Arachidonic Acid/ppara Enhancement of Ca2+-Regulated Exocytosis in Antral Mucous Cells of Guinea Pig

Abstract

Indomethacin (IDM, 10 μM) enhanced the Ca2+-regulated exocytosis stimulated by 1 μM ACh in guinea-pig antral mucous cells, but not aspirin (ASA, 10 μM). The differences in pharmacological actions between IDM and ASA suggest that IDM accumulates arachidonic acid (AA), which enhances Ca2+-regulated exocytosis. AA (2 μM) enhanced Ca2+-regulated exocytosis in antral mucous cells similarly to IDM, moreover, an analogue of AA, AACOCF3 (Arachidonyltrifluoromethyl ketone, a PLA2 blocker) also enhanced it. These indicate that the Ca2+-regulated exocytosis is directly enhanced by AA, not by the products of the AA cascade, such as PGs, LXs and LTs. We examined the effects of MK886 (an inhibitor of peroxisome proliferation activation receptor α, PPARα) on the AA-induced enhancement of Ca2+-regulated exocytosis, because AA is a natural ligand for PPARα. MK-886 (40 μM) abolished the enhancement of Ca2+-regulated exocytosis induced by AA, IDM and AACOCF3. Moreover, WY14643 (a PPARα agonist) enhanced the Ca2+-regulated exocytosis, similarly to AA. MK-886 decreased the frequency of the Ca2+-regulated exocytosis activated by 1 μM ACh or thapsigargin by 25-30 %. Western blotting and immunohistochemical examinations demonstrated that PPARα exists in antral mucous cells. Thus, ACh stimulates AA accumulation via increases in [Ca2+]i, and then, AA activates PPARα, which enhances Ca2+-regulated exocytosis in antral mucous cells. A novel autocrine mechanism mediated via PPARα maintains Ca2+-regulated exocytosis of the antral mucous cells of guinea pig.