MULTIPLE COUPLING OF HUMAN D5 DOPAMINE-RECEPTORS TO GUANINE-NUCLEOTIDE-BINDING PROTEINS G(S) AND G(Z)

We have demonstrated previously that D1 dopamine receptors are coupled to both G(s) alpha and G(s) alpha. We examine here the coupling betwe en human D5 dopamine receptors and G proteins in transfected rat pitui tary GH(4)C(1) cells. Similar to D1 receptors, cholera toxin treatment of cells reduced, but did not abolish, D5 agonist high-affinity bindi ng sites, indicating D5 receptors couple to both G(x) alpha and choler a toxin-insensitive G proteins. The interaction between D5 receptors a nd G(s) alpha was confirmed by immunoprecipitation studies and by the ability of D5 receptors to stimulate adenylyl cyclase. Unlike D1 recep tors, D5 receptors did not display any pertussis toxin-sensitive G-pro tein coupling to G(o) alpha or G(i) alpha. D5 receptors were also not coupled to G(q) alpha and were unable to mediate phosphatidylinositol metabolism. Instead, D5 sites appeared to be coupled to an AlF4--sensi tive, N-ethylmaleimide-resistant G protein. Anti-G(z) alpha caused imm unoprecipitation of 24.2 +/- 5.2% of G protein-associated D5 receptors , indicating coupling between D5 and G(z) alpha. The coupling to G(z) alpha was specific for D5 receptors, because similar associations were not detected between D1 receptors and G(z) alpha.