Anoxia In Rat Brain Cortex Mitochondrial Cytochrome Oxidase Activity And Its Subunit Expression Coordinated Research

To understand the mechanism of disorder in brain energy metabolism and explore the contributing role of COX in disorder in mitochondrial respiratory function during hypoxic exposure. We observed the brain cortex mitochondrial COX activity, COX subunits gene expression ecoded by mtDNA and nDNA during rat exposed to hypoxia. Adult male Wistar rats were exposed to simulated high altitude at 5000m for 0(control), 2(2d), 5(5d), 15(1 Sd) and 30 days(30d) in hypobaric chamber. Animals were sacrificed by decaptation under normoxic(control) and hypoxic(other groups)conditions respectively Rats brain cortex was removed and mitochondria were isolated by centrifugation. COX activity was measured by the Clark oxygen electrode. The protein content of COX subunit I and IV in mitochondria were detected by Western blot analysis and mRNA state level of the two COX subunits( I and IV) in tissues by RT.-PCR. The results showed that: 1) Within the 15 days hypoxic exposure, COX activity decreased significantly than control, expecially in I Sd group animals; but restored to 78% of the control level in 30d group animals; 2) During hypoxic exposure , the protein content of COX subunit I and IV in mitochondria from brain cortex did not change ; the ratio of subunit IV/ I also had no significant differences among each groups; 3)The subunit I mRNA state level increased significantly in 2d and Sd than in control, but decreased to control level in 15d and 30d group ; Subunit IV mRNA state level of animals in 2d, Sd and 1 Sd group were dramatically higher than that in control, but lower in 30d group; l2sr RNA state level was higher in 2d group than in control, Sd, 15.d and 30d, but no sinificant differences among control, Sd, 15d and 30d group. Except higher in 1 Sd group than in control, the ratio of mRNA state level of COX subunit IV to I had no significant differences between other groups. Conclusion: 1) COX activity in rat brain cortex decreased during rat exposed to hypoxia .Within 15 days hypoxic exposure, COX activity decreased progressly and then partly recovered when rat further exposure. It showed that the changes of COX activity in rat brain cortex were time-dependent with hypoxic exposure. This results indicated that the changes contribute to the disorder of mitochondrial respiratory function and energy pruduction during hypoxia; 2) The content of COX subunit I and IV protein in mitochondria from rat brain cortex had no differences among each groups of hypoxic exposed animals , which suggested that qualitative control in regulation of COX activity might be the major model during hypoxic exposure; 3) In early of hypoxic exposure (2 days and Sdays), COX subunit I and IV mRNA state level increased coordinately, but disproportionly at 15 days hypoxic exposure. While the content of COX subunit I and IV protein and their ratio in mitochondria from rat brain cortex during hypoxic exposure had no change. This concluded that the regulation of COX subunits gene expression and the their coordination might be adjusted at post-transcription level or protein level.