Dopamine D-1 receptor coupling to Gs/olf and Gq in rat striatum and cortex: A scintillation proximity assay (SPA)/antibody-capture characterization of benzazepine agonists

Cloned, human dopamine D, receptors recruit multiple effectors but the G-protein subtype(s) activated by cerebral populations remain poorly defined, a question addressed using a rapid immunocapture technique. In rat striatum, dopamine (DA) and four selective, benzazepine agonists at D, receptors concentration-dependently enhanced [S-35]GTP gamma S binding to G alpha s/olf. For all drugs, G alpha q was also recruited with similar potencies and efficacies. Comparable observations were made in the cortex wherein profiles of G alpha s/olf vs G alpha q activation were also highly correlated. In contrast to G alpha s/olf and G alpha q, G alpha o and G alpha i were activated neither in the striatum nor in the cortex, except for SKF82958. As compared to DA, both SKF81297 and SKF82958 were full agonists at Gs/olf and Gq in cortex and striatum, whereas SKF38393 behaved as a partial agonist. Likewise, the atypical agonist, SKF83959 only partially activated Gaq and also Gs/olf in these two regions. In both striatum and cortex, the selective D-1 receptor antagonist, SCH23390, abolished the recruitment of G alpha q and G alpha s by DA, and the action of DA was partially attenuated by SKF83959. These findings demonstrate that, in native CNS tissue, DA and other D-1 receptor agonists activate G alpha s and G alpha q with similar potencies and efficacies, suggesting their recruitment via pharmacologically-indistinguishable populations of D-1 receptors, and show that SPA technology is well-adapted to study the coupling of native DA receptors. (c) 2006 Elsevier Ltd. All rights reserved.