Investigations differentiating the mechanism of specific bradycardic agents from that of calcium channel blockers.

The effects of two "specific bradycardic agents", falipamil (AQ-A 39) and the alinidine-congener STH 2148 (2-[N-(cyclopropylmethyl)-N-(2,6-dibromophenyl)amino]-2-imidazolin e), on the spontaneous electrical discharge rate of intact guinea-pig sinus node preparations were investigated in comparison to that of the "calcium channel blocker" verapamil. Addition of falipamil (10 micrograms/ml) to a maximally rate lowering concentration of STH 2148 (30 micrograms/ml) exerted no further bradycardic effect. In contrast, verapamil (0.1 microgram/ml) added to either STH 2148 (30 micrograms/ml) or a maximally effective concentration of falipamil (30 micrograms/ml) resulted in a further, significant reduction of sinus rate. The results are compatible with the idea of a common mechanism of the two specific bradycardic agents, different from that of calcium channel blockers.