title: The chloride/base exchanger in the basolateral cell membrane of rabbit renal proximal tubule S3 segment requires bicarbonate to operate.
abstract: Isolated microperfused S3 segments of rabbit renal proximal tubule were investigated with pH-sensitive double-barrelled intracellular microelectrodes to determine whether the Cl-/base exchanger, which we have previously identified in the basolateral cell membrane of this segment requires HCO3- or can also work in CO2/HCO3- free conditions. Cell pH (pHi) was measured in response to sudden substitution of bath Cl- by gluconate. In control solutions containing 25 mmol/l HCO3 pHi increased initially by 5.0 +/- 0.3 x 10(-3) unit/s but after perfusion with CO2/HCO3(-)-free solutions pHi of the same cells increased only by 1.3 +/- 0.2 x 10(-3) unit/s in response to Cl- substitution. From measurements of the cellular buffering power it was calculated that the control base flux had fallen drastically from 3.7 +/- 0.3 to 0.3 +/- 0.1 x 10(-12) mol/s.cm tubule length. To test whether the remaining flux might have resulted from metabolic CO2, oxidative metabolism was poisoned with cyanide (5 mmol/l). This abolished the pH change (delta pHi) in CO2/HCO3(-)-free solutions, but did not affect the pH shift in the presence of HCO3-. The data indicate that basolateral Cl-/base exchange in S3 segment requires HCO3- to operate. A model in which HCO3- absorption proceeds in form of OH- and CO2 can be largely excluded.
authors: Zentrum der physiologie, J. W. Goethe Universität, Frankfurt/M., Federal Republic of Germany.
authors: G
authors: G
authors: Seki
authors: E
authors: E
authors: Frömter
mesh_terms: D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology*; D002021:Buffers; D002245:Carbon Dioxide / Q000494:pharmacology; D002352:Carrier Proteins / Q000032:analysis* / Q000502:physiology; D002462:Cell Membrane / Q000737:chemistry / Q000187:drug effects / Q000502:physiology; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides / Q000494:pharmacology; D003486:Cyanides / Q000494:pharmacology; D005260:Female; D006863:Hydrogen-Ion Concentration; D007687:Kidney Tubules, Proximal / Q000166:cytology* / Q000502:physiology / Q000648:ultrastructure; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008839:Microelectrodes; D011817:Rabbits
chemical_list: D001639:Bicarbonates; D002021:Buffers; D002352:Carrier Proteins; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides; D003486:Cyanides; D002245:Carbon Dioxide