title: Basolateral membrane Na(+)-independent Cl-/HCO3- exchange in the inner stripe of the rabbit outer medullary collecting tubule.
abstract: 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-/HCO3- transport in this segment, cell pH was measured microfluorometrically 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 [HCO3-] 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 microM 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-/HCO3- 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/HCO3- from the system. The apparent Km for peritubular Cl- determined in the presence of 25 mM luminal and peritubular [HCO3-] 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-/HCO3- exchanger which mediates 90% of basolateral membrane H+/OH-/HCO3- permeability and may be regulated by physiologic Cl- concentrations.
authors.affiliation: Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas 75235.
authors.forename: S R
authors.initials: SR
authors.lastname: Hays
authors.forename: R J
authors.initials: RJ
authors.lastname: Alpern
mesh_terms: D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism*; D005260:Female; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007684:Kidney Tubules / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D011817:Rabbits; D012964:Sodium / Q000378:metabolism*
chemical_list: D001639:Bicarbonates; D002712:Chlorides; D012964:Sodium