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

The D3 dopamine receptor presumably activates G i /G o 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 Ca 2+ ‐channel (N‐type) currents in SH‐SY5Y cells, and enhanced GTPγ 35 S binding in isolated membranes, nearly ten times greater than that observed in HEK293 cell membranes. GTPγ 35 S‐bound Gα subunits from quinpirole‐activated and solubilized membranes were monitored upon immobilization with various Gα‐specific antibodies. Gα o subunits (not Gα i ) were highly labelled with GTPγ 35 S 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 Ca 2+ 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 G o 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 Ca 2+ ‐channels and adenylyl cyclase V). The abundance of G o 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