Differential expression of epithelial sodium channel subunit mRNAs in rat skin

Three subunits (alpha, beta, gamma) of the amiloride-sensitive epithelial sodium channel have been recently characterized. The channel subunits have significant homologies with the Caenorhabditis elegans mec-4, mec-10 and deg-1 genes, which are involved in control of cell volume and mecanotransduction. These subunits are coexpressed at equivalent levels in the renal collecting duct and the distal colon epithelium which are high resistance sodium transporting epithelia. We have investigated whether these subunits were expressed, at the mRNA level, in transporting as well as non transporting epithelial cells of rat skin. In full-thickness abdominal skin only alpha and gamma subunit mRNAs were detected, while all three subunit mRNAs were present in sole skin, as demonstrated by RNase-protection assay. Furthermore, the level of expression of each subunit varied with the epithelial cell type as demonstrated by in situ hybridization: epidermal and follicular keratinocytes express mostly alpha and gamma subunits (while beta was low); a prevalence of beta and gamma was observed in sweat glands. Thus, it appeared that two out of the three subunit mRNAs predominated in each epithelial structure. In addition, mRNAs of the alpha, beta and gamma subunits of the amiloride-sensitive sodium channel were expressed at a higher level in large suprabasal epidermal keratinocytes (which undergo terminal differentiation) than in small proliferative basal keratinocytes.