Sodium entry mechanisms in distal convoluted tubule cells.
Sodium transport across apical membranes of distal convoluted tubules is thought to be mediated by Na-Cl cotransport and conductive Na entry. Immortalized mouse distal convoluted tubule cells were used to characterize Na entry pathways. Chlorothiazide, an inhibitor of Na-Cl cotransport, and amiloride, which blocks epithelial Na channels, reduced ouabain-suppressible oxygen consumption by 40 and 35%, respectively. In simple buffer solutions, free of bicarbonate, phosphate, or formate, chlorothiazide inhibited Na uptake by 44% and Cl uptake by 48%. Michaelis constants of 21 mM for Na and 14 mM for chloride were calculated. Amiloride inhibited Na uptake by 49% and had no effect on Cl uptake. The calculated Hill coefficient of 1.07 and the equivalence of chlorothiazide-sensitive Na and Cl uptake are consistent with the presence of Na-Cl cotransport. Na-Cl cotransport and amiloride-sensitive Na influx account for 85% of Na entry in distal convoluted tubule cells in the absence of phosphate and formate. The selective Na/H exchange inhibitor ethylisopropyl amiloride had no effect on Na uptake; however, it abolished formate-stimulated Na uptake. The anion exchange blocker 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) inhibited Na uptake. These findings are consistent with parallel Na/H and Cl/formate exchange. Na uptake was inhibited 8% by the selective Na/Ca exchange inhibitor, dimethylbenzamil. An additional 7% of Na entry was phosphate dependent and was abolished by phosphonoformic acid, a competitive inhibitor of Na-Pi cotransport. In summary, the majority of Na entry into distal convoluted tubule cells occurs through Na-Cl cotransport and an amiloride-sensitive pathway (75% in presence of phosphate and formate). An additional 13% may enter by Na/H exchange, with the remainder mediated by Na/Ca exchange and Na-Pi cotransport.
Gesek
F A
FA
Department of Pharmacology and Toxicology, Dartmouth Medical School, Hanover, New Hampshire 03755-3835.
Friedman
P A
PA
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000256:Adenoviridae; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology; D001693:Biological Transport, Active / Q000187:drug effects; D002034:Bumetanide / Q000494:pharmacology; D002257:Carbonic Anhydrase Inhibitors / Q000494:pharmacology; D002461:Cell Line, Transformed; D002678:Chimera; D002712:Chlorides / Q000494:pharmacology; D002740:Chlorothiazide / Q000494:pharmacology; D007686:Kidney Tubules, Distal / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D051379:Mice; D009761:Nystatin / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D010101:Oxygen Consumption / Q000187:drug effects; D013539:Simian virus 40; D012964:Sodium / Q000378:metabolism*; D026941:Sodium Channel Blockers; D012965:Sodium Chloride / Q000494:pharmacology; D012979:Sodium Radioisotopes
D001639:Bicarbonates; D002257:Carbonic Anhydrase Inhibitors; D002712:Chlorides; D026941:Sodium Channel Blockers; D012979:Sodium Radioisotopes; D002034:Bumetanide; D009761:Nystatin; D012965:Sodium Chloride; D010042:Ouabain; D002740:Chlorothiazide; D000584:Amiloride; D012964:Sodium; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid