title: Inhibition of cytochrome-c oxidase activity during prolonged hypoxia.
abstract: During acute (< 30 min) hypoxia, cellular respiration is independent of the O2 concentration as long as PO2 remains above a critical value (5-10 Torr). Similarly, state 3 respiration by isolated mitochondria is independent of PO2 above a critical tension of 2-4 Torr. However, rat hepatocytes demonstrate a reversible suppression of respiration and an increase in NAD(P)H concentration during prolonged (2-24 h), but not acute hypoxia [P. T. Schumacker, N. Chandel, and A. G. N. Augusti. Am. J. Physiol. 265 (Lung Cell. Mol. Physiol. 9): L395-L402, 1993]. This study tested whether respiration is similarly inhibited in isolated mitochondria exposed to low PO2 for prolonged periods and whether cytochrome-c oxidase participates in this response. Coupled rat liver mitochondria were incubated under low oxygen conditions (PO2 < 2 Torr) for 2 h. State 3 respiration after reoxygenation to PO2 = 20 Torr was then compared with the value obtained subsequently at 100 Torr. Using succinate and ADP as substrates, we determined that state 3 respiration at 20 Torr was 61.0 +/- 8.4% of the subsequent value at 100 Torr (P < 0.05). By contrast, control mitochondria reoxygenated to 100 Torr first and 20 Torr subsequently showed no significant difference at the two O2 tensions (P = NS).(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Medicine, University of Chicago, Illinois 60637, USA.
authors.forename: N
authors.initials: N
authors.lastname: Chandel
authors.forename: G R
authors.initials: GR
authors.lastname: Budinger
authors.forename: R A
authors.initials: RA
authors.lastname: Kemp
authors.forename: P T
authors.initials: PT
authors.lastname: Schumacker
mesh_terms: D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D015687:Cell Hypoxia; D003576:Electron Transport Complex IV / Q000037:antagonists & inhibitors*; D007700:Kinetics; D008297:Male; D008930:Mitochondria, Liver / Q000201:enzymology* / Q000378:metabolism; D010085:Oxidative Phosphorylation; D010100:Oxygen / Q000494:pharmacology; D010101:Oxygen Consumption / Q000187:drug effects; D010313:Partial Pressure; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D000001:Calcimycin; D003576:Electron Transport Complex IV; D010100:Oxygen