title: Mechanisms involved in postconditioning protection of cardiomyocytes against acute reperfusion injury.
abstract: Experimental and clinical studies demonstrated that postconditioning confers protection against myocardial ischemia/reperfusion injury. However the underlying cellular mechanisms responsible for the beneficial effect of postconditioning are still poorly understood. The aim of the present study was to examine the role of cytosolic and mitochondrial Ca(2+)-handling. For this purpose adult rat cardiomyocytes were subjected to simulated in vitro ischemia (glucose-free hypoxia at pH6.4) followed by simulated reperfusion with a normoxic buffer (pH7.4; 2.5 mmol/L glucose). Postconditioning, i.e., 2 repetitive cycles of normoxic (5s) and hypoxic (2.5 min) superfusion, was applied during the first 5 min of reoxygenation. Mitochondrial membrane potential (ΔΨm), cytosolic and mitochondrial Ca(2+) concentrations, cytosolic pH and necrosis were analysed applying JC-1, fura-2, fura-2/manganese, BCECF and propidium iodide, respectively. Mitochondrial permeability transition pore (MPTP) opening was detected by calcein release. Hypoxic treatment led to a reduction of ΔΨm, an increase in cytosolic and mitochondrial Ca(2+) concentration, and acidification of cardiomyocytes. During the first minutes of reoxygenation, ΔΨm transiently recovered, but irreversibly collapsed after 7 min of reoxygenation, which was accompanied by MPTP opening. Simultaneously, mitochondrial Ca(2+) increased during reperfusion and cardiomyocytes developed spontaneous cytosolic Ca(2+) oscillations and severe contracture followed by necrosis after 25 min of reoxygenation. In postconditioned cells, the collapse in ΔΨm as well as the leak of calcein, the increase in mitochondrial Ca(2+), cytosolic Ca(2+) oscillations, contracture and necrosis were significantly reduced. Furthermore postconditioning delayed cardiomyocyte pH recovery. Postconditioning by hypoxia/reoxygenation was as protective as treatment with cyclosporine A. Combining cyclosporine A and postconditioning had no additive effect. The data of the present study demonstrate that postconditioning by hypoxia/reoxygenation prevents reperfusion injury by limiting mitochondrial Ca(2+) load and thus opening of the MPTP in isolated cardiomyocytes. These effects seem to be supported by postconditioning-induced delay in pH recovery and suppression of Ca(2+) oscillations.
authors: Department of Cardiology and Angiology, University Hospital Giessen and Marburg Klinikstr. 33, 35392 Giessen, Germany.
authors: Tayyab
authors: T
authors: Shahzad
authors: Sascha Andreas
authors: SA
authors: Kasseckert
authors: Wisam
authors: W
authors: Iraqi
authors: Victoria
authors: V
authors: Johnson
authors: Rainer
authors: R
authors: Schulz
authors: Klaus-Dieter
authors: KD
authors: Schlüter
authors: Oliver
authors: O
authors: Dörr
authors: Mariana
authors: M
authors: Parahuleva
authors: Christian
authors: C
authors: Hamm
authors: Yury
authors: Y
authors: Ladilov
authors: Yaser
authors: Y
authors: Abdallah
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D016257:Fura-2 / Q000378:metabolism; D006801:Humans; D000860:Hypoxia / Q000473:pathology; D057775:Ischemic Postconditioning; D008297:Male; D053078:Membrane Potential, Mitochondrial; D008929:Mitochondria, Heart / Q000378:metabolism*; D015428:Myocardial Reperfusion Injury / Q000378:metabolism / Q000473:pathology*; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000473:pathology; D051381:Rats
chemical_list: D002118:Calcium; D016257:Fura-2