Involvement of G-protein βγ subunits in coupling the adenosine A1 receptor to phospholipase C in transfected CHO cells

In transfected Chinese hamster ovary (CHO-A(1)) cells the human adenosine A(1) receptor directly stimulates pertussis toxin-sensitive increases in inositol phosphate production and potentiates (synergistically) the inositol phosphate responses mediated by G(q)-coupled P2Y(2) purinoceptor and CCKA receptors. In the present study we have investigated the role of G beta gamma subunits in mediating adenosine A(1) receptor effects on phospholipase C activation (both direct and synergistic) by transiently transfecting CHO-A(1) cells with a scavenger of G beta gamma subunits: the C-terminus of beta-adrenoceptor kinase 1 (beta ark1 residues 495-689). [H-3]inositol phosphate responses to the selective adenosine A(1) receptor agonist N-6-cyclopentyladenosine (CPA; 1 mu M) were inhibited (41 +/- 1%) in CHO-A(1) cells transiently transfected with the G beta gamma scavenger, beta ark1 (495-689). Expression of beta ark1 (495-689) protein was confirmed by Western blotting. In contrast, adenosine A(1) receptor-mediated inhibition of forskolin stimulated [H-3]cyclic AMP accumulation was unaffected by transient expression of beta ark1 (495-689). beta ark1 (495-689) expression had no significant effect on the [H-3]inositol phosphate responses produced by activation of the endogenous P2Y(2) purinoceptor (100 mu M UTP; 92 +/- 0.8% of control). [H-3]inositol phosphate accumulation in response to adenosine A(1) receptor activation was also attenuated in CHO-K1 cells co-transfected with the beta ark1 (495-689) minigene (59 +/- 4% inhibition of control response to 1 mu M CPA). Finally, transient expression of beta ark1 (495-689) in CHO-A(1) cells inhibited the augmentation of [H-3]inositol phosphate responses resulting from co-activation of adenosine A(1) receptors and P2Y(2) purinoceptors. These experiments indicate that G beta gamma subunits are involved in the direct coupling the adenosine A(1) receptor to phospholipase C and that they also participate in the augmentation of P2Y(2) purinoceptor-mediated [H-3]inositol phosphate responses by the adenosine A(1) receptor. (C) 1998 Elsevier Science B.V. All rights reserved.