Calcein AM (calcein acetoxymethyl ester) is a non-fluorescent, uncharged molecule, which is freely permeable to the plasma membrane of viable cells. Upon entering live cells, calcein AM is cleaved by nonspecific esterases in the cytoplasm to form membrane-impermeant calcein, a fluorescent indicator with absorption and emission maxima of 494 and 517 nm, respectively. Calcein AM has wide-ranging applications in the fields of cell viability, cell-cell communication and cytotoxicity. In addition, calcein is a substrate for multidrug resistance-associated protein 1 (MRP1) and multidrug resistance protein 3 (MDR3, P-glycoprotein 3), which makes calcein AM a useful tool for studying these proteins and their regulation.
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