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Agonist‐stimulated calcium decreases in ovine ciliated airway epithelial cells: role of mitochondria
Author(s) -
Salathe Matthias,
Ivonnet Pedro I.,
Lieb Thomas,
Bookman Richard J.
Publication year - 2001
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.1469-7793.2001.0013j.x
Subject(s) - extracellular , thapsigargin , chemistry , biophysics , calcium , intracellular , vanadate , cytosol , calcium signaling , membrane potential , plasma membrane ca2+ atpase , calcium in biology , acetylcholine , endocrinology , microbiology and biotechnology , medicine , biochemistry , atpase , biology , organic chemistry , enzyme
1 In ovine ciliated tracheal epithelial cells, acetylcholine (ACh) activates signal transduction pathways that not only transiently increase cytoplasmic Ca 2+ ([Ca 2+ ] i ) but also actively lower [Ca 2+ ] i . The pathway for decreasing [Ca 2+ ] i is clearly revealed after depletion of intracellular Ca 2+ stores by thapsigargin (Tg), 2,5‐di‐(tert‐butyl)‐1,4‐benzohydroquinone or NiCl 2 . Measurements with microinjected fura‐2 excluded a [Ca 2+ ] measurement artefact. 2 A four‐compartment model to simulate calcium transients in non‐excitable cells (consisting of a plasma membrane Ca 2+ pump and channel; Ca 2+ store with pump and channel; and cytosolic Ca 2+ buffer) could not account for the observed [Ca 2+ ] i decrease. We therefore explored, by simulation and experimentation, several different mechanisms that could account for it. 3 The ACh‐stimulated [Ca 2+ ] i decrease was not due to an inhibition of Ca 2+ influx (Ca 2+ channel blockers or absence of extracellular calcium had no effect), activation of a plasma membrane Ca 2+ ‐ATPase (two inhibitors, vanadate (30 mM) and lanthanum (10 mM), had no effect) or inhibition of the Na + ‐Ca 2+ exchanger (replacing extracellular Na + with N‐ methylglucamine had no effect). 4 The application of mitochondrial uncouplers (5 μM CCCP or 5 μM FCCP), eliminated the ACh‐induced [Ca 2+ ] i decrease. Addition of CCCP at the nadir of the decrease restored intracellular calcium levels of Tg‐treated cells to baseline faster than controls not exposed to mitochondrial uncouplers. CCCP application to naïve cells did not block the ACh‐induced transient increase in [Ca 2+ ] i . 5 These data suggest that ACh‐induced [Ca 2+ ] i decreases in ciliated cells are caused by stimulated Ca 2+ uptake into mitochondria.