KINETICS OF PHOTO-TOXICITY OF FISCHERS MEDIUM FOR L5178Y LEUKEMIC-CELLS

  • 1 January 1981
    • journal article
    • research article
    • Vol. 41  (6) , 2241-2248
Abstract
The uncontrolled exposure of Fischer''s medium to cool white fluorescent (CWF) light or other sources emitting near UV or visible light absorbable by riboflavin is a crucial random variable in experiments which utilize [murine leukemia] L5178Y cells and this medium. The radiation effects of CWF light result in the rapid development of toxic photoproducts in the medium which are cytostatic at lower doses of radiation and cytotoxic at higher doses. After a 24 h suspension in medium irradiated for 3 or 48 h, the cloning efficiencies of cells subsequently plated in light-protected medium were 87 and 3%, respectively. The corresponding near-UV doses for these periods of exposure to CWF light were 0.22 .times. 104 for a 3 h exposure and 3.47 .times. 104 J/m2 for a 48 h exposure. Cells incubated in lightly irradiated medium resumed growth at nearly normal rates following a 24-48 h period in which no increase in cell numbers occurred. Exposure of medium containing riboflavin, but not tryptophan or tyrosine, to CWF light also produces toxic medium. Tryptophan enhances riboflavin-induced phototoxicity, whereas tyrosine diminishes this effect. As photosusceptibility of this system is very high, Fischer''s medium must be fully protected from all sources of light absorbable by riboflavin.