Responses of two proboscis muscles of Neptunea antiqua (mollusca) to some calcium antagonist drugs

Abstract

1. Both the radular retractor (RR) and radular sac (RS) muscles of Neptunea antiqua depend upon [Ca]₀ to raise the internal calcium concentration of the contractile elements to activation level.

2. The K- and ACh-induced responses of the muscles were strongly inhibited in calcium-free seawater.

3. Calcium antagonist drugs were more inhibitory on ACh-induced responses than on K-responses suggesting a dichotomy of calcium channel activities modulated by these agonists.

4. The calcium ionophore A23187 enhanced ACh-induced responses of both muscles but was without effect on K-induced responses.

5. The responses of these Neptunea muscles to calcium antagonist drugs show some similarities but also differences to those of Buccinum muscles and are quite unlike the excitation induced by organic antagonists in similar muscles of the American whelk Busycon canaliculatum.