Assessment of the NMR visibility of intraerythrocytic sodium by flame photometric and ion‐competitive studies

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Abstract
23Na nuclear magnetic resonance (NMR) studies of intraerythrocytic sodium concentrations were performed at 37°C and the accuracy of the method was evaluated through concomitant emission flame photometric analysis. NMR visibility of intraerythrocytic sodium was estimated to be 75 ± 3%. Verification of the presence of an NMR invisible intraerythrocytic sodium pool and assessment of the mechanisms explaining this invisibility was achieved by measurement of 23Na NMR signal intensities and T1 relaxation times of erythrocyte hemolysate during ion‐competitive sodium release from association sites. Signal intensities after addition of small quantities of K+ and Mg2+ to the hemolysates were significantly larger than that expected from dilution of the sample, implying that the additions have resulted in the release of formerly invisible sodium. Furthermore, the intensities following the addition of K+ were significantly larger than those after the addition of Li+ and choline+. This signifies a specificity of the association sites at which sodium has decreased visibility. Increased T1 values following the additions confirmed the release of bound sodium. © 1989 Academic Press, Inc.