Response of X-ray-sensitive CHO mutant cells (xrs-6c) to radiation. II. Relationship between cell survival and the induction of chromosomal damage with low doses of α 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.