Novel amiloride-sensitive sodium-dependent proton secretion in the mouse proximal convoluted tubule
Joo Young Choi, … , Shmuel Muallem, Michel Baum
Joo Young Choi, … , Shmuel Muallem, Michel Baum
Published April 15, 2000
Citation Information: J Clin Invest. 2000;105(8):1141-1146. https://doi.org/10.1172/JCI9260.
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Article

Novel amiloride-sensitive sodium-dependent proton secretion in the mouse proximal convoluted tubule

Abstract

The proximal convoluted tubule (PCT) reabsorbs most of the filtered bicarbonate. Proton secretion is believed to be mediated predominantly by an apical membrane Na+/H+ exchanger (NHE). Several NHE isoforms have been cloned, but only NHE3 and NHE2 are known to be present on the apical membrane of the PCT. Here we examined apical membrane PCT sodium-dependent proton secretion of wild-type (NHE3+/+/NHE2+/+), NHE3–/–, NHE2–/–, and double-knockout NHE3–/–/NHE2–/– mice to determine their relative contribution to luminal proton secretion. NHE2–/– and wild-type mice had comparable rates of sodium-dependent proton secretion. Sodium-dependent proton secretion in NHE3–/– mice was approximately 50% that of wild-type mice. The residual sodium-dependent proton secretion was inhibited by 100 μM 5-(N-ethyl-N-isopropyl) amiloride (EIPA). Luminal sodium-dependent proton secretion was the same in NHE3–/–/NHE2–/– as in NHE3–/– mice. These data point to a previously unrecognized Na+-dependent EIPA-sensitive proton secretory mechanism in the proximal tubule that may play an important role in acid-base homeostasis.

Authors

Joo Young Choi, Mehul Shah, Min Goo Lee, Patrick J. Schultheis, Gary E. Shull, Shmuel Muallem, Michel Baum

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Figure 1

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(a) PCR analysis of tail DNA from wild-type, NHE2–/+, NHE2–/–, and NHE3–...
(a) PCR analysis of tail DNA from wild-type, NHE2–/+, NHE2–/–, and NHE3–/–/NHE2–/– mice. Primers were designed to amplify a 450-bp product from wild-type NHE2 sequence, or a 221-bp product from the mutant allele that included part of the inserted neomycin resistance gene. (b) PCR analysis of tail DNA from wild-type, NHE3+/–, NHE3–/–, and NHE3–/–/NHE2–/– mice. As is shown, primers amplified a 199-bp product of wild-type NHE3 or a 113-bp product of the mutant allele that contained part of the inserted neomycin resistance gene. (c) Western blot of renal brush border membranes from wild-type and NHE3–/–/NHE2–/– mice. Membranes were probed with anti-rat NHE2 and anti-rat NHE3 antibodies that both detected approximately 90-kDa proteins in brush-border membranes from wild-type mice (WT). Note the total absence of NHE2 and NHE3 protein from renal brush-border membranes in NHE3–/–/NHE2–/– mice. β-Actin shows identical loading of the immunoblots.