Abstract
Colonies of diploid Chinese hamster lung cells (strain V) surviving large doses (1500 r) of 250-kvp x rays have a broad size spectrum which is shown to be due to the variable growth rate of the colonies. The properties of large and small colonies were corapared after isolation and subcultivation. Large colonies give rise to fast-growing populations of high plating efficiency which have the same radiosensitivity as the parent unirradiated cells. Small colonies of 50 cells or more at 12 to 14 days are viable and give rise to sublines which have slow growth rates, poor plating efficiency, and increased radiosensitivity (D/sub 0/ changed from 205 rads to approximates 145 rads, n unaltered). The chromosome number spectrum is broadened for all surviving colonies, severely in some cases to modal tetraploid numbers; but neither this, nor the high frequency of chromosome aberrations, appears to be involved in the radiosensitivity of the survivors. Reirradiation of smallcolony populations appears to produce a further spread in clone size but no further changes in the radiosensitivity of individual clones.
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