Protein kinase C activation enhances K+-stimulated endogenous dopamine release from rat striatal synaptosomes in the absence of an increase in cytosolic Ca2+.
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 Ca2+ transport and endogenous dopamine release from rat striatal synaptosomes. TPA (0.16 and 1.6 microM) significantly increased dopamine release by 24 and 33%, respectively, after a 20-min preincubation with TPA followed by 60 s of depolarization with 30 mM KCl. Depolarization-induced 45Ca2+ uptake, measured simultaneously with dopamine release, was not significantly increased by TPA. Neither 45Ca2+ uptake nor dopamine release was altered under resting conditions. When the time course of K+-stimulated 45Ca2+ uptake and dopamine release was examined, TPA (1.6 microM) enhanced dopamine release after 15, 30, and 60 s, but not 1, 3, or 5 s, of depolarization. A slight increase in 45Ca2+ uptake after 60 s of depolarization was also seen. The addition of 30 mM KCl to synaptosomes which had been preloaded with the Ca2+-sensitive fluorophore fura-2 increased the cytosolic free Ca2+ concentration ([Ca2+]i) from 445 nM to 506 nM after 10 s of depolarization and remained elevated after 60 s. TPA had no effect on [Ca2+]i under depolarizing or resting conditions. Replacing extracellular Ca2+ with 100 microM EGTA reduced K+-stimulated (60 s) endogenous dopamine release by 53% and decreased [Ca2+]i to 120 nM. In Ca2+-free medium, 30 mM KCl did not produce an increase in the [Ca2+]i. TPA (1.6 microM) did not alter the [Ca2+]i under resting or depolarizing conditions, but did increase K+-stimulated dopamine release in Ca2+-free medium.(ABSTRACT TRUNCATED AT 250 WORDS)
Chandler
L J
LJ
Division of Pharmacology, College of Pharmacy, University of Texas, Austin.
Leslie
S W
SW
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003342:Corpus Striatum / Q000378:metabolism* / Q000648:ultrastructure; D003600:Cytosol / Q000378:metabolism; D004789:Enzyme Activation; D009994:Osmolar Concentration; D011188:Potassium / Q000494:pharmacology*; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D013574:Synaptosomes / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D011188:Potassium; D002118:Calcium