title: Oxygen sensitivity of mitochondrial function in rat arterial chemoreceptor cells.
abstract: The mechanism of oxygen sensing in arterial chemoreceptors is unknown but has often been linked to mitochondrial function. A common criticism of this hypothesis is that mitochondrial function is insensitive to physiological levels of hypoxia. Here we investigate the effects of hypoxia (down to 0.5% O2) on mitochondrial function in neonatal rat type-1 cells. The oxygen sensitivity of mitochondrial [NADH] was assessed by monitoring autofluorescence and increased in hypoxia with a P50 of 15 mm Hg (1 mm Hg = 133.3 Pa) in normal Tyrode or 46 mm Hg in Ca(2+)-free Tyrode. Hypoxia also depolarised mitochondrial membrane potential (m, measured using rhodamine 123) with a P50 of 3.1, 3.3 and 2.8 mm Hg in normal Tyrode, Ca(2+)-free Tyrode and Tyrode containing the Ca(2+) channel antagonist Ni(2+), respectively. In the presence of oligomycin and low carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone (FCCP; 75 nm) m is maintained by electron transport working against an artificial proton leak. Under these conditions hypoxia depolarised m/inhibited electron transport with a P50 of 5.4 mm Hg. The effects of hypoxia upon cytochrome oxidase activity were investigated using rotenone, myxothiazol, antimycin A, oligomycin, ascorbate and the electron donor tetramethyl-p-phenylenediamine. Under these conditions m is maintained by complex IV activity alone. Hypoxia inhibited cytochrome oxidase activity (depolarised m) with a P50 of 2.6 mm Hg. In contrast hypoxia had little or no effect upon NADH (P50 = 0.3 mm Hg), electron transport or cytochrome oxidase activity in sympathetic neurons. In summary, type-1 cell mitochondria display extraordinary oxygen sensitivity commensurate with a role in oxygen sensing. The reasons for this highly unusual behaviour are as yet unexplained.
authors.affiliation: Department of Physiology, Anatomy & Genetics, Parks Road, Oxford, UK. keith.buckler@dpag.ox.ac.uk
authors.forename: Keith J
authors.initials: KJ
authors.lastname: Buckler
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Turner
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000502:physiology; D002339:Carotid Arteries / Q000166:cytology; D002344:Carotid Body / Q000502:physiology*; D004579:Electron Transport; D000860:Hypoxia / Q000503:physiopathology; D066298:In Vitro Techniques; D053078:Membrane Potential, Mitochondrial; D008928:Mitochondria / Q000502:physiology*; D009243:NAD / Q000502:physiology; D009474:Neurons / Q000502:physiology; D010100:Oxygen / Q000502:physiology*; D051381:Rats; D017783:Superior Cervical Ganglion / Q000166:cytology
chemical_list: D009243:NAD; D010100:Oxygen; D002118:Calcium