Contributions of A2Aand A2Badenosine receptors in coronary flow responses in relation to the KATPchannel using A2Band A2A/2Bdouble-knockout mice

Abstract

Adenosine plays a role in physiological and pathological conditions, and A2adenosine receptor (AR) expression is modified in many cardiovascular disorders. In this study, we elucidated the role of the A2BAR and its relationship to the A2AAR in coronary flow (CF) changes using A2Bsingle-knockout (KO) and A2A/2Bdouble-KO (DKO) mice in a Langendorff setup. We used two approaches: 1) selective and nonselective AR agonists and antagonists and 2) A2AKO and A2BKO and A2A/2BDKO mice. BAY 60-6583 (a selective A2Bagonist) had no effect on CF in A2BKO mice, whereas it significantly increased CF in wild-type (WT) mice (maximum of 23.3 ± 9 ml·min−1·g−1). 5′- N-ethylcarboxamido adenosine (NECA; a nonselective AR agonist) increased CF in A2BKO mice (maximum of 34.6 ± 4.7 ml·min−1·g−1) to a significantly higher degree compared with WT mice (maximum of 23.1 ± 2.1 ml·min−1·g−1). Also, CGS-21680 (a selective A2Aagonist) increased CF in A2BKO mice (maximum of 29 ± 1.9 ml·min−1·g−1) to a significantly higher degree compared with WT mice (maximum of 25.1 ± 2.3 ml·min−1·g−1). SCH-58261 (an A2A-selective antagonist) inhibited the NECA-induced increase in CF to a significantly higher degree in A2BKO mice (19.3 ± 1.6 vs. 0.5 ± 0.4 ml·min−1·g−1) compared with WT mice (19 ± 3.5 vs. 3.6 ± 0.5 ml·min−1·g−1). NECA did not induce any increase in CF in A2A/2BDKO mice, whereas a significant increase was observed in WT mice (maximum of 23.1 ± 2.1 ml·min−1·g−1). Furthermore, the mitochondrial ATP-sensitive K+(KATP) channel blocker 5-hydroxydecanoate had no effect on the NECA-induced increase in CF in WT mice, whereas the NECA-induced increase in CF in WT (17.6 ± 2 ml·min−1·g−1), A2AKO (12.5 ± 2.3 ml·min−1·g−1), and A2BKO (16.2 ± 0.8 ml·min−1·g−1) mice was significantly blunted by the KATPchannel blocker glibenclamide (to 0.7 ± 0.7, 2.3 ± 1.1, and 0.9 ± 0.4 ml·min−1·g−1, respectively). Also, the CGS-21680-induced (22 ± 2.3 ml·min−1·g−1) and BAY 60-6583-induced (16.4 ± 1.60 ml·min−1·g−1) increase in CF in WT mice was significantly blunted by glibenclamide (to 1.2 ± 0.4 and 1.8 ± 1.2 ml·min−1·g−1, respectively). In conclusion, this is the first evidence supporting the compensatory upregulation of A2AARs in A2BKO mice and demonstrates that both A2AARs and A2BARs induce CF changes through KATPchannels. These results identify AR-mediated CF responses that may lead to better therapeutic approaches for the treatment of cardiovascular disorders.