Developmental expression of the epithelial Na+ channel in kidney and uroepithelia

The epithelial Na+ channel (ENaC) plays an important role in regulating Na balance in neonatal and adult life. Using in situ hybridization, we locali zed alpha-, beta-, and gamma-rat ENaC (rENaC) mRNA in developing rat kidney and uroepithelia. rENaC mRNA was first detectable on fetal day 16, and by fetal day 17, mRNA was abundant in the terminal collecting duct and uroepit helia. After birth, the intensity of the signals for all three subunits inc reased in the cortical collecting ducts and by 9 days after birth had dimin ished in the inner medullary collecting ducts. Expression in uroepithelial cells was different. mRNA for beta- and gamma-rENaC, but not alpha-rENaC, w as detected in pelvis, ureters, and bladder at all stages of development be yond fetal day 16. By RNase protection assay (RPA), the greatest increase i n subunit abundance in the kidney occurred before birth. Between postnatal days 9 and 30, the abundance of beta- and gamma-rENaC decreased relative to alpha-rENaC in outer and inner medulla. The urinary bladder, in contrast, demonstrated the greatest increase in beta- and gamma-rENaC mRNA abundance after birth. We were generally unable to detect alpha-rENaC by RPA in urina ry bladder. Feeding weaned rats a diet of high or low NaCl did not change t he abundance of any of the subunit mRNAs in bladder. These results demonstr ate additional heterogeneity of developmental expression and regulation of ENaC. The differences between the collecting duct and uroepithelial cell, r ENaC mRNA regulation raise the possibility of significant differences in fu nction.