Neonatal rabbit proximal tubule basolateral membrane Na+/H+ antiporter and Cl-/base exchange.
The present in vitro microperfusion study examined the maturation of Na+/H+ antiporter and Cl-/base exchanger on the basolateral membrane of rabbit superficial proximal straight tubules (PST). Intracellular pH (pHi) was measured with the pH-sensitive fluorescent dye 2', 7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein in neonatal and adult superficial PST. Na+/H+ antiporter activity was examined after basolateral Na+ addition in tubules initially perfused and bathed without Na+. Neonatal Na+/H+ antiporter activity was approximately 40% that of adult segment (9.7 +/- 1.5 vs. 23.7 +/- 3.2 pmol. mm-1. min-1; P < 0.001). The effect of bath Cl- removal on pHi was used to assess the rates of basolateral Cl-/base exchange. In both neonatal and adult PST, the Cl-/base exchange activity was significantly higher in the presence of 25 mM HCO-3 than in the absence of HCO-3 and was inhibited by cyanide and acetazolamide, consistent with Cl-/HCO-3 exchange. The proton flux rates in the presence of bicarbonate in neonatal and adult tubules were 14.1 +/- 3.6 and 19.5 +/- 3.5 pmol. mm-1min-1, respectively (P = NS), consistent with a mature rate of Cl-/HCO-3 exchanger activity in neonatal tubules. Basolateral Cl-/base exchange activity in the absence of CO2 and HCO-3, with luminal and bath cyanide and acetazolamide, was greater in adult than in neonatal PST and inhibited by bath DIDS consistent with a maturational increase in Cl-/OH- exchange. We have previously shown that the rates of the apical membrane Na+/H+ antiporter and Cl-/base exchanger were approximately fivefold lower in neonatal compared with adult rabbit superficial PST. These data demonstrate that neonatal PST basolateral membrane Na+/H+ antiporter and Cl-/base exchanger activities are relatively more mature than the Na+/H+ antiporter and Cl-/base exchangers on the apical membrane.
Shah
M
M
Departments of Pediatrics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75235, USA.
Quigley
R
R
Baum
M
M
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000086:Acetazolamide / Q000494:pharmacology; D000375:Aging / Q000378:metabolism; D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn / Q000254:growth & development / Q000378:metabolism*; D017920:Antiporters / Q000378:metabolism*; D001639:Bicarbonates / Q000494:pharmacology; D027963:Chloride-Bicarbonate Antiporters; D003486:Cyanides / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D011817:Rabbits; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*
D017920:Antiporters; D001639:Bicarbonates; D027963:Chloride-Bicarbonate Antiporters; D003486:Cyanides; D017923:Sodium-Hydrogen Exchangers; D000584:Amiloride; D000086:Acetazolamide; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; C039614:ethylisopropylamiloride