Enhancement of Ca2+-regulated exocytosis by indomethacin in guinea-pig antral mucous cells:: arachidonic acid accumulation

Ca2+-regulated exocytosis is enhanced by an autocrine mechanism via the PGE(2)-cAMP pathway in antral mucous cells of guinea-pigs. The inhibition of the PGE(2)-cAMP pathway by H-89 (an inhibitor of protein kinase A, PKA) or aspirin (ASA, an inhibitor of cyclo-oxygenase, COX) decreased the frequency of ACh-stimulated exocytotic events by 60%. Indomethacin (IDM, an inhibitor of COX), however, decreased the frequency of ACh-stimulated exocytotic events only by 30%. Moreover, IDM increased the frequency of ACh-stimulated exocytotic events by 50% in H-89-treated or ASA-treated cells. IDM inhibits the synthesis of Prostaglandin (PGG/H) and (15R)-15-hydroxy-5,8,11 cis-13-trans-eicosatetraenoic acid (15R-HPETE), while ASA inhibits only the synthesis of PGG/H. Thus, IDM may accumulate arachidonic acid (AA). AACOCF(3) or N-(p-amylcinnamoyl) anthranilic acid (ACA; both inhibitors of phospholipase A(2), PLA(2)), which inhibits AA synthesis, decreased the frequency of ACh-stimulated exocytotic events by 60%. IDM, however, did not increase the frequency in AACOCF(3)-treated cells. AA increased the frequency of ACh-stimulated exocytotic events in AACOCF(3)- or ASA-treated cells, similar to IDM in ASA- and H-89-treated cells. Moreover, in the presence of AA, IDM did not increase the frequency of ACh-stimulated exocytotic events in ASA-treated cells. The PGE(2) release from antral mucosa indicates that inhibition of PLA(2) by ACA inhibits the AA accumulation in unstimulated and ACh-stimulated antral mucosa. The dose-response study of AA and IDM demonstrated that the concentration of intracellular AA accumulated by IDM is less than 100 n<smallcapitals>m</smallcapitals>. In conclusion, IDM modulates the ACh-stimulated exocytosis via AA accumulation in antral mucous cells.