title: Preconditioning protects by inhibiting the mitochondrial permeability transition.
abstract: Mitochondrial permeability transition (mPT) is a crucial event in the progression to cell death in the setting of ischemia-reperfusion. We have used a model system in which mPT can be reliably and reproducibly induced to test the hypothesis that the profound protection associated with the phenomenon of myocardial preconditioning is mediated by suppression of the mPT. Adult rat myocytes were loaded with the fluorescent probe tetramethylrhodamine methyl ester, which generates oxidative stress on laser illumination, thus inducing the mPT (indicated by collapse of the mitochondrial membrane potential) and ATP depletion, seen as rigor contracture. The known inhibitors of the mPT, cyclosporin A (0.2 microM) and N-methyl-4-valine-cyclosporin A (0.4 microM), increased the time taken to induce the mPT by 1.8- and 2.9-fold, respectively, compared with control (P < 0.001) and rigor contracture by 1.5-fold compared with control (P < 0.001). Hypoxic preconditioning (HP) and pharmacological preconditioning, using diazoxide (30 microM) or nicorandil (100 microM), also increased the time taken to induce the mPT by 2.0-, 2.1-, and 1.5-fold, respectively (P < 0.001), and rigor contracture by 1.9-, 1.7-, and 1.5-fold, respectively, compared with control (P < 0.001). Effects of HP, diazoxide, and nicorandil were abolished in the presence of mitochondrial ATP-sensitive K(+) (K(ATP)) channel blockers glibenclamide (10 microM) and 5-hydroxydecanoate (100 microM) but were maintained in the presence of the sarcolemmal K(ATP) channel blocker HMR-1098 (10 microM). In conclusion, preconditioning protects the myocardium by reducing the probability of the mPT, which normally occurs during ischemia-reperfusion in response to oxidative stress.
authors.affiliation: The Hatter Institute and Centre for Cardiology, University College London Hospitals and Medical School, Grafton Way, London WC1E 6DB, UK.
authors.forename: Derek J
authors.initials: DJ
authors.lastname: Hausenloy
authors.forename: Derek M
authors.initials: DM
authors.lastname: Yellon
authors.forename: Siva
authors.initials: S
authors.lastname: Mani-Babu
authors.forename: Michael R
authors.initials: MR
authors.lastname: Duchen
mesh_terms: D000818:Animals; D015687:Cell Hypoxia / Q000502:physiology; D003981:Diazoxide / Q000494:pharmacology; D005453:Fluorescence; D007425:Intracellular Membranes / Q000378:metabolism*; D019157:Ischemic Preconditioning, Myocardial / Q000379:methods; D007834:Lasers; D008297:Male; D008564:Membrane Potentials; D018613:Microscopy, Confocal; D008929:Mitochondria, Heart / Q000378:metabolism* / Q000502:physiology; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D020108:Nicorandil / Q000494:pharmacology; D018384:Oxidative Stress; D010539:Permeability / Q000187:drug effects / Q000528:radiation effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D012235:Rhodamines
chemical_list: D012235:Rhodamines; C401833:tetramethylrhodamine methyl ester; D020108:Nicorandil; D003981:Diazoxide