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. Ca2+-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 NG-nitro-l-arginine methyl ester (a nonselective nitric oxide synthase inhibitor) administered either before ischemia or at the onset of reperfusion. Mitochondria isolated from postconditioned hearts required significantly higher in vitro Ca2+ loading than did controls (78 ± 29 &mgr;m vs. 40 ± 25 &mgr;m CaCl2 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 Ca2+, compared with wild-type hearts. However, IsoPC failed to alter infarct size, cardiac function, or the amount of Ca2+ 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-dependent manner. Nitric oxide functions as both a trigger and a mediator of cardioprotection produced by IsoPC.