title: Na-K-ATPase inhibitor dissociated from hypertension-associated plasma protein.
abstract: It has been demonstrated that human plasma contains a low molecular weight sodium-potassium-stimulated adenosine triphosphatase (Na-K-ATPase) inhibitor, which can be dissociated from a circulating protein with a molecular weight of approximately 12,000 daltons. The dissociated factor was found to have a molecular weight <500 daltons, and shared many characteristics with ouabain. Similar to ouabain, this factor was found to be a potent inhibitor of both the Na-K-ATPase and potassium-stimulated para-nitrophenyl phosphatase (K-pNPPase) enzyme systems, and to bind to both high- and low-affinity binding sites on Na-K-ATPase, but unlike ouabain did not cross-react with digoxin antibody. The factor was further separated by HPLC and electrochemical detection into two active compounds (p-NKAI-1 and p-NKAI-2). P-NKAI-1 was demonstrated on mass spectroscopy to have a molecular weight of 408 daltons. In a vasoconstrictor assay employing rabbit femoral artery segments, this compound was a direct vasoconstrictor and potentiated the vasoconstriction produced by norepinephrine. It behaved similarly to ouabain in counteracting the relaxing effect on rabbit femoral artery of increasing potassium concentrations in the tissue bath.
authors.affiliation: Department of Medicine, The Burns and Allen Research Institute, Cedars-Sinai Medical Center, Los Angeles, California 90048, USA.
authors.forename: E W
authors.initials: EW
authors.lastname: Weiler
authors.forename: F
authors.initials: F
authors.lastname: Khalil-Manesh
authors.forename: H C
authors.initials: HC
authors.lastname: Gonick
authors.forename: B A
authors.initials: BA
authors.lastname: Prins
authors.forename: R E
authors.initials: RE
authors.lastname: Purdy
authors.forename: D K
authors.initials: DK
authors.lastname: Sensharma
mesh_terms: D009597:4-Nitrophenylphosphatase / Q000037:antagonists & inhibitors; D000818:Animals; D001667:Binding, Competitive; D001798:Blood Proteins / Q000737:chemistry / Q000302:isolation & purification*; D004077:Digoxin / Q000276:immunology; D004591:Electrophoresis, Polyacrylamide Gel; D004791:Enzyme Inhibitors / Q000097:blood* / Q000737:chemistry / Q000494:pharmacology; D005263:Femoral Artery / Q000187:drug effects / Q000502:physiology; D006801:Humans; D006973:Hypertension / Q000097:blood*; D066298:In Vitro Techniques; D008297:Male; D013058:Mass Spectrometry; D008970:Molecular Weight; D010042:Ouabain / Q000378:metabolism / Q000494:pharmacology; D011817:Rabbits; D011863:Radioimmunoassay; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014316:Tritium; D014661:Vasoconstriction / Q000187:drug effects
chemical_list: D001798:Blood Proteins; D004791:Enzyme Inhibitors; D014316:Tritium; D010042:Ouabain; D004077:Digoxin; D009597:4-Nitrophenylphosphatase; D000254:Sodium-Potassium-Exchanging ATPase