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POST‐IRRADIATION EFFECTS OF PHOTOREACTIVATING LIGHT AND CAFFEINE ON CULTURED MARSUPIAL CELLS EXPOSED TO ULTRAVIOLET LIGHT

Cells from the kidney of the rat kangeroo (Potorous tidactylus) were used for in vitro studies of the postirradiation effects of photoreactivating light and caffeine. Survival curves indicated that the effect of post-uv exposure (100 ergs mm/sup -2/) to photoreactivating light for 30 min was dose modifying; the ratio of doses leading to any level of damage on the two curves was nearly constant with a value of approximately 2.3 plus or minus 0.2. Potorous cells were found to be resistant to the toxic effects of caffeine up to 4.0 mM with only moderate cell killing but long growth delay. Survival curves are presented for cells post-irradiation incubated in 1.0 mM, 1.5 mM, and 4.0 mM caffeine. Incubation for up to 60h showed no subtoxic level that significantly modifed cell survival. It is suggested that these in vitro studies indicate that the presence of photoreactivating enzyme discussed by Cooke, J. S., and Regan, J. D., (Nature 223, 1066-1067, 1969) phylogenetically parallels the presence of photoreactivation of lethal damage. (UK)