The effect of divalent cations on Cloudman melanoma cells.

The effect of Ca2+, Cd2+, Cu2+, Mg2+ and Zn2+ as acetates (10(-3) - 10(-5)M) and of 2% DMSO on the proliferation and differentiation of clone M3 of the Cloudman S91 mouse melanoma was studied and compared with the behaviour of GPK (keratocyte) and MRC5 (fibroblast) cell lines. Whereas neither calcium nor magnesium ions influenced the proliferation of the cells as measured by [3H]-thymidine incorporation, absorbance at 280 nm of NaOH cell digests and cell counts, cadmium, zinc and copper ions selectively inhibited the melanoma line. Cd2+ (10(-5)M) and Zn2+ (10(-4)M) were selectively cytotoxic to melanoma cells in contrast to keratocytes and fibroblasts. No direct effect of the cations on melanogenesis, as estimated from the ratio of absorbance at 350 nm and 280 nm and by tyrosinase assays, was demonstrated. DMSO stimulated melanogenesis in melanoma cells but inhibited their growth. Experiments with ouabain indicate that active transport is involved in the uptake of zinc by melanoma cells.