Reversible and irreversible effects of chemical fixation on the NMR properties of single cells

The effects of chemical fixation are known to alter MR parameters, such as relaxation times and the apparent diffusion coefficient (ADC) of water. It is often assumed that such change are reversible after samples have been reimmersed in a buffer solution for a sufficient period of time. In this study we characterize the changes associated with fixation of single Xenopus laevis oocytes and their subsequent reimmersion in buffer. Sub stantial reductions in both T-1 and T-2 values were measured for all compartments of the cell after fixation, with the cytoplasm showing larger changes than the nucleus. After reimmersion in buffer, there were small but statistically significant difference in MR parameters between fresh and reimmersed cells. Experiments with a gadolinium (Gd) contrast agent showed evidence of irreversible changes in the permeability of cellular membrane., to small molecules.