Functional expression of adenosine A2b receptor in Xenopus oocytes.

RNA was transcribed in vitro from a cDNA clone (RFL9) that encodes the rat adenosine A2b receptor. Xenopus oocytes that had been injected with this RNA several days earlier responded to adenosine (10 microM to 1 mM) with an inward current (45-750 nA) that peaked rapidly and then declined to a lower level; uninjected oocytes showed no effect of adenosine. The current reversed to outward at -25 mV and was blocked by intracellular injection of 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'- tetraacetic acid. The action of adenosine (100 microM) was mimicked by 5'-N-ethylcarboxamidoadenosine (10 microM), but not by ATP, N6-cyclohexyladenosine (10 or 100 microM), N6-cyclopentyladenosine (10 microM), 1-deaza-2-chlorocyclopentyladenosine (50 microM), or CGS21680 (1 or 10 microM). It was substantially blocked by 8-cyclopentyl-1,3-dipropylxanthine (1 microM) and by 3,7-dimethyl-1-propargylxanthine (10 microM). The results indicate that activation of adenosine A2b receptors increases a calcium-dependent chloride conductance in Xenopus oocytes, presumably by stimulating phospholipase C.