Intrinsic and extrinsic P2 purinoceptor-mediated cardioprotection in mice

Abstract

P2 purinoceptor-dependent control of resistance to ischemia reperfusion injuries was studied in Langendorff perfused C57/Bl6 mouse hearts subjected to 20 min ischemia and 45 min reperfusion. Effects of P2 agonism and antagonism were assessed. Control hearts recovered 68 ± 4 mm Hg ventricular pressure (63 ± 3% pre-ischaemia), exhibited sustained diastolic contracture (23 ± 2 mm Hg), and released 26 ± 4 U/g lactate dehydrogenase (LDH) during reperfusion, evidencing oncosis. Treatment with 250 nM of the P2 agonist uridine 5′-triphosphate (UTP) for 10 min prior to and 10 min after ischemia reduced diastolic contracture by not, vert, similar 50% (9 ± 2 mm Hg), improved pressure development (85 ± 5 mm Hg; 77 ± 2% of baseline), and reduced LDH loss by 60% (11 ± 2 U/g). In contrast, P2Y1 agonism with 50 nM 2-methyl-thio-ATP was ineffective. P2 antagonism with 200 μM suramin impaired post-ischemic outcomes, exaggerating contractile dysfunction (41 ± 2 mm Hg diastolic pressure; 33 ± 5 mm Hg developed pressure) and LDH loss (53 ± 9 U/g). In the presence of suramin, UTP no longer modified post-ischemic function or oncosis. Evidence of intrinsic P2-mediated protection is consistent with ischemic elevations in microdialysate [UTP], [ATP] and [ADP]. In summary, these data evidence myocardial protection via endogenous and exogenous P2 agonists: enhanced recoveries with UTP, together with exaggeration of intrinsic injury and inhibition of UTP-protection with suramin, support protection via exogenously and intrinsically activated P2 purinoceptors. Data implicate P2Y2 receptors in cardioprotection, though further work is required to identify the sub-type involved.