Fig. 1. HaCaT cell cultures exhibit phenotypic differences in response to Ca²⁺ concentration. (A) Phase-contrast microscopy of HaCaT cells maintained in low [Ca²⁺] medium (0.03 mM Ca²⁺) or in high [Ca²⁺] medium (2.8 mM Ca²⁺). Upon Ca²⁺ addition to the medium, basal HaCaT cells take 4-7 days to assume a complete differentiated state. Inversely, upon Ca²⁺ depletion, differentiated HaCaT cells take about 3 weeks to revert to a basal phenotype. (B) RT-PCR analyses of total mRNA harvested from basal (0.03 mM Ca²⁺) and differentiated HaCaT (2.8 mM Ca²⁺) cultures. (C) Immunoblot analyses showing expression of keratin 1, involucrin, and -tubulin in total cell extracts harvested from basal (0.03 mM Ca²⁺) and differentiated (2.8 mM Ca²⁺) HaCaT cultures.