A Comparison of the Effects of Scorpion Venom Tityustoxin and Ouabain on the Release of Acetylcholine From Incubated Slices of Rat Brain¹

The increase in the release of acetylcholine (ACh) from cortical slices of rat brain elicited by the depolarizing agents, ouabain and tityustoxin (TsTX) was compared in the presence of tetrodotoxin, an inhibitor of Na + transport and of ethyleneglycol tetraacetic acid, a specific chelator of Ca 2+ . TsTX stimulated the release of ACh independently of K 1 but required both Na + and Ca 2+ . Unlike ouabain, TsTX failed to inhibit the Na + , K + ‐ATPase of rat brain homogenates. The uptake of 24 Na + and of 45 Ca 2+ by the slices was significantly enhanced by TsTX over the entire incubation period during which this process was compared to TsTX‐free controls. A hypothesis of TsTX action is proposed which differs from that necessary to explain the ACh releasing effect of ouabain.