FluxOR™ thallium assay has been widely recognized for hERG activity test. This assay is optically based and can be performed on 96-well or 384-well plates as a homogenous assay for high-throughput screening (HTS) measurements of potassium ion channel and transporter activities.

Creative Bioarray provides FluxOR™ assays and services for HTS measurements of potassium ion channels in evaluating drug effects on potassium channel activity.

Fig.1 FluxOR™ thallium assay sensitivity to known pharmacologically active compounds

FluxOR™ thallium assay is carried out in a physiological, normal-chloride saline. Multiple potassium channels including Kv1.3, Kv7.2/Kv7.3, Kv11.1 (hERG), Kir1.1, Kir2.1, Kv1.1, Kv2.1 are expressed in cell lines. Using these cells, FluxOR™ assay can be run to identify and characterize channel-specific inhibitory compounds provided by customers. The FluxOR™ assay has been proven identified several known specific inhibitors of Kv7.2/7.3 or hERG, highlighting its potential to identify novel and more efficacious small-molecule modulators.

This assay is based on the permeability of potassium channels to thallium. To run the assay, cells are loaded with non-fluorescent, thallium-specific FluxOR™ dye. The thallium ions flow freely through open potassium channels, acting as a surrogate indicator of potassium ion channel activity. When potassium channels are opened by a stimulus, the activation of FluxOR™, a novel fluorescent dye with a high affinity for thallium can report channel activity showing a large fluorogenic response that is proportional to the number of open potassium channels on the cell, making it extremely useful for studying K⁺ channel targets.

The activity of ion channels and transporters that are permeant to thallium can be quantitatively indicated by the fluorogenic signal change. Fluorescence reported in the FluxOR™ system thus becomes a surrogate indicator of activity for any ion channel or transporter that is permeable to thallium.

Fig.2 Comparison of efficacy of selected compounds using Tl⁺ flux and whole-cell voltage-clamp assays

Highlights

• K⁺ channel specific: measuring ion flux in both voltage- and ligand-gated potassium channels.

• Fast: performing screens in high-throughput mode with reproducible results and excellent signal/noise ratio without quenching dye.

• Pharmacologically relevant: known blockers show dose-dependent inhibition in a large signal window.

• Rapid and robust high-throughput screening (HTS) of potassium channel targets in a novel equilibrium measurement, reproducibly giving IC₅₀ values that are predictive of block or modulation in lower-throughput platforms.

• Sensitive: low mM levels of extracellular thallium give large signals in high-throughput mode.

• Target flexibility and ease of operation: The assay provides a concentrated thallium solution and all necessary buffers, allowing a homogenous format that has been demonstrated for use with cells stably expressing hERG, as well as expression of other target channels.

References

1. Raphemot R, et al. High-throughput screening for small-molecule modulators of inward rectifier potassium channels. J Vis Exp. 2013; 27(71).

2. Du Y, et al. Development and Validation of a Thallium Flux-Based Functional Assay for the Sodium Channel Nav1.7 and Its Utility for Lead Discovery and Compound Profiling. ACS Chem. Neurosci. 2015; 6: 871–878.

Related Section

• Manual Patch-clamp Technique
• Automated Patch-clamp
• Multi-Electrode Array (MEA)
• FLIPR Detection System
• Optogenetics
• Neuronal Tract Tracing