Interference of S-alkyl derivatives of glutathione with brain ionotropic glutamate receptors

The effects of glutathione, glutathione sulfonate and S-alkyl derivatives of glutathione on the binding of glutamate and selective ligands of ionotropic N-methyl-D-aspartate (NMDA) and non-NMDA receptors were studied with mouse synaptic membranes. The effects of glutathione and its analogues on Ca-45(2+) influx were also estimated in cultured rat cerebellar granule cells. Reduced and oxidized glutathione, glutathione sulfonate, S-methyl-, -ethyl-, -propyl-, -butyl- and -pentylglutathione inhibited the Na+-independent binding of L-[H-3]glutamate. They strongly inhibited also the binding of (S)-2-amino-3-hydroxy-5-[H-3]methyl-4-isoxazolepropionate [H-3]AMPA (IC50 values: 0.8-15.9 mu M). S-Alkylation of glutathione rendered the derivatives unable to inhibit [H-3]kainate binding. The NMDA-sensitive binding of L-[H-3]glutamate and the binding of 3-[(R)- 2-carboxypiperazin-4-yl][1,2-H-3]propyl-1-phosphonate ([H-3]CPP, a competitive antagonist at NMDA sites) were inhibited by the peptides at micromolar concentrations. The strychnine-insensitive binding of the NMDA coagonist [H-3]glycine was attenuated only by oxidized glutathione and glutathione sulfonate. All peptides slightly enhanced the use-dependent binding of [H-3]dizocilpine (MK-801) to the NMDA-gated ionophores. This effect was additive with the effect of glycine but not with that of saturating concentrations of glutamate or glutamate plus glycine. The glutamate- and NMDA-evoked influx of Ca-45(2+) into cerebellar granule cells was inhibited by the S-alkyl derivatives of glutathione. We conclude that besides glutathione the endogenous S-methylglutathione and glutathione sulfonate and the synthetic S-alkyl derivatives of glutathione act as ligands of the AMPA and NMDA receptors. In the NMDA receptor-ionophore these glutathione analogues bind preferably to the glutamate recognition site via their gamma-glutamyl moieties.