HNO Protects the Myocardium against Reperfusion Injury, Inhibiting the mPTP Opening via PKCe Activation

Donors of nitroxyl (HNO), the one electron-reduction product of nitric oxide (NO.), positively modulate cardiac contractility/relaxation while limiting ischemia-reperfusion (I/R) injury. The mechanisms underpinning HNO anti-ischemic effects remain poorly understood. Using isolated perfused rat hearts subjected to 30 min global ischemia/1 or 2 h reperfusion, here we tested whether, in analogy to NO., HNO protection requires PKCe translocation to mitochondria and KATP channels activation. To this end, we compared the benefits afforded by ischemic preconditioning (IPC; 3 cycles of I/R) with those eventually granted by the NO. donor, diethylamine/NO, DEA/NO, and two chemically unrelated HNO donors: Angeli 39;s salt (AS, a prototypic donor) and isopropylamine/NO (IPA/NO, a new HNO releaser). All donors were given for 19 min before I/R injury. In control I/R hearts (1 h reperfusion), infarct size (IS) measured via tetrazolium salt staining was 66 177; 5.5% of the area at risk. Both AS and IPA/NO were as effective as IPC in reducing IS [30.7 177; 2.2 (AS), 31 177; 2.9 (IPA/NO), and 31 177; 0.8 (IPC), respectively)], whereas DEA/NO was significantly less so (36.2 177; 2.6%, p < 0.001 vs. AS, IPA/NO, or IPC). IPA/NO protection was still present after 120 min of reperfusion, and the co-infusion with the PKCe inhibitor (PKCV1-2500 nM) prevented it (IS = 30 177; 0.5 vs. 61 177; 1.8% with IPA/NO alone, p < 0.01). Irrespective of the donor, HNO anti-ischemic effects were insensitive to the KATP channel inhibitor, 5-OH decanoate (5HD, 100 µM), that, in contrast, abrogated DEA/NO protection. Finally, both HNO donors markedly enhanced the mitochondrial permeability transition pore (mPTP) ROS threshold over control levels (?35-40%), an action again insensitive to 5HD. Our study shows that HNO donors inhibit mPTP opening, thus limiting myocyte loss at reperfusion, a beneficial effect that requires PKCe translocation to the mitochondria but not mitochondrial K+ channels activation.

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