Fig. (5) Hereditary Disorders of the Collecting Duct. Sodium enter the principal cell via the epithelial sodium channel (ENaC) which is composed of the α. Β, and γ subunits. In Liddle syndrome mutated β or γ subunit keeps the channel open longer and increases sodium absorption. In pseudohypoaldosteronism, a mutated α, β, or γ subunit impairs the function of the ENaC. WNK4 protein inhibits ( ) potassium secretion via the ROMK transporter. In Gordon syndrome, a mutated WNK4 protein more strongly inhibits ROMK activity. In the intercalated cell (IC) distal RTA is caused by either a mutated anion exchanger (AE1) or either the ATP6V1B1 ( ) or the ATP6V0A4 ( ) subunit of the H+-ATPase.