MDCK cells have been treated with a mixed surfactant at low concentrations to study the induced morphological changes. The most significant change at the light microscope level was the appearance of multiple large vesicles, which increased in size with time, up to ≃40 μm in diameter. Vesicle formation was shown to be linked with the uptake of the fluid medium, as judged by the presence of FITC-dextran within the vesicles, but was not a result of pinocytosis because cytochalasin D treatment had no effect on their formation. Furthermore, nile red staining demonstrated that the vesicles did not represent fusion of pre-existing lipid droplets. Transmission electron microscopy (TEM) analysis indicated that the vesicles lacked any obvious structure. It is hypothesised that the vesicles are large mixed structures synthesised as a result of interactions between cell membranes and detergent components after saturation with the surfactants. This effect is contrasted with the diffuse uptake of dyes and fluorescently labelled proteins following simple anionic or ionic detergent treatment. The effect of vesicle formation was reversible if the cells were placed in fresh medium lacking detergent. Other effects of mixed detergent included the loss of rounded compact colonies, an increase in mean cell diameter and the almost complete loss of surface microvilli as seen with scanning electron microscopy (SEM). In the TEM the cell ultrastructure was seen to have changed markedly following detergent treatment, with a loss of rough endoplasmic reticulum and an apparent clumping of the cytoplasmic constituents.
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