Involvement of NADPH oxidase in A2A adenosine receptor-mediated increase in coronary flow in isolated mouse hearts

Adenosine increases coronary flow mainly through the activation of A(2A) and A(2B) adenosine receptors (ARs). However, the mechanisms for the regulation of coronary flow are not fully understood. We previously demonstrated that adenosine-induced increase in coronary flow is in part through NADPH oxidase (Nox) activation, which is independent of activation of either A(1) or A(3)ARs. In this study, we hypothesize that adenosine-mediated increase in coronary flow through Nox activation depends on A(2A) but not A(2B)ARs. Functional studies were conducted using isolated Langendorff-perfused mouse hearts. Hydrogen peroxide (H2O2) production was measured in isolated coronary arteries from WT, A(2A)AR knockout (KO), and A(2B)AR KO mice using dichlorofluorescein immunofluorescence. Adenosine-induced concentration-dependent increase in coronary flow was attenuated by the specific Nox2 inhibitor gp91 ds-tat or reactive oxygen species (ROS) scavenger EUK134 in both WT and A(2B) but not A(2A)AR KO isolated hearts. Similarly, the A(2A)AR selective agonist CGS-21680-induced increase in coronary flow was significantly blunted by Nox2 inhibition in both WT and A(2B)AR KO, while the A(2B)AR selective agonist BAY 60-6583-induced increase in coronary flow was not affected by Nox2 inhibition in WT. In intact isolated coronary arteries, adenosine-induced (10 mu M) increase in H2O2 formation in both WT and A(2B)AR KO mice was attenuated by Nox2 inhibition, whereas adenosine failed to increase H2O2 production in A(2A)AR KO mice. In conclusion, adenosine-induced increase in coronary flow is partially mediated by Nox2-derived H2O2, which critically depends upon the presence of A(2A)AR.