NMR studies of intracellular water at 300 MHz: T 2 ‐specific relaxation mechanisms in synchronized or EGF‐stimulated cells

Responses specific to the spin‐spin relaxation time ( T 2 ) have been observed in two time‐dependent studies of the intracellular water in normal and transformed Syrian hamster fetal fibroblasts. At 300‐MHz (7.0 T), the spin‐lattice relaxation time ( T 1 ) was insensitive to several aspects of cellular physiology that produced changes in the T 2 and the apparent self‐diffusion coefficient ( D app ) of intracellular water. In normal cells stimulated with epidermal growth factor (EGF), T 1 was insensitive to time‐dependent changes detected by T 2 and D app . In synchronized tumor cells, T 1 was insensitive to cell‐cycle‐dependent changes detected by T 2 . The strongly coupled behavior of T 2 and D app that was observed as a function of time in EGF‐stimulated cells indicates that the diffusion of intracellular water through inhomogeneous local magnetic field gradients produced effects observable in T 2 . Conformational changes in large intracellular macromolecular assemblies such as chromatin or the cytoskeleton may alter the magnitude and inhomogeneity of local field gradients, producing responses in T 2 and D app only. © 1991 Academic Press, Inc.