title: Isolated respiring heart mitochondria release reactive oxygen species in states 4 and 3.
abstract: Isolated mitochondria respiring on physiological substrates, both in state 4 and 3, are reported to be or not to be a source of reactive oxygen species (ROS). The cause of these discrepancies has been investigated. As protein concentration was raised in in vitro assays at 37 degrees C, the rate of H2O2 release by rat heart mitochondria supplemented with pyruvate/malate or with succinate (plus rotenone) was shown to increase (0.03-0.15 mg protein/ml), to decrease (0.2-0.5 mg protein/ml) and to be negligible (over 0.5 mg protein/ml). The inhibition of mitochondrial respiration (with rotenone or antimycin A) or the increase in the oxygen concentration dissolved in the assay medium allowed an enhancement of ROS production rate throughout the studied range of protein concentrations. In mitochondria respiring in state 3 on pyruvate/malate or on succinate (plus rotenone), ROS release vanished for protein concentrations over 0.5 or 0.2 mg/ml, respectively. However, ROS production rates measured with low protein concentrations (below 0.1 mg/ml) or in oxygen-enriched media were similar or even slightly higher in the active respiratory state 3 than in the resting state 4 for both substrates. Consequently, these findings indicate that isolated mitochondria, respiring in vitro under conditions of forward electron transport, release ROS with Complex I- and II-linked substrates in the resting condition (state 4) and when energy demand is maximal (state 3), provided that there is sufficient oxygen dissolved in the medium.
authors.affiliation: Faculty of Chemistry, Department of Biochemistry and Molecular Biology I, Complutense University, 28040 Madrid, Spain. asaborido@quim.ucm.es
authors.forename: Ana
authors.initials: A
authors.lastname: Saborido
authors.forename: Laura
authors.initials: L
authors.lastname: Soblechero
authors.forename: Alicia
authors.initials: A
authors.lastname: Megías
mesh_terms: D000818:Animals; D019069:Cell Respiration; D004579:Electron Transport; D006861:Hydrogen Peroxide / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008298:Maleates / Q000378:metabolism; D008929:Mitochondria, Heart / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism; D019289:Pyruvic Acid / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D017382:Reactive Oxygen Species / Q000378:metabolism*; D019802:Succinic Acid / Q000378:metabolism; D013696:Temperature
chemical_list: D008298:Maleates; D024101:Mitochondrial Proteins; D017382:Reactive Oxygen Species; D019289:Pyruvic Acid; C030272:maleic acid; D019802:Succinic Acid; D006861:Hydrogen Peroxide; D010100:Oxygen