title: Mechanisms of bicarbonate transport by cultured rabbit inner medullary collecting duct cells.
abstract: The inner medullary collecting duct (IMCD) is the final portion of the mammalian renal tubule that is able to significantly regulate systemic acid-base balance. Although the H+ transporters of this segment are relatively well studied, little is known regarding the mechanisms of HCO3- transport. The mechanisms of HCO3- transport in primary cultures of rabbit IMCD were studied using the pH-sensitive dye, 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein, in CO2/HCO3(-)-containing solutions at 37 degrees C. Removal of Cl- from the extracellular solution caused reversible intracellular alkalinization, demonstrating the presence of Cl-/HCO3- exchange. Alkalinization with Cl- removal was independent of changes in membrane potential, did not require the presence of extracellular Na+, and was inhibited by the disulfonic stilbene, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS, 10(-4) M). Half-maximal intracellular pH (pHi) recovery with readdition of Cl- to the extracellular solution occurred at a Cl- concentration of 37.4 +/- 5.7 mM. When rabbit IMCD were cultured on permeable support membranes, Cl-/HCO3- exchange activity was found only on the basolateral membrane. However, there was no evidence of band 3 protein immunoreactivity. In contrast, no evidence for Na(+)-(HCO3-)n > 1 cotransport activity was found. Depolarization of IMCD cells by acute increases in extracellular K+ did not alter pHi, nor was Na(+)-dependent, 5-(N-ethyl-N-isopropyl)amiloride-insensitive pHi recovery from an acid load inhibited by DIDS (10(-4) M). Finally, recovery from intracellular alkalosis induced by incubation in 0 mM Cl-, 50 mM HCO3- extracellular solution required Cl- and was independent of Na+. These studies indicate that the major mechanism of HCO3- transport in primary cultures of the rabbit IMCD is via a band 3 protein-negative, Na(+)-independent, basolateral, Cl-/HCO3- exchanger.
authors.affiliation: Division of Nephrology, Hypertension and Transplantation, University of Florida College of Medicine, Gainesville 32610.
authors.forename: A E
authors.initials: AE
authors.lastname: Weill
authors.forename: C C
authors.initials: CC
authors.lastname: Tisher
authors.forename: M F
authors.initials: MF
authors.lastname: Conde
authors.forename: I D
authors.initials: ID
authors.lastname: Weiner
mesh_terms: D000468:Alkalies / Q000378:metabolism; D000818:Animals; D001457:Anion Exchange Protein 1, Erythrocyte / Q000276:immunology; D000906:Antibodies / Q000276:immunology; D017920:Antiporters / Q000378:metabolism; D001639:Bicarbonates / Q000378:metabolism*; D001692:Biological Transport; D002478:Cells, Cultured; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D007679:Kidney Medulla; D007685:Kidney Tubules, Collecting / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D008564:Membrane Potentials; D011817:Rabbits; D012964:Sodium / Q000502:physiology; D013267:Stilbenes / Q000494:pharmacology
chemical_list: D000468:Alkalies; D001457:Anion Exchange Protein 1, Erythrocyte; D000906:Antibodies; D017920:Antiporters; D001639:Bicarbonates; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides; D013267:Stilbenes; D012964:Sodium