Mitochondrial permeability transition in rat hepatocytes after anoxia/reoxygenation: Role of Ca 2+-dependent mitochondrial formation of reactive oxygen species

Jae Sung Kim, Jin Hee Wang, John J. Lemasters

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62 Scopus citations

Abstract

Onset of the mitochondrial permeability transition (MPT) is the penultimate event leading to lethal cellular ischemia-reperfusion injury, but the mechanisms precipitating the MPT after reperfusion remain unclear. Here, we investigated the role of mitochondrial free Ca 2++ and reactive oxygen species (ROS) in pH- and MPT-dependent reperfusion injury to hepatocytes. Cultured rat hepatocytes were incubated in anoxic Krebs-Ringer-HEPES buffer at pH 6.2 for 4 h and then reoxygenated at pH 7.4 to simulate ischemia-reperfusion. Some cells were loaded with the Ca 2++ chelators, BAPTA/AM and 2-[(2-bis-[carboxymethyl] aono-5-methoxyphenyl)-methyl-6-methoxy-8-bis[carboxymethyl] aminoquinoline, either by a cold loading protocol for intramitochondrial loading or by warm incubation for cytosolic loading. Cell death was assessed by propidium iodide fluorometry and immunoblotting. Mitochondrial Ca 2+, inner membrane permeability, membrane potential, and ROS formation were monitored with Rhod-2, calcein, tetramethylrhodamine methylester, and dihydrodichlorofluorescein, respectively. Necrotic cell death increased after reoxygenation. Necrosis was blocked by 1 μM cyclosporin A, an MPT inhibitor, and by reoxygenation at pH 6.2. Confocal imaging of Rhod-2, calcein, and dichlorofluorescein revealed that an increase of mitochondrial Ca 2++ and ROS preceded onset of the MPT after reoxygenation. Intramitochondrial Ca 2++ chelation, but not cytosolic Ca 2++ chelation, prevented ROS formation and subsequent necrotic and apoptotic cell death. Reoxygenation with the antioxidants, desferal or diphenylphenylenediamine, also suppressed MPT-mediated cell death. However, inhibition of cytosolic ROS by apocynin or diphenyleneiodonium chloride failed to prevent reoxygenation-induced cell death. In conclusion, Ca 2++- dependent mitochondrial ROS formation is the molecular signal culminating in onset of the MPT after reoxygenation of anoxic hepatocytes, leading to cell death.

Original languageEnglish
Pages (from-to)G723-G731
JournalAmerican Journal of Physiology - Gastrointestinal and Liver Physiology
Volume302
Issue number7
DOIs
StatePublished - Apr 1 2012

Keywords

  • Cell death
  • Ischemia
  • Reperfusion

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