Pyrimidine dimer induction and repair in cultured human skin keratinocytes or melanocytes after irradiation with monochromatic ultraviolet radiation.

We compared the susceptibilities of cultured melanocytes and keratinocytes to dimer induction in DNA by monochromatic ultraviolet (UV) radiation. Keratinocytes as well as melanocytes were derived from human foreskin, grown as a monolayer in petri dishes, covered with phosphate-buffered saline containing 0.1% glucose, and irradiated. UV irradiation was carried out at 254, 297, and 302 nm as well as with a light source emitting predominantly 312 nm. The induction of pyrmidine dimers was assessed by determination of the number of T4 endonuclease V-sensitive sites (ESS). We found a slightly higher response for dimer induction in melanocytes at 254, 297, and 302 nm; this difference was only significant at the 297-nm wavelength. Action spectra for pyrimidine dimer induction were derived from the exposure-response data obtained. The action spectra mimic to a large degree the action spectra for dimer induction in other cultured mammalian cells. The repair rate during a post-irradiation period lasting up to 24 h was substantially the same for the two cell types. The percentage of T4 endonuclease V-sensitive sites (ESS) remaining 9 and 24 h after irradiation was 45% and 30%, respectively.