| It is known that brain is the most sensitive organ to hypoxia and mitochondrial dyfunction resulted from acute hypoxia is a key factor for the disorder in brain energy metabolism. Objective To understand the changing aspects of mitochondrial oxidative phosphorylation function and cytochrome c oxidase activity during acute hypoxia exposure and their mechanism regulated by gene expression encoded by mtDNA and nDNA. An animal model set by chloramphenicol(CAP) administration ,CAP is a specific inhibitor for mitochondrial protein synthesis,was used. Methods Adult male Wistar rats were divided into four groups.They were hypoxia exposure group(H group), medication group(M group), medication plus hypoxia exposure group(MH group) and control group(C group). Medication was administrated by giving CAP(50mg/kg, intraperitoneal injection) every 12 hours for 7 days. Hypoxia exposure was administrasted by exposing rats to a hypobaric chamber simulated 5000m high altitude for 24 hours. C group received only equal amount of normal saline by intraperitoneal injection every 12 hours for 7 days. All animals were sacrificed by decapitation under normoxic(C and M) and hypoxic(H and MH)conditions respectively at 12 hours after the last injection. The rat cerebral cortex was removed and the mitochondria was isolated by centrifugation programme. Mitochondrial respiratory function and COX activity were measured by Clark oxygen electrode. The protein content of COX subunit I and IV in mitochondria and NRF-1 in cerebral tissues was detected by Western blot analysis. And mRNA state levels of COXâ… ,COXâ…£,12s rRNA,mtTFA and NRF-1 in tissues were determined by RT-PCR. Results 1) Compared with C group, H group showed elevated state 4 respiration(ST4) and decreased state 3 respiration(ST3) and respiratory control rate(RCR) in mitochondrial respiration during acute hypoxic exposure significantly; ST3 in MH group was significantly lower than that in C group but not decrease than in H group,while ST4 in MH group is lower significantly than that in H group as well as C group. RCR in MH group was higher than that in H group but lower than that in C group; 2) COXactivity in H group decreased significantly than in C group. In MH group, COX activity increased and was higher than that in H group, but which was still lower than in C group, restored from 65.7% to 86.5% of the control(C group) level; 3) A decreased protein content of COX subunit I and an elevated ratio of subunit IV/ I were observed in H group than in C group. There was no significant difference of the protein content of COXI and the ratio of subunit IV/ I between C and MH groups. But a mutual effect by two factors(medication and acute hypoxia) was observed in MH group.The protein content of COXIV and NRF-1 remained similar among all groups; 4) Compared with C group, H group showed significant decreased COXIV, mtTFA and NRF-1 mRNA state level, while 12s rRNA, COXI and the ratio of subunit IV/ I mRNA had no significant change among groups; In MH group, mtTFA,COXI , COXIV mRNA and the ratio of subunit IV/ I mRNA showed significant higher than those in H group but not than in C group. The state level of NRF-1 mRNA decreased significantly in MH group than in C group, but not than in H group;12s rRNA state level had no significant changes among all groups.Conclusion:1) Acute hypoxic exposure could lead to mitochondrial respiratory dyfunction, bur CAP admistration might be beneficial to the recovering of rat respiratory function and oxidative phosphorylation efficiency during acute hypoxic exposure. The change of COX activity is consistent with that of mitochondrial respiratory function during acute hypoxic exposure and CAP-admistration, which indicated that COX played an important role in oxidative phosphorylation function of motochondria from cerebral cortex of hypoxic and CAP-administrated rats; 2) The alteration in content of COX subunit I protein in mitochondria from cerebral cortex of rats exposed to acute hypoxia and CAP-administrated, is consistent with that of COX activity... |
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