title: Basolateral membrane Na/base cotransport is dependent on CO2/HCO3 in the proximal convoluted tubule.
abstract: The mechanism of basolateral membrane base transport was examined in the in vitro microperfused rabbit proximal convoluted tubule (PCT) in the absence and presence of ambient CO2/HCO3- by means of the microfluorometric measurement of cell pH. The buffer capacity of the cells measured using rapid NH3 washout was 42.8 +/- 5.6 mmol.liter-1.pH unit-1 in the absence and 84.6 +/- 7.3 mmol.liter-1.pH unit-1 in the presence of CO2/HCO3-. In the presence of CO2/HCO3-, lowering peritubular pH from 7.4 to 6.8 acidified the cell by 0.30 pH units and lowering peritubular Na from 147 to 0 mM acidified the cell by 0.25 pH units. Both effects were inhibited by peritubular 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonate (SITS). In the absence of exogenous CO2/HCO3-, lowering peritubular pH from 7.4 to 6.8 acidified the cell by 0.25 pH units and lowering peritubular Na from 147 to 0 mM decreased cell pH by 0.20 pH units. Lowering bath pH from 7.4 to 6.8 induced a proton flux of 643 +/- 51 pmol.mm-1.min-1 in the presence of exogenous CO2/HCO3- and 223 +/- 27 pmol.mm-1.min-1 in its absence. Lowering bath Na from 147 to 0 mM induced proton fluxes of 596 +/- 77 pmol.mm-1.min-1 in its absence. The cell acidification induced by lowering bath pH or bath Na in the absence of CO2/HCO3- was inhibited by peritubular SITS or by acetazolamide, whereas peritubular amiloride had no effect. In the absence of exogenous CO2/HCO3-, cyanide blocked the cell acidification induced by bath Na removal, but was without effect in the presence of exogenous CO2/HCO3-. We reached the following conclusions. (a) The basolateral Na/base n greater than 1 cotransporter in the rabbit PCT has an absolute requirement for CO2/HCO3-. (b) In spite of this CO2 dependence, in the absence of exogenous CO2/HCO3-, metabolically produced CO2/HCO3- is sufficient to keep the transporter running at 30% of its control rate in the presence of ambient CO2/HCO3-. (c) There is no apparent amiloride-sensitive Na/H antiporter on the basolateral membrane of the rabbit PCT.
authors.affiliation: Department of Medicine, University of California, San Francisco 94143.
authors.forename: R
authors.initials: R
authors.lastname: Krapf
authors.forename: R J
authors.initials: RJ
authors.lastname: Alpern
authors.forename: F C
authors.initials: FC
authors.lastname: Rector
authors.forename: C A
authors.initials: CA
authors.lastname: Berry
mesh_terms: D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000494:pharmacology; D000086:Acetazolamide / Q000494:pharmacology; D000468:Alkalies / Q000378:metabolism*; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000502:physiology*; D001692:Biological Transport / Q000187:drug effects; D002021:Buffers; D002245:Carbon Dioxide / Q000502:physiology*; D002352:Carrier Proteins / Q000378:metabolism*; D003486:Cyanides / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D011817:Rabbits; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers
chemical_list: D000468:Alkalies; D001639:Bicarbonates; D002021:Buffers; D002352:Carrier Proteins; D003486:Cyanides; D017923:Sodium-Hydrogen Exchangers; D002245:Carbon Dioxide; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D000584:Amiloride; D012964:Sodium; D000086:Acetazolamide