Sudden Reversion to Normal Radiosensitivity to the Effects of X Irradiation and Plutonium-238 α Particles by a Radioresistant Rat-Mouse Hybrid Cell Line

Abstract

A radioresistant rat-mouse hybrid cell line ( ${\rm HD}_{1}$) evolved after a year in tissue culture into a cell line ( ${\rm HD}_{1{\rm a}}$) that exhibited normal radiosensitivity. The D0 of the original ${\rm HD}_{1}$ cells dropped from 200 to 125 rad for ${\rm HD}_{1{\rm a}}$ after exposure to X rays and from 105 to 90 rad after exposure to ${}^{238}{\rm Pu}$ α particles. The decrease in radioresistance in ${\rm HD}_{1{\rm a}}$ cells was accompanied by a decreased amount of cellular DNA and a reduction in chromosome number. There were no measurable differences in ability to repair sublethal or potential lethal damage in either cell line.