Comparison of radiation sensitivity of rat respiratory tract epithelial cells

Lung model of ICRP publication 66 describes that cells at risk in respiratory tract tissues are secretory and basal cells in bronchial airways, and Clara and Type II cells in alveolar interstitial region. It is, however, unclear whether there is a difference in radiation sensitivities between the target cells. The purpose of this study is to compare the dose-response relationships of radiation-induced cell death and transformation in primarily cultured rat tracheal epithelial (RTE) and rat lung epithelial (RLE) cells. The RLE cells were isolated from lung of female Wistar rats (4-6-week-old) by enzyme digestion and gradient centrifugation. Tracheae were filled with enzyme solution, and then the RTE cells were rinsed from inside the tracheae. The RLE and RTE cells were cultured in serum free medium including epidermal growth factor and other necessary factors. The cells were irradiated using an alpha source of 238Pu (3.6MeV, 0.8Gy/min) or a gamma source of 137Cs (8.2Gy/min). The cytotoxic responses of the cells to irradiations were determined in colony formation assay. Transformants formed dense colonies in 2% serum containing and growth factor-free selective medium, and transformation frequencies (TF) were calculated from number of the colonies.The irradiation caused similarly an exponential decrease in survival in the RLE and RTE cells, and D37 of alpha particle and gamma ray were 0.65 Gy and 3.6 Gy, respectively. Relative biological effectiveness (RBE) for cell killing was 5.5 in the both types of cell. TF for the RLE and RTE were 3.7x10-3E and 2.4x10-3E at 2 Gy of alpha particle, respectively. At 7.5 Gy of gamma ray, TF for the RLE and RTE increased to 8.0x10-3E and 7.1x10-3E, respectively. The RBE for transformation of RLE was 1.7, and that of RTE was 1.3. These results indicate that there is no difference between the radiation sensitivities of the RLE and the RTE cells in culture condition. This primary epithelial cell culture system of rat lung will be useful for analysis of radiation sensitivity among the different target cells and mechanistic studies of early changes in radiation-induced carcinogenesis.13th international Congress of Radiation Researc