Adenosine and ATP/UTP are main components of the purinergic system that modulate cellular and tissue functions via specific adenosine and P2 receptors, respectively. Here, we explored the possibility that A(1) adenosine receptor (A(1)R) and P2Y(2) receptor (P2Y(2)R) form heterodimers with novel pharmacological properties. Coimmunoprecipitation showed these receptors directly associate in A(1)R/P2y(2)R-cotransfected HEK293T cells. Agonist binding by the AIR was significantly inhibited by P2Y(2)R agonists only in membranes from cotransfected cells. The functional activity of AIR, as indicated by the G(i/o)-mediated inhibition of adenylyl cyclase, in the cotransfected cells was attenuated by the simultaneous addition of AIR and P2Y(2)R agonists. The increase in intracellular Ca2+ levels induced by P2Y(2)R activation of G(9/11) was synergistically enhanced by the simultaneous addition of an A, R agonist in the coexpressing cells. These results suggest that oligomerization of AIR and P2Y(2)R generates a unique complex in which the simultaneous activation of the two receptors induces a structural alteration that interferes signaling via G(i/o) but enhances signaling via G(9/11). (c) 2006 Elsevier Inc. All rights reserved.