Alteration of gamma-ray-induced chromosome aberration by 0.5 M NaCl in Chinese hamster cells.

Hypertonic treatment (0.5 M NaCl in phosphate-buffered saline, pH 7.2) at 37 degrees C for 20 min slightly delayed the mitotic frequency for non-irradiated cells in G1 and G2 phases. The mitotic frequency for irradiated cells in G2 was delayed by hypertonic treatment, and that in G1 was slightly delayed by hypertonic treatment. Hypertonic treatment in non-irradiated cells did not induce any chromosomal or chromatid aberrations in either G1 or G2. Chromosomal aberrations caused by gamma-irradiation were slightly enhanced by hypertonic treatment, and chromatid aberrations were markedly enhanced by hypertonic treatment. The enhancement ratio of gamma-irradiation-induced chromatid breaks and exchanges was 1.4 and 3.0, respectively. This cell cycle dependency of chromosome aberrations induced by postirradiation hypertonic treatment was the same as that of cell survival. These findings suggested that hypertonic treatment modifies the rejoining of DNA strand breaks in G2, but slightly modifies that in G1.