title: Actin- and Myosin-Dependent Vesicle Loading of Presynaptic Docking Sites Prior to Exocytosis.
abstract: Variance analysis of postsynaptic current amplitudes suggests the presence of distinct docking sites (also called release sites) where vesicles pause before exocytosis. Docked vesicles participate in the readily releasable pool (RRP), but the relation between docking site number and RRP size remains unclear. It is also unclear whether all vesicles of the RRP are equally release competent, and what cellular mechanisms underlie RRP renewal. We address here these questions at single glutamatergic synapses, counting released vesicles using deconvolution. We find a remarkably low variance of cumulative vesicle counts during action potential trains. This, combined with Monte Carlo simulations, indicates that vesicles transit through two successive states before exocytosis, so that the RRP is up to 2-fold higher than the docking site number. The transition to the second state has a very rapid rate constant, and is specifically inhibited by latrunculin B and blebbistatin, suggesting the involvement of actin and myosin.
authors.affiliation: Laboratory of Brain Physiology, CNRS UMR 8118, Paris Descartes University, 45 rue des Saints Pères, 75006 Paris, France.
authors.forename: Takafumi
authors.initials: T
authors.lastname: Miki
authors.affiliation: Laboratory of Brain Physiology, CNRS UMR 8118, Paris Descartes University, 45 rue des Saints Pères, 75006 Paris, France.
authors.forename: Gerardo
authors.initials: G
authors.lastname: Malagon
authors.affiliation: Laboratory of Brain Physiology, CNRS UMR 8118, Paris Descartes University, 45 rue des Saints Pères, 75006 Paris, France.
authors.forename: Camila
authors.initials: C
authors.lastname: Pulido
authors.affiliation: Laboratory of Brain Physiology, CNRS UMR 8118, Paris Descartes University, 45 rue des Saints Pères, 75006 Paris, France.
authors.forename: Isabel
authors.initials: I
authors.lastname: Llano
authors.affiliation: Max Planck Institute for Biophysical Chemistry, am Fassberg 11, D37077 Göttingen, Germany.
authors.forename: Erwin
authors.initials: E
authors.lastname: Neher
authors.affiliation: Laboratory of Brain Physiology, CNRS UMR 8118, Paris Descartes University, 45 rue des Saints Pères, 75006 Paris, France. Electronic address: alain.marty@parisdescartes.fr.
authors.forename: Alain
authors.initials: A
authors.lastname: Marty
mesh_terms: D000199:Actins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000818:Animals; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D002531:Cerebellum / Q000502:physiology; D004533:Egtazic Acid / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D005089:Exocytosis; D006576:Heterocyclic Compounds, 4 or More Rings / Q000494:pharmacology; D008561:Membrane Fusion / Q000187:drug effects; D008959:Models, Neurological; D009010:Monte Carlo Method; D009218:Myosins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D013572:Synaptic Vesicles / Q000187:drug effects / Q000378:metabolism*; D053778:Thiazolidines / Q000494:pharmacology
chemical_list: D000199:Actins; D019086:Bridged Bicyclo Compounds, Heterocyclic; D006576:Heterocyclic Compounds, 4 or More Rings; D053778:Thiazolidines; C472645:blebbistatin; D004533:Egtazic Acid; D009218:Myosins; C037068:latrunculin B