Interactions between A_2A adenosine receptors, hydrogen peroxide, and K_ATP channels in coronary reactive hyperemia

Myocardial metabolites such as adenosine mediate reactive hyperemia, in part, by activating ATP-dependent K⁺ (K_ATP) channels in coronary smooth muscle. In this study, we investigated the role of adenosine A_2A and A2B receptors and their signaling mechanisms in reactive hyperemia. We hypothesized that coronary reactive hyperemia involves A_2A receptors, hydrogen peroxide (H₂O₂), and K_ATP channels. We used A_2A and A2B knockout (KO) and A_2A/2B double KO (DKO) mouse hearts for Langendorff experiments. Flow debt for a 15-s occlusion was repaid 128 ± 8% in hearts from wild-type (WT) mice; this was reduced in hearts from A_2A KO and A_2A/2B DKO mice (98 ± 9 and 105 ± 6%; P < 0.05), but not A2B KO mice (123 ± 13%). Patch-clamp experiments demonstrated that adenosine activated glibenclamide-sensitive K_ATP current in smooth muscle cells from WT and A2B KO mice (90 ± 23% of WT) but not A_2A KO or A_2A/A2B DKO mice (30 ± 4 and 35 ± 8% of WT; P < 0.05). Additionally, H₂O₂ activated K_ATP current in smooth muscle cells (358 ± 99%; P < 0.05). Catalase, an enzyme that breaks down H₂O₂, attenuated adenosine-induced coronary vasodilation, reducing the percent increase in flow from 284 ± 53 to 89 ± 13% (P < 0.05). Catalase reduced the repayment of flow debt in hearts from WT mice (84 ± 9%; P < 0.05) but had no effect on the already diminished repayment in hearts from A_2A KO mice (98 ± 7%). Our findings suggest that adenosine A_2A receptors are coupled to smooth muscle K_ATP channels in reactive hyperemia via the production of H₂O₂ as a signaling intermediate.