BACKGROUND: Phycocyanin can relieve decrease of mitochondrial membrane potential through reducing production of active oxygen so as to protect neurons after hypoxia/reoxygenation. OBJECTIVE: To observe the effect of phycocyanin on activity of PC12 cells and mitochondrial membrane potential after hypoxia/reoxygenation. DESIGN: Randomized controlled study. SETTING: Cerebrovascular Disease Institute of Affiliated Hospital, Medical College of Qingdao University. MATERIALS: The experiment was carried out at the Key Laboratory of Prevention and Cure for cerebropathia in Shandong Province from October to December 2005. PC12 cells, rat chromaffin tumor cells, were provided by Storage Center of Wuhan University; phycocyanin was provided by Ocean Institute of Academia Sinica; Thiazoyl blue tetrazolium bromide (MTT) and rhodamine 123 were purchased from Sigma Company, USA; RPMI-1640 medium, fetal bovine serum and equine serum were purchased from Gibco Company, USA. METHODS: ① Culture of PC12 cells: PC12 cells were put into RPMI-1640 medium which contained 100 g/L heat inactivation equine serum and 0.05 volume fraction of fetal bovine serum and incubated in CO2 incubator at 37 ℃. Number of cells was regulated to 4 × 105 L-1, and cells were inoculated at 96-well culture plate. The final volume was 100 μL. ② Model establishing and grouping: Cultured PC12 cells were randomly divided into three groups: phycocyanin group, model control group and non-hypoxia group. At 24 hours before hypoxia, culture solution in phycocyanin group was added with phycocyanin so as to make sure the final concentration of 3 g/L , but cells in model control group did not add with phycocyanin. Cells in non-hypoxia group were also randomly divided into adding phycocyanin group (the final concentration of 3 g/L) and non-adding phycocyanin group. Cells in model control group and phycocyanin group were cultured with hypoxia for 1 hour and reoxygenation for 1, 2 and 3 hours; meanwhile, cells in non-hypoxia group were cultured with oxygen and were measured at 1 hour after hypoxia/reoxygenation. ③ Detecting items: At 1, 2 and 3 hours after reoxygenation, absorbance (A value) of PC12 cells was measured with MTT technique so as to observe activity and quantity of cells. Fluorescence intensity of PC12 cells marked by rhodamine 123 was measured with confocal microscope in order to observe changes of mitochondrial membrane potential. MAIN OUTCOME MEASURES: Comparisons between quantity and activity of PC12 cells and mitochondrial membrane potential at 1, 2 and 3 hours after reoxygenation. RESULTS: ① Effect of phycocyanin on quantity and activity of PC12 cells: A value was 0.924±0.027 in adding phycocyanin group and 0.924±0.033 in non-adding phycocyanin group. A value was lower in model control group and phycocyanin group than that in non-hypoxia group at 1, 2 and 3 hours after reoxygenation (0.817±0.053, 0.838±0.037, 0.875±0.029; 0.842±0.029, 0.872±0.025, 0.906±0.023, P < 0.05). A value was higher in phycocyanin group than that in model control group at 1, 2 and 3 after culture (P < 0.05). With culture time being longer, A value was increased gradually in phycocyanin group and model control group after reoxygenation (P < 0.05). ② Effect of phycocyanin on mitochondrial membrane potential of PC12 cells: Fluorescence intensity was 2.967±0.253 in adding phycocyanin group and 2.962±0.294 in non-adding phycocyanin group. Fluorescence intensity was lower in model control group and phycocyanin group than that in non-hypoxia group at 1, 2 and 3 hours after hypoxia/reoxygenation (1.899±0.397, 2.119±0.414, 2.287±0.402; 2.191±0.377, 2.264±0.359, 2.436±0.471, P < 0.05); but it was higher in phycocyanin group than that in model control group at 1, 2 and 3 after reoxygenation (P < 0.05). With culture time being longer, fluorescence intensity was increased gradually in phycocyanin group and model control group after reoxygenation (P < 0.05). CONCLUSION: Phycocyanin and reoxygenation can protect PC12 cells after hypoxia