Adenosine produces nitric oxide and prevents mitochondrial oxidant damage in rat cardiomyocytes

Objective: To examine if adenosine prevents oxidant-induced mitochondrial dysfunction by producing nitric oxide (NO) in cardiomyocytes. Methods and results: Adenosine significantly enhanced the fluorescence of DAF-FM, a dye specific for NO, implying that adenosine induces synthesis of NO. Adenosine-induced NO production was blocked by both the nonspecific NOS inhibitor N-G-nitro-L-arginine methyl ester (L-NAME) and N-5-(1-Iminoethyl)-L-ornithine dihydrochloride (L-NIO), an inhibitor of endothelial NOS (eNOS), but not by N-6-(I-Iminoethyl)-L-lysine hydrochloride (L-NIL), an inhibitor of inducible NOS (iNOS), indicating that adenosine activates eNOS. Adenosine also enhances eNOS phosphorylation and its activity. The adenosine A(2) receptor antagonist 8-(3-chlorostyryl)caffeine but not the A, antagonist 8-cyclopentyl-1,3-dipropylxanthine prevented the increase in NO production. CGS21680, an adenosine A(2) receptor agonist, markedly increased NO, further supporting the involvement of A2 receptors. Adenosine-induced NO production was blocked by 4-Amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo 3,4-d)pyrimidine (PP2), a selective Src tyrosine kinase inhibitor, suggesting that Src tyrosine kinase is crucial for adenosine-induced NO production. Adenosine-induced NO production was partially reversed by both wortmannin and Akt inhibitor indicating an involvement of PI3-kinase/Akt. Pretreatment of cells with adenosine prevented H2O2-induced depolarization of mitochondrial membrane potential (AT.). The protective effect was blocked by L-NAME and L-NIO but not by L-NIL, indicating that eNOS plays a role in the action of adenosine. The protective effect of adenosine was further suppressed by KT5823, a specific inhibitor of protein kinase G (PKG), indicating the PKG may serve as a downstream target of adenosine. Conclusion: Adenosine protects mitochondria from oxidant damage through a pathway involving A(2) receptors, eNOS, NO, PI3-kinase/Akt, and Src tyrosine kinase. (C) 2004 European Society of Cardiology. Published by Elsevier B.V. All rights reserved.