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Effect of Protein Kinase C Activation on the Release of [3H]Acetylcholine in the Presence of Vesamicol
Authors:J. Barbosa  Jr.    A. D. Clarizia  M. V. Gomez  M. A. Romano-Silva  V. F. Prado   M. A. M. Prado
Affiliation:Laboratório de Neurofarmacologia, Departamentos de Farmacologia,; Bioquímica-Imunologia, ICB, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brasil
Abstract:Abstract: The present work tested whether pharmacological activation of protein kinase C (PKC) influences the release of [3H]-acetylcholine ([3H]ACh) synthesized in the presence of vesamicol, an inhibitor of the vesicular acetylcholine transporter (VAChT). Newly synthesized [3H]ACh was released from hippocampal slices by field stimulation (15 Hz) in the absence of vesamicol, but as expected [3H]ACh synthesized during exposure to vesamicol was not released significantly by stimulation. Treatment of slices with the PKC activator phorbol myristate acetate (PMA) decreased the inhibitory effect of vesamicol on [3H]ACh release. The effect of PMA was dose-dependent, was sensitive to calphostin C, a PKC-selective inhibitor, and could not be mimicked by α-PMA, an inactive phorbol ester. PMA did not alter the release of [3H]ACh in the absence of vesamicol, suggesting that the site of PKC action could be related to the VAChT. In agreement with this observation, immunoprecipitation of VAChT from 32P-labeled synaptosomes showed that phosphorylation occurs and that incorporation of 32P in the VAChT protein increases in the presence of PMA. We suggest that PKC alters the output of [3H]ACh formed in the presence of vesamicol and also provide circumstantial evidence for a role of phosphorylation of VAChT in this process.
Keywords:Acetylcholine release    Vesamicol    Vesicular acetylcholine transporter    Synaptic vesicles    Protein kinase C
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