Prostacyclin attenuates oxidative damage of myocytes by opening mitochondrial ATP-sensitive K+ channels via the EP3 receptor

Abstract

Prostacyclin (PGI₂) and the PGE family alleviate myocardial ischemia-reperfusion injury and limit oxidative damage. The cardioprotective effects of PGI₂ have been traditionally ascribed to activation of IP receptors. Recent advances in prostanoid research have revealed that PGI₂ can bind not only to IP, but also to EP, receptors, suggesting cross talk between PGI₂ and PGEs. The mechanism(s) whereby PGI₂ protects myocytes from oxidative damage and the specific receptors involved remain unknown. Thus fresh isolated adult rat myocytes were exposed to 200 μM H₂O₂ with or without carbaprostacyclin (cPGI₂), IP-selective agonists, and ONO-AE-248 (an EP₃-selective agonist). Cell viability was assessed by trypan blue exclusion after 30 min of H₂O₂ superfusion. cPGI₂ and ONO-AE-248 significantly improved cell survival during H₂O₂ superfusion; IP-selective agonists did not. The protective effect of cPGI₂ and ONO-AE-248 was completely abrogated by pretreatment with 5-hydroxydecanoate or glibenclamide. In the second series of experiments, the mitochondrial ATP-sensitive K⁺ (K_ATP) channel opener diazoxide (Dx) reversibly oxidized flavoproteins in control myocytes. Exposure to prostanoid analogs alone had no effect on flavoprotein fluorescence. A second application of Dx in the presence of cPGI₂ or ONO-AE-248 significantly increased flavoprotein fluorescence compared with Dx alone, but IP-selective agonists did not. This study demonstrates that PGI₂ analogs protect cardiac myocytes from oxidative stress mainly via activation of EP₃. The data also indicate that activation of EP₃ receptors primes the opening of mitochondrial K_ATP channels and that this mechanism is essential for EP₃-dependent protection.