What is a calcium flux assay?

A calcium flux assay is a fluorescence-based assay used to detect intracellular calcium mobilization in cells and follow the release of Ca²⁺ into the cytoplasm. It involves preloading cells with a calciumsensitive fluorescent dye that is capable of crossing the cell membrane. The dye binds the calcium released from intracellular store and its fluorescence intensity increases. The change in the fluorescence intensity is directly correlated to the amount of intracellular calcium released into cytoplasm in response to ligand activation of receptor 15. In some cells, the anion transporter is particularly active. The addition of probencid, an inhibitor of anion transporter, is required for retention of this dye in the cell. 

Cell-based calcium flux assays are widely used in high throughput screening (HTS) to determine agonist-stimulated and antagonist-inhibited signaling through G protein-coupled receptors (GPCRs), a large family of integral membrane proteins and an important target class in drug discovery. Indicators such as fluo-4, Fluo-8, Cal-520, Calbryte™ 520, Fura-2 and Indo-1 have been extensively used in calcium flux assays.