ADP-ribosylation and post-irradiation cellular recovery in two strains of L5178Y cells.

Two strains of murine lymphoma cells, L5178Y-R (LY-R) and L5178Y-S (LY-S) differ in radiosensitivity (D0 ca 1.0 and 0.5 Gy) In this cellular system we tested the influence of poly (adenosine diphosphoribose) transferase (ADPRT) inhibitors, benzamide and caffeine, in combination with X or gamma irradiation under aerobic conditions, on the cellular response. We found a small difference between LY-R and LY-S cell strains in incorporation of 3H from [3H]-NAD (nicotinamide dinucleotide) into permeabilized cells. The incorporation was related to DNA degradation initiated by the permeabilization procedure. The post-irradiation inhibition of DNA synthesis was reversed only in LY-S cells by 2mM benzamide or 2mM caffeine treatment. Changes in the cell cycle, as determined by flow-cytometry, were of similar character in both LY-R and LY-S cells, within 12 h after irradiation, whereas the effect of treatment on survival differed: only LY-S cells were radiosensitized by benzamide; both LY strains were sensitized by caffeine, but to different extents. From these observations it followed that there was a pattern of relations between the extent of postirradiation DNA synthesis, duration of mitotic delay and recovery.