Pendrin Modulates ENaC Function by Changing Luminal HCO3-

The epithelial Na+ channel, ENaC and the Cl-/HCO3- exchanger, pendrin, mediate NaCl absorption within the cortical collecting duct and the connecting tubule Although pendrin and ENaC localize to different cell types, ENaC subunit abundance and activity are lower in aldosterone-treated pendrin null mice relative to wild-type mice Because pendrin mediates HCO3- secretion, we asked if increasing distal delivery of HCO3- through a pendrin-independent mechanism 'rescues ENaC function in pendrin-null mice We gave aldosterone and NaHCO3 to increase pendrin-dependent HCO3- secretion within the connecting tubule and cortical collecting duct, or gave aldosterone and NaHCO3 plus acetazolamide to increase luminal HCO3- concentration, [HCO3-], independent of pendrin Following treatment with aldosterone and NaHCO3 pendrin-null mice had lower urinary pH and [HCO3-] as well as lower renal ENaC abundance and function than wild type mice With the addition of acetazolamide, however, acid-base balance as well as ENaC subunit abundance and function was similar in pendrin-null and wild type mice We explored whether [HCO3-] directly alters ENaC abundance and function in cultured mouse principal cells (mpkCCD) Amiloride-sensitive current and ENaC abundance rose with increased [HCO3-] on the apical or the basolateral side, independent of the substituting anion However, ENaC was more sensitive to changes in [HCO3-] on the basolateral side of the monolayer Moreover, increasing [HCO3-] on the apical and basolateral side of Xenopus kidney cells increased both ENaC channel density and channel activity We conclude that pendrin modulates ENaC abundance and function, at least in part by increasing luminal [HCO3-] and/or pH