Salt restriction induces pseudohypoaldosteronism type 1 in mice expressinglow levels of the beta-subunit of the amiloride-sensitive epithelial sodium channel

The amiloride-sensitive epithelial sodium channel (ENaC) is a heteromultime r of three homologous subunits (alpha-, beta-, and gamma-subunits). To stud y the role of the beta-subunit in vivo, we analyzed mice in which the beta ENaC gene locus was disrupted. These mice showed low levels of beta ENaC mR NA. expression in kidney (approximate to 1%), lung (approximate to 1%), and colon (approximate to 4%). In homozygous mutant beta ENaC mice, no beta EN aC protein could be detected with immunofluorescent staining. At birth, the re was a small delay in lung-liquid clearance that paralleled diminished am iloride-sensitive Na+ absorption in tracheal explants. With normal salt int ake, these mice showed a normal growth rate. However, in vivo, adult beta E NaC m/m mice exhibited a significantly reduced ENaC activity in colon and e levated plasma aldosterone levels, suggesting hypovolemia and pseudohypoald osteronism type 1. This phenotype was clinically silent, as beta ENaC m/m m ice showed no weight loss, normal plasma Na+ and K+ concentrations, normal blood pressure, and a compensated metabolic acidosis. On low-salt diets, be ta ENaC-mutant mice developed clinical symptoms of an acute pseudohypoaldos teronism type 1 (weight loss, hyperkalemia, and decreased blood pressure), indicating that beta ENaC is required for Na+ conservation during salt depr ivation.