BASOLATERAL MEMBRANE NA+-INDEPENDENT CL-/HCO3- EXCHANGE IN THE INNER STRIPE OF THE RABBIT OUTER MEDULLARY COLLECTING TUBULE

The inner stripe of the outer medullary collecting tubule is a major distal nephron segment in urinary acidification. To examine the mechanism of basolateral membrane H+/OH-/HCO−3 transport in this segment, cell pH was measured micr of luorometrically in the inner stripe of the rabbit outer medullary collecting tubule perfused in vitro using the pH-sensitive fluorescent dye, (2',7')-bis(carboxyethyl)-(5,6)-carboxyfluorescein. Decreasing peritubular pH from 7.4 to 6.8 (changing [HCO−3] from 25 to 5 mM) caused a cell acidification of 0.25 ± 0.02 pH units, while a similar luminal change resulted in a smaller cell acidification of only 0.04 ± 0.01 pH units. Total replacement of peritubular Cl− with gluconate caused cell pH to increase by 0.18 ± 0.04 pH units, an effect inhibited by 100 µM peritubular DIDS and independent of Na+. Direct coupling between Cl− and base was suggested by the continued presence of peritubular Cl− removal-induced cell alkalinization under the condition of a cell voltage clamp (K+-valinomycin). In addition, 90% of basolateral membrane H+/OH−/HCO−3 permeability was inhibited by complete removal of luminal and peritubular Cl−. Peritubular Cl−-induced cell pH changes were inhibited two-thirds by removal of exogenous CO2/HCO−3 from the system. The apparent K+ for peritubular Cl− determined in the presence of 25 mM luminal and peritubular [HCO−3] was 113.5 ± 14.8 mM. These results demonstrate that the basolateral membrane of the inner stripe of the outer medullary collecting tubule possesses a stilbene-sensitive Cl−/HCO−3 exchanger which mediates 90% of basolateral membrane H+/OH−/HCO−3 permeability and may be regulated by physiologic Cl− concentrations. © 1990, Rockefeller University Press., All rights reserved.