Flow cytometry analysis of apoptosis and the cell cycle. A: ATP induced apoptosis in NPC cells. 5-8 F and CNE-2 cells were treated with ATP for 48 h at a concentration of 100 μM; a flow cytometry analysis (staining with propidium iodide and annexin V-FITC) for cell death was performed. The lower left section of each graph represents the viable cells, the lower right section represents the apoptotic cells, and the upper right section represents the necrotic and late apoptotic cells. The total percentage of the counts in the lower right and upper right sections was calculated. B: ATP induced S phase arrest in NPC cells. 5-8 F and CNE-2 cells were treated with ATP for 24 h at a concentration of 100 μM, and the cells were subjected to a flow cytometry analysis. ATP showed a significant influence on the distribution of the cell cycle in 5-8 F and CNE-2 cells. C: The level of Bax was elevated, whereas Bcl-2 decreased in the ATP-treated NPC cells; the cleaved band of caspase-3 indicated that apoptosis had occurred in the ATP-treated NPC cells. Statistical significance between the control and treated conditions: *P < 0.05, **P < 0.01 and ***P < 0.001.