Abnormal accumulation of G2/M-phase cells from LEC strain rats after X-irradiation at S phase

The effect of X-irradiation on the progression of the cell cycle in cell li nes from LEC and WKAH rats was investigated by a flow cytometer. When the c ells were exposed to 5 Gy of X-rays at S phase, the proportion of S-phase c ells in both cell populations decreased with incubation time and that of G2 /M-phase cells was approximately 80% at 6 hr post-irradiation. At 12 hr pos t-irradiation, approximately 45% of the WKAH rat cells appeared in the G1 p hase. However, 80-90% of LEC rat cells remained in the G2/M phase and less than 5% in the G1 phase during 6-12 hr post-irradiation. Thus, the LEC rat cells irradiated at S phase remained in the G2/M phase for at least 6 hr lo nger than did the WKAH rat cells.