Xu Yu, Liu Jun-Ze, Xia Chen
Department of Pathophysiology and Altitude Physiology, the Third Military Medical University, Chongqing 400038, China.
Sheng Li Xue Bao. 2008 Feb 25;60(1):59-64.
To reveal the roles of uncoupling proteins (UCPs) in disorder of mitochondrial oxidative phosphorylation induced by free fatty acid during hypoxic exposure, the effects of palmitic acid on activity of UCPs, proton leak and mitochondrial membrane potential in hypoxia-exposed rat brain mitochondria were observed in vitro. Adult Sprague-Dawley (SD) rats were set randomly into control, acute hypoxia and chronic hypoxia groups (n=8 in each group). The acute and chronic hypoxic rats were exposed to simulated 5000 m high altitude in a hypobaric chamber 23 h/d for 3 d and 30 d, respectively. The brain mitochondria were isolated by centrifugation. UCP content and activity were detected by [(3)H]-GTP binding method. The proton leak was measured by TPMP(+) electrode and oxygen electrode. The membrane potential of mitochondria was calculated by detecting the fluorescence from Rodamine 123. Hypoxic exposure resulted in an increase in UCP activity and content as well as proton leak, but a decrease in the membrane potential of rat brain mitochondria. Palmitic acid resulted in further increases in UCP activity and content as well as proton leak, and further decrease in membrane potential of brain mitochondria in vitro from hypoxia-exposed rats, but hypoxic exposure decreased the reactivity of cerebral mitochondria to palmitic acid, especially in the acute hypoxia group. There was a negative correlation between mitochondrial proton leak and K(d) value (representing derivative of UCP activity, P<0.01, r = -0.906), and a positive correlation between proton leak and B(max) (representing the maximal content of UCPs in mitochondrial inner membrane, P<0.01, r = 0.856). Cerebral mitochondrial membrane potential was negatively correlated with proton leak (P<0.01, r = -0.880). It is suggested that hypoxia-induced proton leak enhancement and membrane potential decrease are correlated with the increased activity of UCPs. Hypoxia can also decrease the sensitivity of cerebral mitochondria to palmitic acid, which may be a self-protective mechanism in high altitude environment.
为揭示解偶联蛋白（UCPs）在低氧暴露期间游离脂肪酸诱导的线粒体氧化磷酸化紊乱中的作用，体外观察了棕榈酸对低氧暴露大鼠脑线粒体中UCPs活性、质子泄漏和线粒体膜电位的影响。成年Sprague-Dawley（SD）大鼠随机分为对照组、急性低氧组和慢性低氧组（每组n = 8）。急性和慢性低氧大鼠分别在低压舱中每天23小时暴露于模拟的5000米高海拔环境，持续3天和30天。通过离心分离脑线粒体。采用[³H]-GTP结合法检测UCP含量和活性。用TPMP⁺电极和氧电极测量质子泄漏。通过检测罗丹明123的荧光计算线粒体膜电位。低氧暴露导致大鼠脑线粒体UCP活性和含量以及质子泄漏增加，但膜电位降低。棕榈酸导致低氧暴露大鼠体外脑线粒体UCP活性和含量以及质子泄漏进一步增加，膜电位进一步降低，但低氧暴露降低了脑线粒体对棕榈酸的反应性，尤其是在急性低氧组。线粒体质子泄漏与K(d)值（代表UCP活性的导数，P<0.01，r = -0.906）呈负相关，质子泄漏与B(max)（代表线粒体内膜中UCPs的最大含量，P<0.01，r = 0.856）呈正相关。脑线粒体膜电位与质子泄漏呈负相关（P<0.01，r = -0.880）。提示低氧诱导的质子泄漏增强和膜电位降低与UCPs活性增加有关。低氧还可降低脑线粒体对棕榈酸的敏感性，这可能是高原环境中的一种自我保护机制。
