Mechanisms of Airway Goblet Cell Mucin Release: Studies with Cultured Tracheal Surface Epithelial Cells

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Abstract
Confluent hamster tracheal surface epithelial (HTSE) cells in primary culture are enriched with secretory cells that synthesize and release mucins. Using this cell culture system, we investigated possible mechanisms of goblet cell mucin release by altering the media bathing the apical surface of HTSE cells: medium hyperosmolarity decreased mucin release, whereas hypo-osmolarity increased release without causing a cytoplasmic leak due to plasma membrane damage. A Ca2+ ionophore, A23187, did not influence mucin release. Both acidic (pH less than 4) and basic (pH greater than 9) media caused significant increases in mucin release secondary to cell membrane damage. Physiologic concentrations of chemical mediators such as prostaglandins (PGE2 and PGF2 alpha) and leukotrienes (LTC4 and LTD4) did not influence mucin release. Both elastase and cathepsin G derived from human neutrophils caused marked increases in release, whereas trypsin from the porcine pancreas produced a small increase only at a high concentration. We conclude that mucin release by cultured airway goblet cells can be enhanced by: (1) irritant gases, (2) luminal fluid osmolarity, (3) pharmacologic concentrations of LTC4 and LTD4, and (4) cationic proteases, each presumably acting by different mechanisms. Each of these mechanisms may play a role in epithelial mucin secretion associated with airway inflammation.