COMPARISON OF VARIOUS CALCIUM-CHANNEL BLOCKERS ON GUINEA-PIG ISOLATEDCOMMON BILE-DUCT

1. The inhibitory effects of various calcium channel blockers; nifedip ine, verapamil, diltiazem and a heterogenous compound, dantrolene, hav e been investigated on isolated common bile duct from guinea-pig. 2. A ll the compounds tested induced a concentration-dependent reduction of the amplitude of contractile response to electrical stimulation or in creasing the calcium concentration of the bathing media. 3. Nifedipine was the most potent compound whereas the least potent was dantrolene; verapamil and diltiazem had intermediate potency. 4. The IC50 values for these compounds were calculated as: nifedipine 3.68 x 10-(9) M; ve rapamil, 4.93 x 10(-8) M; diltiazem, 4.2 x 10(-7) M; and dantrolene 5. 51 x 10(-5) M. 5. All the compounds displaced the concentration-respon se curve of calcium chloride to the right in a concentration-dependent manner. Among the compounds studied, nifedipine had the highest and d antrolene had the lowest potency. 6. These results indicate the striki ng pharmacological effects of the calcium channel blockers on the comm on bile duct and may indicate a possible role for these compounds in t he treatment of biliary colic.