Airway mucus plays an important defensive role in the lung. Its function is contributed mainly by the physicochemical property of mucous glycoproteins or mucins. Mucins are produced by two different cell types; goblet cells in the surface epithelium and mucous cells in the submucosal glands. Goblet cell mucin release is stimulated in certain pathologic and toxic states, but little is known about its regulation under normal conditions. In order to study the regulation of mucin secreion, our laboratory has developed an in vitro model of the airway goblet cell. Confluent hamster tracheal surface epithelial cell cultures are highly enriched for airway goblet cells as judged morphologically by lectin binding characteristics, and by release of high molecular weight mucin-like glycoproteins (MLGP). Using this unique culture system, we have tested the effects of a large number of agents on MLGP release. We have found that extracellular ATP and ATP analogues stimulate MLGP release in a concentration-dependent fashion. The relative potency of ATP analogues for MLGP release and its inhibition by putative antagonists indicate that the action of ATP may be mediated by the recently described P2-type ATP receptor, likely the P2y subtype. These data suggest that extracellular ATP may be involved in the regulation of goblet cell mucin secreion under normal conditions. We propose to extend this observation by: (1) characterizing pharmacologically the putative P2-type ATP receptor responsible for MLGP release; (2) elucidating biochemical mechanisms involved in ATP-induced MLGP release; and (3) producing antibodies to the HTSE cell ATP receptor in order to perform immunohistochemical characterization of the distribution of the receptor in normal and diseased airways. The experiments proposed in this project will enhance understanding of the regulation of goblet cell mucin release in health and disease, provide a means of developing new pharmacologic agents that can control mucus secretion, and provide a valuable new system for the study of the function of extracellular ATP.
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