Survival of Synchronized Cultured Human Liver Cells Following Single and Fractionated Exposures to Ultraviolet Light

Abstract
Experiments were designed to determine whether or not cultured human cells recover from sublethal UV light injury during DNA-synthesis (S) phase as rodent cells do. Human liver (Chang) cells were synchronized by 2.5 mM thymidine or hydroxyurea blockage of DNA synthesis or by mitotic selection of cells previously blocked by excess thymidine. Cell survival was determined on the basis of colony formation. Following all 3 synchrony methods cell survival increased from the early S phase to the end of the division cycle. Cells irradiated in the G1 phase and allowed to progress through the ensuing prolonged (about 30 h) S phase survived subsequent irradiation as if they had not been irradiated. Apparently Chang liver cells recover from sublethal injury inflicted by UV light.