Production of thymine base damage in ultrasound exposed EMT6 mouse mammary sarcoma cells

Abstract

Mouse mammary sarcoma cells, line EMT6 Ro, were exposed for 1 min to 1‐MHz continuous wave ultrasound over a range of intensities from 0.5 to 30 W/cm2. The presence of thymine base damage products of the 5,6‐dihydroxy‐dihydrothymine type was determined by an alkali degradation assay. Production of damage was found to be greatest at an intensity of 10 W/cm2 and fell off rapidly above and below this intensity. Cells were also exposed for up to 5 rain at 5 W/cm2. A linear increase in thymine base damage was demonstrated with increasing time of exposure such that the rate of production at 5 min was approximately 4 times greater than that of a 1 min exposure. As a positive control, cells received absorbed doses of 60Co gamma rays up to 930 Gy. The amount of base damage produced at 10 W/cm2 ultrasound was approximately equivalent to a gamma ray absorbed dose of 177 Gy. Assay of cells immediately after sonication at 10 W/cm2 showed that approximately 14% of the cells had lysed. Survival data demonstrated that of...