Nuclear magnetic resonance (NMR) characteristics of water in perfused single neurons undergoing a 20% hypotonic perturbation were examined quantitatively using NMR microscopy. The transverse relaxation times (T2) in the cytoplasm and nucleus increased by 24.0 +/- 8.5% (average +/- SE, n = 8) and 29.7 +/- 5.3% (n = 6), respectively, whereas the apparent diffusion coefficients (ADC) showed no significant change. These findings are consistent with the behaviors of a perfect osmometer and with accepted molecular relaxation and diffusion models and have significant impacts on current views of properties of cellular water. Furthermore, the results suggest that the increase of tissue intracellular-to-extracellular volume ratio during cell swelling is the predominant mechanism underlying the ADC reduction in acute brain ischemia. These data are the first direct quantitative measurements of the NMR characteristics of water in the cytoplasm and nucleus of single cells undergoing physiological perturbations and may lead to an improved diagnostic capability for NMR imaging in a variety of disease states.
