Differential effects of Bay k 8644, a presumed calcium channel activator, on sinoatrial nodal and ventricular automaticity of the dog heart.

Bay k 8644 is suggested to increase calcium influx through the voltage-dependent calcium channel. In isolated, blood-perfused sinoatrial node preparations of the dog. Bay k 8644 injected intra-arterially increased sinus rate as isoprenaline did. In isolated, blood-perfused papillary muscle preparations of the dog isoprenaline injected intra-arterially increased both the force of contraction of the papillary muscle and its spontaneous beating rate. In these preparations, however, Bay k 8644 failed to increase the beating rate, although it increased the force of contraction. These results are consistent with the concept that the slow inward current plays a role in sinoatrial nodal automaticity but not in automaticity of Purkinje fibres which was reflected as ventricular automaticity of the papillary muscle preparations used here.