Ligand-Gated Ion-Channel Target Screening New Systems Enable Fast Compound Additions and Continuous Electrophysiological Recording

Cristian Ionescu-Zanetti, Ph.D
Jan 1, 2010 (Vol. 30, No. 1)

Introduction

Ligand-gated ion channels (LGICs) represent an important class of drug targets that play a critical role in the function of the central nervous system. Compounds acting on ligand-gated channels are used to treat a wide range of conditions.
Effective screening campaigns against these targets require both the ability to conduct true electrophysiology measurements at high throughput and the ability to measure real-time changes in current during compound addition. The real-time recording requirement is driven by the fact that many LGICs desensitize quickly after the application of an activator molecule. Ion-channel screening strategies can be rendered ineffective if the current is recorded following a long delay after the activating ligand is applied.
Of the few commercially available systems for automated electrophysiology, there is no solution that offers fast compound addition and meets the rigorous cost and throughput requirements of HTS. Therefore, strategies for large screens against ligand-gated targets have typically required alternate approaches from voltage-gated target screens.
LGIC screens often start with indirect fluorescence or radioligand binding assays. While useful because of their speed and relatively low cost, indirect assays have often produced false negatives and positives. Furthermore, these indirect assays have shown poor correlation with downstream electrophysiology assays.
The IonFlux HT platform from Fluxion Biosciences was developed to provide high-throughput patch-clamp measurements for a diverse range of ion-channel targets. The system enables fast compound additions and continuous electrophysiological recording, both of which are necessary to screen against fast-acting ligand-gated targets.
The IonFlux platform has a unique design based on standard well-plate formats and has a plate-reader style form factor. These attributes enable integration with standard HTS equipment including fluid-handling robots. In this article, we will describe assay characteristics and compound pharmacology for the GABAA receptor, a well-studied LGIC target.

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