Adenosine released during cardiac ischemia exerts a marked protective effect in the heart that is mediated by the A 1 and A 3 subtypes of adenosine receptors. The signaling pathways activated by these adenosine receptors have now been characterized in a chick embryo ventricular myocyte culture model of cardioprotection against ischemia. Selective A 1 and A 3 receptor agonists were shown to activate phospholipases C and D, respectively, to achieve their distinct cardioprotective effects. The specificity of the A 3 receptor-phospholipase D interaction was also demonstrated in chick embryo atrial myocytes (which do not express endogenous A 3 receptors) that had been transfected with a vector encoding the human A 3 receptor. Activation of both endogenous A 1 and A 3 receptors in ventricular myocytes resulted in a protective response greater than that induced by stimulation of either receptor alone. Agonists that activate both adenosine A 1 and A 3 receptors may thus prove beneficial for the treatment of myocardial ischemia.-Parsons, M., Young, L., Lee, J. E., Jacobson, K. A., Liang, B. T. Distinct cardioprotective effects of adenosine mediated by differential coupling of receptor subtypes to phospholipases C and D. Keywords ischemia; ventricular myocyte; PKC activity; cardioprotectionAdenosine is released in substantial amounts during myocardial ischemia and exerts a marked protective effect in the heart (1). Furthermore, adenosine released during a brief ischemic episode is able to protect the heart against injury during a subsequent period of prolonged ischemia, resulting in a reduction in infarct size (2)(3)(4)(5)(6)(7)(8). Brief exposure of the heart to adenosine, instead of to ischemia, induces a similar protective effect against subsequent ischemia-induced damage. Although both A 1 and A 3 subtypes of adenosine receptors HHS Public AccessAuthor manuscript FASEB J. Author manuscript; available in PMC 2017 August 23. Author Manuscript Author ManuscriptAuthor Manuscript Author Manuscript mediate cardioprotection, the respective protective effects are distinct (9). The signaling mechanisms that underlie these distinct receptor-mediated responses have remained unknown.A culture model for simulating ischemia and cardioprotection has been developed with embryonic chick cardiac ventricular myocytes (5,9,10,11). This model exhibits adenosineinduced protective effects similar to those apparent in the intact heart (4, 6-8, 12, 13). With this cardiac cell model, the objective of the current study was to investigate whether the signaling mechanism underlying the adenosine A 1 receptor-mediated cardioprotective effect differs from that used by the adenosine A 3 receptor. Specifically, the study was aimed at testing the hypothesis that the distinct cardioprotective effects were mediated by differential coupling of adenosine A 1 and A 3 receptors to phospholipase C (PLC) and phospholipase D (PLD), respectively. MATERIALS AND METHODS Preparation of cultured cardiac atrial and ventricular myocytes and simulation of is...

Adenosine released during cardiac ischemia exerts a marked protective effect in the heart that is mediated by the A 1 and A 3 subtypes of adenosine receptors. The signaling pathways activated by these adenosine receptors have now been characterized in a chick embryo ventricular myocyte culture model of cardioprotection against ischemia. Selective A 1 and A 3 receptor agonists were shown to activate phospholipases C and D, respectively, to achieve their distinct cardioprotective effects. The specificity of the A 3 receptor-phospholipase D interaction was also demonstrated in chick embryo atrial myocytes (which do not express endogenous A 3 receptors) that had been transfected with a vector encoding the human A 3 receptor. Activation of both endogenous A 1 and A 3 receptors in ventricular myocytes resulted in a protective response greater than that induced by stimulation of either receptor alone. Agonists that activate both adenosine A 1 and A 3 receptors may thus prove beneficial for the treatment of myocardial ischemia.-Parsons, M., Young, L., Lee, J. E., Jacobson, K. A., Liang, B. T. Distinct cardioprotective effects of adenosine mediated by differential coupling of receptor subtypes to phospholipases C and D. Keywords ischemia; ventricular myocyte; PKC activity; cardioprotectionAdenosine is released in substantial amounts during myocardial ischemia and exerts a marked protective effect in the heart (1). Furthermore, adenosine released during a brief ischemic episode is able to protect the heart against injury during a subsequent period of prolonged ischemia, resulting in a reduction in infarct size (2)(3)(4)(5)(6)(7)(8). Brief exposure of the heart to adenosine, instead of to ischemia, induces a similar protective effect against subsequent ischemia-induced damage. Although both A 1 and A 3 subtypes of adenosine receptors HHS Public AccessAuthor manuscript FASEB J. Author manuscript; available in PMC 2017 August 23. Author Manuscript Author ManuscriptAuthor Manuscript Author Manuscript mediate cardioprotection, the respective protective effects are distinct (9). The signaling mechanisms that underlie these distinct receptor-mediated responses have remained unknown.A culture model for simulating ischemia and cardioprotection has been developed with embryonic chick cardiac ventricular myocytes (5,9,10,11). This model exhibits adenosineinduced protective effects similar to those apparent in the intact heart (4, 6-8, 12, 13). With this cardiac cell model, the objective of the current study was to investigate whether the signaling mechanism underlying the adenosine A 1 receptor-mediated cardioprotective effect differs from that used by the adenosine A 3 receptor. Specifically, the study was aimed at testing the hypothesis that the distinct cardioprotective effects were mediated by differential coupling of adenosine A 1 and A 3 receptors to phospholipase C (PLC) and phospholipase D (PLD), respectively. MATERIALS AND METHODS Preparation of cultured cardiac atrial and ventricular myocytes and simulation of is...