Calcium-modulated desmosome formation and sodium-regulated keratinization in frog skin cultures

The processes of desmosome formation and keratinization were studied in isolated frog skins cultured in a two-compartment (mucosal and serosal) chamber. Before culture, the skin fragments were trypsinized (stratum corneum together with some parts of stratum granulosum and spinosum were scraped off with forceps) allowing the stratum germinativum to remain on the dermis. When both the mucosal and the serosal culture media contained 1.5 mM calcium and 86 mM sodium concentrations, fully developed desmosomes were differentiated and no keratinization occurred. When the mucosal medium was lowered in two steps to a final calcium concentration of 0.5 mM by dilution with tridistilled sterile water, poorly developed desmosomes were formed, keratinocytes interdigitated and the keratinization was strongly enhanced. The calcium-dependent desmosome formation was affected by the salt gradient established across the skin. These two effects, modulated desmosome formation (calcium) and increased keratinization (sodium), were concomitant with but did not complement one another.