Sources for superoxide release: lessons from blockade of electron transport, NADPH oxidase, and anion channels in diaphragm.
Isolated diaphragm releases low levels of superoxide (O2*-) at rest and much higher levels during heat stress. The molecular source is unknown. The hypothesis was tested that heat stress stimulates mitochondrial complex activity or NADPH oxidases, resulting in increased O2*- release. The mitochondria within intact rat diaphragm were inhibited at complex I (amobarbital or rotenone) or complex I and II (rotenone plus thenoyltrifluoroacetone). NADPH oxidases were blocked by diphenyliodonium. None of these treatments inhibited O2*- release. Conversely, most blockers stimulated O2*- release. As intracellular O2*- generators require a mechanism for O2*- transport across the membrane, anion channel blockers, probenecid and 4,4'-diisothiocyanato-stilbene-2,2'-disulfonic acid, were also tested. Neither blocker had any inhibitory effect on O2*- release. These results suggest that O2*- released from diaphragm is not directly dependent on mitochondrial complex activity and that it is not a reflection of passive diffusion of O2*- through anion channels. Although the molecular source for extracellular O2*- remains elusive, it is clearly sensitive to temperature and conditions of "chemical hypoxia" induced by partial or complete mitochondrial inhibition.
The Ohio State University Medical Centre, Department of Internal Medicine, Dorothy M. Davis Heart & Lung Research Institute, Division of Pulmonary and Critical Care Medicine, Columbus, OH 43210, USA.
Li
L
Zuo
Silviu
S
Pasniciuc
Valerie P
VP
Wright
A John
AJ
Merola
Thomas L
TL
Clanton
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000654:Amobarbital / Q000494:pharmacology; D000818:Animals; D000838:Anions / Q000378:metabolism; D000968:Antimycin A / Q000494:pharmacology; D001713:Biphenyl Compounds / Q000494:pharmacology; D045304:Cytochromes c / Q000378:metabolism; D003964:Diaphragm / Q000187:drug effects / Q000378:metabolism*; D004579:Electron Transport / Q000187:drug effects / Q000502:physiology*; D042967:Electron Transport Complex I / Q000037:antagonists & inhibitors / Q000378:metabolism; D014450:Electron Transport Complex III / Q000037:antagonists & inhibitors / Q000378:metabolism; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D008297:Male; D019255:NADPH Oxidases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009861:Onium Compounds / Q000494:pharmacology; D010084:Oxidation-Reduction; D010101:Oxygen Consumption / Q000187:drug effects; D011339:Probenecid / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012402:Rotenone / Q000494:pharmacology; D013482:Superoxide Dismutase / Q000494:pharmacology; D013481:Superoxides / Q000378:metabolism*; D013696:Temperature; D013804:Thenoyltrifluoroacetone / Q000494:pharmacology
D000838:Anions; D001713:Biphenyl Compounds; D007473:Ion Channels; D009861:Onium Compounds; D012402:Rotenone; C031291:diphenyliodonium; D013481:Superoxides; D013804:Thenoyltrifluoroacetone; D000968:Antimycin A; D045304:Cytochromes c; D013482:Superoxide Dismutase; D019255:NADPH Oxidases; D042967:Electron Transport Complex I; D014450:Electron Transport Complex III; D000654:Amobarbital; D011339:Probenecid; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid