Further Studies on the Survival of Non-proliferating Human Diploid Fibroblasts Irradiated with Ultraviolet Light

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Abstract
Labeling index data showed that in AG1518 cells, a diploid human fibroblast strain, there was a lag period of at least 14 h between subculture from the density-inhibited plateau phase of growth and entry into DNA synthesis. Cells irradiated with 254 nm wavelength UV light 8 h after subculture did not exhibit the same degree of resistance as cells irradiated in plateau phase and subucultured immediately. When cells were arrested from proliferation by maintenance in an arginine and glutamine deficient medium for 72 h, they were nearly as resistant to UV light as plateau phase cells, although maintenance in this medium for 24 h after irradiation supported further recovery only after low UV doses. One strain of Cockayne syndrome fibroblasts was resistant to UV light in plateau phase, while another strain had the same survival response whether it was irradiated in the plateau or log phase of growth.