Pharmacological characterization of threo-3-methylglutamic acid with excitatory amino acid transporters in native and recombinant systems.
The glutamate analog (+/-) threo-3-methylglutamate (T3MG) has recently been reported to inhibit the EAAT2 but not EAAT1 subtype of high-affinity, Na(+)-dependent excitatory amino acid transporter (EAAT). We have examined the effects of T3MG on glutamate-elicited currents mediated by EAATs 1-4 expressed in Xenopus oocytes and on the transport of radiolabeled substrate in mammalian cell lines expressing EAATs 1-3. T3MG was found to be an inhibitor of EAAT2 and EAAT4 but a weak inhibitor of EAAT1 and EAAT3. T3MG competitively inhibited uptake of D-[(3)H]-aspartate into both cortical and cerebellar synaptosomes with a similar potency, consistent with its inhibitory activity on the cloned EAAT2 and EAAT4 subtypes. In addition, T3MG produced substrate-like currents in oocytes expressing EAAT4 but not EAAT2. However, T3MG was unable to elicit heteroexchange of preloaded D-[(3)H]-aspartate in cerebellar synaptosomes, inconsistent with the behavior of a substrate inhibitor. Finally, T3MG acts as a poor ionotropic glutamate receptor agonist in cultured hippocampal neurons: concentrations greater than 100 microM T3MG were required to elicit significant NMDA receptor-mediated currents. Thus, T3MG represents a pharmacological tool for the study of not only the predominant EAAT2 subtype but also the EAAT4 subtype highly expressed in cerebellum.
Eliasof
S
S
Neurocrine Biosciences Inc., San Diego, California, USA Wyeth Neuroscience, Wyeth-Ayerst Research, Princeton, New Jersey, USA.
McIlvain
H B
HB
Petroski
R E
RE
Foster
A C
AC
Dunlop
J
J
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D018528:ATP-Binding Cassette Transporters / Q000037:antagonists & inhibitors* / Q000235:genetics; D000200:Action Potentials / Q000187:drug effects; D027322:Amino Acid Transport System X-AG; D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism; D002352:Carrier Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics; D002460:Cell Line; D002531:Cerebellum / Q000187:drug effects / Q000378:metabolism; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism; D004285:Dogs; D027341:Excitatory Amino Acid Transporter 1; D027342:Excitatory Amino Acid Transporter 2; D050580:Excitatory Amino Acid Transporter 3; D050581:Excitatory Amino Acid Transporter 4; D050491:Glutamate Plasma Membrane Transport Proteins; D018698:Glutamic Acid / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology*; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism; D007668:Kidney / Q000166:cytology; D007700:Kinetics; D014179:Neurotransmitter Uptake Inhibitors / Q000494:pharmacology*; D009865:Oocytes; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D017470:Receptors, Glutamate / Q000235:genetics; D017981:Receptors, Neurotransmitter / Q000037:antagonists & inhibitors* / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000037:antagonists & inhibitors / Q000235:genetics; D027981:Symporters; D013574:Synaptosomes / Q000378:metabolism; D014982:Xenopus laevis
C425779:3-methylglutamic acid; D018528:ATP-Binding Cassette Transporters; D027322:Amino Acid Transport System X-AG; D002352:Carrier Proteins; D027341:Excitatory Amino Acid Transporter 1; D027342:Excitatory Amino Acid Transporter 2; D050580:Excitatory Amino Acid Transporter 3; D050581:Excitatory Amino Acid Transporter 4; D050491:Glutamate Plasma Membrane Transport Proteins; D014179:Neurotransmitter Uptake Inhibitors; D011810:Quinoxalines; D017470:Receptors, Glutamate; D017981:Receptors, Neurotransmitter; D011993:Recombinant Fusion Proteins; C493398:Slc1a1 protein, rat; C493395:Slc1a2 protein, rat; C493392:Slc1a3 protein, rat; C493389:Slc1a6 protein, rat; D027981:Symporters; C062865:2,3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline; D001224:Aspartic Acid; D018698:Glutamic Acid; D015763:2-Amino-5-phosphonovalerate