Two mucous cell types revisited after quick-freezing and cryosubstitution.

The ultrastructures of mucous cell from mouse colon and quail oviduct were revisited after quick-freezing followed by cryosubstitution and compared with results from standard fixation. After quick-freezing, the mucous cells of both models do not show the classical aspect of the goblet cell. The secretory granules which contain a dense product do not swell and coalesce as observed after standard fixation. The large condensing vacuoles which are formed in the Golgi region can be discriminated from mature granules only after quick-freezing. Cytoplasmic organelles and cytoskeletal elements are observed between the secretory granules. The nucleus is ovoid and contains dispersed chromatin, whereas it has a reduced volume and contains condensed chromatin after standard fixation. It is assumed that during standard fixation, the membrane of mucous granules becomes permeable to water inducing hydration of mucous and swelling of granules. The term "goblet cell" could be descriptive of a fixation artefact.