Effects of P1 and P2 receptor antagonists on β,γ-methyleneATP- and CGS21680-induced cyclic AMP formation in NG108-15 cells

1 We have previously shown that ATP increased cyclic AMP in NG108-15 cells, which was inhibited by P-1 receptor antagonist methylxanthines. In the present study, we examined the effects of P-1 and P2 receptor antagonists on cyclic AMP formation induced by beta,gamma-methyleneATP (beta,gamma-MeATP) and CGS21680, an A(2A) adenosine receptor agonist, in NG108-15 cells. 2 beta,gamma-MeATP and CGS21680 increased intracellular cyclic AMP with EC50 values of 8.0 +/- 98 mu M (n = 4) and 42 +/- 7.5 nM (n = 4), respectively. 3 Several P-1 receptor antagonists inhibited both beta,gamma-MeATP- and CGS21680-induced cyclic AMP increase with a similar rank order of potency; ZM241385 > CGS15943 > XAC > DPCPX. However, the pK(i) values of these antagonists for beta,gamma-MeATP were larger than those for CGS21680. 4 Alloxazine, a P-1 receptor antagonist, and several P2 receptor antagonists (PPADS, iPPADS, reactive blue-2) inhibited beta,gamma-MeATP-induced response, while these antagonists little affected CGS21680-induced one. Suramin was effective only for beta,gamma-MeATP-induced response at 1 mM. 5 2-chloroadenosine (2CADO) and 2-chloroATP (2ClATP) increased cyclic AMP with similar potencies. The effects of these agonists were both inhibited by ZM241385, but only 2ClATP-induced response was inhibited by PPADS. 6 ATP- and beta,gamma-MeATP-induced responses were little affected by alpha,beta-methyleneADP, a 5'-nucleotidase inhibitor. 7 These results clearly demonstrate that ATP-stimulated cyclic AMP formation can be distinguished from the A(2A) receptor agonist-induced one by using the several P-1 and P2 receptor antagonists.