SKF83959 selectively regulates phosphatidylinositol-linked D1 dopamine receptors in rat brain

Previously a distinct D-1-like dopamine receptor (DAR) that selectively couples to phospholipase C/phosphatidylinositol (PLC/PI) was proposed. However, lack of a selective agonist has limited efforts aimed at characterizing this receptor. We characterized the in vitro and in vivo effects of SKF83959 in regulating PI metabolism. SKF83959 stimulates (EC50, 8 mum) phosphatidylinositol 4,5-biphosphate hydrolysis in membranes of frontal cortex (FC) but not in membranes from PC12 cells expressing classical D-1A DARs. Stimulation of FC PI metabolism was attenuated by the D-1 antagonist, SCH23390, indicating that SKF83959 activates a D-1 -like DAR. The PI-linked DAR is located in hippocampus, cerebellum, striatum and FC. Most significantly, administration of SKF83959 induced accumulations of IP3 in striatum and hippocampus. In contrast to other D-1 DAR agonists, SKF83959 did not increase cAMP production in brain or in D-1A DAR-expressing PC12 cell membranes. However, SKF83959 inhibited cAMP elevation elicited by the D-1A DAR agonist, SKF81297, indicating that the compound is an antagonist of the classical D-1A DAR. Lastly, we demonstrated that SKF83959 enhances [S-35]guanosine 5'-O-(3-thiotriphosphate) binding to membrane Galphaq and Galphai proteins, suggesting that PI stimulation is mediated by activation of these guanine nucleotide-binding regulatory proteins. Results indicate that SKF83959 is a selective agonist for the PI-linked D-1-like DAR, providing a unique tool for investigating the functions of this brain D-1 DAR subtype.