Validation of a Fluorescent Imaging Plate Reader Membrane Potential Assay for High-Throughput Screening of Glycine Transporter Modulators

Abstract

A fluorescent imaging plate reader (FLIPR) membrane potential (V_m) assay was evaluated for pharmacological characterization and high-throughput screening (HTS) of rat glycine transporter type 2 (rGlyT₂) in a stable rGlyT₂-HEK cell line. Data show that glycine activation of rGlyT₂ consistently results in a concentration-dependent V_m response on the FLIPR that is blocked by the potent and selective GlyT₂ antagonist 4-benzyloxy-3,5-dimethoxy-N-[1-dimethylamino-cyclopentyl)methyl]-benz-amide (Org-25543). Agonist and antagonist pharmacologies match those reported using conventional [³H]glycine uptake assays and electrophysiology. The glycine response is dependent on buffer ionic composition consistent with GlyT₂ physiology. Assay signal-to-background and coefficient of variation meets sufficient statistical criteria to conduct HTS. The results of a screen of the chemical inventory demonstrate that the assay is able to successfully identify and confirm GlyT₂ inhibitors. The advantages of this assay are its homogeneity, compatibility with both 96- and 384-well formats, and lack of radioactivity usage. Thus, the authors conclude that a fluorescence-based V_m assay on FLIPR is a viable approach for identification and pharmacological profiling of small molecule modulators of the electrogenic transporter rGlyT₂.