Enhanced IPC by activation of pertussis toxin-sensitive and -insensitive G protein-coupled purinoceptors

Abstract

Extracellular ATP plays an important role in ischemic preconditioning (IPC) through the activation of P(2y) purinoceptors. This study examined whether ATP-stimulated P(2y) purinoceptors are coupled to pertussis toxin (PTX)-insensitive G protein and whether activation of this pathway enhances myocardial protection afforded by IPC. The rat was treated with PTX for 48 h, and the heart was then isolated and buffer perfused. The heart underwent IPC by three cycles of 5-min ischemia and 5-min reperfusion before 25 min of global ischemia. Isovolumic left ventricular function was measured, and functional recovery at 30 min after reperfusion was taken as an end point of myocardial protection. PTX pretreatment partially inhibited functional protection by IPC. Treatment with 100 microM 8-(p-sulfophenyl) theophylline (SPT) during IPC had no further effect on PTX-induced inhibition of functional protection by IPC, whereas suramin (300 microM) or reactive blue (RB) (10 microM) completely abolished myocardial protection in the preconditioned heart pretreated with PTX. Supplementation with adenosine (30 microM), ATP (30 microM), or UTP (50 microM) significantly enhanced IPC-induced functional protection, although preconditioning with these nucleotides without IPC had no protective effect. Adenosine-enhanced IPC was inhibited by pretreatment with PTX and SPT but not by suramin or RB, whereas ATP-enhanced IPC was inhibited by suramin or RB in combination with PTX pretreatment. On the other hand, UTP-enhanced IPC was not affected by PTX pretreatment but was inhibited by suramin or RB. Adenosine supplemented IPC without PTX pretreatment and ATP supplemented IPC with PTX pretreatment were not affected by nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester (100 microM). Although the protein kinase C inhibitor Ro318425 (0.3 microM) or tyrosine kinase inhibitor genistein (50 microM) had no significant effect on the functional protection afforded by adenosine-supplemented IPC without PTX pretreatment and ATP-supplemented IPC with PTX pretreatment, the combination of Ro318425 and genistein attenuated functional protection afforded by both the purinoceptor agonist-supplemented IPC. These results suggest the crucial involvement of PTX-sensitive and -insensitive G protein coupled purinoceptors in enhanced IPC by supplementation with adenosine, ATP, and UTP.

Uridine-5′-triphosphate (UTP) reduces infarct size and improves rat heart function after myocardial infarct

“…It was found that ATP and UTP provoked an increase in coronary flow in a dose-dependent manner [18]. It has been reported that UTP has a vasodilatory effect, via the activation of specific P2Y purinoceptors [27].…”

“…DAG activates protein kinase C (PKC) and mitogen-activated protein kinases [19]. Whereas the effects of purine nucleosides and nucleotides in myocardial infarction and ischemia have been intensively studied [2,20], the role of pyrimidine nucleotides under hypoxic conditions has not been well explored [18], although the level of both ATP and UTP were found to be elevated as a result of ischemia [7]. Using rat cell culture we found that UTP protected cardiomyocytes from hypoxic damage through the activation of P2Y 2 receptors [26].…”

Pacing-Induced Dys-Synchrony Preconditions Rabbit Myocardium Against Ischemia/Reperfusion Injury

“…This also holds for the possibility to combine dys-synchrony-induced preconditioning with other triggers to increase the protective effect, as shown for combining ischemic preconditioning with drug administration. 22 …”

P2 Purinoceptor-Mediated Cardioprotection in Ischemic-Reperfused Mouse Heart

“…Two recent studies provide evidence that UTP may mediate protective actions in ischemic hearts (Yitzhaki et al, 2006) and hypoxic myocytes (Yitzhaki et al, 2005) from rats. However, not all investigations detect such effects of UTP under similar conditions (Ninomiya et al, 2002b), and a number of issues arise from prior studies, foremost among these being the use of very high UTP concentrations to trigger protection (Ninomiya et al, 2002b;Yitzhaki et al, 2005). These prior studies use levels Ͼ2 orders of magnitude above those required to activate the P2Y 2 receptors implicated in the responses (von Kü gelgen and Wetter, 2000;Jacobson et al, 2002;von Kü gelgen, 2006).…”

“…The physiological (even pathological) relevance of responses to such high agonist levels is questionable, and it is difficult to ascribe effects to specific receptor subtypes, because such concentrations will even activate P2 receptors classified as UTP-insensitive (e.g., P2Y 1 receptors). Furthermore, in the only study of intact perfused hearts (Ninomiya et al, 2002b) myocyte death was not assessed, and the primary measure of ischemic outcome (contractile recovery) was complicated by uncontrolled and thus variable heart rate. This renders interpretation of rate-dependent contractile function problematic, potentially explaining lack of effect of UTP in this work (Ninomiya et al, 2002b).…”