Abstract
Indomethacin (IDM, 10 mu m), not aspirin (ASA; 10 mu m), enhanced the Ca2+-regulated exocytosis stimulated by 1 mu m acetylcholine (ACh) in guinea-pig antral mucous cells. Indomethacin inhibits prostaglandin G/H (PGG/H) and 15R-hydroperoxy-eicosatetraenoic acid (15R-HPETE) production from arachidonic acid (AA), while ASA inhibits PGG/H production but accelerates 15R-HPETE production. This suggests that IDM accumulates AA. Arachidonic acid (2 mu m) enhanced Ca2+-regulated exocytosis in antral mucous cells to a similar extent to IDM. Moreover, a stable analogue of AA, arachidonyltrifluoromethyl ketone (AACOCF(3)), also enhanced Ca2+-regulated exocytosis, indicating that AA, not products from AA, enhances Ca2+-regulated exocytosis. We hypothesized that AA activates peroxisome proliferation activation receptor alpha (PPAR alpha), because AA is a natural ligand for PPAR alpha. A PPAR alpha agonist (WY14643; 1 mu m) enhanced Ca2+-regulated exocytosis, and a PPAR alpha blocker (MK886; 50 mu m) abolished the enhancement of Ca2+-regulated exocytosis induced by AA, IDM, AACOCF(3) and WY14643. Western blotting and immunohistochemical examinations demonstrated that PPAR alpha exists in antral mucous cells. Moreover, MK886 decreased the frequency of Ca2+-regulated exocytosis activated by 1 mu m ACh or 2 mu m thapsigargin alone by 25-30%. Thus, ACh stimulates AA accumulation via an [Ca2+](i) increase, which activates PPAR alpha, leading to enhancement of Ca2+-regulated exocytosis in antral mucous cells. A novel autocrine mechanism mediated via PPAR alpha enhances Ca2+-regulated exocytosis in guinea-pig antral mucous cells.