Nucleotide-induced mucin release from primary hamster tracheal surface epithelial cells involves the P-2u purinoceptor

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 ATP gamma S-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 ATP gamma S-35-binding (median inhibitory concentrations (IC50s) 240 vs 2.9 mu M); 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.