Assessment of the cytoprotective role of adenosine in an in vitro cellular model of myocardial ischemia

This work aimed to detect functional adenosine receptors in isolated rat cardiomyocytes and to study the influence of stimulation of these receptors in an in vitro model of ischemia. Cultures of cardiomyocytes were prepared from newborn rat ventricles. The contractions were photometrically monitored. In this preparation, adenosine induced a positive chronotropic response. This effect was reproduced by CGS 21680 (2-(4-[2-carboxyethyl]-phen-ethyl-amino) adenosine-5′ N-ethylunosamide), a specific adenosine A 2 receptor agonist, and antagonized by DMPX (3,7-dimethyl-1-propargylxanthine), an adenosine A 2 receptor antagonist. However, R-PIA ( R- N 6-(2-phenylisopropyl)-adenosine; a specific adenosine A 1 receptor agonist) induced a negative chronotropic effect that was abolished by its corresponding adenosine A 1 antagonist DPCPX (1,3-dipropyl-8-cyclo-pentyl-adenosine). Substrate-free hypoxia, as simulation of ischemia, induced a progressive decrease and then arrest of spontaneous cell contractions. The spontaneous rhythmic contractile activity was restored during reoxygenation following simulated ischemia. Adenosine A 1 receptor stimulation with R-PIA induced a decrease of hypoxia-induced damage. This effect was antagonized by DPCPX, an adenosine A 1 receptor antagonist. Conversely, the cells treated with CGS 21680 did not display complete recovery after reoxygenation. In addition, this effect was abolished by DMPX, since the cells recovered normal function after reoxygenation. To conclude, it appeared that cardiomyocytes possess both functional adenosine A 1 and A 2 receptors and that only the activation of adenosine A 1 receptor had a cytoprotective effect against simulated ischemia-induced cardiac cell injury.