Abstract
The micronucleus (MN) test is one of the cytogenetic indicators reflecting DNA damage. Experiments have been carried out using human whole-blood cultures to determine the effects of sampling times and to study the fate of micronuclei in the MN frequencies following exposure to mitomycin C (MMC). Cells were pulse-treated for 1h with MMC at G0, and then sampled at 6h in intervals up to 96h after the stimulation of cultures with phytohemagglutinin (PHA). Results showed that MMC-treatment induced an approximate 6h proliferation delay per cell cycle, and that the frequencies of MMC-induced MN increased at 60h and then stayed almost constant after that time. These data indicate that the formation of MN appeared after the time when the cell-cycle had doubled. In subsequent experiments, after incubation periods of 72h and 96h, lymphocyte preparations were prepared using 2 different methods, the conventional method and the cytokinetics-block (CB) micronucleus method. Results showed that the frequencies of MN did not change between 72h and 96h using either method. These results suggest that some MN remain in the daughter cells. The CB method was developed to overcome the kinetic problems inheritant in the use of human lymphocytes by Fenech and Morley. Comparison of the results obtained with the conventional method and the CB method found that the conventional method underestimates this effect.
