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Docking of LDCVs Is Modulated by Lower Intracellular [Ca2+] than Priming

By Mathias Pasche, Ulf Matti, Detlef Hof, Jens Rettig and Ute Becherer


Many regulatory steps precede final membrane fusion in neuroendocrine cells. Some parts of this preparatory cascade, including fusion and priming, are dependent on the intracellular Ca2+ concentration ([Ca2+]i). However, the functional implications of [Ca2+]i in the regulation of docking remain elusive and controversial due to an inability to determine the modulatory effect of [Ca2+]i. Using a combination of TIRF-microscopy and electrophysiology we followed the movement of large dense core vesicles (LDCVs) close to the plasma membrane, simultaneously measuring membrane capacitance and [Ca2+]i. We found that a free [Ca2+]i of 700 nM maximized the immediately releasable pool and minimized the lateral mobility of vesicles, which is consistent with a maximal increase of the pool size of primed LDCVs. The parameters that reflect docking, i.e. axial mobility and the fraction of LDCVs residing at the plasma membrane for less than 5 seconds, were strongly decreased at a free [Ca2+]i of 500 nM. These results provide the first evidence that docking and priming occur at different free intracellular Ca2+ concentrations, with docking efficiency being the most robust at 500 nM

Topics: Research Article
Publisher: Public Library of Science
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Provided by: PubMed Central

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