title: Stimulation of chloride transport by HCO3-CO2 in rabbit cortical collecting tubule.
abstract: We examined both the role of HCO3-CO2 in Cl transport as well as the effect of in vivo acid-base status on Cl transport by the rabbit cortical collecting tubule. The lumen-to-bath 36Cl tracer flux, expressed as the rate coefficient KCl, was measured in either HEPES-buffered (CO2-free) or HCO3-CO2-containing solutions. Amiloride was added to the perfusate to minimize the transepithelial voltage and thus the electrical driving force for Cl diffusion. Because KCl fell spontaneously with time in HCO3-CO2 solutions in the absence but not the presence of cAMP, we used cAMP throughout to avoid time-dependent changes. Acute in vitro removal of bath HCO3-CO2 reduced KCl. Acetazolamide addition in HEPES-buffered solutions also lowered KCl; KCl could be restored to control values by adding exogenous HCO3-CO2 in the presence of acetazolamide. In vivo acid-base effects on Cl transport were determined by dissecting tubules from either NaHCO3-loaded or NH4Cl-loaded rabbits. Tubules from HCO3-loaded rabbits had higher rates of Cl self exchange. Acute in vitro addition of bath HCO3-CO2 increased KCl and did so to a greater degree in tubules from HCO3-loaded rabbits. Most of this effect of HCO3-CO2 addition on KCl could not be accounted for by Cl-HCO3 exchange; rather, it appeared due to stimulation of Cl self exchange. The data are consistent with 36Cl transport occurring via Cl-HCO3 exchange as well as Cl self exchange. Both processes are acutely stimulated by HCO3 and/or Co2, and both are chronically regulated by in vivo acid-base status.
mesh_terms: D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000086:Acetazolamide / Q000494:pharmacology; D000136:Acid-Base Equilibrium / Q000187:drug effects; D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology*; D001692:Biological Transport / Q000187:drug effects; D002021:Buffers; D002245:Carbon Dioxide / Q000494:pharmacology*; D002712:Chlorides / Q000378:metabolism*; D005260:Female; D006531:HEPES; D007684:Kidney Tubules / Q000187:drug effects*; D007685:Kidney Tubules, Collecting / Q000187:drug effects*; D008433:Mathematics; D011188:Potassium / Q000378:metabolism; D011817:Rabbits; D013997:Time Factors
chemical_list: D001639:Bicarbonates; D002021:Buffers; D002712:Chlorides; D002245:Carbon Dioxide; D015124:8-Bromo Cyclic Adenosine Monophosphate; D000086:Acetazolamide; D011188:Potassium; D006531:HEPES