INTRACELLULAR CA2+ CONCENTRATION CHANGE OF T24 CELL UNDER IRRADIATION IN THE PRESENCE OF TIO2 ULTRAFINE PARTICLES

We reported that malignant cells are inactivated by photo-excited TiO2 particles (Cai, R.-X., et al. (1992) Cancer Res. 52, 2346-2348). In the present study, the process of cell death of a human bladder cell line T24 with TiO2 irradiated TiO2 was investigated by monitoring the time course change in intracellular calcium concentration ([Ca2+](i)) under UV irradiation using calcium fluorescence indicator, fura-2. In the presence of photo-excited TiO2 particles (100 mu g/ml), [Ca2+](i) showed a sapid two-step increase; while in the absence of TiO2, it exhibited only a slight and monotonous increase or maintained a constant level. The rapid elevation of [Ca2+](i) in the presence of photo-excited TiO2 particles was caused by the influx of extracellular Ca2+ through the plasma membrane and cell death occurred only after the second rapid elevation of [Ca2+](i). These results suggested that the cell membrane permeability to Ca2+ was promoted prior to cell death.