Influence of a transepithelial NaCl gradient on the moulting cycle, keratinization and active sodium transport of isolated frog skin cultured with or without aldosterone.

Isolated frog skins were maintained, in organ culture in a modified Ussing chamber for up to 9 days with or without transepithelial NaCl gradient and aldosterone. Without gradient, (86 mM NaCl Ringer in the mucosal compartment and Wolf and Quimby amphibian medium culture in the serosal compartment), the structural organization of the epithelium, moulting cycle, keratinization and active sodium transport were similar to those observed before culture. In the absence of gradient, aldosterone slightly intensified keratinization and was necessary to maintain a high rate of active sodium transport. In the presence of a transepithelial ionic gradient (5 mM NaCl Ringer in the mucosal compartment and Wolf and Quimby amphibian medium culture in the serosal compartment), skins evolved towards the ultimate stage of the moulting cycle and the rate and the degree of keratinization were strongly enhanced. Aldosterone obviously promoted overlapping of the last two phases of the cycle and further intensified keratinization. It also strikingly raised active sodium transport. The epithelia of trypsinized skins, stripped of their stratum corneum and stratum granulosum were able to restructure themselves in culture. In this newly formed epithelium, the former regular structural organization was not preserved and the moulting cycle was no longer distinguishable. Moreover, when there was no transepithelial gradient, the keratinization process slowed down considerably. The presence of a gradient (28 mM NaCl Ringer in the mucosal compartment and Wolf and Quimby culture medium in the serosal compartment) promoted keratinization and led to the formation of cornified layers, which were sometimes detached from the underlying epithelial layers.