Lethal effect of near-ultraviolet irradiation on mammalian cells in culture.

Abstract

Experiments are described to study the effect of black light'' (near- ultraviolet) on mammalian cells in tissue culture. The cells used were mouse 3T6, Chinese hamster V79 clone, and human D98/AH/sub 2/, and the light sources were General Electric F15T8 BLB integral filter black light tubes with emission in the 290 to 420 nm range, peaking at 365nm. The culture disk lids excluded irradiation below 300 nm. Exposure intensity was 4 mu W/mm/sup 2/ at the cell surface. The cells were killed by the irradiation, both reproductively, as evidenced by clone-forming ability, and physiologically, as evidenced by staining with trypan blue. The killing effect was, however, density dependent, human and mouse cells being killed when up to 10/sup 5/ cells were plated per 60 mm tissue culture disk, and hamster cells at densities up to 10/sup 4/ cells per disk. When 10/sup 6/ cells were plated no decrease in viability was observed. Differences in the effects, at the molecular level, of far-ultraviolet (<300nm) and near-ultraviolet (300 to 420 nm) radiation on biological systems are described; these are quite different. Far-ultraviolet leads to lethality by directly altering the DNA through dimer formation, while near-ultraviolet, at the dosage used in the experimentsmore » described, does not produce dimers in bacterial systems. It is conceivable that toxic photoproducts are produced in the culture medium which, when taken up by the cells, leads to lethality, and the finding that the cell killing effect is density dependent could be due to the fact that when more cells were present the amount of photoproducts absorbed by each cell was correspondingly less. The possible mutagenic and carcinogenic action of the radiation also needs to be carefully examined. (UK)« less