title: NH+4 transport mediated by Na(+)-K(+)-ATPase in rat inner medullary collecting duct.
abstract: The interaction of K+ and NH+4 on the basolateral membrane of cultured rat inner medullary collecting duct cells (IMCD) was explored using 86Rb+ as a K+ congener. Ouabain addition decreased Rb+ uptake to 22.0 +/- 2.6% of control. Possible ouabain-sensitive NH+4 transport was therefore explored. Replacement of N-methyl-D-glucamine chloride with NH4Cl or KCl decreased both total and ouabain-sensitive Rb+ uptake. This inhibition of Rb+ uptake by NH+4 was not due to changes in intracellular pH or differences in cell viability. We conclude that NH+4 competes with K+ for binding on the Na(+)-K(+)-adenosinetriphosphatase (ATPase). An inhibitory constant (Ki) for NH+4 of 11.0 +/- 1.6 and a Michaelis constant (Km) for K+ of 1.9 +/- 0.7 mM were measured. To extend these observations, NH+4 was tested as a substrate for ouabain-sensitive ATPase activity in native permeabilized IMCD cells. With 20 mM K+, activity was 202 +/- 73 nmol ATP hydrolyzed.min-1.mg protein-1, and with 20 mM NH+4, activity was 259 +/- 81 nmol ATP hydrolyzed.min-1.mg protein-1. Thus NH+4 substitution for K+ on the Na(+)-K(+)-ATPase is a likely mechanism for NH+4 uptake by the IMCD.
authors.affiliation: Division of Nephrology, University of Texas Medical School at Houston 77030.
authors.forename: S M
authors.initials: SM
authors.lastname: Wall
authors.forename: L M
authors.initials: LM
authors.lastname: Koger
mesh_terms: D000641:Ammonia / Q000378:metabolism*; D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002478:Cells, Cultured; D005665:Furosemide / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007679:Kidney Medulla / Q000201:enzymology / Q000502:physiology* / Q000648:ultrastructure; D007685:Kidney Tubules, Collecting / Q000201:enzymology / Q000502:physiology* / Q000648:ultrastructure; D007700:Kinetics; D008297:Male; D008536:Meglumine / Q000494:pharmacology; D008744:Methylamines / Q000494:pharmacology; D008854:Microscopy, Electron; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D011422:Propionates / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012413:Rubidium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013997:Time Factors
chemical_list: D008744:Methylamines; D011422:Propionates; D000643:Ammonium Chloride; D010042:Ouabain; D011189:Potassium Chloride; D008536:Meglumine; D000641:Ammonia; D005665:Furosemide; D000254:Sodium-Potassium-Exchanging ATPase; C029658:propionic acid; C023336:trimethylamine; D012413:Rubidium; D011188:Potassium