DIFFERENTIAL EXPRESSION OF EPITHELIAL SODIUM-CHANNEL SUBUNIT MESSENGER-RNAS IN RAT SKIN

Three subunits (alpha,beta,gamma) of the amiloride-sensitive epithelia l sodium channel have been recently characterized. The channel subunit s have significant homologies with the Caenorhabditis elegans mec-4, m ec-10 and deg-P genes, which are;involved in control of cell volume an d mecano-transduction. These subunits are coexpressed at equivalent le vels in the renal collecting duct and the distal colon epithelium whic h are high resistance sodium transporting epithelia. We have investiga ted whether these subunits were expressed, at the mRNA level, in trans porting as well as non transporting epithelial cells of rat skin. In f ull-thickness abdominal skin only alpha and gamma subunit mRNAs were d etected, while all three subunit mRNAs were present in sole skin, as d emonstrated by RNase-protection assay. Furthermore, the level of expre ssion of each subunit varied with the epithelial cell type as demonstr ated by in situ hybridization: epidermal and follicular keratinocytes express mostly alpha and gamma subunits (while beta was low); a preval ence of beta and gamma was observed in sweat glands. Thus, it appeared that two out of the three subunit mRNAs predominated in each epitheli al structure. In addition, mRNAs of the alpha,beta and gamma subunits of the amiloride-sensitive sodium channel were expressed at a higher l evel in large suprabasal epidermal keratinocytes (which undergo termin al differentiation) than in small proliferative basal keratinocytes.