Potent excitatory effect of scaritoxin on the guinea-pig vas deferens, taenia caeci and ileum

Abstract

Scaritoxin (STX), a potent toxic substance isolated from poisonous fish induced a dose-dependent contraction of the isolated guinea-pig vas deferens at concentrations of 10(-8) to 10(-6) g/ml. This contraction was abolished or inhibited by tetrodotoxin, low Na+ medium, phentolamine or reserpine, but not by atropine, chlorpheniramine or methysergide. STX shifted to the left the dose-contractile response curve for norepinephrine, KCI or acetylcholine in the vas deferens. STX caused a release of norepinephrine from the vas deferens, in a dose-dependent manner, which was blocked by tetrodotoxin, Mg++ or Ca++-free medium. In the guinea-pig taenia caeci or ileum, STX elicited a dose-dependent contraction. The contractions of both tissues were blocked completely by tetrodotoxin and were inhibited markedly by atropine but not by mecamylamine or chlorpheniramine. These results suggest that the STX-induced contraction is the result of an indirect action mediated through the norepinephrine release from adrenergic nerve terminals of the vas deferens and acetylcholine release from cholinergic nerve endings of the taenia caeci or the ileum. It is also suggested that STX causes an increase in Na+ permeability of the cell membrane of these tissues, which may play an important role in the release of chemical transmitters induced by STX.