title: C(a2+)-dependent glutamate release involves two classes of endoplasmic reticulum Ca(2+) stores in astrocytes.
abstract: Astrocytes can modulate synaptic transmission by releasing glutamate in a Ca(2+)-dependent manner. Although the internal Ca(2+) stores have been implicated as the predominant source of Ca(2+) necessary for this glutamate release, the contribution of different classes of these stores is still not well defined. To address this issue, we cultured purified solitary cortical astrocytes and monitored changes in their internal Ca(2+) levels and glutamate release into the extracellular space. Ca(2+) levels were monitored by using the Ca(2+) indicator fluo-3 and quantitative fluorescence microscopy. Glutamate release was monitored by an L-glutamate dehydrogenase-linked detection system. Astrocytes were mechanically stimulated with a glass pipette, which reliably caused an increase in internal Ca(2+) levels and glutamate release into the extracellular space. Although we find that the presence of extracellular Cd(2+), a Ca(2+) channel blocker, significantly reduces mechanically induced glutamate release from astrocytes, we confirm that internal Ca(2+) stores are the predominant source of Ca(2+) necessary for this glutamate release. To test the involvement of different classes of internal Ca(2+) stores, we used a pharmacological approach. We found that diphenylboric acid 2-aminoethyl ester, a cell-permeable inositol 1,4,5-trisphosphate (IP(3)) receptor antagonist, greatly reduced mechanically induced glutamate release. Additionally, the preincubation of astrocytes with caffeine or ryanodine also reduced glutamate release. Taken together, our data are consistent with dual IP(3)- and caffeine/ryanodine-sensitive Ca(2+) stores functioning in the control of glutamate release from astrocytes.
authors.affiliation: Department of Cell Biology and Neuroscience, and Center for Nanoscale Science and Engineering, University of California, Riverside, California 92521, USA.
authors.forename: Xue
authors.initials: X
authors.lastname: Hua
authors.forename: Erik B
authors.initials: EB
authors.lastname: Malarkey
authors.forename: Vice
authors.initials: V
authors.lastname: Sunjara
authors.forename: Steven E
authors.initials: SE
authors.lastname: Rosenwald
authors.forename: Wen-Hong
authors.initials: WH
authors.lastname: Li
authors.forename: Vladimir
authors.initials: V
authors.lastname: Parpura
mesh_terms: D000814:Aniline Compounds; D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D005110:Extracellular Space / Q000378:metabolism; D005456:Fluorescent Dyes; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism*; D007091:Image Processing, Computer-Assisted; D007150:Immunohistochemistry; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D015388:Organelles / Q000378:metabolism / Q000648:ultrastructure; D010782:Photolysis; D010812:Physical Stimulation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012433:Ryanodine / Q000494:pharmacology; D014793:Visual Cortex / Q000166:cytology / Q000648:ultrastructure; D014966:Xanthenes
chemical_list: D000814:Aniline Compounds; D002614:Chelating Agents; D005456:Fluorescent Dyes; D005904:Glial Fibrillary Acidic Protein; D014966:Xanthenes; D012433:Ryanodine; C059715:Fluo-3; D018698:Glutamic Acid; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium