COUPLING OF A TRANSFECTED HUMAN BRAIN A(1)-ADENOSINE RECEPTOR IN CHO-K1 CELLS TO CALCIUM MOBILIZATION VIA A PERTUSSIS-TOXIN-SENSITIVE MECHANISM

1 The presence of A1 adenosine receptors in CHO-K1 cells transfected with the human brain A1 sequence was confirmed by ligand binding studies using 8-cyclopentyl-[H-3] 1,3-dipropylxanthine ([H-3]-DPCPX). 2 Alterations in intracellular calcium ([Ca2+]i) were measured with the calcium-sensitive dye, fura-2. 3 N6-cyclopentyladenosine (CPA), the selective A1 agonist, and 5'-N-ethylcarboxaminoadenosine (NECA), a relatively non-selective adenosine receptor agonist, elicited rapid, biphasic increases in [Ca2+]i which involved both mobilisation from intracellular stores and calcium entry. 4 The calcium response to CPA was significantly inhibited by the selective A1 antagonist DPCPX. The non-selective adenosine receptor, xanthine amino congener (XAC), was less potent. 5 The calcium response to CPA was completely prevented by pretreatment of the cells with pertussis toxin implicating the involvement of G(i) in the receptor-mediated response. 6 In summary, we present evidence for the coupling of transfected human brain A1 adenosine receptors in CHO-K1 cells to mobilisation of [Ca2+]i via a pertussis toxin-sensitive G protein.