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.