Thallium Flux Assays and Indicators

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

Thallium Assays and Indicators

Sodium (Na⁺) and potassium (K⁺) are the two most physiologically important monovalent metal cations. Transporters and ion channels for Na⁺ and K⁺ are found in every cell of every known organism and are critical for life. While drugs targeting these channels and transporters are used to treat indications ranging from type II diabetes, to epilepsies, to blood pressure, the therapeutic potential of this incredibly diverse set of proteins remains largely unknown. Therefore, ion channel assays are essential to promote the rapid discovery and evaluation of monovalent cation channels and transporters as potential therapeutic targets.

While ION’s class-leading Na⁺ and K⁺-sensitive fluorescent indicators are excellent tools for studying cellular Na⁺ and K⁺ dynamics, the relatively small changes in the intracellular concentrations of Na⁺ and K⁺ under normal physiological conditions can make Na⁺ and K⁺ indicators challenging to use, particularly for high-throughput screening (HTS) applications. In many instances, the thallium flux assay offers an outstanding alternative to fluorescent potassium and sodium 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.

HeLa cells loaded with Thallos in the presence (+) or the absence (-) of 0.5 mM Tl⁺

Indicator forms and formats

Thallos is a small, synthetic fluorochrome which incorporates a Tl⁺-binding moiety with excellent selectivity for Tl⁺ over most other physiologically relevant metal cations (e.g. Ca²⁺). Under conditions where Tl⁺ is not bound, the fluorescence of the sensor is significantly quenched. When Tl⁺ is bound, the quenching is relieved, and the fluorescence of the sensor dramatically increases.

Thallos is compatible with a wide variety of detectors including fluorescent microscopes, plate readers, flow cytometers. Over the last 20 years, since Dr. David Weaver invented the Tl⁺ flux assay, Tl⁺-sensitive indicators have found numerous uses including high-throughput screening (HTS) of potassium channel, sodium channel, other monovalent cation channels, some monovalent cation transporters, and the Gi/o class of G protein-coupled receptors (GPCR).

In addition to dye, we also offer a selection of Brilliant Thallium Assay kits with individually packaged reagents to provide you with the ultimate flexibility to optimize your ion channel assays. Our 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. 

(EX 490 nm, EM 515 nm) is 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 530 nm, EM 550 nm) Brilliant Thallium Gold includes Thallos Gold – ION’s gold fluorescent 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. 10 plates

(EX 490 nm, EM 515 nm) High-throughput, no wash thallium (Tl⁺) assay. The most flexible solution for measuring the activity of potassium (K⁺), sodium (Na⁺), and non-selective cation channels and their effectors including transporters and GPCRs. 10 plates

High-throughput, no wash thallium (Tl⁺) Snapshot assay. A thallium flux assay adaptation designed to work with standard plate readers, microscopes, flow cytometers, and more, for measuring flux through potassium (K⁺), sodium (Na⁺), and non-selective cation channels and their effectors including transporters and GPCRs. 10 plates

Cell permeable, acetoxymethyl group (AM) esters

The native form of Thallos is 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 Thallos indicator readily crosses the plasma membrane, there are other factors that can affect how well Thallos loads into cells. Because Thallos-AM is 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 Thallos into 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 outside 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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Brilliant thallium flux assay express packaging, dark background
A potassium channel assay, and so much more. ION’s high-throughput, no wash thallium (Tl⁺) flux assay is an optimal solution for measuring the activity of potassium (K⁺), sodium (Na⁺), and non-selective cation channels and their effectors including transporters and GPCRs. Our Express kit can also be customized for your screening needs - reducing waste, increasing reproducibility, and maximizing convenience. 100 plates
490/515
FITC, GFP
$3,270.00
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Min: 1
Step: 1
Thallium flux assay packaging
A potassium channel assay, and so much more. ION's high-throughput, no wash thallium (Tl⁺) flux assay is an optimal solution for measuring the activity of potassium (K⁺), sodium (Na⁺), and non-selective cation channels, transporters, and their effectors such as GPCRs. 10 plates
490/515
FITC, GFP
$192.00-$430.00
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Min: 1
Step: 1
Brilliant thallium gold thallium flux assay product packaging
A potassium channel assay, and so much more. Brilliant Thallium Gold includes Thallos Gold - ION’s gold fluorescent (Ex/Em = 528/552 nm) thallium (Tl+) indicator. Red-shifted excitation and emission enable multiplexing with GFP-expressing cells or other green fluorescent indicators. Useful for fluorescence-based potassium (K+) channel assays and for studying a wide variety of monovalent cation channels (sodium channels), transporters, and GPCRs.
530/550
YFP
$192.00-$430.00
Max:
Min: 1
Step: 1
Brilliant Thallium Gold Snapshot is a multi-instrument compatible assay solution for well plate-based, high-throughput measurements of thallium flux through potassium, sodium, and non-selective cation channels, as well as some Na+ or K+ transporters. Our patent-pending Snapshot technology generates a long-lasting signal so you can easily detect and quantify changes in ion channel or transporter activity on most fluorescence-capable instruments. The inclusion of Thallos Gold AM, our red-shifted thallium indicator, makes this kit the ideal option when using GFP-expressing cells to run potassium channel assays. 
530/550
YFP
$192.00-$430.00
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Min: 1
Step: 1
Brilliant thallium snapshot packaging with an image demonstration microscope compatibility
An endpoint-compatible potassium channel assay. ION's Brilliant Thallium Snapshot kit is a thallium flux assay adaptation designed to work with standard plate readers, microscopes, flow cytometers, and more, for measuring flux through potassium (K⁺), sodium (Na⁺), and non-selective cation channels, transporters, and their effectors, including GPCRs.
490/515
FITC, GFP
$192.00-$430.00
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Min: 1
Step: 1
Thallos AM product packaging with thallium (Tl+) ion sticker, dark background
Best in class, green fluorescent, thallium (Tl⁺) indicator, membrane permeable. Works with potassium (K⁺), sodium (Na⁺), and monovalent cation channels, and transporters.
490/515
DMSO
FITC, GFP
$220.00-$495.00
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Min: 1
Step: 1
Thallos gold, thallium indicator for thallium flux assay product packaging
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.
530/550
DMSO
YFP
$220.00-$495.00
Max:
Min: 1
Step: 1
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