Isoflurane Postconditioning Protects against Reperfusion Injury by Preventing Mitochondrial Permeability Transition by an Endothelial Nitric Oxide Synthase-dependent Mechanism

Background: The role of endothelial nitric oxide synthase (eNOS) in isoflurane postconditioning (IsoPC)-elicited cardioprotection is poorly understood. The authors addressed this issue using eNOS(-/-) mice. Methods: In vivo or Langendorff-perfused mouse hearts underwent 30 min of ischemia followed by 2 h of reperfusion in the presence and absence of postconditioning produced with isoflurane 5 min before and 3 min after reperfusion. Ca(2+)-induced mitochondrial permeability transition (MPT) pore opening was assessed in isolated mitochondria. Echocardiography was used to evaluate ventricular function. Results: Postconditioning with 0.5, 1.0, and 1.5 minimum alveolar concentrations of isoflurane decreased infarct size from 56 +/- 10% (n = 10) in control to 48 +/- 10%, 41 +/- 8% (n = 8, P < 0.05), and 38 10% (n = 8, P < 0.05), respectively, and improved cardiac function in wild-type mice. Improvement in cardiac function by IsoPC was blocked by N(G)-nitro-L-arginine methyl ester (a nonselective nitric oxide synthase inhibitor) administered either before schemia or at the onset of reperfusion, Mitochondria isolated from post-conditioned hearts required significantly higher in vitro Ca(2+) loading than did controls (78 +/- 29 Am vs. 40 +/- 25 mu m CaCl(2) per milligram of protein, n = 10, P < 0.05) to open the MPT pore. Hearts from eNOS(-/-) mice displayed no marked differences in infarct size, cardiac function, and sensitivity of MPT pore to Ca(2+), compared with wild-type hearts. However, IsoPC failed to alter infarct size, cardiac function, or the amount of Ca(2+) necessary to open the MPT pore in mitochondria isolated from the eNOS(-/-) hearts compared with control hearts. Conclusions: IsoPC protects mouse hearts from reperfusion injury by preventing MPT pore opening in an eNOS-dependerit manner. Nitric oxide functions as both a trigger and a mediator of cardio-protection produced by IsoPC.