Recovery of cells from induced, potentially lethal damage.

The recovery of mammalian cells after a variety of treatments is, in part, governed by the cells' ability to deal with repairable, but potentially lethal, lessions. Kinetics of such recovery show a T1/2 of 10-20 hours after ultraviolet (UV) irradiation and 1.5-2.5 hours after X-irradiation. Recovery after exposure to mechlorethamine and bleomycin (BLM) is similar to X-ray recovery; after methylmethane sulfonate, recovery has components similar to X-ray and UV recovery. The sequential treatments of cells with 43 degrees C hyperthermia and X-rays (or reverse order) modify both the immediate survival after treatments as well as the subsequent recovery kinetics. Very similar results are found after BLM and hyperthermia treatments, suggesting strongly that after exposure to that drug a real repair system is operative. However, although recovery after X-irradiation is similar in vitro and in vivo, after BLM the site of treatment and of recovery strongly influences the magnitude and kinetics of recovery.