An increase in intracellular free calcium is an early event during differentiation of cultured human keratinocytes.

The effect of [Ca2+]o on [Ca2+]i in cultured human keratinocytes was studied using dual-wavelength microspectrofluorometric techniques. The results show that increasing [Ca2+]o from 70 microM to 1 mM causes an early rise in [Ca2+]i complete by 2 h. Heterogeneity within cultures was demonstrated. The [Ca2+]i in spontaneously differentiated cells of low Ca2+ cultures was similar to that of Ca2+ induced differentiated cells. The increase in [Ca2+]i preceded the morphological changes and growth inhibition induced by increasing [Ca2+]o. These observations are consistent with an increase in [Ca2+]i mediating differentiation of human keratinocytes.