Effect of scorpion venom, tityustoxin, on the release of acetylcholine from incubated slices of rat brain

Abstract— Purified tityustoxin (TsTX) from the venom of the scorpion, Tityus serrulatus, when incubated in vitro with slices of rat cerebral cortex, increased the amount of free ace-tylcholine (ACh) in the incubation medium and, simultaneously, reduced the amount of bound ACh in the slices. The effect was optimal at pH 7.4 and was dependent upon time of incubation, an energy source and the concentration of toxin. Tityustoxin increased the synthesis of ACh, but this effect seemed to be related to an increase in the release of ACh. The effect of the TsTX was independent of the concentration of K⁺ ion but was dependent on the presence of Na⁺ and Ca²⁺ in the incubation medium. Hexamethonium and hemicholinium reduced the effect of tityustoxin, but cocaine had no effect on the release of ACh stimulated by the TsTX. Tetrodotoxin blocked completely the stimulation caused by the tityustoxin. We suggest that probably both tityustoxin and tetrodotoxin exert different and antagonistic effects competing in the Na⁺ channels.