LARGE VESICLE FORMATION WITHIN CELLS INDUCED BY TREATMENT WITH A MIXED SURFACTANT

MDCK cells have been treated with a mixed surfactant at low concentrat ions to study the induced morphological changes. The most significant change at the light microscope level was the appearance of multiple la rge vesicles, which increased in size with time, up to approximate to 40 mu m 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 cyto chalasin D treatment had no effect on their formation. Furthermore, ni le red staining demonstrated that the vesicles did not represent fusio n of pre-existing lipid droplets. Transmission electron microscopy (TE M) analysis indicated that the vesicles lacked any obvious structure. It is hypothesised that the vesicles are large mixed structures synthe sised as a result of interactions between cell membranes and detergent components after saturation with the surfactants. This effect is cont rasted with the diffuse uptake of dyes and fluorescently labelled prot eins 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 t he loss of rounded compact colonies, an increase in mean cell diameter and the almost complete loss of surface microvilli as seen with scann ing electron microscopy (SEM). In the TEM the cell ultrastructure was seen to have changed markedly following detergent treatment, with a lo ss of rough endoplasmic reticulum and an apparent clumping of the cyto plasmic constituents. Copyright (C) 1996 Elsevier Science Ltd.