The determination of intracellular sodium concentration in human red blood cells: nuclear magnetic resonance measurements.

The intracellular sodium concentration and intracellular volume of human red blood cells were determined from 23Na and 1H NMR spectra. It is shown that sodium dissolved in the intracellular water has a concentration higher than that previously published. The intracellular sodium concentration measured was 11.4 +/- 3.1 mM. A comparison of different NMR methods used to determine sodium concentration is given.