RADIATION-INDUCED CHROMOSOMAL-ABERRATIONS IN MOUSE 10T1 2 CELLS - DEPENDENCE ON THE CELL-CYCLE STAGE AT THE TIME OF IRRADIATION/

Cell-cycle stage radiosensitivity for the induction of chromosome aber rations has been investigated in C3H 10T1/2 cells. Exponentially growi ng cells were irradiated with 3 Gy X-rays (80 kVp) or 0.6 Gy alpha-par ticles (LET= 101 keV/mu m). The two doses produce the same survival le vel (37%) in the asynchronous population. Cells were harvested at four different times following irradiation and cell-cycle phase at the tim e of irradiation was assessed by using the differential replication st aining technique. The frequency of chromosome aberrations produced in a given stage of the cell cycle was not constant as a function of the sampling time, but this could not be simply related to the existence o f subphases exhibiting different radiosensitivity, because of cell-cyc le perturbation introduced by radiation. X-radiation induced more exch anges than deletions, whereas a predominance of isochromatid deletions was observed after alpha-irradiation. This can be interpreted on the basis of the different patterns of energy deposition of densely- and s parsely-ionizing radiation. Both X- and alpha-rays produced a signific ant increase in the frequency of Robertsonian translocations when cell s were exposed in G(1) or S phase, but not in G(2) phase.