Structure and Action of Nemertine Toxins

Bacq (1936, 1937) discovered two substances by pharmacologicalexperiments using whole body extracts of various nemertine species."Amphiporine," found only in hoplonemertines, stimulated nicotinicacetylcholine receptor-mediated events. "Nemertine" evoked spontaneousaction potentials in isolated crab nerves. Both substances causedconvulsions when injected into crabs. Anabaseine, a pyridinealkaloid isolated from the hoplonemertine Paranemertes peregrina,has chemical and pharmacological properties equivalent to "amphiporine."Hoplonemertines produce a wide variety of pyridine toxins dependingon the species. The heteronemertine Cerebratulus lacteus contains cytolytic(10,000 dalton) and neurotoxic (6,000 dalton) proteins. Theneurotoxic polypeptides most closely resemble "nemertine": theycause repetitive spiking in isolated crustacean axons. Severalcytolytic and neurotoxic "isotoxins" occur within Cerebratulus. Both the hoplonemertine and heteronemertine toxins are localizedin the integumentary tissues of the body wall and proboscis.So far, the pyridine alkaloid toxins are only found in the Enoplanspecies, where they probably function as both offensive anddefensive toxins. Protein toxins have only been found in Anoplanspecies; they probably serve as a chemical defense against somepredators.