Effects of neurotoxins (veratridine, sea anemone toxin, tetrodotoxin) on transmitter accumulation and release by nerve terminals in vitro

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Abstract
Veratridine and the sea anemone toxin provoke neurotransmitter release from synaptosomes; tetrodotoxin prevents the action of both veratridine and the sea anemone toxin. The half-maximum effects of veratridine and sea anemone toxin actions on [rat] synaptosomes are K0.5 = 10 and 0.02 .mu.M, respectively. Although veratridine and the sea anemone toxin similarly provoke neurotransmitter release, they act on different receptor structures in the membrane. Tetrodotoxin antagonizes the effects of both veratridine and the sea anemone toxin. The half-maximum inhibitory concentration of tetrodotoxin is K0.5 = 4 nM for veratridine and 7.9 nM for ATXII [sea anemone neurotoxin]. It is very similar to the Kd measured from direct binding experiments with the radioactive toxin. The analysis of this antagonistic action offers an easy in vitro assay for tetrodotoxin interaction with its receptor.