| Research Abstract |
Nuclear morphological chage, intracellular calcium ion concentration ([Ca^<2+>]_i) and DNA fragmentation were examined on human leukemia cell lines (HL-60, Molt-4, U937) 6 hours after X-irradiation by light-microscopy, digital image analysis using fura-2 and biochemical analysis, respectively. High percentage of the apoptotic cells, the DNA fragmentation and the appearance of cells showing high [Ca^<2+>]_i were observed only in Molt-4 cells. Increase of Ca^<2+> influx after irradiation was also observed only in Molt-4 cells. When X-irradiated Molt-4 cells after exposure to 5 Gy were incubated in the medium containing 5 muM of intracellular Ca^<2+> chelator, BAPTA-AM,the radiation-induced apoptosis and DNA fragmentation were partially suppressed. On the other hand, hyperthermia induced the increase of [Ca^<2+>]_i and the apoptosis at similar level among these cell lines, but BAPTA-AM did not prevent the DNA fragmentation induced by hyperthermia. These results indicate that intracellular Ca^<2+> plays a cardinal role in the regulation of apoptosis in Molt-4 cells. Molecular mechanism of UV-induced apoptosis in U937 cells was also investigated.
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