Survival of heated or irradiated Chinese hamster ovary microcolonies that develop after an initial dose of heat.

Asynchronous or synchronous G1 cells were heated initially and then heated or irradiated a second time when the multiplicity of viable cells in microcolonies that developed from cells surviving the first heat dose had increased to 6-30. The survival of these microcolonies was compared with the survival of single cells that were heated or irradiated after the microcolonies had been trypsinized and dispersed into single cells. The survival of the single cells was similar to the survival of the microcolonies and much higher than single cell survival calculated by correcting microcolony survival for multiplicity. However, when microcolonies developed from control unheated cells, the observed single cell survival corresponded to single cell survival calculated by correcting microcolony survival for multiplicity. Therefore, multiplicity corrections, which assume that cells within a microcolony survive independently from one another, are not valid when the microcolony has developed from a cell surviving an initial heat treatment.