Cocaine produces D₂R-mediated conformational changes in the adenosine A_2AR-dopamine D₂R heteromer

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• 作者：Daniel Marcellino ; Gemma Navarro ; Kristoffer Sahlholm ; Johanna Nilsson ; Luigi F. Agnati ; Enric I. Canela ; Carme Lluí ; s ; Peter Å ; rhem ; Rafael Franco ; Kjell Fuxe
• 关键词：Dopamine D₂ receptor ; Adenosine A_2A receptor ; Heteromerization ; G protein-coupled receptors ; Allosteric modulation ; Cocaine
• 刊名：Biochemical and Biophysical Research Communications
• 出版年：2010
• 出版时间：16 April 2010
• 年：2010
• 卷：394
• 期：4
• 页码：988-992
• 全文大小：332 K

文摘

Adenosine A_2A receptors (A_2ARs) and dopamine D₂ receptors (D₂Rs) 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_2ARs 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_2AR and D_2LR formed heteromers in transiently co-transfected HEK-293T cells. In vitro treatment of cocaine was found to produce changes in D₂R homodimers and in A_2AR–D₂R heterodimers detected through bioluminescent energy transfer (BRET). Cocaine was found to produce a time- and concentration-dependent reduction in the BRET_max between A_2AR–D_2LR heterodimers and D_2LR homodimers, but not A_2AR homodimers, indicating its effect on D₂R. Cocaine was evaluated with regard to D₂R binding using a human D_2LR stable expressing CHO cell line and was found to produce an increase in the affinity of hD_2LR for DA. At the level of G protein-coupling, cocaine produced a small, but significant increase in DA-stimulated binding of GTPγS. However, cocaine failed to modulate D₂R agonist-induced inhibition of cAMP in stable hD_2LR 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_2LR, that results in enhanced agonist recognition, G protein-coupling and an altered conformational state of D₂R homodimers and A_2AR–D₂R heterodimers.