[Increase of potassium conductance and spontaneous electric activity in vitro: comparison of nicorandil and cicletanine].

Nicorandil (N) increases potassium conductance in vascular smooth muscle and so induces vasodilation; N also dose-dependently reduces action potential duration (APD). However, it is unclear whether increased potassium conductance, and concomitant APD shortening, might be arrhythmogenic, particularly when myocardial ischemia (where potassium efflux is increased) concurs. Data on the anti-arrhythmic effectiveness of N have also been published: N reduced the spontaneous discharge of sino-atrial node and so reduced heart rate, both in vitro and man. On the other hand, among other vasodilators, cicletanine (C) has been reported to increase potassium conductance, an effect which was advocated to explain its antiarrhythmic potency. In the present investigation the direct myocardial effects of N were compared to those following C in 63 experiments (from 13 Guinea-pigs), using atrial strips (containing sino-atrial node) superfused in 1-compartment bath with normal Tyrode's solution. Using glass microelectrodes, standard electrophysiologic variables were recorded (APA, RMP, APD50%, Vmax) in spontaneously beating atrial tissue, either in Tyrode, dimethyl-sulfoxide (DMSO 1:100, as solvent), C 10(-5) M (in DMSO 1:100), and N 10(-3) M (in DMSO 1:100), whose respective perfusion periods (15 min) were randomized, always following 15 min of washout with Tyrode. Only N was tested in experiments of both 15 and 30 min duration.(ABSTRACT TRUNCATED AT 250 WORDS)