title: (1R,3S)-1-Aminocyclopentane-1,3-dicarboxylic acid (RS-ACPD) reduces intracellular glutamate levels in astrocytes.
abstract: (+/-)-1-Aminocyclopentane-trans-1,3-dicarboxylic acid (t-ACPD) is an equimolar mixture of two enantiomers: (1S,3R)-1-Aminocyclopentane-1,3-dicarboxylic acid (SR-ACPD) and 1R,3S-1-Aminocyclopentane-1,3-dicarboxylic acid (RS-ACPD). t-ACPD and SR-ACPD have been commonly used as agonists for metabotropic glutamate receptors (mGluR). Here we demonstrated that RS-ACPD, but not SR-ACPD, is transported into astrocytes with a K(m) of 6.51 +/- 2.38 mM and V(max) of 22.8 +/- 3.4 nmol/mg/min. This low-affinity transport is Na(+)-dependent and is competitively blocked by glutamate or other substrates for the glutamate transporter. RS-ACPD therefore is probably taken up by the glutamate transporter. Prolonged incubation with high levels of RS-ACPD (> 500 microM) induced significant swelling of astrocytes. At lower concentrations (100 microM), RS-ACPD reduced intracellular glutamate content ([Glu](i)) by > 50% without obvious morphological changes. The reduction in [Glu](i) was accompanied by an increase in [glutamine](i). The RS-ACPD's effect on [Glu](i) required glutamine and high levels of phosphate, suggesting that RS-ACPD inhibited phosphate-activated glutaminase (PAG). These data suggest that astrocytic PAG is actively involved in determining the equilibrium between intracellular glutamate and glutamine. By reducing [Glu](i), RS-ACPD reduces the amount of glutamate available for release.
authors.affiliation: Department of Neurology, University of Washington, Seattle, Washington, USA.
authors.forename: Z C
authors.initials: ZC
authors.lastname: Ye
authors.forename: B R
authors.initials: BR
authors.lastname: Ransom
authors.forename: H
authors.initials: H
authors.lastname: Sontheimer
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D048429:Cell Size / Q000187:drug effects; D002478:Cells, Cultured; D003515:Cycloleucine / Q000031:analogs & derivatives / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism*; D005972:Glutaminase / Q000037:antagonists & inhibitors; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D007424:Intracellular Fluid / Q000378:metabolism*; D008968:Molecular Conformation; D018696:Neuroprotective Agents / Q000494:pharmacology*; D011188:Potassium / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors
chemical_list: D004791:Enzyme Inhibitors; D018696:Neuroprotective Agents; D003515:Cycloleucine; C036361:1-amino-1,3-dicarboxycyclopentane; D018698:Glutamic Acid; D012964:Sodium; D005972:Glutaminase; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium