Evaluation of agonist selectivity with glutamate receptor ion channel sensors

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1. The magnitude of agonist-induced integrated single-channel current, corresponding to the number of ions passed through a single glutamate receptor (GluR) channel in bilayer lipid membranes (BLMs) during a unit time, was quanrified as a new measure of agonist selectivity. The agonist selectivity among the typical agonists, NMDA, L-glutamate and L-CCG-IC, in terms of the integrated single-channel current was in the order of L-CCG-IV>L-glutamate>NMDA.2. To quantify the ion-permeation ability of the recombinant ε1-4/ζ1 N-methyl-D-aspartate (NMDA) channels activated by agonists, the magnitude of agonist-induced integrated single-channel currents for the ε1-4/ζ1 NMDA receptor channels in BLMs was evaluated. It was found that the magnitude of L-glutamate-induced integrated current depends on ε-subunit composition and the signal transduction abilty of the ε1-4/ζ1 NMDA receptor is not parallel to its binding ability.3. The magnitude of Ca^<2+> release from GluR-incorporated liposomes, which was measured by a Ca^<2+> ion-selective electrode with a thin-layer mode, was proposed as a measure of agonist selectivity for NMDA receptor.4. A single-channel method for evaluating agonist selectivity in terms of the very number of Ca^<2+> ions passed through the ε4/ζ1 NMDA receptor ion channel in BLMs was proposed.