Inhibition of Membrane Transport Systems in Synaptosomes from Torpedo Electric Organ by Snake Neurotoxins

Abstract

Recently there has been considerable interest in the use of naturally occurring neurotoxins as probes for elucidating the molecular processes which underly chemical and electrical transmission in the nervous system. Of those neurotoxins which have been both chemically and pharmacologically characterized a large number occur in the venoms of poisonous snakes. According to Lee (7), snake toxins can be broadly classified into five groups: curaremimetic postsynaptic toxins, cardiotoxins, presynaptic neurotoxins, myonecrotic toxins and toxins affecting Na channels. As tools, the curaremimetic neurotoxins (e.g. α-bungarotoxin) have so far proved to be the most useful since they bind to nicotinic cholinoceptors with high specificity in a quasi-irreversible fashion. Pharmacological evidence suggests that toxins from the other groups exhibit a similar degree of specificity at least at the cellular level of organization. At the molecular level much less is known about the nature of the target sites to which these toxins are directed. The present chapter is concerned with studies aimed at a better understanding of the target sites for the presynaptic neurotoxin group.