title: Specificity and actions of an arylaspartate inhibitor of glutamate transport at the Schaffer collateral-CA1 pyramidal cell synapse.
abstract: In this study we characterized the pharmacological selectivity and physiological actions of a new arylaspartate glutamate transporter blocker, L-threo-ß-benzylaspartate (L-TBA). At concentrations up to 100 µM, L-TBA did not act as an AMPA receptor (AMPAR) or NMDA receptor (NMDAR) agonist or antagonist when applied to outside-out patches from mouse hippocampal CA1 pyramidal neurons. L-TBA had no effect on the amplitude of field excitatory postsynaptic potentials (fEPSPs) recorded at the Schaffer collateral-CA1 pyramidal cell synapse. Excitatory postsynaptic currents (EPSCs) in CA1 pyramidal neurons were unaffected by L-TBA in the presence of physiological extracellular Mg(2+) concentrations, but in Mg(2+)-free solution, EPSCs were significantly prolonged as a consequence of increased NMDAR activity. Although L-TBA exhibited approximately four-fold selectivity for neuronal EAAT3 over glial EAAT1/EAAT2 transporter subtypes expressed in Xenopus oocytes, the L-TBA concentration-dependence of the EPSC charge transfer increase in the absence of Mg(2+) was the same in hippocampal slices from EAAT3 +/+ and EAAT3 -/- mice, suggesting that TBA effects were primarily due to block of glial transporters. Consistent with this, L-TBA blocked synaptically evoked transporter currents in CA1 astrocytes with a potency in accord with its block of heterologously expressed glial transporters. Extracellular recording in the presence of physiological Mg(2+) revealed that L-TBA prolonged fEPSPs in a frequency-dependent manner by selectively increasing the NMDAR-mediated component of the fEPSP during short bursts of activity. The data indicate that glial glutamate transporters play a dominant role in limiting extrasynaptic transmitter diffusion and binding to NMDARs. Furthermore, NMDAR signaling is primarily limited by voltage-dependent Mg(2+) block during low-frequency activity, while the relative contribution of transport increases during short bursts of higher frequency signaling.
authors: Center for Structural and Functional Neuroscience, The University of Montana, Missoula, Montana, United States of America.
authors: Weinan
authors: W
authors: Sun
authors: Katie M
authors: KM
authors: Hoffman
authors: David C
authors: DC
authors: Holley
authors: Michael P
authors: MP
authors: Kavanaugh
mesh_terms: D027322:Amino Acid Transport System X-AG / Q000037:antagonists & inhibitors*; D000818:Animals; D001224:Aspartic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D008274:Magnesium / Q000494:pharmacology; D051379:Mice; D018345:Mice, Knockout; D009474:Neurons / Q000378:metabolism; D017966:Pyramidal Cells / Q000378:metabolism*; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism; D013379:Substrate Specificity; D009435:Synaptic Transmission / Q000187:drug effects
chemical_list: D027322:Amino Acid Transport System X-AG; D004791:Enzyme Inhibitors; C508335:L-beta-threo-benzyl-aspartate; D016194:Receptors, N-Methyl-D-Aspartate; D001224:Aspartic Acid; D008274:Magnesium