title: The rat D4 dopamine receptor couples to cone transducin (Galphat2) to inhibit forskolin-stimulated cAMP accumulation.
abstract: Based on its expression pattern and pharmacology, the D4 dopamine receptor may play a role in schizophrenia. Thus it is of interest to know what signaling pathways are utilized by this receptor. Previously, we showed that activation of D4 receptors in a mouse mesencephalic neuronal cell line (MN9D) inhibited forskolin-stimulated cAMP accumulation in a pertussis toxin-sensitive (Ptx-sensitive) fashion. Of the known Ptx-sensitive G-protein alpha subunits, MN9D-expressed Galphai2, GalphaoA, and GalphaoB; however, none of these coupled to the D4 receptor. Using a low stringency polymerase chain reaction cloning method, we found an additional Ptx-sensitive G-protein cone transducin (Galphat2) expressed in the MN9D cells. We also found that Galphat2 mRNA is highly expressed in rat mesencephalic tissue. To test the hypothesis that the D4 receptor couples to Galphat2, we cotransfected MN9D cells with the D4 receptor and a mutagenized Ptx-resistant Galphat2 subunit (mGalphat2). Application of the dopaminergic agonist quinpirole to cotransfected cells inhibited forskolin-stimulated cAMP accumulation in the presence or absence of Ptx. To our knowledge, this is the first report demonstrating that the D4 dopamine receptor functionally couples to a specific G-protein and that a non-opsin-like receptor can couple with a transducin subunit.
authors.affiliation: Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
authors.forename: I
authors.initials: I
authors.lastname: Yamaguchi
authors.forename: S K
authors.initials: SK
authors.lastname: Harmon
authors.forename: R D
authors.initials: RD
authors.lastname: Todd
authors.forename: K L
authors.initials: KL
authors.lastname: O'Malley
mesh_terms: D000818:Animals; D002460:Cell Line; D005576:Colforsin / Q000494:pharmacology*; D000242:Cyclic AMP / Q000096:biosynthesis*; D019204:GTP-Binding Proteins / Q000502:physiology*; D051379:Mice; D051381:Rats; D017448:Receptors, Dopamine D2 / Q000502:physiology*; D050638:Receptors, Dopamine D4
chemical_list: C493600:Drd4 protein, mouse; C493601:Drd4 protein, rat; D017448:Receptors, Dopamine D2; D050638:Receptors, Dopamine D4; D005576:Colforsin; D000242:Cyclic AMP; D019204:GTP-Binding Proteins