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

Abstract

BACKGROUND: Non-type-A intercalated cells (IC) in the collecting duct system express the luminal Cl - /HCO 3- 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 responses of Atp6v1b1-/- and Atp6v1b1+/+ mice to an alkali load and to chronic treatment with furosemide.
RESULTS: An alkali load or one 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 IC of ex vivo microperfused cortical collecting ducts (CCDs) were reduced, and β2-adrenergic stimulation of pendrin activity was blunted in ATP6v1b1-/- mice. Basolateral H + -ATPase activity was strongly reduced, even though basolateral expression of the B2 isoform was increased. Ligation assays for H + -ATPase subunits indicated impaired assembly of V 0 and V 1 H + -ATPase domains. During chronic furosemide treatment, ATP6v1b1-/- mice also showed polyuria and hyperchloruria versus Atp6v1b1+/+ . Expression of pendrin, the water channel AQP2, and subunits of the epithelial sodium channel ENaC were reduced.
CONCLUSION: Our data demonstrate a critical role of H + -ATPases in non-type-A IC 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.