The role of dose rate in the induction of micronuclei in deep-lung fibroblasts in vivo after exposure to cobalt-60 gamma rays

To evaluate the influence of low-dose-rate exposures on biological damage, it is necessary to have cells that can be maintained in the same stage of the cell cycle for long periods. Normal rat lung fibroblasts represent a stable cell type with a slow turnover rate in vivo. These cells can be stimulated to divide by placing them in tissue culture. Therefore, a constant cell population can be exposed over a protracted time and stimulated to divide, and the cytogenetic damage can be evaluated at the first cell division after exposure. By placing rats at different distances from a60 Co source, they were exposed to graded doses of γ rays-0.0, 3.9, 7.4 and 11.3 Gy-protracted over either 4 or 67 h. Fibroblasts were isolated from the lung and cultured for 24 h; after cytochalasin B was added, the cells were cultured for an additional 69 to 72 h. The percentage binucleated cells in fibroblasts of animals exposed for 4 or 67 h was 47.1 ± 4.3 and 62.1 ± 3.9. There was no influence of dose on the percentage binucleat...