Interaction of some antiarrhythmic drugs with the heart sarcolemmal Na+-Ca2+ exchange system

The effects of some Class I antiarrhythmics (quinidine, procainamide and lidocaine) and some Class II antiarrhythmics (propranolol, atenolol and acebutolol) on canine cardiac sarcolemmal Na+-Ca2+ exchange activity were studied. Both quinidine (5-100 microM) and procainamide (1-100 microM), unlike lidocaine, inhibited Na+-dependent Ca2+ uptake in sarcolemmal vesicles. The effective concentrations of these agents were well within their respective therapeutic ranges; about 30% inhibition was seen by 10 microM quinidine or procainamide. Propranolol showed a 25% inhibition of the Na+-Ca2+ exchange activity at 100 microM, which concentration is well above its therapeutic range. Acebutolol (0.1-100 microM) had no significant effects, whereas atenolol (10-100 microM), which appeared to inhibit Na+-dependent Ca2+ uptake, also stimulated nonspecific Ca2+ uptake. These results indicate that the cardiac sarcolemmal Na+-Ca2+ exchange system may be one of the sites for the antiarrhythmic actions of quinidine and procainamide.