The effect of high dose long-wave ultraviolet radiation (UVA) on epidermal melanocytes in human skin: a transmission electron microscopic study.

Five healthy subjects with skin type III and IPD (immediate pigment darkening reaction) were irradiated with a glass-filtered UVA-sun 2000 lamp and exposed to 50, 100 and 150 J cm-2 of UVA. Transmission electron microscopy showed a statistically significant increase in the number of epidermal melanocytes with enlarged Golgi apparatus with associated vesicles, predominantly of the coated variant, swollen mitochondria with ruptured cristae, and extensive endo/exocytotic activity. Cells with 2 nuclei were also observed. It is concluded that UVA alone, in doses producing erythema, can give rise to these ultrastructural changes, interpreted as an increased secretory activity in a portion of the epidermal melanocytes.