Department of Zoology, The University of British Columbia, Vancouver, BC, Canada.
J Exp Biol. 2013 Sep 1;216(Pt 17):3283-93. doi: 10.1242/jeb.087155.
The freshwater turtle Trachemys scripta can survive in the complete absence of O2 (anoxia) for periods lasting several months. In mammals, anoxia leads to mitochondrial dysfunction, which culminates in cellular necrosis and apoptosis. Despite the obvious clinical benefits of understanding anoxia tolerance, little is known about the effects of chronic oxygen deprivation on the function of turtle mitochondria. In this study, we compared mitochondrial function in hearts of T. scripta exposed to either normoxia or 2 weeks of complete anoxia at 5°C and during simulated acute anoxia/reoxygenation. Mitochondrial respiration, electron transport chain activities, enzyme activities, proton conductance and membrane potential were measured in permeabilised cardiac fibres and isolated mitochondria. Two weeks of anoxia exposure at 5°C resulted in an increase in lactate, and decreases in ATP, glycogen, pH and phosphocreatine in the heart. Mitochondrial proton conductance and membrane potential were similar between experimental groups, while aerobic capacity was dramatically reduced. The reduced aerobic capacity was the result of a severe downregulation of the F1FO-ATPase (Complex V), which we assessed as a decrease in enzyme activity. Furthermore, in stark contrast to mammalian paradigms, isolated turtle heart mitochondria endured 20 min of anoxia followed by reoxygenation without any impact on subsequent ADP-stimulated O2 consumption (State III respiration) or State IV respiration. Results from this study demonstrate that turtle mitochondria remodel in response to chronic anoxia exposure and a reduction in Complex V activity is a fundamental component of mitochondrial and cellular anoxia survival.
淡水龟赤蠵龟可以在完全缺氧（缺氧）的情况下存活数月。在哺乳动物中，缺氧会导致线粒体功能障碍，最终导致细胞坏死和凋亡。尽管了解缺氧耐受的明显临床益处，但对于慢性缺氧对龟线粒体功能的影响知之甚少。在这项研究中，我们比较了在 5°C 下暴露于常氧或 2 周完全缺氧的 T. scripta 心脏中的线粒体功能，以及在模拟急性缺氧/再氧合期间。在通透性心肌纤维和分离的线粒体中测量了线粒体呼吸、电子传递链活性、酶活性、质子传导和膜电位。2 周的 5°C 缺氧暴露导致心脏中乳酸增加，ATP、糖原、pH 和磷酸肌酸减少。实验组之间的线粒体质子传导和膜电位相似，而有氧能力显著降低。有氧能力的降低是由于 F1FO-ATP 酶（复合物 V）的严重下调所致，我们将其评估为酶活性的降低。此外，与哺乳动物模式形成鲜明对比的是，分离的龟心脏线粒体在缺氧 20 分钟后再氧合，而对随后的 ADP 刺激的 O2 消耗（状态 III 呼吸）或状态 IV 呼吸没有任何影响。这项研究的结果表明，龟线粒体在慢性缺氧暴露后发生重塑，并且复合物 V 活性的降低是线粒体和细胞缺氧存活的基本组成部分。
