Single and multiple desipramine exposures of cultured cells: Changes in cellular anisotropy and in lipid composition of whole cells and of plasma membranes

Effects of the antidepressant drug desipramine (DMI) on fluorescence anisotropy were studied in living cultured human fibroblasts, rat brain astrocytes and rat ROC-1 hybridoma cells (oligodendrocytes × C6). Fluorescence anisotropy, a measure for fluidity, was measured by means of a fluorescence polarization technique using a set of n-(9-anthroyloxy) fatty acids as markers. Apparent fluorescence anisotropies were determined in cells following single or multiple dose exposures to 5 μm DMI at 37° and compared to control cells. In all three cell types single doses of DMI led to significant decreases in anisotropies of the deeper layers (12-AS) of the membranes only, suggesting increases in fluidity. Repeated exposures to 5 μM DMI led to cell specific, significant changes in anisotropies of the superficial membrane layers, as determined by 2-AP, 6-, 7- and 9-AS. The resulting anisotropy values of the three different cell types became more alike than prior to DMI exposure. Alterations in anisotropies were accompanied with changes in the phospholipid patterns of whole cells and isolated plasma membrane vesicles. The changes of PC/PE ratios were consistent with changes observed in fluorescence anisotropies. Such alterations may be individual regulatory responses of the cells to the chronic presence of the drug within the membranes.