title: Evidence of chloride/bicarbonate exchange mediating bicarbonate efflux from S3 segments of rabbit renal proximal tubule.
abstract: The mechanism of HCO3- exit from rabbit renal proximal tubule S3 segments was investigated. Isolated tubules were perfused luminally and peritubularly with test solutions and cell pH (pHi), cell Cl- activity ([Cl-]i) and cell Na+ activity ([Na+]i) were measured with ion-selective microelectrodes. From the response of pHi and [Cl-]i to changes in bath Cl- or HCO3- concentrations a Cl-/HCO3- exchanger was identified in the basolateral cell membrane. It was reversibly inhibited by millimolar concentrations of the disulfonic stilbene SITS (4-acetamido-4'-isothiocyanato-stilbene-2,2'-disulfonic acid). Cell potential measurements and preliminary determinations of initial ion flux rates suggested a stoichiometry of Cl- to HCO3- flux near 1.0. The transport rate appeared to saturate already at low bath Cl- concentrations (approximately 30 mmol/l), but it was independent of bath pH in the range of 7.4-6.4. Cl-/HCO3- exchange was not directly coupled to Na+ flux although in approximately half of the experiments long-term incubation in Na(+)-free solutions indirectly inhibited the exchanger. Sudden application of SITS under control conditions revealed that the exchanger normally facilitates the exit of HCO3- from cell to interstitium at the expense of Cl- uptake into the cell. How Cl- ions recirculate towards the peritubular surface is presently not known.
authors.affiliation: Zentrum der Physiologie, Johann-Wolfgang-Goethe-Universität, Frankfurt, Federal Republic of Germany.
authors.forename: Y
authors.initials: Y
authors.lastname: Kondo
authors.forename: E
authors.initials: E
authors.lastname: Frömter
mesh_terms: D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism* / Q000494:pharmacology; D002352:Carrier Proteins / Q000502:physiology*; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides / Q000378:metabolism / Q000494:pharmacology; D005260:Female; D006863:Hydrogen-Ion Concentration; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D008565:Membrane Proteins / Q000502:physiology; D009994:Osmolar Concentration; D011817:Rabbits; D012964:Sodium / Q000378:metabolism
chemical_list: D001639:Bicarbonates; D002352:Carrier Proteins; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides; D008565:Membrane Proteins; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D012964:Sodium