Submitted on March 13, 2007
Accepted on August 1, 2007
[Cl-]i modulation of Ca2+-regulated exocytosis in ACh-stimulated antral mucous cells of guinea pig
Chikao Shimamoto1, Eiji Umegaki2, Ken-ichi Katsu2, Masumi Kato3, Shoko Fujiwara4, Takahiro Kubota3, and Takashi Nakahari3*
1 Internal Medicine, Osaka Medical College, Takatski, Osaka, Japan
2 Internal Medicine, Osaka Medical College, Takatsuki, Osaka, Japan
3 Physiology, Osaka Medical College, Takatsuki, Osaka, Japan
4 Takatsuki, Osaka, Japan; Physiology, Osaka Medical College, Takatsuki, Osaka, Japan
* To whom correspondence should be addressed. E-mail: takan{at}art.osaka-med.ac.jp.
The effects of intracellular Cl- concentration ([Cl- ]i ) on acetylcholine (ACh)- stimulated exocytosis were studied in guinea pig antral mucous cells using video microscopy. ACh activated an initial phase followed by a sustained phase. Bumetanide (20 µM) or a Cl- -free (NO3 - ) solution enhanced it, contrary, 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 (DNP) 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. Bumetanide and NO3 - solution enhanced the ACh-stimulated [Ca2+ ]i increase. [Cl- ]i measurements revealed that ACh decreases [Cl- ]i , and that bumetanide and NO3 - solution decreased [Cl- ]i and enhanced the ACh-evoked [Cl- ]i decrease; contrary, 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.
