23Na-NMR studies of Na+ interaction with human red cell membranes from normotensives and hypertensives.
Na+ interaction with unsealed human red cell ghosts has been studied by 23Na-NMR relaxation rate (R1) measurements. Data on a total of nine subjects including seven volunteer normotensives (NBP) and two untreated hypertensives (HBP) are presented. Qualitative treatment of the data gives information on the dynamic behavior of Na+ undergoing fast exchange between the free and bound states. The excess longitudinal relaxation rate (delta R)-1 plotted against total [Na+], known as the James-Noggle plot, exhibits different behavior for NBP and HBP ghosts, with a relatively low binding constant of approx. 100 M-1 for HBP (p less than 0.025) compared to a high constant of 500-1000 M-1 for NBP. To associate our NMR data with membrane-bound (Na+ + K+)-ATPase, 23Na relaxation rates were measured in the presence of 5 mM ouabain. James-Noggle plots constructed for ouabain-sensitive excess relaxation rates show the binding for NBP to be even high affinity (greater than 10(3) M-1) but low capacity. These data may suggest that for a given amount of intracellular Na+, the binding affinity could determine the distribution of Na+ between the membrane and cytoplasm, and that the (Na+ + K+)-ATPase which is primarily responsible for the Na+ affinity might assume an abnormal transport mechanism in HBP membranes.
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D000293:Adolescent; D000328:Adult; D004910:Erythrocyte Membrane / Q000378:metabolism*; D005260:Female; D006801:Humans; D006973:Hypertension / Q000097:blood*; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008875:Middle Aged; D010042:Ouabain / Q000494:pharmacology; D012016:Reference Values; D012964:Sodium / Q000097:blood*
D010042:Ouabain; D012964:Sodium