Cell kinetic analysis after irradiation in L929- and LLC-MK2-cells by a BrdU/DNA assay

Exponentially growing L929- and LLC-MK2-cells were X-irradiated in vitro. Irradiation-induced cell cycle kinetic effects were examined by the calculation of the cell number doubling time (TD), the duration of the cell cycle phases by the BrdU/DNA assay and the number of micronuclei. The number of cells arrested in G2/M and the duration of the delay are dose-related. The effect of irradiation on the duration of cell cycle phases was estimated by following the BrdU-labeled cells through the cell cycle. With increasing radiation doses the duration of the G2/M-phase increases whereas G1- and S-phase show only slight variations. Due to the problems involved in evaluation of radiation effects on the cell cycle a comparison with other methods proves the BrdU/DNA-assay to be a valuable instrument in those experiments. The micronucleus frequency is dependent on irradiation dose. However, after 7.52 Gy the number of micronuclei increases, whereas no cells in G1-phase and no increase of cell number could be detected, indicating a mechanism of micronucleus formation that is not linked with mitosis.