The B1 H+-ATPase (Atp6v1b1) Subunit in Non–Type A Intercalated Cells is Required for Driving Pendrin Activity and the Renal Defense Against Alkalosis

Abstract

Background Non–type A ICs in the collecting duct system express the luminal Cl−/HCO3 − exchanger pendrin and apical and/or basolateral H+-ATPases containing the B1 subunit isoform. Non–type A ICs excrete bicarbonate during metabolic alkalosis. Mutations in the B1 subunit (ATP6V1B1) cause distal renal tubular acidosis due to its role in acid secretory type A ICs. The function of B1 in non–type A ICs has remained elusive. Methods We examined the responses of Atp6v1b1 −/− and Atp6v1b1 +/+ mice to an alkali load and to chronic treatment with furosemide. Results An alkali load or 1 week of furosemide resulted in a more pronounced hypokalemic alkalosis in male ATP6v1b1 −/− versus Atp6v1b1 +/+ mice that could not be compensated by respiration. Total pendrin expression and activity in non–type A ICs of ex vivo microperfused cortical collecting ducts were reduced, and β 2-adrenergic stimulation of pendrin activity was blunted in ATP6v1b1 −/− mice. Basolateral H+-ATPase activity was strongly reduced, although the basolateral expression of the B2 isoform was increased. Ligation assays for H+-ATPase subunits indicated impaired assembly of V0 and V1 H+-ATPase domains. During chronic furosemide treatment, ATP6v1b1 −/− mice also showed polyuria and hyperchloremia versus Atp6v1b1 +/+ . The expression of pendrin, the water channel AQP2, and subunits of the epithelial sodium channel ENaC were reduced. Conclusions Our data demonstrate a critical role of H+-ATPases in non–type A ICs function protecting against alkalosis and reveal a hitherto unrecognized need of basolateral B1 isoform for a proper H+-ATPase complexes assembly and ability to be stimulated.