Molecular and Cellular PharmacologyReciprocal interactions between adenosine A2A and dopamine D2 receptors in Chinese hamster ovary cells co-transfected with the two receptors
Section snippets
Chemicals
Adenosine deaminase was obtained from Boehringer Mannheim. Cyclic AMP, bacitracin, BSA, 1-10 phenanthroline, GDP, Gpp(NH)p, dithiothreitol, 2-chloroadenosine, NECA, and forskolin were purchased from Sigma. Dopamine, quinpirole, and CGS 21680 were obtained from Research Biochemicals International. SCH 58261 was a gift from Dr. E. Ongini, Schering-Plough Research Institute, Milan, Italy. [3H]CGS 21680, [3H]raclopride, and [3H]cAMP were obtained from Du Pont NEN. [35S]GTPγS was from New England
Saturation binding experiments
The expression of dopamine D2 and adenosine A2A receptors was determined using radioligand-binding experiments (Fig. 1). The cells showed high specific binding of the dopamine D2 receptor antagonist radioligand [3H]raclopride (Bmax 3600 ± 140 fmol mg−1 protein; Kd 7.4 ± 0.6 nM; mean ± SEM, N = 3) (Fig. 1) with a better fit for one binding site than for two sites (data not shown). Non-specific binding was less than 10% at concentrations of [3H]raclopride close to the Kd value. The adenosine A2A
Discussion
The present results show reciprocal interactions between adenosine A2A and dopamine D2 receptors co-transfected in CHO cells. We have confirmed that stimulation of adenosine A2A receptors can decrease agonist affinity at dopamine D2 receptors and demonstrate that this is related to a small change in the potency of a dopamine D2 receptor agonist to induce some functional responses. Conversely, we show that activation of dopamine D2 receptors effectively reduces signaling induced by adenosine A2A
Acknowledgements
These studies were supported by the Swedish Medical Research Council (project nr 2553, 715, 12707), Knut och Alice Wallenbergs stiftelse, and by the European Commission (Biomed II: adenosine-dopamine interactions).
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