Malvin G M, Havlen P, Baldwin C
Institute for Basic and Applied Medical Research, Lovelace Institutes, Albuquerque, New Mexico 87108.
Am J Physiol. 1994 Jul;267(1 Pt 2):R349-52. doi: 10.1152/ajpregu.1994.267.1.R349.
An important adaptation to hypoxia is a regulated reduction in body temperature because it lowers metabolic rate when oxygen supply is limited. Although this beneficial response occurs in organisms ranging from protozoans to mammals, little is known of the cellular mechanisms responsible for the hypoxia-induced reduction in temperature. Using the unicellular protozoan, Paramecium caudatum, we showed that inhibition of oxidative phosphorylation with sodium azide (NaN3) under normoxic conditions mimics the thermoregulatory effects of hypoxia, causing this species to select a lower temperature in a thermal gradient (P < 0.0001). Under control conditions, selected temperature (Tsel) was 28.3 +/- 0.3 degrees C. NaN3 concentrations of 0.1 mM and above significantly reduced Tsel (P < 0.0001). Ten millimolar NaN3 produced the maximal reduction in Tsel, 11.4 degrees C, and the dose that produced 50% of the maximal response was 0.7 mM. The reduction in temperature was beneficial because both O2 consumption and survival were significantly less affected by NaN3 at lower temperatures. These results suggest that O2 does not directly affect thermoregulation in the paramecium. Rather, the hypoxia-induced reduction in Tsel results from inhibition of oxidative phosphorylation.
对缺氧的一种重要适应性反应是体温的调节性降低，因为在氧气供应受限的情况下，它会降低代谢率。尽管这种有益反应在从原生动物到哺乳动物的各种生物体中都会出现，但对于缺氧诱导体温降低的细胞机制却知之甚少。我们利用单细胞原生动物尾草履虫进行研究，结果表明，在常氧条件下用叠氮化钠（NaN₃）抑制氧化磷酸化可模拟缺氧的体温调节效应，使该物种在温度梯度中选择较低的温度（P < 0.0001）。在对照条件下，选择的温度（Tsel）为28.3±0.3摄氏度。0.1 mM及以上浓度的NaN₃显著降低了Tsel（P < 0.0001）。10 mM的NaN₃使Tsel出现最大降幅，为11.4摄氏度，产生最大反应50%的剂量为0.7 mM。温度降低是有益的，因为在较低温度下，NaN₃对氧气消耗和存活率的影响显著较小。这些结果表明，氧气并不直接影响草履虫的体温调节。相反，缺氧诱导的Tsel降低是由氧化磷酸化的抑制所致。
