Thermal sensitivity of chinese hamster V79 cells related to time after plating and cell-cycle redistribution

Abstract

1. 1.|Cultured Chinese hamster V79 cells were trypsinized plated and grown attached or inoculated into spinner flasks and grown in suspension from exponnential growth to plateau-phase growth and their thermal sensitivity was measured after various growth times. 2. 2.|For attached cells, cultures were trypsinized and replated either 2 h before or after heating and the results were qualitatively the same: the thermal sensitivity remained approximately the same for the first 20 h and then increased and reached a maximum at 40–70 h. During this time, cells were in an exponential growth phase, and little or no change was observed in the cell-cycle age distribution as measured by flow cytometry (FMF) or [ 3H]thymidine pulse ([ 3H]Tdr) labelling. 3. 3.|At longer times after plating, cells grew into plateau phase, and thermal sensitivity decreased and became less than for the cells in exponential growth phase at the beginning of the experiment. 4. 4.|FMF and [ 3H]Tdr labelling showed that cells were accumulating in G 1 phase as the population density increased and that this accumulation was maximum at about 120–140 h as cells grew into plateau phase. This would account for the decrease in heat sensitivity and the increase in radiosensivity observed in plateau-phase cells. 5. 5.|For cells cultured in suspension there was no change in thermal sensitivity while cells were in exponential growth phase, As cell entered plateau phase, thermal resistance increased and most of the cell population had accumulated in G 1 as measured by FMF.