[The blocking effects of six antiarrhythmic drugs on transient outward current in rat ventricular myocytes].

The effects of six antiarrhythmic drugs on transient outward current (Ito) in rat ventricular myocytes were examined by using the patch-clamp whole-cell recording technique. Quinidine, nifedipine, and imipramine resulted in a concentration-dependent inhibition of Ito with IC50s of 5.4, 10.9 and 6.0 mumol.L-1, respectively. All three agents produced a concentration-dependent increase in the rate of inactivation of Ito. Disopyramide, procainamide and E-4031 produced little inhibition of Ito even when present at 100 mumol.L-1. The results from this study show that quinidine, nifedipine and imipramine are potent inhibitors of Ito and that inhibition is mediated through preferential interaction with the open channel.