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...

Citrus peel has been used in Asian traditional medicine for the treatment of cough, asthma, and bronchial disorders. However, the anti-inflammatory effect of quercetogetin (QUE), a polymethoxylated flavone isolated from the peel of citrus unshui is poorly understood. We investigated the anti-inflammatory effect and the molecular mechanisms of QUE in lipopolysaccharide (LPS)-induced RAW264.7 cells. QUE inhibited the production of NO and prostaglandin E2 by suppressing the LPS-induced expression of inducible nitric oxide synthase and cyclooxygenase-2 at both the mRNA and protein levels. QUE suppressed the production of proinflammatory cytokines, such as interleukin (IL)-1β, IL-6, and tumor necrosis factor-α. QUE also inhibited the translocation of the nuclear factor kappa B subunit, p65, into the nucleus by interrupting the phosphorylation of IκB-α in LPS-induced RAW 264.7 cells. Based on the finding that QUE significantly decreased p-ERK protein expression in LPS-induced RAW264.7 cells, we confirmed that suppression of the inflammatory process by QUE was mediated through the MAPK pathway. This is the first report on the strong anti-inflammatory effects of QUE, which is a compound that can potentially be used as a therapeutic agent for inflammatory diseases.