DIFFERENTIAL-EFFECTS OF OMEGA-CONOTOXIN GVIA AND MVIIC ON NERVE-STIMULATION INDUCED CONTRACTIONS OF GUINEA-PIG ILEUM AND RAT VAS-DEFERENS

omega-Conotoxin GVIA and omega-conotoxin MVIIC caused similar concentr ation-dependent reductions of the electrically induced twitch response s of guinea-pig ileum. The inhibitory effects of omega-conotoxin GVIA were long-lasting whereas those to omega-conotoxin MVIIC were readily reversed. Preincubation with omega-conotoxin MVIIC prevented the irrev ersible inhibition of omega-conotoxin GVIA suggesting a common site of interaction. However, unlike omega-conotoxin GVIA which caused inhibi tion, omega-conotoxin MVIIC did not affect the electrically induced tw itch responses of the rat vas deferens nor did it prevent the irrevers ible inhibition with omega-conotoxin GVIA. This study indicates the po ssible existence of different subtypes of the N-type voltage-dependent calcium channel.