A Calcein AM efflux assay to screen a wide range of compounds for multidrug resistance transporter activity Excitation: 528 nm | Emission: 617 nm Calcein AM is a membrane-permeant, non-fluorescent dye that enters cells passively. Once inside the cytosol of cells, intracellular esterases convert it to fluorescent Calcein (Ex/Em: 495 nm/515 nm), resulting in uniform cytosolic fluorescence. Drug efflux transporters, such as P-glycoprotein (Pgp, MDR1) and multidrug-resistance-associated protein (MRP1), actively extrude Calcein AM from inside the cell before esterases can convert it to Calcein. The presence of additional MDR substrates or inhibitors of MDR expression results in decreased Calcein AM efflux, causing a measurable increase in intracellular fluorescence. In addition to identifying MDR substrates and inhibitors, this kit can also be used to evaluate the activity of MDR transporters in cells. When following our protocol, ION’s MDR Activity kit provides enough reagents to make 100 mL of working solution, enough for ten 96- or 384-well plates or 80 flow cytometry samples. The actual number of assays will vary according to optimal dye concentrations for your application.