DNA damage and repair in chick embryo cells following X-irradiation in vitro as compared to mammalian cells--biochemical and physico-chemical investigations.

Brain cells (b-cells) and liver cells (l-cells) of the chicken embryo and thymic cells (t-cells) of the rat were X-irradiated in vitro at doses of 1.25-50 Gy. When compared to t-cells, b- and l-cells exhibited 1) a lower stimulation of poly (adenosine diphosphate-ribose) transferase and unscheduled DNA synthesis following X-irradiation, 2) an almost fivefold higher inhibition of semiconservative DNA synthesis, 3) a less condensed chromatin, 4) about fourfold higher threshold doses with regard to significant effects on nucleoid sedimentation and viscometry of alkaline cellular lysates, and 5) an apparently two- to threefold lower DNA repair during a 30 min post-exposure repair period. The results suggest that the lower radiation sensitivity of chicken embryo cells is attributable to an initial mechanism of DNA repair and/or DNA protection which may be closely connected to minor chromatin compactness and higher intrinsic activities of repair enzymes.