Pharmacological identification of saxitoxin-like toxins in the cultured purple clam, Hiatula diphos.

An outbreak of poisoning from ingestion of purple clam (Hiatula diphos), obtained from a brackish fish-culture pond, occurred in southern Taiwan in early January 1986. The extract blocked the twitch responses and generation of the action potential of the mouse diaphragm without an effect on the resting membrane potential or the miniature endplate potential. The depolarizations and spontaneous firings of the diaphragm induced by veratridine and crotamine were effectively antagonized by the toxic clam extract, indicating the presence of saxitoxin-like substances, which may have amounted to 0.013% tetrodotoxin equivalent.