The dependence of proton longitudinal and transverse relaxation times on cell-cycle phase: mouse MCA-transformed 10T1/2 TCL-15 cells.

Attempts to determine proton NMR longitudinal relaxation times (T1) as a function of cell-cycle stage using cells synchronized by chemical methods have yielded conflicting results (P. T. Beall, C. F. Hazlewood, and P. N. Rao, Science 192, 904 (1976); R. N. Muller et al., FEBS Lett. 114, 231 (1980); D. N. Wheatley, et al., J. Cell Sci. 88, 13 (1987]. This has raised the question whether a true dependence of T1 on cell-cycle phase exists. In the present study, the centrifugal elutriation technique was used to obtain relatively pure, synchronized cell populations of TCL-15 cells (a methylcholanthrene-transformed line of mouse 10T1/2 cells) for measurement of proton NMR relaxation rates. This technique provides a means to procure synchronized cell populations without the use of chemical agents as in the above-cited investigations and therefore avoid possible effects caused by the chemical agents of the NMR relaxation processes. Both T1 and the transverse relaxation time, T2, of water protons in synchronized-cell pellets obtained in this study, exhibited a dependence on cell-cycle phase at least for the first half of the cell cycle (G1 to S). Cells in G1 phase exhibited quantitatively higher T1 and T2 relaxation times compared to those measured for cells in mid S phase. Such changes were found to correlate with changes in water content. The distribution of cell-cycle phases of each cell population was determined by the DNA histogram using flow cytometric methods. Possible relaxation mechanisms which may contribute to the cell-cycle-specific phenomena of the intracellular T1 and T2 times are discussed.