injury through increasing mitochondrial membrane potential and cellular activity, and the effect is improved gradually with prolonging time of reoxygenation. BACKGROUND: Phycocyanin can relieve decrease of mitochondrial membrane potential through reducing production of active oxygen so as to protect neurons after hypoxia / reoxygenation. OBJECTIVE: To observe the effect of phycocyanin on activity of PC12 cells and mitochondrial membrane potential after hypoxia / reoxygenation. DESIGN: Randomized controlled study. Cerebrovascular Disease Institute of Affiliated Hospital, Medical College of Qingdao University. MATERIALS: The experiment was carried out at the Key Laboratory of Prevention and Cure for cerebropathia in Shandong Province from October to December 2005. PC12 cells, rat chromaffin tumor cells, were provided by Storage Center of Wuhan University; phycocyanin was provided by the Ocean Institute of Academia Sinica; Thiazoyl blue tetrazolium bromide (MTT) and rhodamine 123 were purchased from Sigma Company, USA; RPMI-1640 medium, fetal bovine serum and equine serum were purchased from Gibco Company, USA. METHODS: ① Culture of PC12 ce lls: PC12 cells were put into RPMI-1640 medium which contained 100 g / L heat inactivation equine serum and 0.05 volume fraction of fetal bovine serum and incubated in CO2 incubator at 37 ° C. Number of cells was regulated to 4 × 10 5 L -1 , and the cells were inoculated at 96-well culture plate. The final volume was 100 μL. ② Model establishing and grouping: Cultured PC12 cells were differentiated into three groups: phycocyanin group, model control group and non-hypoxia group. At 24 hours before hypoxia, culture solution in phycocyanin group was added with phycocyanin so as to make sure the final concentration of 3 g / L, but cells in model control group did not add with phycocyanin. Cells in non-hypoxia group were also optionally divided into adding Phycocyanin group (the final concentration of 3 g / L) and non-adding phycocyanin group. Cells in model control group and phycocyanin group were cultured with hypoxia for 1 hour and reoxygenation for 1, 2 and 3 hours; meanwhile, cells in non- hypo xia grou(1 value) of PC12 cells was measured with MTT technique so as to observe the activity and quantity of cells. Fluorescence intensity of PC12 cells marked by rhodamine 123 was measured with confocal microscope in order to observe changes of mitochondrial membrane potential. MAIN OUTCOME MEASURES: Comparisons between quantity and activity of PC12 cells and mitochondrial membrane potential at 1, 2 and 3 hours after reoxygenation. RESULTS: ① Effect of phycocyanin on quantity and activity of PC12 cells: A value was 0.924 ± 0.027 in adding phycocyanin group and 0.924 ± 0.033 in non-adding phycocyanin group. A value was lower in model control group and phycocyanin group than that in non-hypoxia group at 1, 2 and 3 hours after reoxygenation (0.817 ± 0.053, 0.838 ± 0.037, 0.875 ± 0.029; 0.842 ± 0.029, 0.872 ± 0.025, 0.906 ± 0.023, P <0.05) was higher in phycocyanin group than that in model control group at 1, 2 and 3 after culture (P <0.05). With culture time being longer, A value was increased gradually in phycocyanin group and model control group after reoxygenation (P <0.05) . Fluorescence intensity was lower in model control group and phycocyanin group than that in non- hypoxia group at 1, 2 and 3 hours after hypoxia / reoxygenation (1.899 ± 0.397, 2.119 ± 0.414, 2.287 ± 0.402; 2.191 ± 0.377, 2.264 ± 0.359, 2.436 ± 0.471, P <0.05); but it was higher in phycocyanin group than that in model control group at 1, 2 and 3 after reoxygenation (P <0.05). With culture time being longer, fluorescence intensity was increased gradually in phycocyanin group and model control group after reoxygenation (P <0.05). CONCLUSION: Phycocyanin and reox ygenation can protectPC12 cells after hypoxia injury through increasing mitochondrial membrane potential and cellular activity, and the effect is improved gradually with prolonging time of reoxygenation.