1. Conventional microelectrode techniques were used to study the effects of antiarrhythmic drugs (quinidine, 2-20 μM; lidocaine, 5-50 μM; verapamil, 2-20 μM), 4-aminopyridine (4-AP, 50-100 μM), and tetrodotoxin (TTX, 1.5-6 nM) on repetitive electrical discharges induced in the muscle membrane in the presence of 1 μM cevadine. 2. Antiarrhythmic drugs and 4-AP produced progressive reduction of the maximum upstroke velocity (V+max) of the discharges, while the cycle length was prolonged by each drug except 4-AP. 3. The efficacy in depression of V+max and prolongation of cycle length was not proportional in the case of individual drugs. 4. A simple model of the repetitive activity incorporating drug-effects was presented. The cevadine-modified Na+ channels could be blocked by antiarrhythmic agents, however, the efficacy of these drugs on the normal and cevadine-modified Na+ channels were found to be different.
ASJC Scopus subject areas