The Rat D4 Dopamine Receptor Couples to Cone Transducin (Gαt2) 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 α subunits, MN9D-expressed Gαi2, GαoA, and GαoB; 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 (Gαt2) expressed in the MN9D cells. We also found that Gαt2 mRNA is highly expressed in rat mesencephalic tissue. To test the hypothesis that the D4 receptor couples to Gαt2, we cotransfected MN9D cells with the D4 receptor and a mutagenized Ptx-resistant Gαt2 subunit (mGαt2). 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.