title: Isoflurane protects cardiomyocytes and mitochondria by immediate and cytosol-independent action at reperfusion.
abstract: OBJECTIVE
  The volatile anaesthetic isoflurane protects the heart from ischaemia and reperfusion (I/R) injury when applied at the onset of reperfusion [anaesthetic postconditioning (APoC)]. However, the mechanism of APoC-mediated protection is unknown. In this study, we examined the effect of APoC on mitochondrial bioenergetics, mitochondrial matrix pH (pH(m)) and cytosolic pH (pH(i)), and intracellular Ca(2+).
  
  
  METHODS
  Cardiac mitochondria from Wistar rats were isolated after in vivo I/R with or without APoC (1.4%-vol isoflurane, 1 minimum alveolar concentration), and mitochondrial permeability transition pore (mPTP) opening, mitochondrial membrane potential (DeltaPsi(m)), and oxygen consumption were assessed. In isolated cardiomyocytes and isolated mitochondria I/R injury was produced in vitro, with or without APoC (0.5 mM isoflurane). Intracellular Ca(2+), pH(m), pH(i) and DeltaPsi(m) were monitored with SNARF-1, TMRE and fluo-4, respectively. Myocyte survival was assessed when APoC was induced at pH 7.4 and 7.8. In isolated mitochondria oxygen consumption and ATP synthesis were measured.
  
  
  RESULTS
  In vivo APoC protected against mPTP opening, slowed mitochondrial respiration and depolarized mitochondria. APoC decreased the number of hypercontracted cardiomyocytes at pH 7.4, but not at pH 7.8. APoC attenuated intracellular Ca(2+) accumulation, maintained lower pH(m), and preserved DeltaPsi(m) during reoxygenation. Isoflurane did not affect the regulation of cytosolic pH. In mitochondria, APoC preserved ATP production rate and respiration.
  
  
  CONCLUSIONS
  At reperfusion, APoC inhibited mitochondrial respiration, depolarized mitochondria and acidified pH(m). These events may lead to inhibition of mPTP opening and, consequently, to preserved DeltaPsi(m) and ATP synthesis. This reduces intracellular Ca(2+) overload and cell death.
authors.affiliation: Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, USA. danijel.pravdic@gmail.com <danijel.pravdic@gmail.com>
authors.forename: D
authors.initials: D
authors.lastname: Pravdic
authors.forename: Y
authors.initials: Y
authors.lastname: Mio
authors.forename: F
authors.initials: F
authors.lastname: Sedlic
authors.forename: P F
authors.initials: PF
authors.lastname: Pratt
authors.forename: D C
authors.initials: DC
authors.lastname: Warltier
authors.forename: Z J
authors.initials: ZJ
authors.lastname: Bosnjak
authors.forename: M
authors.initials: M
authors.lastname: Bienengraeber
mesh_terms: D000255:Adenosine Triphosphate / Q000096:biosynthesis; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007530:Isoflurane / Q000494:pharmacology*; D008297:Male; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D008929:Mitochondria, Heart / Q000187:drug effects* / Q000378:metabolism; D015428:Myocardial Reperfusion Injury / Q000503:physiopathology / Q000517:prevention & control*; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism; D010101:Oxygen Consumption / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar
chemical_list: D018685:Anesthetics, Inhalation; D000255:Adenosine Triphosphate; D007530:Isoflurane; D002118:Calcium