Is the cardiovascular profile of BRL 34915 characteristic of potassium channel activators?

To see whether the cardiovascular profile of BRL 34915, a potent vasodilator, is characteristic of potassium channel activators, we investigated its cardiac effects by use of isolated, blood-perfused papillary muscle, sinoatrial (SA) node, and atrioventricular (AV) node preparations of dogs. BRL 34915 was injected intraarterially. It produced an increase in (coronary) blood flow in all preparations. In paced papillary muscle preparations, BRL 34915, although in large doses, produced a decrease in the force of contraction, leading nearly to abolition. The negative inotropic effect of BRL 34915 was accompanied by a marked acceleration of the repolarization of field cardiac action potentials. In some preparations, fibrillation occurred after profound negative inotropy and subsided spontaneously. In unpaced papillary muscles, BRL 34915 in large doses decreased rate of ventricular automaticity. In SA node preparations, BRL 34915 in large doses reduced sinus rate down to approximately 64% of the basal rate and produced atrial standstill in some. In AV node preparations, BRL 34915 in large doses slightly prolonged AV conduction time only when injected into the AV node artery. Nevertheless, it produced third-degree AV block in some. These cardiac effects of BRL 34915 are very similar to those of nicorandil and pinacidil, whose cardiac effects result exclusively from an increase in membrane K conductance in cardiac muscle cells. Like nicorandil and pinacidil, BRL 34915 was highly vasoselective.