Direct observation of resolved intracellular and extracellular water signals in intact human red blood cells using H-1 MAS NMR spectroscopy

High resolution 400 MHz H-1 NMR spectra of red blood cell suspensions when measured using magic angle spinning (MAS) show two water resonances separated by 15 Hz. Based on addition of a paramagnetic Mn-EDTA complex, measurement of relaxation times and variation of extracellular H2O/ D2O ratios, these have been assigned as intracellular (linewidth 17.5 Hz) and extracellular water (linewidth 4.6 Hz). This is the first direct observation of intracellular water using NMR spectroscopy and the H-1 MAS NMR spectroscopic approach offers the possibility of studying directly the compartmentation of substances in cells and kinetics of molecular transport.