Water proton spin-lattice relaxation time during the apoptotic process in ultraviolet-irradiated murine erythroleukemia cells.

Ultraviolet (UV) light-induced apoptosis has been extensively examined, but data on properties of intracellular water are insufficient. Thus, we examined the (1)H spin-lattice relaxation time (T1) of intracellular water during apoptosis in murine erythroleukemia (MEL) cells. Values of T1 decreased upon cell shrinkage, whereas increased upon cell swelling. Similar results were obtained in MEL cells exposed to osmotic stress. Furthermore, the increment of T1 values, ultrastructure loss on cell surface, and DNA fragmentation in UV-treated cells were significantly suppressed by pan-caspase inhibitor. Taken together, these results suggest that the T1 of intracellular water can be used to estimate the relative content of bound and free water during UV-induced apoptosis in MEL cells.