title: Isoflurane preconditioning uncouples mitochondria and protects against hypoxia-reoxygenation.
abstract: Ischemic cardiac injury can be substantially alleviated by exposing the heart to pharmacological agents such as volatile anesthetics before occurrence of ischemia-reperfusion. A hallmark of this preconditioning phenomenon is its memory, when cardioprotective effects persist even after removal of preconditioning stimulus. Since numerous studies pinpoint mitochondria as crucial players in protective pathways of preconditioning, the aim of this study was to investigate the effects of preconditioning agent isoflurane on the mitochondrial bioenergetic phenotype. Endogenous flavoprotein fluorescence, an indicator of mitochondrial redox state, was elevated to 195 +/- 16% of baseline upon isoflurane application in intact cardiomyocytes, indicating more oxidized state of mitochondria. Isoflurane treatment also elicited partial dissipation of mitochondrial transmembrane potential, which remained depolarized even after anesthetic withdrawal (tetramethylrhodamine fluorescence intensity declined to 83 +/- 3 and 81 +/- 7% of baseline during isoflurane exposure and washout, respectively). Mild uncoupling, with preserved ATP synthesis, was also detected in mitochondria that were isolated from animals that had been previously preconditioned by isoflurane in vivo, revealing its memory nature. These mitochondria, after exposure to hypoxia and reoxygenation, exhibited better preserved respiration and ATP synthesis compared with mitochondria from nonpreconditioned animals. Partial mitochondrial depolarization was paralleled by a diminished Ca(2+) uptake into isoflurane-treated mitochondria, as indicated by the reduced increment in rhod-2 fluorescence when mitochondria were challenged with increased Ca(2+) (180 +/- 24 vs. 258 +/- 14% for the control). In conclusion, isoflurane preconditioning elicits partial mitochondrial uncoupling and reduces mitochondrial Ca(2+) uptake. These effects are likely to reduce the extent of the mitochondrial damage after the hypoxic stress.
authors.affiliation: Department of Anesthesiology, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA.
authors.forename: Marko
authors.initials: M
authors.lastname: Ljubkovic
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Mio
authors.forename: Jasna
authors.initials: J
authors.lastname: Marinovic
authors.forename: Anna
authors.initials: A
authors.lastname: Stadnicka
authors.forename: David C
authors.initials: DC
authors.lastname: Warltier
authors.forename: Zeljko J
authors.initials: ZJ
authors.lastname: Bosnjak
authors.forename: Martin
authors.initials: M
authors.lastname: Bienengraeber
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D018685:Anesthetics, Inhalation / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D015687:Cell Hypoxia / Q000187:drug effects*; D019610:Cytoprotection; D004334:Drug Administration Schedule; D004734:Energy Metabolism / Q000187:drug effects*; D006352:Heart Ventricles / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D007530:Isoflurane / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D008929:Mitochondria, Heart / Q000187:drug effects* / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000187:drug effects* / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption; D051381:Rats; D017208:Rats, Wistar; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: D018685:Anesthetics, Inhalation; D017382:Reactive Oxygen Species; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D007530:Isoflurane; D010100:Oxygen; D002118:Calcium