title: HCO3- transport in basolateral membrane vesicles isolated from rat renal cortex.
abstract: The mechanism of HCO3- translocation across the proximal tubule basolateral membrane was investigated by testing for Na+-HCO3- cotransport using isolated membrane vesicles purified from rat renal cortex. As indicated by 22Na+ uptake, imposing an inwardly directed HCO3- concentration gradient induced the transient concentrative accumulation of intravesicular Na+. The stimulation of basolateral membrane vesicle Na+ uptake was specifically HCO3(-)-dependent as only basolateral membrane-independent Na+ uptake was stimulated by an imposed hydroxyl gradient in the absence of HCO3-. No evidence for Na+-HCO3- cotransport was detected in brush border membrane vesicles. Charging the vesicle interior positive stimulated net intravesicular Na+ accumulation in the absence of other driving forces via a HCO3(-)-dependent pathway indicating the flow of negative charge accompanies the Na+-HCO3- cotransport event. Among the anion transport inhibitors tested, 4-4'-diisothiocyanostilbene-2,2'-disulfonic acid demonstrated the strongest inhibitor potency at 1 mM. The Na+-coupled transport inhibitor harmaline also markedly inhibited HCO3- gradient-driven Na+ influx. A role for carbonic anhydrase in the mechanism of Na+-HCO3- cotransport is suggested by the modest inhibition of HCO3- gradient driven Na+ influx caused by acetazolamide. The imposition of Cl- concentration gradients had a marked effect on HCO3- gradient-driven Na+ influx which was furosemide-sensitive and consistent with the operation of a Na+-HCO3- for Cl- exchange mechanism. The results of this study provide evidence for an electrogenic Na+-HCO3- cotransporter in basolateral but not microvillar membrane vesicles isolated from rat kidney cortex. The possible existence of an additional basolateral membrane HCO3(-)-translocating pathway mediating Na+-HCO3- for Cl- exchange is suggested.
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001485:Basement Membrane / Q000378:metabolism; D001639:Bicarbonates / Q000378:metabolism*; D002712:Chlorides / Q000494:pharmacology; D005665:Furosemide / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D006878:Hydroxides; D017665:Hydroxyl Radical; D007672:Kidney Cortex / Q000648:ultrastructure*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism
chemical_list: D001639:Bicarbonates; D002712:Chlorides; D006878:Hydroxides; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D017665:Hydroxyl Radical; D005665:Furosemide; D012964:Sodium; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid