K+-dependent stimulation of dopamine synthesis in striatal synaptosomes is mediated by protein kinase C

Dopamine synthesis rate was measured in striatal synaptosomes. Removal of Na+ increased synthesis rate; this was blocked in Ca2+-free medium and by addition of the Ca2+/calmodulin inhibitor N-6-aminohexyl-5-chloro-1-naphthalenesulfonamide (W7). The increase in dopamine synthesis rate caused by the addition of the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) was blocked by the protein kinase C inhibitor polymyxin B. K+-stimulated synthesis was unchanged in Ca2+-free medium or by addition of W7; it was blocked by polymyxin B. The effect of 50 mM K+ was additive with that of 8-Br cyclic AMP and of Na+ removal; the combined effect of 50 mM K+ and TPA was no greater than that of either alone. These results suggest that stimulation of dopamine synthesis in striatal synaptosomes by 50 mM K+ is mediated by protein kinase C.