Damage and repair in mammalian cells after exposure to non-ionizing radiations. I. Ultraviolet and visible light irradiation of cells of the rat kangaroo (Potorous tridactylus) and determination of photorepairable damage in vitro
Harm, H.
Mutation Research 50(3): 353-366
1978
ISSN/ISBN: 0027-5107 PMID: 672919 Document Number: 133913
Cornea cells of the rat kangaroo or "potoroo" (Potorous tridactylus) were exposed to far-UV (254 or 302 nm) radiation, with or without subsequent illumination by near-UV or visible light. The DNA of these cells was extracted and tested for the presence of photoproducts-binding yeast photoreactivating enzyme (PRE). The criterion for the latter was competitive inhibition of an in vitro photorepair system, consisting of UV-irradiated transfoming DNA of Haemophilus influenzae and an extract containing yeast PRE. In UV-irradiated potoroo cornea cells up to appr. 90% of photorepairable DNA damage can be photorepaired within 15 min. However, the extent of cellular photorepair, assessed by the reduction in competitive inhibition of the in vitro repair system depends appreciably on experimental parameters during photoreactivating treatment. Depending on specific conditions, the photoreactivating treatment itself produces a varying amount of DNA damage, which reacts with the PRE in vitro. To avoid most of this kind of damage, cells are nitrogen-gassed and kept at 5.degree. C during illumination. The photoreactivating light must not contain wavelengths shorter than 380-440 nm. Wavelengths > 470 nm are still very effective, whereas wavelengths > 555 nm are ineffective in photorepairing potoroo DNA. For unknown reasons, one particular strain of potoroo cornea cells lost its potential for photorepair. Treatment of unirradiated potoroo cells, or their extracted DNA, with hydrogen peroxide also results in competitive inhibition of photorepair in vitro, resembling that observed after near-UV illumination. Because of the occurrence of synergistic effects it is not clear whether the damage only interacts with PRE or can actually be photorepaired under appropriate conditions.