Effects of calcium antagonist drugs on acetylcholine and high K responses of a molluscan muscle Neptunea antiqua.

The odontophore retractor (OR) muscle of Neptunea antiqua depends on external calcium to raise internal cellular calcium concentration of the contractile system to activation level. The acetylcholine (Ach)-and high K-induced responses were abolished in nominally Ca-free and 2 mmol/l EGTA/Ca/free salines. Diltiazem and nifedipine were inhibitory on both Ach and high K responses of the OR muscle. However, verapamil was inhibitory only on K but not Ach response. Compared with the radular retractor and radular sac muscle, the OR muscle of Neptunea shows some differences but also similarities in its slow calcium channel activities even though all these muscles are bound together in the same organism.