Electrophysiological effects of bunaphtine on isolated rat atria

The effects of a new antiarrhythmic, bunaphtine, on the electrical and mechanical activity of isolated rat atria were compared with those of quinidine and amiodarone. Both electrically stimulated and spontaneously beating atria were used. In spontaneously beating double atria bunaphtine produced a dose-dependent decrease in the rate, contractile force, work index and maximum following frequency at which the atria could respond to electrical stimulation, depressed the pacemaker activity and increased the sinus node recovery time. In isolated left atria bunaphtine prolonged the effective refractory period and decreased atrial excitability. Bunaphtine did not block positive chronotropic and inotropic responses to isoprenaline and did not reduce the positive inotropic effect of raised calcium concentrations. These results support the hypothesis that bunaphtine exerted on isolated atria a direct cardiodepressant effect similar to that of quinidine, and that it may be classified as a class 1 antiarrhythmic according to the classification of Vaughan Williams.