The effects of cell-culture density on cell inactivation by benzo[a]pyrene-4,5-oxide

Initial survival levels of CHO-K1 monolayers following exposure to benzo[a]pyrene-4,5-oxide were found to depend upon the culture density of exponential-phase cells during the exposure portion of the experiment. A continuous increase in the surviving fraction (measured by cloning ability) was observed when culture treatment densities were above 2 x 10(4) cells/cm2 (approximately 15% of maximum density). This effect was not observed with ultraviolet-irradiated cells nor due to increased repair times, frequently observed in plateau (density)-inhibited cultures. Furthermore, treated cells unable to grow at cloning densities (8-15 cells/cm2) continued to grow and divide for at least 9 population doublings following exposure provided post-exposure culture densities were maintained at 6.6 x 10(3) cells/cm2 or greater.