Neonatal rabbit juxtamedullary proximal convoluted tubule acidification

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Abstract

The present in vitro microperfusion study examined apical membrane Na+/H+ antiporter and basolateral membrane Na(HCO3)3 symporter activity in newborn and adult juxtamedullary proximal convoluted tubules. Proton fluxes were determined from the initial rate of change of intracellular pH after a change in the luminal or bathing solution, buffer capacity, and tubular volume of newborn and adult tubules. Intracellular pH (pH(i)) was measured fluorometrically using the pH-sensitive dye (2',7')-bis (carboxyethyl)-(5,6)-carboxyfluorescein (BCECF). Apical Na+/H+ antiporter proton flux, assayed by the effect of sodium removal (147 → 0 meq/liter) on pH(i), was one-third the adult level for the first 2 wk and doubled in the 3rd wk of life. Adult levels were achieved by 6 wk of age. Na+/H+ antiporter activity was not detected on the basolateral membrane of 1-wk-old newborns, indicating that polarity of this transporter was already present. Basolateral membrane Na(HCO3)3 proton flux, assayed by the effect of a bath bicarbonate change (25 → 5 meq/liter) and by a bath sodium change (147 → 0 meq/liter) on pH(i), was 50-60% of adult values in 1-wk-old newborns. Basolateral membrane Na(HCO3)3 proton flux assayed by a bath bicarbonate change (25 → 5 meq/liter) remained at 50-60% of adult values for the 1st mo of life and increased to adult levels by 6 wk of age. This transporter not only plays a role in net acidification, but is an important determinant of cell pH in newborn juxtamedullary proximal convoluted tubules.

Original languageEnglish (US)
Pages (from-to)499-506
Number of pages8
JournalJournal of Clinical Investigation
Volume85
Issue number2
DOIs
StatePublished - Jan 1 1990

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Keywords

  • Na(HCO) symporter
  • Na/H antiporter
  • intracellular pH
  • proton flux

ASJC Scopus subject areas

  • Medicine(all)

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