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Inhibition by trifluoperazine of calmodulin-induced activation of ATPase activity of rat erythrocyte
Journal article   Peer reviewed

Inhibition by trifluoperazine of calmodulin-induced activation of ATPase activity of rat erythrocyte

R.M. Levin and B. Weiss
Neuropharmacology, v 19(2), pp 169-174
1980
PMID: 6444700

Abstract

An endogenous, heat-stable, calcium binding protein (calmodulin). which was previously shown to increase the activity of one of the forms of cyclic nucleotide phosphodiesterase, was found to increase selectively the activity of a (Ca 2+ + Mg 2+)-ATPase of rat erythrocyte membranes. The ED 50 for calmodulin activation was 150 ng calmodulin/ml. The concentration of Ca 2+ required for half-maximum calmodulin-induced activation of erythrocyte ATPase was 20 μM whereas approximately 50 μM Ca 2+ was required for half-maximum calcium-induced activation of ATPase measured in the absence of calmodulin. The phenothaizine trifluoperazine, which specifically inhibits the activation of phosphodiesterase by high-affinity, calcium-specific binding to calmodulin, specifically inhibited the calmodulin-induced acti- vation of ATPase; the I 50 for inhibition of ATPase was 50 μM when measured in the presence of calmodulin but was over 250 μM when measured in its absence. This trifluoperazine-induced inhibition of ATPase could be overcome by adding excess calmodulin. These results indicate that calmodulin activates a specific form of erythrocyte ATPase and that trifluoperazine selectivity inhibits this activation presumably by binding to calmodulin. The results further support the hypothesis that several of the biochemical actions of phenothiazine antipsychotics can be explained by a common mechanism, namely, by selectively binding to calmodulin and thereby inhibiting its action.

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