Abstract
Ca2+ microdomains that form during the opening of voltage-gated Ca2+ channels have been implicated in regulating the kinetics of hormone and transmitter release. Direct assessment of the interaction between a single Ca2+ microdomain and a single secretory vesicle has been impossible because of technical limitations. Using evanescent field imaging of near-membrane micromolar Ca2+ concentration ([Ca2+]) and fluorescently labeled vesicles, we have observed exocytosis of individual chromaffin dense-core vesicles that was triggered by Ca2+ microdomains. Ca2+ microdomains selectively triggered the release of vesicles that were docked within 300 nm. Not all vesicles exposed to a Ca2+ microdomain were released, indicating that some vesicles are docked but are not ready for release. In addition to its established role as a trigger for release, elevated near-membrane [Ca2+] reduced the distance between docked vesicles and Ca2+ entry sites. Our results suggest a new mechanism for stimulation-dependent facilitation of exocytosis, whereby vesicles are moved closer to Ca2+ entry sites, thereby increasing a Ca2+ microdomain's efficacy to trigger vesicle fusion.
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Acknowledgements
We thank J. B. Sørensen for chromaffin cells and carbon-fiber electrodes, B. Barbour, K. Delaney, E. Neher and members of our labs for comments on the manuscript. Supported by the Ministère de la Recherche (ACI 'young investigator group' 5242 to M.O.), the Max-Planck Society and SFB 406 (to W.S. and T.M.) and the Alexander-von-Humboldt Foundation (to U.B. and M.O.).
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Becherer, U., Moser, T., Stühmer, W. et al. Calcium regulates exocytosis at the level of single vesicles. Nat Neurosci 6, 846–853 (2003). https://doi.org/10.1038/nn1087
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DOI: https://doi.org/10.1038/nn1087
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