The effect of calmodulin inhibitors on the release of acetylcholine and protein phosphorylation induced by tityustoxin, K+ and ouabain.

In this paper we describe our studies of the effects of calmodulin inhibitors on the relationship between the release of acetylcholine (ACh) and protein phosphorylation induced by tityustoxin (TsTX), K+ and ouabain. We observed that in cortical slices of brain, the TsTX induced release of ACh was inhibited in the presence of the calmodulin inhibitors trifluoperazine, W-7 and prenylamine, but not by trifluoperazine sulphoxide. The release of ACh elicited by ouabain and K+ (33 mM) was also inhibited by trifluoperazine and chlorpromazine. Studies on protein phosphorylation with crude or purified synaptosome fractions showed that TsTX and K+ (33 mM) increased the incorporation of 32P into a protein with the same apparent molecular weight of synapsin I. Surprisingly, ouabain did not stimulate phosphorylation of this protein. Trifluoperazine, at the same concentrations that inhibited the release of ACh, blocked the stimulatory effect of tityustoxin and K+ on protein phosphorylation. On the other hand, tetrodotoxin inhibited the effect of tityustoxin on protein phosphorylation but had no effect on phosphorylation evoked by K+. Our results demonstrate for the first time that, at least for ouabain, the release of neurotransmitter is not dependent on protein phosphorylation.