Inhibition by Theanine of Binding of [³H]AMPA, [³H]Kainate, and [³H]MDL 105,519 to Glutamate Receptors

In an investigation of the mechanisms of the neuroprotective effects of theanine (gamma-glutamylethylamide) in brain ischemia, inhibition by theanine of the binding of [3H](RS)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), [3H]kainate, and [3H](E)-3-(2-phenyl-2-carboxyethenyl)-4,6-dichloro-1-H-indole-2-carboxylic acid (MDL 105,519) to glutamate receptors was studied in terms of its possible inhibiting effects on the three receptor subtypes (AMPA, kainate, and NMDA glycine), with rat cortical neurons. Theanine bound the three receptors, but its IC50 of theanine was 80- to 30,000-fold less than that of L-glutamic acid.