Effects of glial glutamate transporter inhibitors on intracellular Na+ in mouse astrocytes.
The effects of inhibitors of the glial Na+/glutamate co-transporter on the intracellular Na+ concentration ([Na+](i)) were investigated in mouse cortical astrocytes. [Na+](i) was monitored by fluorescence microscopy on single astrocytes using the Na+-sensitive probe sodium-binding benzofuran isophtalate. Application of the competitive inhibitors threo-beta-hydroxyaspartate (THA) and trans-pyrrolidine-2,4-dicarboxylic acid (t-PDC) resulted in robust and reversible increases in [Na+](i) that were comparable in shape to the response to glutamate but about twice lower in amplitude. As previously observed with glutamate, the amplitude of the [Na+](i) response to these compounds was concentration-dependent with EC(50) values of 11.1 microM (THA) and 7.6 microM (t-PDC), as was the initial rate of [Na+](i) rise (EC(50) values of 14.8 microM for THA and 11.5 microM for t-PDC). Both compounds diminished the response to subsequent glutamate applications, possibly because of an inhibitory effect of the intracellularly-accumulated compounds. In comparison, the newly-developed compound threo-beta-benzyloxyaspartate (TBOA) alone did not cause any significant alteration of [Na+](i) up to a concentration of 500 microM . TBOA inhibited the [Na+](i) response evoked by 200 microM glutamate in a concentration-dependent manner with IC(50) values of 114 and 63 microM, as measured on the amplitude and the initial rate, respectively. The maximum inhibition of glutamate-evoked [Na+](i) increase by TBOA was approximately 70%. The residual response persisted in the presence of a non-NMDA receptor antagonist or the inhibitor of the GLT-1 glutamate transporters, dihydrokainate (DHK). In view of the complete reversibility of its effects, TBOA represents a very useful pharmacological tool for studies of glutamate transporters.
Institute of Physiology and Laboratory of Neurological Research, Department of Neurology, University of Lausanne Medical School, Rue du Bugnon 7, CH-1005 Lausanne, Switzerland. jean-yves.chatton@iphysiol.unil.ch
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Chatton
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Magistretti
D018528:ATP-Binding Cassette Transporters / Q000037:antagonists & inhibitors* / Q000378:metabolism; D027322:Amino Acid Transport System X-AG; D000818:Animals; D001224:Aspartic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D001253:Astrocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D001572:Benzofurans; D001667:Binding, Competitive / Q000187:drug effects; D002478:Cells, Cultured; D003998:Dicarboxylic Acids / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004988:Ethers, Cyclic; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005456:Fluorescent Dyes; D018698:Glutamic Acid / Q000378:metabolism / Q000494:pharmacology; D007424:Intracellular Fluid / Q000378:metabolism*; D007608:Kainic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D051379:Mice; D014179:Neurotransmitter Uptake Inhibitors / Q000494:pharmacology; D020033:Protein Isoforms / Q000037:antagonists & inhibitors / Q000378:metabolism; D011759:Pyrrolidines / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism*; D013237:Stereoisomerism
D018528:ATP-Binding Cassette Transporters; D027322:Amino Acid Transport System X-AG; D001572:Benzofurans; D003998:Dicarboxylic Acids; D004988:Ethers, Cyclic; D018691:Excitatory Amino Acid Antagonists; D005456:Fluorescent Dyes; D014179:Neurotransmitter Uptake Inhibitors; D020033:Protein Isoforms; D011759:Pyrrolidines; C120673:benzyloxyaspartate; C061665:sodium-binding benzofuran isophthalate; C011274:3-hydroxyaspartic acid; D001224:Aspartic Acid; D018698:Glutamic Acid; C020889:dihydrokainic acid; C083486:pyrrolidine-2,4-dicarboxylic acid; D012964:Sodium; D007608:Kainic Acid