The steroid hormone aldosterone promotes sodium reabsorption in the renal distal tubule, playing a fundamental role in long-term blood pressure control. Aldosterone promotes sodium entry at the apical membrane of principal cells of the distal nephron by increasing the activity of amiloride-sensitive sodium channels (ENaCs). However, the molecular mechanisms involved in aldosterone action are only partially understood. Data previously published by our laboratory and others suggest that aldosterone regulates the translation efficiency of ENaC subunits mRNA. We have hypothesized that the 5' and 3' untranslated regions (UTR) of ENaC mRNAs contain translation regulatory sequences. To study the influence of UTR signals on ENaC translation, we fused the UTR sequences to a reporter gene (lacZ). Constructs were transfected in A6 cells, a continuous line of ephitelial cells derived of Xenopus laevis kidney that forms aldosterone-responsive sodium-transporting epithelia when seeded on permeable supports. High-efficiency transfection of lacZ reporter constructs into A6 cells was achieved by using a nucleofection system (Amaxa Biosystems). After transfection cells were seeded in permeable supports and epithelium differentiation was followed by daily measurements of short-circuit current. After 7 days, high-resistance sodium-transporting epithelial had formed. Cells retained expression of the b-galactosidase reporter gene and were responsive to hormones. Aldosterone treatment induced a decrease in b-galactosidase activity when the reporter gene contained the sense 3'UTR signal from alpha ENaC. Controls with antisense 3'UTR or the cDNA of lacZ alone did not respond to aldosterone. Our data suggest that alpha ENaC 3'-UTR includes aldosterone-controlled translation regulatory signals.