Dopamine Stimulates [ 3 H]Phorbol 12,13‐Dibutyrate Binding in Cultured Striatal Cells

The effect of dopamine (DA) on the binding of [ 3 H]phorbol 12,13‐dibutyrate ([ 3 H]PdBu) in cultured rat striatal cells was examined. DA maximally increased specific [ 3 H]PdBu binding by 70 ± 10%, an increase comparable to that observed with norepinephrine (NE). This finding suggests that DA activates protein kinase C in cultured striatal cells, because increases in [ 3 H]PdBu binding reflect translocation of protein kinase C. Half‐maximal stimulation was observed with 10 –6 M DA. The peak response was observed at 2–3 min after addition of 10 –4 M DA, but [ 3 H]PdBu binding was still increased above basal at 30 min. DA was not acting via an adrenergic receptor. Prazosin (10 –6 M ) blocked the response to NE, suggesting mediation by an α 1 ‐adrenergic receptor, but had little effect on the response to DA. Conversely, the D 1 receptor antagonist SCH‐23390 (10 –6 M ) blocked the response to DA, but only partially inhibited the response to NE. Morphine (10 –6 M ) inhibited the response to DA by 46 ± 14%, but did not affect significantly the response to NE. The DA effect on [ 3 H]PdBu binding is apparently independent of the increase in cyclic AMP seen on D 1 receptor activation. Forskolin, apomorphine, and the D 1 agonist SKF‐38393 all increased cyclic AMP in striatal cells, but were less effective than DA in stimulating [ 3 H]PdBu binding. The D 2 agonist quinpirole was ineffective in stimulating either cyclic AMP or [ 3 H]PdBu binding.