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Mucin release by airway surface epithelial cells is regulated by extracellular adenosine triphosphate (ATP) via a P 2 purinoceptor-mediated mechanism. The objective of the present experiment was to examine the possible involvement of uridine triphosphate (UTP) in this purinergic signal transduction pathway.Using primary hamster tracheal surface epithelial cells, ATP and UTP were compared in their abilities: 1) to displace ATPγS 35 -binding to intact cells; 2) to accumulate inositol phosphates; and 3) to stimulate mucin release. Finally, the presence of a P 2u receptor message was examined.Our results showed that: 1) UTP was much less effective than ATP in displacing ATPγS 35 -binding (median inhibitory concentrations (IC50s) 240 vs 2.9 µM); 2) UTP was more potent than ATP in accumulating inositol phosphates (100 vs 43% increase at 2 mM); 3) UTP was equipotent with ATP in stimulating mucin release; 4) Northern blot analysis of messenger ribonucleic acids (mRNAs) with a mouse P 2u receptor complementary deoxyribonucleic acid (cDNA) probe revealed a single specific band (2.8 kb), partial sequencing of which showed a great homology with those of human or mouse P 2u receptors.We conclude that, although both ATP and UTP are equipotent in stimulating mucin release, their binding kinetics to the cell surface are quite different, suggesting the presence of a common binding domain which may be responsible for the mucin release by these nucleotides. We suggest that the P 2u purinoceptor is likely to be responsible for mucin release by these nucleotides, probably via activation of phospholipase C. Eur Respir J., 1996, 9, 542-548 P 2u receptors purely based on agonist potency orders in which UTP = ATP > ATPγS > 2-methylthio ATP > α,β-methylene ATP [6]. However, our recent binding study indicated that, whilst there appears to be a good correlation between the mucin-releasing potency and the ATPγ S 35 displacement potency among various nucleotides, the ATPγS 35 displacement potency of UTP was, surprisingly, lower than ATP [10].Despite a plethora of information regarding the P 2u receptor in various systems, great variations among these systems make it difficult to conclude whether or not these nucleotides indeed act through the same mechanism, especially in the regulation of airway mucin secretion. Therefore, in the present experiment, this problem was approached by directly comparing these two nucleotides using a primary airway epithelial cell culture system, which has been well characterized for secretion of mucin both biochemically and morphologically [11,12]. This is the first report which attempts to elucidate the biochemical mechanism of the nucleotide-induced mucin release at various levels, from receptor-binding to actual secretion.In the airway, mucus plays an important role in the host's defence, and its proper function is believed to be attributed mainly to the quality and quantity of mucus glycoproteins or mucins which are present in the mucus. These airway mucins are secreted by two types of cell; goblet...

Release of mucins from cultured airway surface epithelial cells can be stimulated by extracellular ATP via a P2-purinergic receptor-mediated mechanism (K. C. Kim and B. C. Lee. 1991. Br. J. Pharmacol. 103:1053-1056). In this report, we studied the mechanism by which extracellular ATP induces the mucin release. We found that: (1) ATP increased both mucin release and generation of inositol phosphates in a dose-dependent fashion, and their dose-effect relationships were almost superimposed; (2) the increases in both mucin release and the phosphatidylinositol phosphate (PI) turnover by extracellular ATP were partially, but almost equally, blocked by the pretreatment with pertussis toxin (42% for mucin release and 44% for PI turnover). We conclude that in cultured airway goblet cells extracellular ATP stimulates mucin release by a signal transduction mechanism, which seems to involve coupling of ATP-activated P2 purinoceptors with phospholipase C, at least in part, via pertussis toxin-sensitive GTP-binding proteins. This may be an important finding in understanding the regulation of mucin release by airway goblet cells, since a number of agents present in the airway could influence this signal transduction pathway and subsequently modulate the mucin secretion.

Surface epithelial cells dissociated from hamster tracheas and grown on a thick collagen gel in the presence of 5% fetal bovine serum become highly enriched with secretory cells at confluence. In the present communication, we have analyzed secretory products from this primary hamster tracheal surface epithelial (HTSE) cell culture. The secreted glycoconjugates included high-molecular-weight mucin-like glycoproteins (HMW MLGP) and proteoglycans that comprised 22% and 5% of the total [3H]glycoconjugates secreted when [3H]glucosamine was added as a metabolic precursor. Among the proteoglycans were hyaluronic acids (53%), heparan sulfate proteoglycans (29%), and chrondroitin sulfate proteoglycans (18%). Chondroitin sulfates were mostly 4-sulfated. On the other hand, the secreted lipids included cholesterol, phospholipids, and glycolipids, and most of them were associated with HMW MLGP.