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Am J Physiol Regul Integr Comp Physiol 276: R1792-R1797, 1999;
0363-6119/99 $5.00
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Vol. 276, Issue 6, R1792-R1797, June 1999

Neonatal rabbit proximal tubule basolateral membrane Na+/H+ antiporter and Clminus /base exchange

Mehul Shah1, Raymond Quigley1, and Michel Baum1,2

1 Departments of Pediatrics and 2 Internal Medicine, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75235

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 ~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.

Cl-/HCO-3 exchanger; Cl-/OH- exchanger; Na+-bicarbonate cotransporter; renal development; intracellular pH; microperfusion


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