Corticoid-induced differentiation of amiloride-blockable active Na+ transport across larval bullfrog skin in vitro.

The hormone-induced differentiation of an active Na+ transport across larval bullfrog skin during metamorphosis was investigated in vitro and in vivo. In in vitro experiments, EDTA-treated larval dorsal skin from which apical cells were removed was used. Even in the absence of thyroid hormone, corticoids induced the differentiation. Although aldosterone was the most potent hormone, hydrocortisone or corticosterone was also effective. Prolactin inhibited the corticoid-induced differentiation. The differentiation of the transport system coincided almost exactly with the appearance of adult features of the epidermis, namely, the epidermis at 7 days carried the human blood group antigen A, a specific molecular marker of adult-type bullfrog epidermis. The transport system appeared to develop in cells that had been newly generated from basal cells. On the contrary, in in vivo experiments, the effect of amiloride on the short-circuit current of the skin of tadpoles raised in the presence of aldosterone was very small, suggesting that a mechanism exists to inhibit the ability of aldosterone to induce the differentiation of the transport system in vivo.