| Abstract: | To assess therole of distal nephron apical Na channel (ENaC) gene expression in Nawasting by the immature kidney, ENaC  -,  -, and  -subunit mRNAlevels were examined in the rat by RT-PCR. In microdissected nephronsegments, all three ENaC subunit mRNAs were detected in the distalconvoluted tubule, connecting tubule, cortical collecting duct, andouter medullary collecting duct. The inner medullary collecting ductand all other nephron segments were consistently negative. The mRNAlevels were quantified in kidneys at different developmental stages bymultiplex RT-PCR with "primer dropping," with endoplasmicreticulum-specific cyclophilin mRNA as an internal standard. All threeENaC mRNA levels were low or undetectable on gestationalday 16 and only slightly higher 3 daysbefore birth. A sharp rise was observed between 3 days before and1-3 days after birth; the levels at postnataldays 1-3 were already similar tothose of adult kidneys. The results suggest that ENaC subunit geneexpression is not a limiting factor in the full-term newborn ratkidney, but low levels of expression may limit distal Na absorption inmore immature kidneys, such as those of very premature human infants. |
