The effects of Cl⁻-free solution in Ca²⁺ regulated exocytosis in gunia pig antral mucous cells

Abstract

The Cell shrinkage is known to decrease intracellular Cl⁻ concentration [Cl⁻] _i. Cell shrinkage enhances Ca²⁺ regulated exocytosis in gunia pig antral mucous cells. In the present study, the effects of [Cl⁻]_i on the Ca²⁺ regulated exocytosis were examined, by replacing Cl⁻ of the perfusion solution with NO₃. The exocytotic events in gunia pig antral mucous cells were observed using video-microscopy. The Ca²⁺-regulated exocytosis was activated by acetylcholine (ACh). The Ca²⁺-regulated exocytosis consisted of two phases; an initial transient phase followed by a sustained phase. The replacement of Cl⁻ with NO₃ caused the both phase to increase, and shifted the ACh dose response curve to the lower concentration side. Similar enhancement was induced by bumetanide (an inhibitor Na⁺/K⁺/Cl⁻ cotransport, 20 μM). Thus, inhibition of Cl⁻ influx appears to enhance the ACh-evoked exocytotic events. Contrary NPPB (Cl⁻ channel blocker 2 μM), which inhibits Cl⁻ efflux, decreased the frequency of ACh-stimulated exocytosis and suppressed the enhancement induced by the Cl⁻-free solution. These results indicate that inihibition of Cl⁻ influx increases Ca²⁺ regulated exocytosis, contrary, inhibition of Cl⁻ efflux decreases it. Based on the observation, [Cl⁻]_i appears to play an important role in activation of Ca²⁺ regulated exocytosis. [Jpn J Physiol 55 Suppl:S73 (2005)]