Dopamine-induced changes in protein phosphorylation and polyphosphoinositide metabolism in rat hippocampus

Effects of dopamine (DA) on endogenous phosphorylation of hippocampal proteins and polyphosphoinositides were studied in subcellular fractions from a crude mitocondrial/synaptosomal preparation. DA induced a concentration-dependent decrease in the in vitro phosphorylation of the protein B-50 (-22.1% at 10(-5) M DA), whereas no changes were found in phosphoproteins in other subcellular fractions. Treatment of hippocampal slices with 5 X 10(-4) M DA resulted in a 45.8% increase in post hoc phosphorylation of B-50 in SPM and it affected post hoc phosphorylation of several proteins in a cytosolic fraction. In vitro phosphorylation of SPM with DA (5 X 10(-4) M) increased endogenous TPI phosphorylation (+51.6%), whereas treatment of slices with DA (5 X 10(-4) M) resulted in a 39.4% decrease in post hoc TPI phosphorylation. This decrease could be blocked by haloperidol. Significant changes induced by DA (5 X 10(-4) M) were also found in 32P-incorporation into PA (in vitro: -32.4% and post hoc: +39.3%), but were not found in DPI labeling. The data provide evidence for DA-induced changes in phosphorylation of proteins and polyphosphoinositides in rat hippocampal SPM.