RESPONSE OF X-RAY-SENSITIVE CHO MUTANT-CELLS (XRS-6C) TO RADIATION .2. RELATIONSHIP BETWEEN CELL-SURVIVAL AND THE INDUCTION OF CHROMOSOMAL DAMAGE WITH LOW-DOSES OF ALPHA-PARTICLES

The induction of cytotoxicity, chromosomal aberrations, and sister chromatid exchanges (SCEs) was measured in CHO K-1c cells and in isogenic X-ray-sensitive mutant xrs-6c cells that had been irradiated with X rays and α particles in isoleucine-deficient α-minimal essential medium in G1 phase of the cell cycle. There was a noticeable shoulder region on the survival curve for CHO K-1c cells irradiated with very low doses of α particles, whereas this feature was absent for xrs-6c cells with α-particle doses as low as 0.5 cGy. Higher frequencies of chromatid-type aberrations were induced in G1-phase xrs-6c cells than in G1-phase CHO K-1c cells by both γ- and α-particle irradiation. Induction of nonlethal chromosomal aberrations was observed following exposure to 2-6 cGy of α particles, doses yielding 97-100% cell survival. Irradiation with 0.5 cGy of α particles induced SCE; nearly 60% of irradiated cells contained significantly increased levels of SCE. However, only 3% of the nuclei of cells exposed to 0.5 cGy of α-particle radiation were actually traversed by an α particle. The observation that a large fraction of cells apparently survive exposure to very low doses of α-particle radiation with persistent genetic damage manifested by both chromosomal aberrations and SCEs may have important implications for the carcinogenic hazards of high-LET radiation.