PPARα autocrine regulation of Ca2+-regulated exocytosis in guinea pig antral mucous cells: NO and cGMP accumulation

In antral mucous cells, acetylcholine (ACh, 1 mu M) activates Ca2+-regulated exocytosis, consisting of a peak in exocytotic events that declines rapidly (initial phase) followed by a second slower decline (late phase) lasting during ACh stimulation. GW7647 [a peroxisome proliferation activation receptor alpha (PPAR alpha) agonist] enhanced the ACh-stimulated initial phase, and GW6471 (a PPAR alpha antagonist) abolished the GW7647-induced enhancement. However, GW6471 produced the delayed, but transient, increase in the ACh-stimulated late phase, and it also decreased the initial phase and produced the delayed increase in the late phase during stimulation with ACh alone. A similar delayed increase in the ACh-stimulated late phase is induced by an inhibitor of the PKG, Rp8BrPETcGMPS, suggesting that GW6471 inhibits cGMP accumulation. An inhibitor of nitric oxide synthase 1 (NOS1), N-5-[imino(propylamino)methyl]-L-ornithine hydrochloride (N-PLA), also abolished the GW7647-induced-enhancement of ACh-stimulated initial phase but produced the delayed increase in the late phase. However, in the presence of N-PLA, an NO donor or 8BrcGMP enhanced the ACh-stimulated initial phase and abolished the delayed increase in the late phase. Moreover, GW7647 and ACh stimulated NO production and cGMP accumulation in antral mucosae, which was inhibited by GW6471 or N-PLA. Western blotting and immunohistochemistry revealed that NOS1 and PPAR alpha colocalize in antral mucous cells. In conclusion, during ACh stimulation, a PPAR alpha autocrine mechanism, which accumulates NO via NOS1 leading to cGMP accumulation, modulates the Ca2+-regulated exocytosis in antral mucous cells.