title: The spatial pattern of exocytosis and post-exocytic mobility of synaptopHluorin in mouse motor nerve terminals.
abstract: We monitored the spatial distribution of exo- and endocytosis at 37 degrees C in mouse motor nerve terminals expressing synaptopHluorin (spH), confirming and extending earlier work at room temperature, which had revealed fluorescent 'hot spots' appearing in repeatable locations during tetanic stimulation. We also tested whether hot spots appeared during mild stimulation. Averaged responses from single shocks showed a clear fluorescence jump, but revealed no sign of hot spots; instead, fluorescence rose uniformly across the terminal. Only after 5-25 stimuli given at high frequency did hot spots appear, suggesting a novel initiation mechanism. Experiments showed that about half of the surface spH molecules were mobile, and that spH movement occurred out of hot spots, demonstrating their origin as exocytic sources, not endocytic sinks. Taken together, our results suggest that synaptic vesicles exocytose equally throughout the terminal with mild stimulation, but preferentially exocytose at specific, repeatable locations during tetanic stimulation.
authors.affiliation: Department of Physiology and Biophysics, University of Colorado Denver, Anschutz Medical Campus, Aurora, CO 80045, USA.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Gaffield
authors.forename: Lucia
authors.initials: L
authors.lastname: Tabares
authors.forename: William J
authors.initials: WJ
authors.lastname: Betz
mesh_terms: D000818:Animals; D004058:Diffusion; D004558:Electric Stimulation; D004705:Endocytosis / Q000502:physiology; D005089:Exocytosis / Q000502:physiology*; D036681:Fluorescence Recovery After Photobleaching; D049452:Green Fluorescent Proteins / Q000378:metabolism*; D007091:Image Processing, Computer-Assisted; D051379:Mice; D008822:Mice, Transgenic; D008856:Microscopy, Fluorescence; D009046:Motor Neurons / Q000502:physiology*; D017729:Presynaptic Terminals / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000378:metabolism*; D013570:Synaptic Membranes / Q000502:physiology; D013572:Synaptic Vesicles / Q000502:physiology*; D050988:Vesicle-Associated Membrane Protein 2 / Q000378:metabolism
chemical_list: D011993:Recombinant Fusion Proteins; D050988:Vesicle-Associated Membrane Protein 2; C514578:synaptopHIuorin; C494808:vesicle-associated membrane protein 2, mouse; D049452:Green Fluorescent Proteins