title: Complex III-dependent superoxide production of brain mitochondria contributes to seizure-related ROS formation.
abstract: Brain seizure activity is characterised by intense activation of mitochondrial oxidative phosphorylation. This stimulation of oxidative phosphorylation is in the low magnesium model of seizure-like events accompanied by substantial increase in formation of reactive oxygen species (ROS). However, it has remained unclear which ROS-generating sites can be attributed to this phenomenon. Here, we report stimulatory effects of calcium ions and uncouplers, mimicking mitochondrial activation, on ROS generation of isolated rat and mouse brain mitochondria. Since these stimulatory effects were visible with superoxide sensitive dyes, but with hydrogen peroxide sensitive dyes only in the additional presence of SOD, we conclude that the complex redox properties of the 'Qo' center at respiratory chain complex III are very likely responsible for these observations. In accordance with this hypothesis redox titrations of the superoxide production of antimycin-inhibited submitochondrial particles with the succinate/fumarate redox couple confirmed for brain tissue a bell-shaped dependency with a maximal superoxide production rate at +10 mV (pH=7.4). This reflects the complex redox properties of a semiquinone species which is the direct electron donor for oxygen reduction in complex III-dependent superoxide production. Therefore, we conclude that under conditions of increased energy load the complex III site can contribute to superoxide production of brain mitochondria, which might be relevant for epilepsy-related seizure activity.
authors.affiliation: Laboratory of Intracellular Ion Channels, Nencki Institute of Experimental Biology, 3 Pasteur St., 02-093 Warsaw, Poland.
authors.forename: Dominika
authors.initials: D
authors.lastname: Malinska
authors.forename: Bogusz
authors.initials: B
authors.lastname: Kulawiak
authors.forename: Alexei P
authors.initials: AP
authors.lastname: Kudin
authors.forename: Richard
authors.initials: R
authors.lastname: Kovacs
authors.forename: Christine
authors.initials: C
authors.lastname: Huchzermeyer
authors.forename: Oliver
authors.initials: O
authors.lastname: Kann
authors.forename: Adam
authors.initials: A
authors.lastname: Szewczyk
authors.forename: Wolfram S
authors.initials: WS
authors.lastname: Kunz
mesh_terms: D000818:Animals; D001562:Benzimidazoles / Q000494:pharmacology; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D042967:Electron Transport Complex I / Q000378:metabolism; D014450:Electron Transport Complex III / Q000378:metabolism*; D006624:Hippocampus / Q000378:metabolism; D066298:In Vitro Techniques; D051379:Mice; D008810:Mice, Inbred C57BL; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D008959:Models, Neurological; D010084:Oxidation-Reduction; D010085:Oxidative Phosphorylation; D051381:Rats; D017208:Rats, Wistar; D017382:Reactive Oxygen Species / Q000378:metabolism; D012640:Seizures / Q000378:metabolism*; D013481:Superoxides / Q000378:metabolism*; D014451:Ubiquinone / Q000378:metabolism; D014475:Uncoupling Agents / Q000494:pharmacology
chemical_list: D001562:Benzimidazoles; D017382:Reactive Oxygen Species; D014475:Uncoupling Agents; D013481:Superoxides; D014451:Ubiquinone; C005817:4,5,6,7-tetrachloro-2-trifluoromethylbenzimidazole; D042967:Electron Transport Complex I; D014450:Electron Transport Complex III; D002118:Calcium