Abstract
The high affinity, Na(+)-dependent, electrogenic glial L-glutamate transporters GLAST1 and GLT1, and two neuronal EAAC1 and EAAT4, regulate the neurotransmitter concentration in excitatory synapses of the central nervous system. We dissected the function of the individual transporters in the monogenic null allelic mouse lines, glast1(-/-) and eaac1(-/-), and the derived double mutant glast(-/-)eaac1(-/-). Unexpectedly, the biochemical analysis and the behavioral phenotypes of these null allelic mouse lines were inconspicuous. Inhibition studies of the Na(+)-dependent glutamate transport by plasma membrane vesicles and by isolated astrocytes of wt and glast1(-/-) mouse brains indicated the pivotal compensatory role of GLT1 in the absence particularly of GLAST1 and GLAST1 and EAAC1 mutant mice. In electrophysiological studies, the decay rate of excitatory postsynaptic currents (EPSCs) of Purkinje cells (PC) after selective activation of parallel and climbing fibers proved to be similar in wt and eaac1(-/-), but was significantly prolonged in glast1(-/-) PCs. Bath application of the glutamate uptake blocker SYM2081 prolonged EPSC decay profiles in both wt and double mutant glast1(-/-)eaac1(-/-) PCs by 286% and 229%, respectively, indicating a prominent role of compensatory glutamate transport in shaping glast1(-/-)eaac1(-/-) EPSCs.
Publication types
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Comparative Study
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Research Support, Non-U.S. Gov't
MeSH terms
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Amino Acid Transport System X-AG / genetics
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Amino Acid Transport System X-AG / physiology*
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Animals
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Animals, Newborn
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Astrocytes / drug effects
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Astrocytes / radiation effects
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Blotting, Western / methods
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Brain / cytology
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Brain / physiology
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Cells, Cultured
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Electric Stimulation / methods
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Embryo, Mammalian
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Excitatory Amino Acid Antagonists / pharmacology
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Excitatory Amino Acid Transporter 1 / deficiency*
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Excitatory Amino Acid Transporter 1 / genetics
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Excitatory Postsynaptic Potentials / drug effects
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Excitatory Postsynaptic Potentials / physiology
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Excitatory Postsynaptic Potentials / radiation effects
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Glutamates / pharmacology
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Glutamic Acid / metabolism
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Glutamic Acid / pharmacology
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Immunohistochemistry / methods
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In Situ Nick-End Labeling / methods
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In Vitro Techniques
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Mice
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Mice, Knockout
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Patch-Clamp Techniques / methods
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Piperazines / pharmacology
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Purkinje Cells / physiology*
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Quinoxalines / pharmacology
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RNA / isolation & purification
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Stem Cells / physiology
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Synaptic Transmission / genetics
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Synaptic Transmission / physiology*
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Time Factors
Substances
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Amino Acid Transport System X-AG
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Excitatory Amino Acid Antagonists
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Excitatory Amino Acid Transporter 1
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Glutamates
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Piperazines
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Quinoxalines
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2,3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline
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4-methylglutamic acid
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Glutamic Acid
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RNA
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3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid