title: Loose excitation-secretion coupling in astrocytes.
abstract: Astrocytes play an important housekeeping role in the central nervous system. Additionally, as secretory cells, they actively participate in cell-to-cell communication, which can be mediated by membrane-bound vesicles. The gliosignaling molecules stored in these vesicles are discharged into the extracellular space after the vesicle membrane fuses with the plasma membrane. This process is termed exocytosis, regulated by SNARE proteins, and triggered by elevations in cytosolic calcium levels, which are necessary and sufficient for exocytosis in astrocytes. For astrocytic exocytosis, calcium is sourced from the intracellular endoplasmic reticulum store, although its entry from the extracellular space contributes to cytosolic calcium dynamics in astrocytes. Here, we discuss calcium management in astrocytic exocytosis and the properties of the membrane-bound vesicles that store gliosignaling molecules, including the vesicle fusion machinery and kinetics of vesicle content discharge. In astrocytes, the delay between the increase in cytosolic calcium activity and the discharge of secretions from the vesicular lumen is orders of magnitude longer than that in neurons. This relatively loose excitation-secretion coupling is likely tailored to the participation of astrocytes in modulating neural network processing.
authors.affiliation: Celica Biomedical, Ljubljana, Slovenia.|Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia.
authors.forename: Nina
authors.initials: N
authors.lastname: Vardjan
authors.affiliation: Department of Neurobiology, Center for Glial Biology in Medicine, Civitan International Research Center, Atomic Force Microscopy & Nanotechnology Laboratories, Evelyn F. McKnight Brain Institute, University of Alabama at Birmingham, Birmingham, Alabama.
authors.forename: Vladimir
authors.initials: V
authors.lastname: Parpura
authors.affiliation: Celica Biomedical, Ljubljana, Slovenia.|Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia.
authors.forename: Robert
authors.initials: R
authors.lastname: Zorec
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000166:cytology / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D002450:Cell Communication / Q000502:physiology*; D002462:Cell Membrane / Q000502:physiology*; D005089:Exocytosis / Q000502:physiology*; D006801:Humans; D050600:SNARE Proteins / Q000378:metabolism
chemical_list: D050600:SNARE Proteins; D002118:Calcium
keywords: GPCR; SNAREs; astrocyte secretion; calcium homeostasis; exocytosis; vesicular release