title: Astrocytes contain a vesicular compartment that is competent for regulated exocytosis of glutamate.
abstract: Astrocytes establish rapid cell-to-cell communication through the release of chemical transmitters. The underlying mechanisms and functional significance of this release are, however, not well understood. Here we identify an astrocytic vesicular compartment that is competent for glutamate exocytosis. Using postembedding immunogold labeling of the rat hippocampus, we show that vesicular glutamate transporters (VGLUT1/2) and the vesicular SNARE protein, cellubrevin, are both expressed in small vesicular organelles that resemble synaptic vesicles of glutamatergic terminals. Astrocytic vesicles, which are not as densely packed as their neuronal counterparts, can be observed in small groups at sites adjacent to neuronal structures bearing glutamate receptors. Fluorescently tagged VGLUT-containing vesicles were studied dynamically in living astrocytes by total internal reflection fluorescence (TIRF) microscopy. After activation of metabotropic glutamate receptors, astrocytic vesicles underwent rapid (milliseconds) Ca(2+)- and SNARE-dependent exocytic fusion that was accompanied by glutamate release. These data document the existence of a Ca(2+)-dependent quantal glutamate release activity in glia that was previously considered to be specific to synapses.
authors.affiliation: Department of Cell Biology and Morphology, University of Lausanne, and Cellular Imaging Facility UNIL-CHUV-Technological Development Unit, Switzerland.
authors.forename: Paola
authors.initials: P
authors.lastname: Bezzi
authors.forename: Vidar
authors.initials: V
authors.lastname: Gundersen
authors.forename: José Luis
authors.initials: JL
authors.lastname: Galbete
authors.forename: Gerald
authors.initials: G
authors.lastname: Seifert
authors.forename: Christian
authors.initials: C
authors.lastname: Steinhäuser
authors.forename: Ethel
authors.initials: E
authors.lastname: Pilati
authors.forename: Andrea
authors.initials: A
authors.lastname: Volterra
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000378:metabolism* / Q000648:ultrastructure; D002352:Carrier Proteins / Q000096:biosynthesis* / Q000235:genetics; D002478:Cells, Cultured; D005089:Exocytosis / Q000502:physiology*; D018698:Glutamic Acid / Q000378:metabolism*; D006624:Hippocampus / Q000378:metabolism / Q000648:ultrastructure; D008565:Membrane Proteins / Q000096:biosynthesis / Q000235:genetics; D026901:Membrane Transport Proteins; D051381:Rats; D013572:Synaptic Vesicles / Q000378:metabolism / Q000648:ultrastructure; D022161:Transport Vesicles / Q000378:metabolism / Q000648:ultrastructure; D051040:Vesicle-Associated Membrane Protein 3; D050598:Vesicular Glutamate Transport Protein 1; D050599:Vesicular Glutamate Transport Protein 2; D033921:Vesicular Transport Proteins
chemical_list: D002352:Carrier Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; C493475:Slc17a6 protein, rat; C493466:Slc17a7 protein, rat; D051040:Vesicle-Associated Membrane Protein 3; D050598:Vesicular Glutamate Transport Protein 1; D050599:Vesicular Glutamate Transport Protein 2; D033921:Vesicular Transport Proteins; D018698:Glutamic Acid