Epithelial sodium channels are upregulated during epidermal differentiation

Terminal differentiation of epidermal keratinocytes is linked to transmembr ane ion flux. Previously, we have shown that amiloride, an inhibitor of epi thelial sodium channels, blocks synthesis of differentiation-specific prote ins in normal human keratinocytes. Here, we have identified the specific su bunits of amiloride-sensitive human epithelial sodium channels in relation to differentiation of cultured human keratinocytes, as well as to epidermal development. As assessed by northern hybridization, RNase protection assay , and reverse transcription-polymerase chain reaction, transcripts encoding functional alpha and regulatory beta subunits of human epithelial sodium c hannels were expressed both in cultured keratinocytes and in epidermis at l evels comparable with the kidney. The mRNA expression of both human epithel ial sodium channel-alpha and -beta increased during calcium-induced keratin ocyte differentiation. Whereas the beta subunit of human epithelial sodium channel was induced by elevated concentrations of calcium, the alpha subuni t increased with duration of culture. The regulatory gamma subunit was less abundant but also expressed in epidermis. Both human epithelial sodium cha nnel-alpha and -beta were localized throughout the nucleated layers of huma n adult epidermis, but these channels were not detected in early stages of fetal epidermal development. This co-ordinated expression of subunits sugge sts that epithelial sodium channels may play an important pare in both epid ermal differentiation and skin development, presumably by modulating ion tr ansport required for epidermal terminal differentiation.