[3H](2S,4R)-4-methylglutamate: A novel ligand for the characterization of glutamate transporters

Abstract

[3H](2S,4R)-4-Methylglutamate ([3H]4MG), used previously as a ligand for low-affinity kainate receptors, was employed to establish a binding assay for glutamate transporters (GluTs), as 4MG has also been shown to have affinity for the glial GluTs, GLT1 and GLAST. In rat brain membrane homogenates in the presence of Na+ ions at 4°C, specific binding of [3H]4MG was rapid and saturable (t1/2 ≅ 15 min), representing > 90% of total binding. Dissociation of [3H]4MG occurred in a biphasic manner, however, saturation studies and Scatchard analysis indicated a single site of binding (nH = 0.85) and a Kd of 6.2 ± 0.8 μM with a Bmax of 111.8 ± 23.8 pmol/mg protein. Specific binding of [3H]4MG was Na+-d..