Pharmacological characterization of threo-3-methylglutamic acid with excitatory amino acid transporters in native and recombinant systems

J Neurochem. 2001 Apr;77(2):550-7. doi: 10.1046/j.1471-4159.2001.00253.x.

Abstract

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.

Publication types

  • Comparative Study

MeSH terms

  • 2-Amino-5-phosphonovalerate / pharmacology
  • ATP-Binding Cassette Transporters / antagonists & inhibitors*
  • ATP-Binding Cassette Transporters / genetics
  • Action Potentials / drug effects
  • Amino Acid Transport System X-AG
  • Animals
  • Aspartic Acid / metabolism
  • Carrier Proteins / antagonists & inhibitors*
  • Carrier Proteins / genetics
  • Cell Line
  • Cerebellum / drug effects
  • Cerebellum / metabolism
  • Cerebral Cortex / drug effects
  • Cerebral Cortex / metabolism
  • Dogs
  • Excitatory Amino Acid Transporter 1
  • Excitatory Amino Acid Transporter 2
  • Excitatory Amino Acid Transporter 3
  • Excitatory Amino Acid Transporter 4
  • Glutamate Plasma Membrane Transport Proteins
  • Glutamic Acid / analogs & derivatives
  • Glutamic Acid / metabolism
  • Glutamic Acid / pharmacology*
  • Hippocampus / drug effects
  • Hippocampus / metabolism
  • Kidney / cytology
  • Kinetics
  • Neurotransmitter Uptake Inhibitors / pharmacology*
  • Oocytes
  • Quinoxalines / pharmacology
  • Rats
  • Rats, Sprague-Dawley
  • Receptors, Glutamate / genetics
  • Receptors, Neurotransmitter / antagonists & inhibitors*
  • Receptors, Neurotransmitter / genetics
  • Recombinant Fusion Proteins / antagonists & inhibitors
  • Recombinant Fusion Proteins / genetics
  • Symporters*
  • Synaptosomes / metabolism
  • Xenopus laevis

Substances

  • 3-methylglutamic acid
  • ATP-Binding Cassette Transporters
  • Amino Acid Transport System X-AG
  • Carrier Proteins
  • Excitatory Amino Acid Transporter 1
  • Excitatory Amino Acid Transporter 2
  • Excitatory Amino Acid Transporter 3
  • Excitatory Amino Acid Transporter 4
  • Glutamate Plasma Membrane Transport Proteins
  • Neurotransmitter Uptake Inhibitors
  • Quinoxalines
  • Receptors, Glutamate
  • Receptors, Neurotransmitter
  • Recombinant Fusion Proteins
  • Slc1a1 protein, rat
  • Slc1a2 protein, rat
  • Slc1a3 protein, rat
  • Slc1a6 protein, rat
  • Symporters
  • 2,3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline
  • Aspartic Acid
  • Glutamic Acid
  • 2-Amino-5-phosphonovalerate