A flipr assay is a unique kinetic screen that enables the detection of agonists, antagonists, and allosteric modulators in one assay. This assay was developed to identify compounds that may act as agonists or antagonists at the iGluR1 channel.
FLIPR (Fluorescent Imaging Plate Reader) technology to measure Ca2+ flux in cells was first developed in the early 1990’s and has been a major contributor to HTS and lead optimization applications.
Purpose
The flipr assay is a highly sensitive fluorescent technique that detects G-protein coupled receptor (GPCR) activation by measuring intracellular calcium flux in cells. This technology has become an industry standard for identifying early leads against GPCRs and ion channel receptors during HTS and lead optimization applications.
This assay has been shown to produce robust, stable, and reproducible results at high concentrations of agonists. It also enables the detection of allosteric modulators and antagonists in one assay.
Methods
A flipr assay allows detection of agonists, antagonists, and allosteric modulators simultaneously. Test compounds are added in a first addition and a known agonist is added in a second addition to determine whether the compound is an agonist or an antagonist.
In this assay, ion channels (e.g., glutamate receptors) often desensitize very quickly to agonist exposure, resulting in the need for agents that decrease this rate of desensitization. These modulators can be injected with a high concentration of an agonist to create an ion channel that desensitizes slowly, or they can be added before the test compound is added in the first addition.
Limitations
The purpose of the flipr assay is to evaluate the agonist activity of glutamate receptors and other ion channels by monitoring Ca2+ mobilization in cells. It is a high-throughput, two-fluid addition assay with minimal wash steps that allows detection of agonists, antagonists, and allosteric modulators in one assay.
However, there are some limitations to the flipr assay. For example, some ion channels desensitize rapidly to agonist exposure and thus are not detectable with agonist alone on the FLIPR(tm).
Because of these limitations, it is important to optimize the signal concentration, buffer dilution, and reagents in order to ensure that the flipr assay produces robust and reproducible results. This requires preliminary experiments to determine the optimal combination of cell line, agonist and dye concentrations that provides the largest signal window.
Conclusions
The FLIPR membrane potential assay enables the detection of agonists, antagonists, and allosteric modulators. It provides a rapid response time and is good for detecting kinetic signal changes.
In addition, it is suitable for high-throughput screening with a minimal number of plates. The FLIPR system consists of a 5-W laser that illuminates 96 wells simultaneously and a cooled charge-coupled device (CCD) camera that takes a picture of the test plate bottom and records a signal for each well in real time.