Expression of the epithelial sodium channel (ENaC) during ontogenic differentiation of the renal cortical collecting duct epithelium

The NaCl-reabsorbing collecting duct epithelium develops by budding and bra nching of the embryonic ureter. The expression of Na+ channels during this branching morphogenesis was studied in the outermost branches of rat ureter ic buds (UB; embryonic day E15 to postnatal day P6) and in cortical collect ing ducts (CCD; days P7-P28) in primary monolayer culture. Expression of bo th Na+ channel mRNA and of Na+-selective membrane conductance were estimate d by quantitative reverse-transcriptase polymerase chain reaction (RT-PCR) and by patch-clamp recording, respectively. UB and CCD uniformly represente d a principal-like cell type in culture. Messenger RNA encoding the alpha-E NaC subunit was detected in oligo-dT primed cDNA (5 ng) of embryonic UB cel ls (E15-17) after 30 PCR cycles. The abundance of alpha-ENaC mRNA, when nor malized by reference to p-actin, was higher by a factor of 2 in postnatal ( P1-6) UB and by a factor of 5 in CCD cells (P7-14) compared with the embryo nic stage. Highly Na+-selective, low-conductance channels were identified i n apical patches from both UB and CCD monolayers, but only CCD cells exhibi ted macroscopic, amiloride-sensitive Na+ currents in whole-cell patch-clamp recordings. We conclude that alpha-ENaC mRNA and functional Na+ channel pr otein are expressed already before morphogenesis of the CCD is completed an d prior to the onset of epithelial NaCl reabsorption.