title: Munc13-1 acts as a priming factor for large dense-core vesicles in bovine chromaffin cells.
abstract: In chromaffin cells the number of large dense-core vesicles (LDCVs) which can be released by brief, intense stimuli represents only a small fraction of the 'morphologically docked' vesicles at the plasma membrane. Recently, it was shown that Munc13-1 is essential for a post-docking step of synaptic vesicle fusion. To investigate the role of Munc13-1 in LDCV exocytosis, we overexpressed Munc13-1 in chromaffin cells and stimulated secretion by flash photolysis of caged calcium. Both components of the exocytotic burst, which represent the fusion of release-competent vesicles, were increased by a factor of three. The sustained component, which represents vesicle maturation and subsequent fusion, was increased by the same factor. The response to a second flash, however, was greatly reduced, indicating a depletion of release-competent vesicles. Since there was no apparent change in the number of docked vesicles, we conclude that Munc13-1 acts as a priming factor by accelerating the rate constant of vesicle transfer from a pool of docked, but unprimed vesicles to a pool of release-competent, primed vesicles.
authors.affiliation: Max-Planck-Institute for Biophysical Chemistry, Department of Membrane Biophysics, Am Fassberg 11, 37077 Göttingen, Germany.
authors.forename: U
authors.initials: U
authors.lastname: Ashery
authors.forename: F
authors.initials: F
authors.lastname: Varoqueaux
authors.forename: T
authors.initials: T
authors.lastname: Voets
authors.forename: A
authors.initials: A
authors.lastname: Betz
authors.forename: P
authors.initials: P
authors.lastname: Thakur
authors.forename: H
authors.initials: H
authors.lastname: Koch
authors.forename: E
authors.initials: E
authors.lastname: Neher
authors.forename: N
authors.initials: N
authors.lastname: Brose
authors.forename: J
authors.initials: J
authors.lastname: Rettig
mesh_terms: D000818:Animals; D001921:Brain; D002118:Calcium / Q000378:metabolism; D002395:Catecholamines / Q000378:metabolism; D002417:Cattle; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000166:cytology* / Q000378:metabolism; D003198:Computer Simulation; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D004553:Electric Conductivity; D005089:Exocytosis; D007700:Kinetics; D008561:Membrane Fusion; D008854:Microscopy, Electron; D008954:Models, Biological; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D010782:Photolysis; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D051381:Rats; D013572:Synaptic Vesicles / Q000378:metabolism; D013574:Synaptosomes / Q000378:metabolism; D014617:Vacuoles / Q000378:metabolism*
chemical_list: D002395:Catecholamines; D009419:Nerve Tissue Proteins; D020033:Protein Isoforms; C103912:Unc13a protein, rat; C085112:2-nitrophenyl-EGTA; D004533:Egtazic Acid; D002118:Calcium