Effect of the dose of ultraviolet radiation on the pigment formation by human melanocytes in vitro.

Human melanocytes were cultivated under different conditions with phorbol ester (TPA), or with bovine pituitary extract (BPE). The cells altered their morphology with the different culture conditions. With TPA they were predominantly bipolar, while with BPE most of the cells had a dendritic cell shape. In order to investigate the effect of UV irradiation, the cells were irradiated with 50, 100 and 200 mJ/cm2 UVA/B. After irradiation with 200 mJ/cm2 UVA/B the cells cultured with TPA also showed a dendritic shape. We determined the tyrosinase activity, the cellular melanin content and the cell number 3 days after irradiation. In all cases the number of cells decreased depending on the UVA/B doses. In melanocytes we found a marked increase in tyrosinase activity and melanin content after irradiation with 200 mJ/cm2. The UV-induced effect on tyrosinase activity was higher in melanocytes cultured with BPE than in those cultured with TPA. The results were compared with two human melanoma cell lines. Only little pigment formation could be measured in the tested melanoma cell lines without change after UV irradiation.