Characterization of the human brain putative A(2B) adenosine receptor expressed in Chinese hamster ovary (CHO.A(2B4)) cells

1 An [H-3]-adenine pre-labelling methodology was employed to assay cyclic AMP generation by adenosine analogues in Chinese hamster ovary (CHO.A(2B4)) cells, transfected with cDNA which has been proposed to code for the human brain A(2B) adenosine receptor, and in guinea-pig cerebral cortical slices. 2 Adenosine analogues showing the following rank order of potency in the CHO.A(2B4) cells (pD(2) value): 5'-N-ethylcarboxamidoadenosine (NECA, 5.91) > adenosine (5.69) > 2-chloroadenosine (5.27) > N-6-(2-(4-aminophenyl)-ethylamino)adenosine (APNEA, 4.06). The purportedly A(2A)-selective agonist, CGS 21680, failed to elicit a significant stimulation of cyclic AMP generation at concentrations up to 10 mu M in CHO.A(2B4) cells. In the guinea-pig cerebral cortex, NECA was more potent than APNEA with pD(2) values of 5.91 and 4.60, respectively. 3 Of these agents, NECA was observed to exhibit the greatest intrinsic activity in CHO.A(2B4) cells (ca. 10 fold stimulation of cyclic AMP), while, in comparison, maximal responses to adenosine (32% NECA response), 2-chloroadenosine (61%), and APNEA (73%) were reduced. 4 Antagonists of NECA-evoked cyclic AMP generation showed the rank order of apparent affinity (apparent pA(2) value in CHO.A(2B4) cells: guinea-pig cerebral cortex): XAC (7.89: 7.46) > CGS 15943 (7.75: 7.33) > DPCPX (7.16: 6.91) > PD 115,199 (6.95: 6.39) > 8FB-PTP (6.52: 6.55) > 3-propylxanthine (4.63: 4.59). 5 We conclude that, using the agents tested, the A(2B) adenosine receptor cloned from human brain expressed in Chinese hamster ovary cells exhibits an identical pharmacological profile to native A(2B) receptors in guinea-pig brain.