Basolateral membrane sodium-independent Cl-/HCO3- exchanger in rat inner medullary collecting duct cell.
Previous studies have shown that the middle third of the rat inner medullary collecting duct (IMCD-2) secretes protons despite the absence of intercalated cells, the cell thought to secrete protons in other portions of the collecting duct. A new cell, the IMCD cell, is the predominant cell in IMCD-2. The mechanism responsible for base exit in the IMCD cell was characterized by measuring cell pH of isolated perfused tubules with 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein. Reduction of bath HCO3- caused a significant and reversible decrease in cell pH, whereas a similar change in luminal HCO3- had a significantly smaller effect, indicating that the HCO3-/H+ permeability of the basolateral membrane is much larger than the apical membrane. The rate of cell acidification induced by reduction in bath HCO3-, a measure of basolateral HCO3- transport, was significantly decreased in the absence of bath and lumen Cl. Decreases in bath Cl caused a significant and reversible increase in cell pH, which was not changed significantly by complete removal of Na from perfusate and bath, but was significantly inhibited by basolateral 4',5'-diisothiocyanostilbene-2,2'-disulfonic acid. A chemical voltage clamp did not inhibit the rate of cell alkalinization after bath Cl removal, indicating that Cl-/HCO3- exchange is not via parallel Cl and HCO3- conductances. Cell pH was measured in single cells by low-light-level imaging to show that most cells contain the chloride-dependent HCO3- pathway. We conclude that the rat IMCD cell possesses a basolateral Na-independent CL-/HCO3- exchanger which may serve as the base exit step for transepithelial proton secretion.
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Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas 75235-8856.
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D000136:Acid-Base Equilibrium; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D002451:Cell Compartmentation; D002462:Cell Membrane / Q000378:metabolism; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007679:Kidney Medulla / Q000166:cytology / Q000378:metabolism*; D007684:Kidney Tubules / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000166:cytology / Q000378:metabolism*; D008564:Membrane Potentials; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000502:physiology; D014634:Valinomycin / Q000494:pharmacology
D001639:Bicarbonates; D002352:Carrier Proteins; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides; D014634:Valinomycin; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D012964:Sodium; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid