The Action of Radiation on Mammalian Cells

Abstract

The action of X-irradiation on mammalian cells was studied in vitro, by means of single cell survival curves, and direct chromosome visualization after varying doses of radiation. The normal, diploid human cell exhibits a mean lethal doses (D[degree]) of 50 r while that for aneuploid hyperploid human cells is about 100 r. The primary radiobiologic action in this dose range is damage to the genetic apparatus, and primarily to the chromosomes. 20-40 r introduces an average of 1 chromosome break per cell in normal diploid human cells in vitro, which restitute normally and leave no visible evidence of their presence. If many breaks are introduced in each cell, abnormal recombinations such as dicentric chromosomes and other aberrations are formed. Analysis of the survival curves demonstrates that some cells, like the normal diploid human cell is killed reproductively to a significant extent by single-hit events, but that hyperploid aneuploid cells require multiple hits, which produce complex chromosomal forms. The effects of UV, which produces gene mutations but relatively few chromosome breaks, are readily explainable by these considerations. By means of the concept, chromosome breakage and the attending destruction of cell reproductive function, it is possible to understand both qualitatively and quantitatively many of the features of the acute whole body radiation syndrome in mammals.