Pendrin-null mice develop severe hypokalemia following dietary Na and K restriction: role of ENaC.

Pendrin is an intercalated cell Cl/[Formula: see text] exchanger thought to participate in K-sparing NaCl absorption. However, its role in K homeostasis has not been clearly defined. We hypothesized that pendrin-null mice will develop hypokalemia with dietary K restriction. We further hypothesized that pendrin knockout (KO) mice mitigate urinary K loss by downregulating the epithelial Na channel (ENaC). Thus, we examined the role of ENaC in Na and K balance in pendrin KO and wild-type mice following dietary K restriction. To do so, we examined the relationship between Na and K balance and ENaC subunit abundance in K-restricted pendrin-null and wild-type mice that were NaCl restricted or replete. Following a NaCl-replete, K-restricted diet, K balance and serum K were similar in both groups. However, following a Na, K, and Cl-deficient diet, pendrin KO mice developed hypokalemia from increased K excretion. The fall in serum K observed in K-restricted pendrin KO mice was enhanced with ENaC stimulation but eliminated with ENaC inhibition. The fall in serum K observed in K-restricted pendrin KO mice was enhanced with ENaC stimulation but eliminated with ENaC inhibition. However, reducing ENaC activity also reduced blood pressure and increased apparent intravascular volume contraction, since KO mice had lower serum Na, higher blood urea nitrogen and hemoglobin, greater weight loss, greater metabolic alkalosis, and greater NaCl excretion. We conclude that dietary Na and K restriction induces hypokalemia in pendrin KO mice. Pendrin-null mice limit renal K loss by downregulating ENaC. However, this ENaC downregulation occurs at the expense of intravascular volume. Pendrin is an apical Cl/[Formula: see text] exchanger that provides renal K-sparing NaCl absorption. The pendrin-null kidney has an inability to fully conserve K and limits renal K loss by downregulating the epithelial Na channel (ENaC). However, with Na restriction, the need to reduce ENaC for K balance conflicts with the need to stimulate ENaC for intravascular volume. Therefore, NaCl restriction stimulates ENaC less in pendrin-null mice than in wild-type mice, which mitigates their kaliuresis and hypokalemia but exacerbates volume contraction.