Thallium indicators

Thallium can be used as a surrogate ion to measure the activity of potassium and sodium channels and transporters.

Thallium Flux Assays and Indicators

Thallium Assays and Indicators

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.

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Thallium indicator forms and formats

Potassium and sodium channel assays using thallium flux

Cell permeable, acetoxymethyl group (AM) esters

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.

Reagents for improving indicator loading, retention and background suppression

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.

Be Brilliant! Explore our line of Thallium Indicators and Assays

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Image Products Excitation Emission Kd Price Quantity Action
Thallos AM product packaging with thallium (Tl+) ion sticker, dark background
Thallos AM
Best in class, green fluorescent, thallium (Tl⁺) indicator, membrane permeable. Works with potassium (K⁺), sodium (Na⁺), and monovalent cation channels, and transporters.
$242.00$545.00
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Thallos gold, thallium indicator for thallium flux assay, product packaging
Thallos Gold AM
Thallos Gold is a gold fluorescent (Ex/Em = 528/552 nm) intracellular thallium (Tl+) indicator. Red-shifted excitation and emission enable multiplexing with GFP-expressing cells or other green fluorescent indicators. Useful for fluorescence-based potassium channel assays and for studying a wide variety of monovalent cation channels (sodium channels), transporters, and GPCRs.
$242.00$545.00
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