title: Blocking endocytosis enhances short-term synaptic depression under conditions of normal availability of vesicles.
abstract: It is commonly thought that clathrin-mediated endocytosis is the rate-limiting step of synaptic transmission in small CNS boutons with limited capacity for synaptic vesicles, causing short-term depression during high rates of synaptic transmission. Here, we show by analyzing synaptopHluorin fluorescence that 200 action potentials evoke the same cumulative amount of vesicle fusion, irrespective of the frequency of stimulation (5-40 Hz), implying the absence of vesicle reuse, since the method used (alkaline-trapping) measures only first-round exocytosis. After blocking all slow or specifically clathrin-mediated endocytosis, however, the same stimulation patterns cause a rapid stimulation-frequency-dependent release depression. This form of depression does not reflect insufficient vesicle supply, but appears to be the result of slow clearance of vesicular components from the release site. Our findings uncover an important yet overlooked role of endocytic proteins for release site clearance in addition to their well-characterized role in endocytosis itself.
authors.affiliation: Department of Membrane Biophysics, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany; Department of Cellular Biophysics, Institute for Medical Physics and Biophysics, University of Münster, 48149 Münster, Germany.
authors.forename: Yunfeng
authors.initials: Y
authors.lastname: Hua
authors.forename: Andrew
authors.initials: A
authors.lastname: Woehler
authors.forename: Martin
authors.initials: M
authors.lastname: Kahms
authors.forename: Volker
authors.initials: V
authors.lastname: Haucke
authors.forename: Erwin
authors.initials: E
authors.lastname: Neher
authors.forename: Jürgen
authors.initials: J
authors.lastname: Klingauf
mesh_terms: D033942:Adaptor Proteins, Vesicular Transport / Q000502:physiology; D000818:Animals; D004558:Electric Stimulation; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology*; D006624:Hippocampus / Q000378:metabolism / Q000502:physiology; D006835:Hydrazones / Q000494:pharmacology; D009474:Neurons / Q000378:metabolism / Q000502:physiology*; D061251:Primary Cell Culture; D051381:Rats; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D013572:Synaptic Vesicles / Q000378:metabolism*
chemical_list: D033942:Adaptor Proteins, Vesicular Transport; D006835:Hydrazones; C511794:N'-(3,4-dihydroxybenzylidene)-3-hydroxy-2-naphthahydrazide