Effect of ultraviolet radiation on melanogenesis in four different types of cultured bovine ocular pigmented cells

Ultraviolet radiation is thought to play a causative role in various ocular diseases such as macular degeneration, cataract, and possibly melanomas. Since most of the energy is absorbed by pigmented cells, the aim of this study was to examine and compare the reactions of different ocular melanocytic cells to ultraviolet light in vitro. Bovine iris melanocytes, choroidal melanocytes, iris pigment epithelial cells, and retinal pigment epithelial cells were isolated and cultured. Semiconfluent cultures were exposed to ultraviolet radiation (280-380 nm). Cell number and melanin content were measured 10 days after radiation. Selected samples were examined by transmission electron microscopy. Following irradiation with ultraviolet light for 30 s, 60 s, and 120 s, the number of cells in culture decreased markedly. In contrast, total melanin content in the cultures of iris melanocytes, choroidal melanocytes, and iris pigment epithelial cells did not decrease despite the reduced number of cells. This finding suggested an increase in melanin per cell. However, the increase in average melanin content observed was not due to melanogenesis, because treatment with the melanogenesis inhibitor alpha-methyl-p-tyrosine did not reduce the melanin content of the cultures and electron-microscopic examination showed no morphological evidence of increased melanogenesis. In vitro, there was no convincing evidence of ultraviolet radiation-induced melanogenesis in ocular pigmented cells. Thus, it seems that ultraviolet radiation is a selection factor: more densely pigmented cells survive the treatment better than less pigmented cells.