High-resolution ²³Na-NMR studies of human erythrocytes: Use of aqueous shift reagents

Aqueous shift reagents were used to clearly distinguish intra- and extracellular ²³Na-nuclear magnetic resonance (NMR) signals in samples consisting of whole blood or suspensions of washed human erythrocytes (both fresh and outdated). The lanthanide chelates Dy(PPP)₂^7- and Tm(TTHA)^3- were used to shift the extracellular signals upfield, and Dy(TTHA)^3- and Tm(PPP)₂^7- were similarly used to shift extracellular resonance downfield. The absolute intensities of the signals were used along with the measured hematocrit to simultaneously determine the intra- and extracellular Na⁺ concentrations. The results were generally within 5% of the values determined by more time-consuming centrifugation-flame emission photometry measurements on the same samples. Thus the ²³Na-NMR signals from both intra- and extracellular cations suffer no NMR invisibility within experimental error. The lower level of intracellular Na⁺ in fresh erythrocytes (<12 mM) is easily distinguished from the higher level (~30 mM) in erythrocytes that have been stored (in the cold) outside the body for some weeks.