Intestinal cell radiosensitivity: a comparison for cell death assayed by apoptosis or by a loss of clonogenicity.

Apoptotic and reproductive cell death have been assayed in the crypt of the small intestine. These two approaches result in survival curves with mean lethal doses (D0) that differ by a factor of 10. Widely differing doses and times of assay post-irradiation were used for the assays employing apoptosis in one case and clonogenicity in the other. The results obtained by the two approaches are compared. It is concluded that the cells that die via apoptosis represent a very sensitive subpopulation of the crypt (about 6 cells per crypt) that may or may not be clonogenic. Most clonogenic cells die at a later time by some other mechanism. If the apoptoses represent dead clonogenic cells they must be either a very sensitive subpopulation or, as deduced here, a subpopulation which is part of a uniformly resistant population of cells when clonogenicity is considered, but which is very sensitive to an early form of death.