Abstract
Adenosine increases coronary flow mainly through the activation of A2A and A2B 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 A1 or A3ARs. In this study, we hypothesize that adenosine-mediated increase in coronary flow through Nox activation depends on A2A but not A2BARs. Functional studies were conducted using isolated Langendorff-perfused mouse hearts. Hydrogen peroxide (H2O2) production was measured in isolated coronary arteries from WT, A2AAR knockout (KO), and A2BAR 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 A2B but not A2AAR KO isolated hearts. Similarly, the A2AAR selective agonist CGS-21680-induced increase in coronary flow was significantly blunted by Nox2 inhibition in both WT and A2BAR KO, while the A2BAR 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 μM) increase in H2O2 formation in both WT and A2BAR KO mice was attenuated by Nox2 inhibition, whereas adenosine failed to increase H2O2 production in A2AAR KO mice. In conclusion, adenosine-induced increase in coronary flow is partially mediated by Nox2-derived H2O2, which critically depends upon the presence of A2AAR.