A(2A) D-2 RECEPTOR INTERACTIONS ARE NOT OBSERVED IN COS-7 CELLS TRANSIENTLY TRANSFECTED WITH DOPAMINE D-2 AND ADENOSINE A(2A) RECEPTOR CDNA

The rat D-2 receptor and the dog A(2a) receptor subcloned into the pXM vector were transiently transfected into COS-7 cells using the DEAE-dextran method. The transfected cells expressed approx. 200 fmol D-2 receptors/mg protein and approx. 5 pmol/mg protein of the A(2)a receptor as judged by binding experiments with [H-3]raclopride [or [H-3]-N-propyl-apomorphine (NPA)] and [H-3]-CGS 21680, respectively. The high affinity K-D values were 0.43 and 19 nM for D-2 and A(2a) receptors, respectively, in agreement with results obtained from other cells and tissues. The non-selective adenosine receptor agonist NECA stimulated cAMP accumulation both in non-transfected and transfected COS-7 cells with only a slight difference in potency, suggesting that most of the stimulation is due to activation of A(2b) receptors known to be present on virtually every cell. The two A(2a) Selective agonists CGS 21680 and CV-1808 were essentially inactive in transfected COS-7 cells, but were very active in PC-12 cells known to possess functional A(2a) receptors. Dopamine did not decrease cAMP accumulation in the transfected COS-7 cells. CGS 21680 (30 nM) did not affect the binding characteristics of D, receptors in the co-transfected COS-7 cells in contrast to the increased K-H, K-L and R(H) values found previously in rat striatal membranes after CGS 21680 treatment. The present findings indicate that transiently transfected A(2a) and D-2 receptors in COS-7 cells have normal binding properties, but couple poorly to adenylyl cyclase, despite the presence of G(s) protein and adenylyl cyclase in these eels. Our results also demonstrate that the previously reported interactions between A(2a) receptors and D-2 receptors do not occur when only the receptor proteins are expressed in COS-7 cells, suggesting that the two receptor molecules do not interact directly to influence binding characteristics.