title: Stimulation of Cl- self exchange by intracellular HCO3- in rabbit cortical collecting duct.
abstract: In rabbit cortical collecting duct, Cl- self exchange accounts for most of the transepithelial Cl- tracer rate coefficient, KCl (nm/s); a small fraction is effected by Cl--HCO3- exchange and Cl- diffusion. We previously reported that changing from a CO2-free N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) bath to a 5% CO2-25 mM HCO3- bath stimulates Cl- self exchange. Here, we examine in further detail the individual components of the CO2-HCO3- system that stimulate KCl. Addition of 0.5% CO2 to a HEPES bath (final pH = 7.24) stimulated KCl by 70 +/- 19 nm/s, a delta KCl comparable to that induced by 1% CO2 (pH 7.12), 6% CO2 (pH 6.6), or 6% CO2-25 mM HCO3- (pH 7.4). The roles of intracellular pH (pHi) and HCO3- concentration were examined by clamping pHi using high K+ and nigericin. Increasing pHi from 6.9 to 7.6 in solutions without exogenous CO2 or HCO3- increased KCl by 71 +/- 17 nm/s. These results suggest that pHi might regulate anion exchange. However, during such a pHi-shift experiment, metabolically derived CO2 produces a concomitant change in intracellular HCO3- concentration [( HCO3-]i). To determine whether an increase in [HCO3-]i could stimulate Cl- self exchange, we replaced HEPES with 6% CO2-5 mM HCO3- isohydrically (pHi clamped at 6.9). With this increase in [HCO3-]i at constant pHi, KCl increased by 51 +/- 10 nm/s. These maneuvers had negligible effects on Cl- diffusion and Cl--HCO3- exchange. These experiments demonstrate that increases in cell [HCO3-] (or perhaps CO2) can stimulate transepithelial anion exchange.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Internal Medicine, University of Iowa College of Medicine, Iowa City 52242.
authors.forename: K
authors.initials: K
authors.lastname: Matsuzaki
authors.forename: J B
authors.initials: JB
authors.lastname: Stokes
authors.forename: V L
authors.initials: VL
authors.lastname: Schuster
mesh_terms: D000818:Animals; D001639:Bicarbonates / Q000378:metabolism / Q000494:pharmacology*; D002245:Carbon Dioxide / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides / Q000378:metabolism*; D004058:Diffusion; D004848:Epithelium / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007684:Kidney Tubules / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000187:drug effects / Q000378:metabolism*; D009550:Nigericin / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011817:Rabbits; D012966:Sodium Cyanide / Q000494:pharmacology
chemical_list: D001639:Bicarbonates; D002352:Carrier Proteins; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides; D002245:Carbon Dioxide; D012966:Sodium Cyanide; D009550:Nigericin; D011188:Potassium