Growth and differentiation of primary tracheal epithelial cells in culture: Regulation by extracellular calcium

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Abstract
Growth and differentiation of primary monkey tracheal epithelial (MTE) cells maintained on collagen gel substrata were studied in a defined serum‐free culture medium containing 0.03 to 3.0 mM extracellular calcium. Cell attachment efficiency (40‐60%) was not altered by different calcium levels. Growth of primary MTE cells on collagen gel substrata, which was vitamin A dependent, was enhanced 50% in the medium supplemented with high calcium (≥ 0.3 mM). High calcium medium also increased cell‐cell interactions, formation of desmosomes, and multi‐cell layering. The relative content of mucous cells, which were identified by a mucin‐specific monoclonal antibody and the presence of mucus‐secreting granules at the ultrastructural level, was greater in the high‐calcium medium. Furthermore, the secretion of mucin into the medium, determined either by an ELISA or by the incorporation of 3H‐glucosamine into mucous glycoprotein fractions, was also increased more than 5‐fold in media containing high calcium content ( ≥ 0.6 mM). In contrast, MTE cells cultured in low calcium medium ( < 0.15 mM) were squamous‐like with prominent tonofiiaments, and their secretory product was mainly hyaluronate. These results demonstrate that media containing a high calcium content promote conducting airway epithelium to express mucous cell differentiation, while media with low calcium content promote squamous cell differentiation.