Dose-Rate Effects in Plateau-Phase Cultures of S3 HeLa and V79 Cells

Abstract

Dose-rate effects on cell survival were studied for log-, fed plateau- and unfed plateau-phase cultures of V79 and S3 HeLa cells. For log-phase cultures, repair, cell-cycle redistribution and cell division during exposure can contribute to the overall dose-rate effect, but their relative contributions were difficult to determine. With plateau-phase cultures, the cell-cycle times were greatly lengthened for cells in cycle. The contribution to the overall dose-rate effect of cell-cycle redistribution and cell division during the exposure may be minimized using plateau-phase cultures. A clear loss in effectiveness in the acute dose survival curves occurred when the dose rate was lowered to 154 rad/h for fed and unfed plateau-phase HeLa and V79 cells. No further reduction in effectiveness per unit dose occurred when the dose rate was reduced to 55 rad/h. Since virtually no cell division or cell-cycle redistribution occurred, a limit to the repair-dependent dose-rate effect at 37.degree. C apparently was reached at a dose rate of 154 rad/h.