Budinger G R, Duranteau J, Chandel N S, Schumacker P T
Pulmonary and Critical Care Medicine, The University of Chicago, Chicago, Illinois 60637, USA.
J Biol Chem. 1998 Feb 6;273(6):3320-6. doi: 10.1074/jbc.273.6.3320.
During myocardial hibernation, decreases in coronary perfusion elicit inhibition of contraction, suggesting that energy demand is attenuated. We previously found an inhibition of contraction and O2 consumption during hypoxia (3% O2; PO2 = 20 torr for >2 h) in cardiomyocytes, which was reversible after reoxygenation. This study sought to determine whether mitochondria function as cellular O2 sensors mediating this response. Embryonic cardiomyocytes were studied under controlled O2 conditions. Hypoxia produced no acute decrease in mitochondrial potential as assessed using tetramethylrhodamine ethylester (TMRE). Cellular [ATP] was preserved throughout hypoxia, as assessed using the probe Magnesium Green. Thus, ATP synthesis and utilization remained closely coupled. Cells adapted to hypoxia for >2 h exhibited a 4% increase in mitochondrial potential upon reoxygenation, suggesting that a partial inhibition of cytochrome c oxidase had existed. To test whether the oxidase serves as an O2 sensor, azide was administered (1 mM) to simulate the effects of hypoxia by lowering the Vmax of the oxidase. The effects of azide on contraction and mitochondrial potential mimicked the response to hypoxia. We conclude that partial inhibition of cytochrome oxidase during hypoxia allows mitochondria to function as the O2 sensor mediating the decreases in ATP utilization and O2 consumption during hypoxia.
在心肌冬眠期间，冠状动脉灌注减少会引发收缩抑制，这表明能量需求减弱。我们之前发现，在缺氧（3%氧气；PO2 = 20托，持续超过2小时）条件下，心肌细胞的收缩和氧气消耗受到抑制，复氧后这种抑制是可逆的。本研究旨在确定线粒体是否作为细胞氧气传感器介导这种反应。在可控的氧气条件下对胚胎心肌细胞进行了研究。使用四甲基罗丹明乙酯（TMRE）评估发现，缺氧并未使线粒体膜电位立即下降。使用镁绿探针评估发现，在整个缺氧过程中细胞内[ATP]得以维持。因此，ATP的合成与利用仍紧密偶联。适应缺氧超过2小时的细胞在复氧时线粒体膜电位增加了4%，这表明细胞色素c氧化酶存在部分抑制。为了测试该氧化酶是否作为氧气传感器，给予叠氮化物（1 mM）以通过降低氧化酶的Vmax来模拟缺氧的影响。叠氮化物对收缩和线粒体膜电位的影响与对缺氧的反应相似。我们得出结论，缺氧期间细胞色素氧化酶的部分抑制使线粒体能够作为氧气传感器，介导缺氧期间ATP利用和氧气消耗的减少。
