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 extra cellular 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 ep ithelial cells, ATP and UTP were compared in their abilities: 1) to di splace ATP gamma S-35-binding to intact cells; 2) to accumulate inosit ol phosphates; and 3) to stimulate mucin release, Finally, the presenc e 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-bin ding (median inhibitory concentrations (IC50s) 240 vs 2.9 mu M); 2) UT P 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 acid s (mRNAs) with a mouse P-2u receptor complementary deoxyribonucleic ac id (cDNA) probe revealed a single specific band (2.8 kb), partial sequ encing of which showed a great homology with those of human or mouse P -2u receptors. We conclude that, although both ATP and UTP are equipot ent in stimulating mucin release, their binding kinetics to the cell s urface are quite different, suggesting the presence of a common bindin g domain which may be responsible for the mucin release by these nucle otides, We suggest that the P-2u purinoceptor is likely to be responsi ble for mucin release by these nucleotides, probably via activation of phospholipase C.