title: Adult astroglia is competent for Na+/Ca2+ exchanger-operated exocytotic glutamate release triggered by mild depolarization.
abstract: Glutamate release induced by mild depolarization was studied in astroglial preparations from the adult rat cerebral cortex, that is acutely isolated glial sub-cellular particles (gliosomes), cultured adult or neonatal astrocytes, and neuron-conditioned astrocytes. K+ (15, 35 mmol/L), 4-aminopyridine (0.1, 1 mmol/L) or veratrine (1, 10 micromol/L) increased endogenous glutamate or [3H]D-aspartate release from gliosomes. Neurotransmitter release was partly dependent on external Ca2+, suggesting the involvement of exocytotic-like processes, and partly because of the reversal of glutamate transporters. K+ increased gliosomal membrane potential, cytosolic Ca2+ concentration [Ca2+]i, and vesicle fusion rate. Ca2+ entry into gliosomes and glutamate release were independent from voltage-sensitive Ca2+ channel opening; they were instead abolished by 2-[2-[4-(4-nitrobenzyloxy)phenyl]ethyl]isothiurea (KB-R7943), suggesting a role for the Na+/Ca2+ exchanger working in reverse mode. K+ (15, 35 mmol/L) elicited increase of [Ca2+]i and Ca2+-dependent endogenous glutamate release in adult, not in neonatal, astrocytes in culture. Glutamate release was even more marked in in vitro neuron-conditioned adult astrocytes. As seen for gliosomes, K+-induced Ca2+ influx and glutamate release were abolished by KB-R7943 also in cultured adult astrocytes. To conclude, depolarization triggers in vitro glutamate exocytosis from in situ matured adult astrocytes; an aptitude grounding on Ca2+ influx driven by the Na+/Ca2+ exchanger working in the reverse mode.
authors.affiliation: Department of Experimental Medicine, Pharmacology and Toxicology Section, University of Genoa, Genoa, Italy.
authors.forename: Silvio
authors.initials: S
authors.lastname: Paluzzi
authors.forename: Susanna
authors.initials: S
authors.lastname: Alloisio
authors.forename: Simona
authors.initials: S
authors.lastname: Zappettini
authors.forename: Marco
authors.initials: M
authors.lastname: Milanese
authors.forename: Luca
authors.initials: L
authors.lastname: Raiteri
authors.forename: Mario
authors.initials: M
authors.lastname: Nobile
authors.forename: Giambattista
authors.initials: G
authors.lastname: Bonanno
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D017077:Culture Media, Conditioned / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D018698:Glutamic Acid / Q000378:metabolism; D008561:Membrane Fusion / Q000187:drug effects / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D019831:Sodium-Calcium Exchanger / Q000187:drug effects / Q000378:metabolism*; D013574:Synaptosomes; D022161:Transport Vesicles / Q000187:drug effects / Q000378:metabolism; D014702:Veratrine / Q000494:pharmacology; D050496:Vesicular Glutamate Transport Proteins / Q000187:drug effects / Q000378:metabolism
chemical_list: D015220:Calcium Channels; D017077:Culture Media, Conditioned; D026902:Potassium Channel Blockers; D019831:Sodium-Calcium Exchanger; D050496:Vesicular Glutamate Transport Proteins; D018698:Glutamic Acid; D014702:Veratrine; D011188:Potassium; D002118:Calcium