Ultrastructure of rat oral epithelium in long‐term cell culture

— The purpose of the present study was to describe the ultrastructural appearance of squamous epithelium formed in vitro. The epithelium was formed by outgrowing cells from original explants of rat oral mucosa. Fifty-four explants from the lower surface of the tongues of 12 rats were cultured in a modified Eagle's basal medium, pH 7.2, at 32°C for up to 110 d. Subsequently the cells were prepared for electron microscopic examination. Epithelium from the lower surface of the tongues of eight rats served as control material. The in vitro specimens consisted of an extremely flattened stratified squamous epithelium. The basal cells varied from those of the control specimens by the lack of distinct bundles of tonofibrils. The intermediate cell layer exhibited a marked decrease in the number of organelles and an increase in the number of tonofilaments. No lamellated bodies or keratohyalin granules were found. The intercellular spaces were usually narrow with only a few, small desmosomes, which showed a simplified structure. The superficial cell layers showed, as did the corresponding cells of the control tissue, a distinct keratin pattern and an electron dense cytoplasmic zone along the cell membrane. It is concluded that rat oral epithelial cells grown in long-term cell culture are able to form a differentiating squamous epithelium.