Thallium can be used as a surrogate ion to measure the activity of potassium and sodium channels and transporters.
The thallium flux assay takes advantage of a Tl⁺-selective fluorescent indicator, Thallos, and the fact that potassium channels and transporters, as well as sodium channels and transporters, readily accept Tl⁺ as surrogate cation. When Tl⁺ is added to the outside of cells loaded with Thallos, Tl⁺ entering cells through ion channels and transporters permeable to Na⁺ or K⁺ results in a dramatic increase in fluorescence. Although the Tl+ flux assay is the most commonly associated with HTS of potassium channels, it is equally suitable for HTS of sodium channels and sodium transporters, as well as non-selective, monovalent cation channels.
(EX 490 nm, EM 515 nm) The best-in-class Tl⁺-sensitive fluorescent indicator. It boasts outstanding cell loading and excellent compatibility with a wide variety of detectors including fluorescent microscopes, plate readers, and flow cytometers using commonly available filter FITC filters.
(EX 525 nm, EM 550 nm) A red-shifted Tl⁺-sensitive fluorescent indicator that is less sensitive to acidic pH environments than Thallos. It boasts outstanding cell loading and excellent compatibility with a wide variety of detectors including fluorescent microscopes, plate readers, and flow cytometers using commonly available YFP filters.
In addition to individual dyes, we also offer the largest selection of Brilliant Thallium Assay kits with individually packaged reagents to provide you with the ultimate flexibility to optimize your ion channel assays. Our endpoint compatible, Brilliant Thallium Snapshot assay is designed to make thallium flux assays more accessible, enabling you to run functional ion channel screens without automation and on readily available, fluorescence-capable instruments. Learn more about our thallium assay kits for sodium and potassium channels here.
A localizable thallium indicator that can be selectively targeted to individual cells or organelles using HaloTag® technology. ION Thallos-HTL is a ligand for the HaloTag® enzyme. It can be used to conduct cell-specific potassium channel assays in mixed cell populations, or to probe organellar ion channels in their native environment. Cells expressing HaloTag® are required when using ION Thallos-HTL.
A localizable thallium indicator that can be selectively targeted to individual cells or organelles using HaloTag® technology. ION Thallos Gold-HTL is a ligand for the HaloTag® enzyme, and displays red-shifted excitation and emission relative to ION Thallos-HTL. It can be used to conduct cell-specific potassium channel assays in mixed cell populations, or to probe organellar ion channels in their native environment. Cells expressing HaloTag® are required when using this product.
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The native forms of Thallos and Thallos Gold are negatively charged and membrane impermeable. However, masking the negative charge using non-polar, ester-linked moieties (AM esters) allow the molecules to enter cells through passive diffusion. Once inside the cell, ubiquitous intracellular esterase enzymes promote rapid hydrolysis of the AM esters leaving the active, highly polar form of the indicator trapped inside the cell.
Although the AM form of thallium indicators readily cross the plasma membrane, there are other factors that can affect how well these dyes load into cells. Because Tl+-sensitive indicator are quite hydrophobic, it is common to use the non-ionic surfactant, Pluronic F-127, to improve its solubility in aqueous solution thus improving its loading into cells. Pluronic F-127 at the concentrations employed for loading indicators into cells is generally well tolerated. While Pluronic F-127 isn’t absolutely essential for loading these dyesinto cells, it is highly recommended.
Another factor that can affect cell loading and intracellular localization is the presence of transport proteins capable of transporting many ion-sensitive, fluorescent indicators. In many cell types, the activity of these transporters can result in compartmentalization of the indicators into intracellular compartments as well as extrusion of the indicators out of the cell. Both of these processes can dramatically reduce the signal-to-background levels and in some cell types (e.g. CHO cells), make adequate loading of Tl⁺-selective fluorescent indicators nearly impossible. Fortunately, inhibitors of these transport proteins can be an effective means of improving cytoplasmic localization and indicator retention. ION offers a convenient, 100X ION-Pro inhibitor solution that may be used in conjunction with any of our Tl⁺-sensitive fluorescent indicators.
