INTERPHASE DEATH AND REPRODUCTIVE DEATH IN X-IRRADIATED MOLT-4 CELLS

The killing effects of ionizing radiation on MOLT-4 cells were studied using colony formation assays, dye exclusion tests, and cell growth analysis. When MOLT-4 cells were exposed to X rays, the fraction of cells stained with erythrosin B increased markedly during the incubation after irradiation at 37°C and reached a maximum within 24 h. In contrast, no such increase was observed for L5178Y cells or their derivative, radiosensitive mutant M10 cells, at a dose resulting in the same level of cell survival as measured by the colony formation assay. Detailed analysis of cell survival as measured by the dye exclusion test in comparison with that measured by the colony formation assay in MOLT-4 cells indicated that MOLT-4 cells are subject to interphase death as well as reproductive death. Analysis of subclones showed a wide variety of differences in the level of stained cells using the dye exclusion test. The results confirmed the population heterogeneity of MOLT-4 cells. Moreover, none of the subclones showed exactly the same cell survival when this was measured with the two assays. The present results strongly suggest that both modes of cell death may occur in single MOLT-4 cells. Possibly apoptosis is the mechanism accounting for both modes of death in these cells.