[Cl ]i modulation of Ca -regulated exocytosis in ACh-stimulated antral mucous cells of guinea pig

Shimamoto C, Umegaki E, Katsu K, Kato M, Fujiwara S, Kubota T, Nakahari T. [Cl ]i modulation of Ca -regulated exocytosis in ACh-stimulated antral mucous cells of guinea pig. Am J Physiol Gastrointest Liver Physiol 293: G824–G837, 2007. First published August 2, 2007; doi:10.1152/ajpgi.00125.2007.—The effects of intracellular Cl concentration ([Cl ]i) on acetylcholine (ACh)-stimulated exocytosis were studied in guinea pig antral mucous cells by video microscopy. ACh activated Ca -regulated exocytosis (an initial phase followed by a sustained phase). Bumetanide (20 M) or a Cl -free (NO3 ) solution enhanced it; in contrast, 5-nitro-2-(3phenylpropylamino)benzoic acid (NPPB, a Cl channel blocker) decreased it and eliminated the enhancement induced by bumetanide or NO3 solution. ACh and Ca dose-response studies demonstrated that NO3 solution does not shift their dose-response curves, and ATP depletion studies by dinitrophenol or anoxia demonstrated that exposure of NO3 solution prior to ATP depletion induced an enhanced initial phase followed by a sustained phase, whereas exposure of NO3 solution after ATP depletion induced only a sustained phase. Intracellular Ca concentration ([Ca ]i) measurements showed that bumetanide and NO3 solution enhanced the ACh-stimulated [Ca ]i increase. Measurements of [Cl ]i revealed that ACh decreases [Cl ]i and that bumetanide and NO3 solution decreased [Cl ]i and enhanced the ACh-evoked [Cl ]i decrease; in contrast, NPPB increased [Cl ]i and inhibited the [Cl ]i decrease induced by ACh, bumetanide, or NO3 solution. These suggest that [Cl ]i modulates [Ca ]i increase and ATP-dependent priming. In conclusion, a decrease in [Cl ]i accelerates ATP-dependent priming and [Ca ]i increase, which enhance Ca -regulated exocytosis in ACh-stimulated antral mucous cells.