Basolateral membrane Cl(-)-, Na(+)-, and K(+)-coupled base transport mechanisms in rat MTALH.
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.
Bourgeois
Soline
S
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.
Massé
Sandrine
S
Paillard
Michel
M
Houillier
Pascal
P
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*
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