotalol both inhibited I K, and this action appears to be mainly responsible for their Class III effect.