ROLE OF GAMMA-ENAC SUBUNIT IN LUNG LIQUID CLEARANCE AND ELECTROLYTE BALANCE IN NEWBORN MICE

Genetic evidence supports a critical role for the epithelial sodium ch annel (ENaC) in both clearance of fetal lung liquid at birth and total body electrolyte homeostasis. Evidence from heterologous expression s ystems suggests that expression of the alpha ENaC subunit is essential for channel function, whereas residual channel function can be measur ed in the absence of beta or gamma subunits. We generated mice without gamma ENaC (gamma ENaC -/-) to test the role of this subunit in neona tal lung liquid clearance and total body electrolyte balance. Relative to controls, gamma ENaC (-/-) pups showed low urinary [K+] and high u rinary [Na+] and died between 24 and 36 h, probably from hyperkalemia (gamma ENaC -/- 18.3 mEq/l, control littermates 9.7 mEq/l). Newborn ga mma ENaC (-/-) mice cleared lung liquid more slowly than control litte rmates, but lung water at 12 h (wet/dry = 5.5) was nearly normal (wet/ dry = 5.3). This study suggests that gamma ENaC facilitates neonatal l ung liquid clearance and is critical for renal Na+ and K+ transport, a nd that low level Na+ transport may be sufficient for perinatal lung l iquid absorption but insufficient to maintain electrolyte balance by t he distal nephron. The gamma ENaC (-/-) newborn exhibits a phenotype t hat resembles the clinical manifestations of human neonatal PHA1.