Effects of palmitic acid on activity of uncoupling proteins and proton leak in in vitro cerebral mitochondria from the rats exposed to simulated high altitude hypoxia / 生理学报

ABSTRACT

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.