OBJECTIVE To determine the transcriptional expression ofmitochondrial genome (mtDNA) in MGC803 cell lines subjectedby various time-phase hypoxic dispositions, and further to discussthe influence of mtDNA transcripts on hypoxic resistance toirradiation.METHODS The MGC803 cells exposed to anoxic environmentwere divided into control group (0 h), hypoxic group (2 h, 8 h,16 h, 24 h) and irradiated group after exposing the hypoxia. RT-PCR was applied to detect the transcripts of cytochrome oxidasesubunit I (COI), NADH dehydrogenase subunit 4 (ND4), ND5,cytochrome b (cyt-b) and ATPase6 (ATP-6) in MGC803 cell lines atvarious time-phases of hypoxic, and after X-ray irradiation. Flowcytometry and colony formation assay were conducted to evaluatethe cell cycle phase and survival fraction.RESULTS COI and ND4 transcripts of MGC803 cell lineswere influenced remarkably by hypoxia. COI transcripts weredecreased remarkably with the elongation time of exposing thehypoxic, and reduced to one fourth of its original amount of pre-hypoxia 24 h after exposing the hypoxia. ND4 transcripts wereincreased initially, and elevated to two folds 8 h after exposing thehypoxia, and then reduced to one second 24 h after exposing thehypoxia. Hypoxia resulted in G_1 phase blockage, especially afterhypoxia for 16 h. The survival fraction of MGC803 cells exposingthe hypoxia in irradiated group showed that as the time ofexposing the hypoxic before irradiation is prolonged, the survivalfraction of MGC803 cells may have an elevated tendency.CONCLUSION The tumor cells with lower expression levelsof the COI and the ND4 after exposing the hypoxic have strongerresistance to the radiation, which indicates that increasing theexpression levels of the COI and the ND4 might be advantageousto enhance the sensitivity of hypoxic tumor cells to theradiotherapy. OBJECTIVE To determine the transcriptional expression of mitochondrial genome (mtDNA) in MGC803 cell lines by various time-phase hypoxic dispositions, and further to discussthe influence of mtDNA transcripts on hypoxic resistance to irradiation. METHODS The MGC803 cells exposed to anoxic environmentwere divided into control group (0 h), hypoxic group (2 h, 8 h, 16 h, 24 h) and irradiated group after exposing the hypoxia. RT-PCR was applied to detect the transcripts of cytochrome oxidasesubunit I (COI), NADH dehydrogenase subunit 4 (ND4) , Cytochrome b (cyt-b) and ATPase6 (ATP-6) in MGC803 cell lines at various times-phases of hypoxic, and after X-ray irradiation. Flowcytometry and colony formation assay were conducted to evaluate the cell cycle phase and survival fraction .RESULTS COI and ND4 transcripts of MGC803 cell linesweremended remarkably by hypoxia. COI transcripts were created with remarkably with the elongation time of exposing the hypoxic, and reduced to one fourth of it s original amount of pre-hypoxia 24 h after exposing the hypoxia. ND4 transcripts were in creased initially, and elevated to two folds 8 h after exposing the hypoxia, and then reduced to one second 24 h after exposing the hypoxia. Hypoxia resulted in G_1 phase blockage, especially afterhypoxia for 16 h. The survival fraction of MGC803 cells exposing the hypoxia in irradiated group showed that as the time of post-hypoxic before irradiation is prolonged, the survival fraction of MGC803 cells may have an elevated tendency. CONCLUSION The tumor cells with lower expression levels of the COI and the ND4 after exposing the hypoxic have strongerresistance to the radiation, which indicates that increasingexpressionexpression of the COI and the ND4 might be advantageousto enhance the sensitivity of hypoxic tumor cells to theradiotherapy.