Release of [3H]GABA evoked by glutamate agonists from hippocampal slices: effects of dithiothreitol and glutathione.
The effects of dithiothreitol (DTT) and, reduced (GSH) and oxidized (GSSG), glutathione on the release of [3H]GABA evoked by glutamate and its agonists were studied in rat hippocampal slices. DTT had no effect on the basal release of [3H]GABA but it enhanced and prolonged the glutamate agonist-evoked release. This effect was abolished by (+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclohept-5,10-imine hydrogen maleate (MK-801), a noncompetitive NMDA antagonist, and blocked by Mg2+ ions. It was only slightly attenuated by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a non-NMDA receptor antagonist, and not affected by L-(+)-2-amino-3-phosphonopropionate (L-AP3), a selective antagonist of the metabotropic glutamate receptor. The effect of DTT on the NMDA-evoked release of GABA was only slightly affected by extracellular Ca2+ but completely blocked by verapamil even in the absence of Ca2+. GSH and GSSG attenuated or abolished the effects of DTT on the agonist-induced release of [3H]GABA. The results imply that the enhanced and prolonged release of GABA evoked by the coexistence of DTT and excitatory amino acids and attenuated by endogenous GSH and GSSG is a consequence of sustained activation of the NMDA receptor-governed ionophores, which contain functional thiol groups. DTT, GSH and GSSG may regulate the redox state and accessibility of these groups. In addition to the influx of extracellular Ca2+, DTT mobilizes Ca2+ from intracellular pools distinct from those regulated by metabotropic glutamate receptors.
Janáky
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R
Tampere Brain Research Center, Department of Biomedical Sciences, University of Tampere, Finland.
Varga
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V
Oja
S S
SS
Saransaari
P
P
D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000409:Alanine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D004229:Dithiothreitol / Q000494:pharmacology*; D016291:Dizocilpine Maleate / Q000494:pharmacology; D018755:GABA Agonists / Q000494:pharmacology*; D005978:Glutathione / Q000494:pharmacology*; D005998:Glycine / Q000494:pharmacology; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D016202:N-Methylaspartate / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D018094:Receptors, Metabotropic Glutamate / Q000037:antagonists & inhibitors; D014316:Tritium; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D018755:GABA Agonists; D018094:Receptors, Metabotropic Glutamate; C000211:2-amino-3-phosphonopropionic acid; D014316:Tritium; D005680:gamma-Aminobutyric Acid; D016202:N-Methylaspartate; D016291:Dizocilpine Maleate; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D005978:Glutathione; D008274:Magnesium; D000409:Alanine; D004229:Dithiothreitol; D005998:Glycine