title: Isolation and characterization of a sodium pump inhibitor from human plasma.
abstract: An endogenous sodium pump inhibitor has been purified from human plasma. The purification scheme involved large scale dialysis, extraction of lyophilized dialysate by methanol followed by preparative and semipreparative scale reverse-phase high-performance chromatography. A single peak of biologically active material was obtained enriched by a factor of greater than 10 billion. This material showed high chromatographic polarity, was inactivated by charring, strong acid, or alkali, and was resistant to short-term boiling. The purified material had a molecular weight between 300 and 900 g/mol and was insensitive to type I esterase and a variety of proteolytic enzymes. The purified factor inhibited the ouabain-sensitive uptake of 86Rb by human erythrocytes, binding of [3H]ouabain, and activity of dog kidney Na,K-adenosine triphosphatase (ATPase) with high affinity (less than 0.3 nM) in a time- and dose-dependent manner. Maximally effective concentrations of the digitalislike factor showed no effect on either human red blood cell Mg- or Ca-ATPase, rabbit muscle sarcoplasmic reticulum Ca-ATPase, or guinea pig stomach H,K-ATPase. The purified material is a highly potent selective inhibitor of the ion transport, receptor, and hydrolytic functions of the sodium pump. The characteristic properties of this substance suggest it may be a mammalian endogenous digitalis and may be similar to the sodium transport inhibitor detected in the plasma of volume-sensitive forms of experimental and human hypertension.
authors.affiliation: Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland 21201.
authors.forename: J M
authors.initials: JM
authors.lastname: Hamlyn
authors.forename: D W
authors.initials: DW
authors.lastname: Harris
authors.forename: M A
authors.initials: MA
authors.lastname: Clark
authors.forename: A C
authors.initials: AC
authors.lastname: Rogowski
authors.forename: R J
authors.initials: RJ
authors.lastname: White
authors.forename: J H
authors.initials: JH
authors.lastname: Ludens
mesh_terms: D000328:Adult; D000368:Aged; D001798:Blood Proteins / Q000302:isolation & purification* / Q000378:metabolism / Q000494:pharmacology; D002298:Cardenolides; D055598:Chemical Phenomena; D002621:Chemistry; D002845:Chromatography / Q000379:methods; D004077:Digoxin; D004912:Erythrocytes / Q000378:metabolism; D006801:Humans; D008875:Middle Aged; D012413:Rubidium / Q000097:blood; D012503:Saponins; D015222:Sodium Channels / Q000187:drug effects*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D001798:Blood Proteins; D002298:Cardenolides; D012503:Saponins; D015222:Sodium Channels; C034504:digoxin-like factors; D004077:Digoxin; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium