Pharmacological analysis of a dopamine D2Short:Gαo fusion protein expressed in Sf9 cells

A dopamine D_2Short receptor:G_αo fusion protein was expressed in Sf9 cells using the baculovirus expression system. [³H]Spiperone bound to D_2Short:G_αo with a pK_d≈10. Dopamine stimulated the binding of [³⁵S]guanosine-5′-O-(3-thio)triphosphate (GTPγS) to D_2Short:G_αo expressed with Gβ₁γ₂ (E_max>460%; pEC₅₀ 5.43±0.06). Most of the putative D₂ antagonists behaved as inverse agonists (suppressing basal [³⁵S]GTPγS binding) at D_2Short:G_αo/Gβ₁γ₂ although (−)-sulpiride and ziprasidone were neutral antagonists. Competition of [³H]spiperone binding by dopamine and 10,11-dihydroxy-N-n-propylnorapomorphine revealed two binding sites of different affinities, even in the presence of GTP (100 μM). The D_2Short:G_αo fusion protein is therefore a good model for characterising D₂ receptors. [Copyright &y& Elsevier]