Effects of hypertonic conditions on cytoskeletal and adhesion structures of EUE cells

The distribution of cytoskeletal structures has been studied by electron and immunofluorescence microscopy in human embryonic epithelial cells (EUE cells) exposed to a hypertonic medium containing 0.274 M NaCl. A first noticeable effect involved an increase of cell size. Microtubules, microfilaments and intermediate filaments were also considerably changed under these experimental conditions. The most marked effect was on intermediate filaments of the keratin type which formed very thick bundles around the nucleus and gave rise to an intracellular cagework which is likely i) to increase mechanical resistance and ii) to avoid cell collapse in conditions of hyperosmolarity. A remarkable increase in complexity of the microfilamentous network was also found: stress fibers became thicker and more densely arranged and vinculin-containing streaks at focal cell-substratum contacts increased in number and size; this indicated improved cellular adhesion. The phenotypic adaptation of EUE cells to conditions of hyperosmolarity is slowly reversible under defined experimental conditions.