A study on the mode of action and composition of a toxin from the female abdomen and eggs of Arctia caja (L.) (Lep. Arctiidae): An electrophysiological, ultrastructural and biochemical analysis

Cajin, the toxic principle extracted from the female abdomen and eggs of the aposematic moth Arctia caja, was investigated by means of column chromatography, and its effects on tissues were studied by electrophysiology and electron microscopy. Partial purification suggests that one fraction is a polypeptide with a molecular weight (mol. wt) of about 1000. It is lethal to both mammals and insects if injected into the body, but inactive via the oral route. Crude extracts applied to insect muscles produce a slow contracture which lasts for over 1 1 2 hr and is irreversible. Fine structural analyses of insect tissues after 5 min toxin treatment reveal disruption of both internal membranous systems and mitochondria. Unlike many other toxins, cajin appears to act by stimulating the muscle directly. The results of experiments involving Ca 2+-free solutions plus cajin suggest that it may increase the permeability of the muscle membrane to Ca 2+, perhaps behaving as a calcium ionophore, or may act as an analogue of an insect neurotransmitter.