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Isosmotic modulation of Ca 2+ ‐regulated exocytosis in guinea‐pig antral mucous cells: role of cell volume
Author(s) -
Fujiwara Shoko,
Shimamoto Chikao,
Katsu Kenichi,
Imai Yusuke,
Nakahari Takashi
Publication year - 1999
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1999.085aa.x
Subject(s) - exocytosis , extracellular , bumetanide , chemistry , ionomycin , acetylcholine , thapsigargin , intracellular , biophysics , medicine , endocrinology , microbiology and biotechnology , ion transporter , biochemistry , biology , secretion , membrane
1 Exocytotic events and changes of cell volume in mucous cells from guinea‐pig antrum were examined by video‐enhanced optical microscopy. 2 Acetylcholine (ACh) evoked exocytotic events following cell shrinkage, the frequency and extent of which depended on the ACh concentration. ACh actions were mimicked by ionomycin and thapsigargin, and inhibited by Ca 2+ ‐free solution and Ca 2+ channel blockers (Ni 2+ , Cd 2+ and nifedipine). Application of 100 μM W‐7, a calmodulin inhibitor, also inhibited the ACh‐induced exocytotic events. These results indicate that ACh actions are mediated by intracellular Ca 2+ concentration ([Ca 2+ ] i ) in antral mucous cells. 3 The effects of ion channel blockers on exocytotic events and cell shrinkage evoked by ACh were examined. Inhibition of KCl release (quinine, Ba 2+ , NPPB or KCl solution) suppressed both the exocytotic events and cell shrinkage evoked by ACh. 4 Bumetanide (inhibition of NaCl entry) or Cl − ‐free solution (increasing Cl − release and inhibition of NaCl entry) evoked exocytotic events following cell shrinkage in unstimulated antral mucous cells and caused further cell shrinkage and increases in the frequency of exocytotic events in ACh‐stimulated cells. However, Cl − ‐free solution did not evoke exocytotic events in unstimulated cells in the absence of extracellular Ca 2+ , although cell shrinkage occurred. 5 To examine the effects of cell volume on ACh‐evoked exocytosis, the cell volume was altered by increasing the extracellular K + concentration. The results showed that cell shrinkage increases the frequency of ACh‐evoked exocytotic events and cell swelling decreases them. 6 Osmotic shrinkage or swelling caused the frequency of ACh‐evoked exocytotic events to increase. This suggests that the effects of cell volume on ACh‐evoked exocytosis under anisosmotic conditions may not be the same as those under isosmotic conditions. 7 In antral mucous cells, Ca 2+ ‐regulated exocytosis is modulated by cell shrinkage under isosmotic conditions.