Cardiac myocytes rendered ischemia resistant by expressing the human adenosine A(1) or A(3) receptor

Adenosine is an important mediator of the endogenous defense against ischem ia-induced injury in the heart. Adenosine can achieve cardioprotection by m ediating the effect of ischemic preconditioning and by protecting against m yocyte injury when it is present during the infarct-producing ischemia. A n ovel adenosine A(3) receptor can mediate this protective function. One appr oach to achieve cardioprotection is to enhance myocardial sensitivity to th e endogenous adenosine by increasing the number of adenosine receptors inst ead of administering an adenosine receptor agonist. The objective of the pr esent study was to investigate whether genetic manipulation of the cardiac myocyte, achieved by gene transfer and overexpression of the human A(3) rec eptor cDNA, renders the myocytes resistant to the deleterious effect of isc hemia. Prolonged hypoxia with glucose deprivation, causing myocyte injury a nd adenosine release, was used to simulate ischemia in cultured chick embry o ventricular myocytes. During simulated ischemia, cultured myocytes with e nhanced expression of the human A(3) receptor and showed significantly high er ATP content, fewer cells killed, and less creatine kinase released into the medium than either control or mock-transfected myocytes. Also, increase d expression of the A(3) receptor caused an enhanced cardioprotective effec t by the preconditioning ischemia. Overexpressing the adenosine A(1) recept or also led to increased protection against ischemia-induced myocyte injury as well as an enhanced preconditioning effect. Thus, increasing the recept or level improves the myocyte sensitivity to the endogenous adenosine, whic h in turn causes all of the cardioprotective effects found for exogenously administered adenosine agonists. The study provides the first proof for the new concept that an increased expression of the human A(3) receptor in the cardiac myocyte can be an important cardioprotective therapeutic approach.