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

Abstract

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 A(2B) receptors and their signaling mechanisms in reactive hyperemia. We hypothesized that coronary reactive hyperemia involves A(2A) receptors, hydrogen peroxide (H(2)O(2)), and KATP channels. We used A(2A) and A(2B) 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 A(2B) KO mice (123 ± 13%). Patch-clamp experiments demonstrated that adenosine activated glibenclamide-sensitive KATP current in smooth muscle cells from WT and A(2B) KO mice (90 ± 23% of WT) but not A(2A) KO or A(2A)/A(2B) DKO mice (30 ± 4 and 35 ± 8% of WT; P < 0.05). Additionally, H(2)O(2) activated KATP current in smooth muscle cells (358 ± 99%; P < 0.05). Catalase, an enzyme that breaks down H(2)O(2), 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 KATP channels in reactive hyperemia via the production of H(2)O(2) as a signaling intermediate.

Low Coronary Microcirculatory Resistance Associated With Profound Hypotension During Intravenous Adenosine Infusion

“…[17][18][19] When activated, adenylate cyclase leads to the production and accumulation of cAMP that activates protein kinase A, which ultimately produces smooth muscle cell hyperpolarization and relaxation, particularly through the activation of intermediate-conductance K Ca channels. [20][21][22] Therefore, adenosine-induced peripheral and coronary dilatation is mainly mediated through the activation of A 2A and A 2B receptors. However, on the other side, it has been consistently observed that the inhibition of adenylate cyclase (mediated by the A 1 and A 3 receptors) leads to vasoconstriction.…”

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

“…Hearts with persistent arrhythmias were excluded from the study. As a positive control, a 15-s flow occlusion resulted in a twofold increase in coronary flow over baseline [19,38], indicating that bufferperfused hearts have minimum hypoxia and coronary vessels have the capacity to further dilate.…”

“…Furthermore, pertinent to this effect, it may also be possible that adenosine-generated ROS is involved in mediating reactive or functional hyperemia, despite the role of adenosine in functional hyperemia remaining controversial [19]. Indeed, the involvement of adenosine in either reactive or functional hyperemia has been shown to be mediated by endogenously released vasodilators, including NO, prostacyclin, and endothelium-derived hyperpolarizing factor [38,40,63,64]. The influence and interaction of these vasoactive factors in generation of ROS by A 2A AR in the coronary circulation remain unclear.…”

“…Therefore, with the focus on the adenosine signaling, the first aim of the present study was to further investigate whether A 2A and/or A 2B AR are involved in Nox2-derived ROS-mediated coronary vasodilation. Given the previous findings that adenosine A 2A AR coupled to H 2 O 2 contributes to coronary reactive hyperemia [38] and Nox2 acts as a functional source for H 2 O 2 resulting in coronary vasodilation [32], the second aim of the present study was to examine whether Nox2-derived ROS production contributing to adenosine-mediated coronary flow is through H 2 O 2 and which adenosine receptors are required in this process. We performed exogenous infusion of adenosine in Langendorff-perfused isolated hearts as well as immunohistochemistry in isolated coronary arteries from wild type (WT), A 2A AR knockout (KO), and A 2B AR KO mice for these studies.…”

Metabolic hyperemia requires ATP-sensitive K+ channels and H2O2 but not adenosine in isolated mouse hearts

“…In addition, the complexity of the combined intrinsic (e.g., myogenic, shear-mediated, metabolic, and endothelium-originated mediators) with extrinsic (neural hormonal regulatory mechanism) blood flow control mechanisms make whole animal study a nonoptimal model for the mechanistic exploration in local metabolic coronary blood flow regulation. Therefore, there is a need to reexamine the functional role of adenosine in coronary metabolic hyperemia using combined AR knockout (KO) mice with traditional pharmacological agents in isolated Langendorff-perfused hearts.Increasing evidence suggests that H 2 O 2 , an endogenous metabolite, acts as an important mediator responsible for metabolic coronary vasodilation (37,42,53,54). We (42, 57) have previously demonstrated that A 2A AR-mediated H 2 O 2 production opens ATP-sensitive K ϩ (K ATP ) channels in coronary smooth muscle cells, contributing to the coronary ischemic vasodilation (42, 57).…”