(Cl-)i modulation of Ca 2+ -regulated exocytosis in ACh-stimulated antral mucous cells

[Cl-](i) modulation of Ca2+ -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 Ca2+ -regulated exocytosis (an initial phase followed by a sustained phase). Bumetanide (20 mu M) or a Cl- -free (NO3-) solution enhanced it; in contrast, 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB, a Cl- channel blocker) decreased it and eliminated the enhancement induced by bumetanide or NO3- solution. ACh and Ca2+ 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 Ca2+ concentration([Ca2+](i)) measurements showed that bumetanide and NO3- solution enhanced the ACh-stimulated [Ca2+](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[Ca2+](i) increase and ATP-dependent priming. In conclusion, a decrease in [Cl-](i) accelerates ATP-dependent priming and [Ca2+](i) increase, which enhance Ca2+ -regulated exocytosis in ACh-stimulated antral mucous cells.