Efficient functional coupling of the human D3 dopamine receptor to Go subtype of G proteins in SH-SY5Y cells

The D3 dopamine receptor presumably activates Gi/Go subtypes of G-proteins, like the structurally analogous D2 receptor, but its signalling targets have not been clearly established due to weak functional signals from cloned receptors as heterologously expressed in mostly non-neuronal cell lines. In this study, recombinant human D3 receptors expressed in a human neuroblastoma cell line, SH-SY5Y, produced much greater signals than those expressed in a human embryonic kidney cell line, HEK293. Quinpirole, a prototypic agonist, markedly inhibited forskolin-stimulated cyclic AMP production and Ca2+-channel (N-type) currents in SH-SY5Y cells, and enhanced GTPγ35S binding in isolated membranes, nearly ten times greater than that observed in HEK293 cell membranes. GTPγ35S-bound Gα subunits from quinpirole-activated and solubilized membranes were monitored upon immobilization with various Gα-specific antibodies. Gαo subunits (not Gαi) were highly labelled with GTPγ35S in SH-SY5Y, but not in HEK293 cell membranes, despite their abundance in the both cell types, as shown with reverse transcription-polymerase chain reaction and Western blots. N-type Ca2+ channels and adenylyl cyclase V (D3-specific effector), on the other hand, exist only in SH-SY5Y cells. More efficient coupling of the D3 receptor to Go subtypes in SH-SY5Y than HEK293 cells may be attributed, at least in part, to the two D3 neuronal effectors only present in SH-SY5Y cells (N-type Ca2+-channels and adenylyl cyclase V). The abundance of Go subtypes in the both cell lines seems to indicate their availability not a limiting factor. British Journal of Pharmacology (1999) 128, 1181–1188; doi:10.1038/sj.bjp.0702905