Cellular recovery kinetics for postirradiation treatments.

Abstract

Postirradiation cellular recovery kinetics for delayed plating, araA, hypertonic saline (HS) treatments and their combinations, were analysed in the framework of the previously developed dsb model (Ostashevsky 1989). Two possible types of DNA double-strand break (dsb) repair kinetics were considered: cooperative, where the rate-limiting step is related to a DNA molecule, and non-cooperative, where the rate-limiting step is related to a dsb. The following estimates were made for plateau-phase V79 cells: (1) HS induces a temporary block of dsb repair. The estimates for the dsb repair block duration are about 0.6 h for a 10-min treatment and about 1.2 h for a 20-min treatment. (2) HS creates additional DNA fragments. The number of these fragments calculated for 0.37 M NaCl treatment, in a way independent of the type of dsb repair, was consistent with the number estimated for 0.5 M NaCl treatment for cooperative dsb repair, but not for noncooperative dsb repair. (3) The estimated time constant for the process restricting the formation of DNA fragments was 10-20 min. In the presence of 200-400 microM araA, the rate of this process should decrease 2-5-fold. (4) The time constant for the araA recovery kinetics coincides with that for dsb repair, in agreement with experimental data. (5) For delayed plating recovery the kinetics curve calculated for cooperative dsb repair fits well experimental data, in contrast to the curve calculated for non-cooperative dsb repair.