title: Response of plateau-phase mouse embryo fibroblasts to ultra-violet light.
abstract: Clonogenic survival was measured in plateau-phase cultures of the 10T1/2 mouse cell line exposed to 254 nm ultra-violet light. The survival curve was found to be biphasic, Do for the two components being 37 and 1191 erg/mm2 respectively. This extreme resistance at higher doses can only be partly accounted for by the increased cytoplasmic absorption of U.V.L. due to an increased thickness of plateau-phase cells. When the cultures were held for 24 hours in plateau phase in conditioned medium after irradiation, recovery yielding a 1.4-fold enhancement of survival was found at higher doses. This recovery process was inhibited by neither caffeine nor cycloheximide. When caffeine was given for 48 hours after sub-culture, the effect on survival was also negligible. We propose that this plateau-phase recovery process is associated with excision repair of DNA adducts induced by U.V.L. Delayed sub-culturing favours the excision mode of repair and renders the post-replication mode less necessary.
mesh_terms: D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002453:Cell Cycle / Q000528:radiation effects*; D002460:Cell Line; D002470:Cell Survival / Q000528:radiation effects*; D003513:Cycloheximide / Q000494:pharmacology; D004260:DNA Repair / Q000187:drug effects; D004307:Dose-Response Relationship, Radiation; D051379:Mice; D014466:Ultraviolet Rays
chemical_list: D002110:Caffeine; D003513:Cycloheximide