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Protein Kinase C Activation Enhances K + ‐Stimulated Endogenous Dopamine Release from Rat Striatal Synaptosomes in the Absence of an Increase in Cytosolic Ca 2+
Author(s) -
Chandler L. Judson,
Leslie Steven W.
Publication year - 1989
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1989.tb07275.x
Subject(s) - depolarization , dopamine , synaptosome , egta , chemistry , biophysics , medicine , neurotransmitter , endocrinology , calcium , biochemistry , biology , receptor , organic chemistry
The possibility that protein kinase C modulates neurotransmitter release in brain was investigated by examining the effects of 12‐ O ‐tetradecanoylphorbol 13‐acetate (TPA) on Ca 2+ transport and endogenous dopamine release from rat striatal synaptosomes. TPA (0.16 and 1.6 μ M ) significantly increased dopamine release by 24 and 33%, respectively, after a 20‐min preincubation with TPA followed by 60 s of depolarization with 30 m M KCl. Depolarization‐induced 45 Ca 2+ uptake, measured simultaneously with dopamine release, was not significantly increased by TPA. Neither 45 Ca 2+ uptake nor dopamine release was altered under resting conditions. When the time course of K + ‐stimulated 45 Ca 2+ uptake and dopamine release was examined, TPA (1.6 μ M ) enhanced dopamine release after 15, 30, and 60 s, but not 1, 3, or 5 s, of depolarization. A slight increase in 45 Ca 2+ uptake after 60 s of depolarization was also seen. The addition of 30 m M KCl to synaptosomes which had been preloaded with the Ca 2+ ‐sensitive fluorophore fura‐2 increased the cytosolic free Ca 2+ concentration ([Ca 2+ ] i ) from 445 n M to 506 n M after 10 s of depolarization and remained elevated after 60 s. TPA had no effect on [Ca 2+ ] i under depolarizing or resting conditions. Replacing extracellular Ca 2+ with 100 μ M EGTA reduced K + ‐stimulated (60 s) endogenous dopamine release by 53% and decreased [Ca 2+ ] i to 120 n M . In Ca 2+ ‐free medium, 30 m M KCl did not produce an increase in the [Ca 2+ ] i . TPA (1.6 μ M ) did not alter the [Ca 2+ ] i under resting or depolarizing conditions, but did increase K + ‐stimulated dopamine release in Ca 2+ ‐free medium. The inactive 4α‐phorbol had no effect under any of the above experimental conditions. The demonstration that TPA induced an increase in dopamine release without an increase in the [Ca 2+ ] i may suggest that protein kinase C increases the sensitivity of the exocytotic release process to Ca 2+ .