Comparison of various calcium channel blockers on guinea-pig isolated common bile duct

1. The inhibitory effects of various calcium channel blockers; nifedipine, verapamil, diltiazem and a heterogenous compound, dantrolene, have been investigated on isolated common bile duct from guinea-pig. 2. All the compounds tested induced a concentration-dependent reduction of the amplitude of contractile response to electrical stimulation or increasing 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; verapamil, 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-response curve of calcium chloride to the right in a concentration-dependent manner. Among the compounds studied, nifedipine had the highest and dantrolene had the lowest potency. 6. These results indicate the striking pharmacological effects of the calcium channel blockers on the common bile duct and may indicate a possible role for these compounds in the treatment of biliary colic.