Urea inhibits Na-K-2Cl cotransport in medullary thick ascending limb cells.
We examined the effect of physiological concentrations of urea (100-500 mM) on Na-K-2Cl cotransport in cultured cells from mouse medullary thick ascending limb (mTAL). Urea acutely inhibited bumetanide-sensitive K influx in mTAL cells in a concentration-dependent fashion, with a statistically significant inhibition (19%) at 100 mM and 86% inhibition at 500 mM. The effect of urea was entirely reversible and was blocked by prior treatment with okadaic acid, a phosphatase inhibitor, suggesting that urea exerts its action upstream of the phosphorylation-dephosphorylation step. Cell volume was unchanged in the presence of 500 mM urea. The number of [3H]bumetanide binding sites, a measure of the number of functioning cotransporter sites, was decreased in the presence of urea, and the decrease in bumetanide binding was proportional to the decrease in bumetanide-sensitive K influx. Urea also stimulated the Ba-sensitive swelling-activated K efflux from mTAL cells. Thus urea, in concentrations that prevail in the renal medulla, alters ion transport in mTAL cells.
Kaji
D M
DM
Department of Medicine, Veterans Affairs Medical Center, Bronx, New York 10468, USA.
Diaz
J
J
Parker
J C
JC
D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D002034:Bumetanide / Q000378:metabolism / Q000494:pharmacology; D002352:Carrier Proteins / Q000037:antagonists & inhibitors*; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007679:Kidney Medulla; D008138:Loop of Henle / Q000166:cytology / Q000378:metabolism*; D008387:Marine Toxins; D051379:Mice; D019319:Okadaic Acid / Q000494:pharmacology; D009994:Osmolar Concentration; D010080:Oxazoles / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D028021:Sodium-Potassium-Chloride Symporters; D014508:Urea / Q000494:pharmacology*
D002352:Carrier Proteins; D004791:Enzyme Inhibitors; D008387:Marine Toxins; D010080:Oxazoles; D028021:Sodium-Potassium-Chloride Symporters; D002034:Bumetanide; D019319:Okadaic Acid; C059041:calyculin A; D014508:Urea; D011188:Potassium