期刊
COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY A-MOLECULAR & INTEGRATIVE PHYSIOLOGY
卷 142, 期 2, 页码 111-117出版社
ELSEVIER SCIENCE INC
DOI: 10.1016/j.cbpb.2005.05.004
关键词
calcium; cytochrome oxidase; dehydrogenases; hypoxia; Krebs cycle; mitochondria; nitric oxide; oxygen; mitochondrial nitric-oxide synthase; normoxia; nitric-oxide synthase
资金
- NIEHS NIH HHS [ES012691] Funding Source: Medline
- NIGMS NIH HHS [GM66768] Funding Source: Medline
Studies with isolated mitochondria are performed at artificially high pO(2) (220 to 250 mu M oxygen), although this condition is hyperoxic for these organelles. It was the aim of this study to evaluate the effect of hypoxia (20-30 mu M) on the calcium-dependent activation of 2-oxoglutarate dehydrogenase (or 2-ketoglutarate dehydrogenase; OGDH) and mitochondrial nitric-oxide synthase (mtNOS). Mitochondria had a P/O value 15% higher in hypoxia than that in normoxia, indicating that oxidative phosphorylation and electron transfer were more efficiently coupled, whereas the intramitochondrial free calcium concentrations were higher (2-3-fold) at lower pO(2). These increases were abrogated by ruthenium red indicating that the higher uptake via the calcium uniporter was involved in this process. Mitochondria at high calcium concentration microdomains may produce nitric oxide, given the K-0.5 of calcium for OGDH (0.16 mu M) and mtNOS (similar to 1 mu M). Nitric oxide, by binding to cytochrome oxidase in competition with oxygen, decreases the rate of oxygen consumption. This condition is highly beneficial for the following reasons: i, these mitochondria are still able to produce ATP and support calcium clearance; ii.. it prevents the accumulation of ROS by slowing the rate of oxygen consumption (hence ROS production); iii, the onset of anoxia is delayed, allowing oxygen to diffuse back to these sites, thereby ameliorating the oxygen gradient between regions of high and low calcium concentration. In this way, oxygen depletion at the latter sites is prevented. This, in turn, assures continued aerobic metabolism which may involve the activated dehydrogenases. (C) 2005 Elsevier Inc. All rights reserved.
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