Selective activation of Gα(o) by D(2L) dopamine receptors in NS20Y neuroblastoma cells

D(2L) dopamine receptor activation results in rapid inhibition and delayed heterologous sensitization of adenylate cyclase in several host cell types. The D(2L) dopamine receptor was stably transfected into NS20Y neuroblastoma cells to examine inhibition and sensitization in a neuronal cell environment and to identify the particular G-proteins involved. Acute activation of D(2L) receptors with the selective D₂ agonist quinpirole inhibited forskolin-stimulated cAMP accumulation, whereas prolonged incubation (2 hr) with quinpirole resulted in heterologous sensitization (more than twofold) of forskolin-stimulated cAMP accumulation in NS20Y-D(2L) cells. To unambiguously identify the pertussis toxin (PTX)-sensitive G- proteins responsible for inhibition and sensitization, we used vital-mediated gene delivery to assess the ability of genetically engineered PTX-resistant G-proteins (Gα(i1)*, Gα(i2)*, Gα(i3)*, and Gα(o)*) to rescue both responses after PTX treatment. The expression and function of individual recombinant G-proteins was confirmed with Western blotting and inhibition of GTPγS-stimulated adenylate cyclase, respectively. To assess the specificity of D(2L)-Gα coupling, cells were infected with herpes simplex virus (HSV) recombinants expressing individual PTX-resistant G-protein α subunits and treated with PTX, and quinpirole-induced responses were measured. Infection of NS20Y-D(2L) cells with HSV-Gα(o)* rescued both inhibition and sensitization in PTX-treated cells, whereas infection with HSV-Gα(i)*, HSV- Gα(i2)*, or HSV-Gα(i3)* failed to rescue either response. In summary, the current study provides strong evidence that the D(2L) dopamine receptor couples to Gα(o) in neuronal cells, and that this coupling is responsible for both the acute and subacute effects of D₂ receptor activation on adenylate cyclase activity.