The multisubunit vacuolar-type H(+)
ATPases mediate acidification of various intracellular organelles and in some tissues mediate H(+) secretion across the plasma membrane. Mutations in the B1-subunit of the apical
H(+)ATPase that secretes
protons in the distal nephron cause
distal renal tubular acidosis in humans, a condition characterized by
metabolic acidosis with an inappropriately alkaline urine. To examine the detailed cellular and organismal physiology resulting from this mutation, we have generated mice deficient in the B1-subunit (Atp6v1b1(-/-) mice). Urine pH is more alkaline and
metabolic acidosis is more severe in Atp6v1b1(-/-) mice after oral
acid challenge, demonstrating a failure of normal urinary acidification. In Atp6v1b1(-/-) mice, the normal urinary acidification induced by a lumen-negative potential in response to
furosemide infusion is abolished. After an acute intracellular acidification, Na(+)-independent pH recovery rates of individual Atp6v1b1(-/-) intercalated cells of the cortical collecting duct are markedly reduced and show no further decrease
after treatment with the selective
H(+)ATPase inhibitor concanamycin. Apical expression of the alternative B-subunit
isoform, B2, is increased in Atp6v1b1(-/-) medulla and colocalizes with the
H(+)ATPase E-subunit; however, the greater severity of
metabolic acidosis in Atp6v1b1(-/-) mice after oral
acid challenge indicates that the B2-subunit cannot fully functionally compensate for the loss of B1. Our results indicate that the B1
isoform is the major B-subunit
isoform that incorporates into functional, plasma membrane H(+)
ATPases in intercalated cells of the cortical collecting duct and is required for maximal urinary acidification.