Cocaine produces D2R-mediated conformational changes in the adenosine A(2A)R-dopamine D2R heteromer (original) (raw)

2010, Biochemical and biophysical research communications

Adenosine A 2A receptors (A 2A Rs) and dopamine D 2 receptors (D 2 Rs) form constitutive heteromers in living cells and exhibit a strong functional antagonistic interaction. Recent findings give neurochemical evidence that extended cocaine self-administration in the rat give rise to an up-regulation of functional A 2A Rs in the nucleus accumbens that return to baseline expression levels during cocaine withdrawal. In the present work, the acute in vitro effects of a concentration of cocaine known to fully block the dopamine (DA) transporter without exerting any toxic actions were investigated on A 2A R and D 2L R formed heteromers in transiently co-transfected HEK-293T cells. In vitro treatment of cocaine was found to produce changes in D 2 R homodimers and in A 2A R-D 2 R heterodimers detected through bioluminescent energy transfer (BRET). Cocaine was found to produce a time-and concentration-dependent reduction in the BRET max between A 2A R-D 2L R heterodimers and D 2L R homodimers, but not A 2A R homodimers, indicating its effect on D 2 R. Cocaine was evaluated with regard to D 2 R binding using a human D 2L R stable expressing CHO cell line and was found to produce an increase in the affinity of hD 2L R for DA. At the level of G protein-coupling, cocaine produced a small, but significant increase in DA-stimulated binding of GTPcS. However, cocaine failed to modulate D 2 R agonist-induced inhibition of cAMP in stable hD 2L R CHO cells or the gating of GIRK channels in oocytes. Taken together, these results indicate a direct and specific effect of a moderate concentration of cocaine on the DA D 2L R, that results in enhanced agonist recognition, G protein-coupling and an altered conformational state of D 2 R homodimers and A 2A R-D 2 R heterodimers.