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MUCOSAL BIOLOGY

cGMP modulation of ACh-stimulated exocytosis in guinea pig antral mucous cells

Departments of ¹Molecular Cell Physiology and ⁵Respiratory Molecular Medicine, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto; and Departments of ⁴Physiology and ²Internal Medicine and ³Central Research Laboratory (Nakahari Project), Osaka Medical College, Takatsuki, Japan

Submitted 28 July 2005 ; accepted in final form 14 January 2006

In guinea pig antral mucous cells, ACh stimulates the Ca²⁺-regulated exocytosis, which has a characteristics feature: an initial transient phase followed by a sustained phase. The effects of cGMP on ACh-stimulated exocytosis were studied in guinea pig antral mucous cells using video microscopy. cGMP enhanced the frequency of ACh-stimulated exocytotic events, whereas cGMP alone did not induce any exocytotic events under the ACh-unstimulated condition. cGMP did not stimulate either Ca²⁺ mobilization or cAMP accumulation. The Ca²⁺ dose-response studies demonstrated that cGMP shifted the dose-response curve upward with no shift to the lower concentration. This indicates that cGMP increased maximal responsiveness of the Ca²⁺-regulated exocytosis, but not the Ca²⁺ sensitivity. Moreover, under a condition of ATP depletion by dinitrophenol (DNP) or anoxia (N₂ bubbling), ACh evoked only a sustained phase in exocytotic events with no initial transient phase. However, ACh evoked an initial transient phase followed by a sustained phase with addition of cGMP before ATP depletion, whereas only a sustained phase was evoked in a case of cGMP addition after ATP depletion. Thus cGMP-induced enhancement in ACh-stimulated exocytotic events requires ATP, suggesting that cGMP modulates ATP-dependent priming of Ca²⁺-regulated exocytosis in antral mucous cells. In conclusion, cGMP increases the number of primed granules via acceleration of the ATP-dependent priming, which enhances the Ca²⁺-regulated exocytosis stimulated by ACh.

gastric mucin secretion; guanosine 3' -cyclic monophosphate; exocytosis; acetylcholine; intracellular calcium concentration

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