Similarities in the Repair Kinetics of Sublethal and Potentially Lethal X-ray Damage in Log Phase Chinese Hamster V79 Cells

Summary We have compared the repair kinetics of X-ray-induced sublethal damage (SLD) and potentially lethal damage (PLD) in V79 cells during postirradiation incubation in growth medium at 37°C. Kinetics of SLD repair were studied by dose fractionation (D1 + D2 = 2 + 2, 4 + 2, 4 + 4, 10 + 4 and 10 + 7 Gy). Kinetics of PLD repair were studied by incubating cells with 0·5 m hypertonic saline (HS) for 20 min at various times after irradiation. The repair of SLD, after 2, 4 and 10 Gy, was complete in about 11, 23 and 62 min, respectively. This repair time was independent of the magnitude of dose D2 (test dose). The repair of PLD, after 2, 4 and 10 Gy, was also complete in about 9, 23 and 61 min, respectively. These data indicate that: (1) the kinetics of repair of SLD for a given dose are independent of the magnitude of the test dose D2; (2) the time taken to complete the repair (repair time) is dependent on dose D1, i.e. the larger the dose D1 the longer the repair time; (3) for a given dose, the repair times assayed either by dose fractionation or by HS treatment are similar; and (4) similarities in the repair times may imply that SLD and PLD are the same. The relationship between the repair kinetics and the shape of the shoulder on fractionated survival curves is discussed.