title: Basolateral membrane Cl(-)-, Na(+)-, and K(+)-coupled base transport mechanisms in rat MTALH.
abstract: Mechanisms involved in basolateral HCO transport were examined in the in vitro microperfused rat medullary thick ascending limb of Henle (MTALH) by microfluorometric monitoring of cell pH. Removing peritubular Cl(-) induced a cellular alkalinization that was inhibited in the presence of peritubular 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) and blunted in the absence of external CO(2)/HCO. The alkalinization elicited by removing peritubular Cl(-) persisted in the bilateral absence of Na(+), together with a voltage clamp. When studied in Cl(-)-free solutions, lowering peritubular pH induced a base efflux that was inhibited by peritubular DIDS or by the absence of external CO(2)/HCO. Removing peritubular Na(+) elicited a cellular acidification that was accounted for by stimulation of a DIDS- and ethylisopropylamiloride (EIPA)-insensitive Na(+)-HCO cotransport and inhibition of a basolateral Na(+)/H(+) exchange. Increasing bath K(+) induced an intracellular alkalinization that was inhibited in the absence of external CO(2)/HCO. At 2 mM, peritubular Ba(2+), which inhibits the K(+)-Cl(-) cotransport, did not induce any change in transepithelial voltage but elicited a cellular alkalinization and inhibited K(+)-induced cellular alkalinization, consistent with the presence of a basolateral, electroneutral Ba(2+)-sensitive K(+)-Cl(-) cotransport that may operate as a K(+)-HCO cotransport. This cotransport was inhibited in the peritubular presence of furosemide, [(dihydroindenyl)oxy]alkanoic acid, 5-nitro-2-(3-phenylpropylamino)benzoate, or DIDS. At least three distinct basolateral HCO transport mechanisms are functional under physiological conditions: electroneutral Cl(-)/HCO exchange, DIDS- and EIPA-insensitive Na(+)-HCO cotransport, and Ba(2+)-sensitive electroneutral K(+)-Cl(-)(HCO) cotransport.
authors.affiliation: Université Pierre et Marie Curie, Institut National de la Santé et de la Recherche Médicale Unité 356, Institut Fédératif de Recherche 58, Hôpital Européen Georges Pompidou, Assistance Publique-Hôpitaux de Paris, 75015 Paris, France.
authors.forename: Soline
authors.initials: S
authors.lastname: Bourgeois
authors.forename: Sandrine
authors.initials: S
authors.lastname: Massé
authors.forename: Michel
authors.initials: M
authors.lastname: Paillard
authors.forename: Pascal
authors.initials: P
authors.lastname: Houillier
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000584:Amiloride / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000494:pharmacology; D001693:Biological Transport, Active; D002021:Buffers; D027963:Chloride-Bicarbonate Antiporters / Q000378:metabolism; D004594:Electrophysiology; D004847:Epithelial Cells / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007700:Kinetics; D008138:Loop of Henle / Q000166:cytology / Q000378:metabolism*; D008297:Male; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D028021:Sodium-Potassium-Chloride Symporters / Q000378:metabolism*
chemical_list: D002021:Buffers; D027963:Chloride-Bicarbonate Antiporters; D028021:Sodium-Potassium-Chloride Symporters; D001464:Barium; D000584:Amiloride; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; C039614:ethylisopropylamiloride