Neonatal rabbit juxtamedullary proximal convoluted tubule acidification.
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 (pHi) 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 pHi, 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 pHi, 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.
Baum
M
M
Department of Pediatrics, University of Texas Southwestern Medical Center, Dallas 75235.
D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism*; D001639:Bicarbonates / Q000378:metabolism; D002021:Buffers; D002352:Carrier Proteins / Q000032:analysis; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007679:Kidney Medulla / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D011817:Rabbits; D017923:Sodium-Hydrogen Exchangers; D000254:Sodium-Potassium-Exchanging ATPase / Q000032:analysis
D001639:Bicarbonates; D002021:Buffers; D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D000254:Sodium-Potassium-Exchanging ATPase