Dopamine D1 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 D1 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 D1 receptors concentration-dependently enhanced [35S]GTPγS binding to Gαs/olf. For all drugs, Gαq was also recruited with similar potencies and efficacies. Comparable observations were made in the cortex wherein profiles of Gαs/olf vs Gαq activation were also highly correlated. In contrast to Gαs/olf and Gαq, Gαo and Gαi 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 Gαq and also Gs/olf in these two regions. In both striatum and cortex, the selective D1 receptor antagonist, SCH23390, abolished the recruitment of Gαq and Gαs by DA, and the action of DA was partially attenuated by SKF83959. These findings demonstrate that, in native CNS tissue, DA and other D1 receptor agonists activate Gαs and Gαq with similar potencies and efficacies, suggesting their recruitment via pharmacologically-indistinguishable populations of D1 receptors, and show that SPA technology is well-adapted to study the coupling of native DA receptors.