RADIATION-INDUCED DNA-DAMAGE IN CANINE HEMATOPOIETIC-CELLS AND STROMAL CELLS AS MEASURED BY THE COMET ASSAY

Stromal cell progenitors (fibroblastoid colony-forming unit; CFU-Fs) o re representative of the progenitor cell population of the hemopoietic microenvironment in bone marrow (BM). Previous studies of the radiati on dose-effect relationships for colony formation have shown that cani ne CFU-Fs are relatively radioresistant as characterized by a Do value of about 2.4 Gy. In contrast, hemopoietic progenitors are particularl y radiosensitive (D-0 values = 0.12-0.60 Gy). In the present study, th e alkaline single-cell gel electrophoresis technique for the in situ q uantitation of DNA strand breaks and alkali-labile sites was employed. Canine buffy coat cells from BM aspirates and cells harvested from CF U-F colonies or from mixed populations of adherent BM stromal cell (SC ) layers were exposed to increasing doses of X-rays, embedded in agaro se gel on slides, lysed with detergents, and placed in on electric fie ld. DNA migrating from single cells in the gel was made visible as ''c omets'' by ethidium bromide staining. Immediate DNA damage was much le ss in cultured stromal cells than in hemopoietic cells in BM aspirates . These results suggest that the observed differences in clonogenic su rvival could be partly due to differences in the type of the initial D NA damage between stromal cells and hemopoietic cells. (C) 1996 Wiley- Liss, Inc.