title: Vesicular proteins exocytosed and subsequently retrieved by compensatory endocytosis are nonidentical.
abstract: Upon exocytosis, synaptic vesicle proteins are released into the plasma membrane and have to be retrieved by compensatory endocytosis. When green fluorescent protein-labeled versions of the vesicle proteins synaptobrevin-2 and synaptotagmin-1 are overexpressed in rat hippocampal neurons, up to 30% are found on axonal membranes under resting conditions. To test whether and to what extent these plasma membrane-stranded proteins participate in exo-endocytic cycling, a new proteolytic approach was used to visualize the fate of newly exocytosed proteins separately from that of the plasma membrane-stranded ones. We found that both pools were mixed and that endocytosed vesicles were largely composed of previously stranded molecules. The degree of nonidentity of vesicular proteins exo- and endocytosed depended on stimulus duration. By using an antibody to the external domain of synaptotagmin-1, we estimated that under physiological conditions a few percent of vesicular proteins were located near the active zone, from where they were preferentially recycled upon stimulation.
authors.affiliation: Department of Membrane Biophysics, Max-Planck-Institute for Biophysical Chemistry, Am Fassberg 11, D-37077 Goettingen, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Wienisch
authors.forename: Jurgen
authors.initials: J
authors.lastname: Klingauf
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D004705:Endocytosis / Q000502:physiology*; D005089:Exocytosis / Q000502:physiology*; D006624:Hippocampus / Q000166:cytology; D008561:Membrane Fusion; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D013572:Synaptic Vesicles / Q000737:chemistry / Q000378:metabolism; D050863:Synaptotagmin I / Q000235:genetics / Q000378:metabolism*; D050988:Vesicle-Associated Membrane Protein 2 / Q000235:genetics / Q000378:metabolism*
chemical_list: D011993:Recombinant Fusion Proteins; D050863:Synaptotagmin I; C494312:Syt1 protein, rat; C494706:Vamp2 protein, rat; D050988:Vesicle-Associated Membrane Protein 2