Fluo-4 AM Ester is the membrane-permeant form of Fluo-4. Fluo-4 AM ester itself does not bind Ca2+, but is readily hydrolyzed to Fluo-4 by intracellular esterases. Fluo-4, essentially nonfluorescent without Ca2, , shows an increase in fluorescence at least 100 times upon Ca2+ binding. It has a higher Kd than fura-2 and indo-1, making it more useful for measuring high transient intracellular Ca2+ concentrations during Ca2+ spikes. It can be used in high-throughput drug screening assays in live cells, and is detectable using fluorescence microscopy, flow cytometry, or fluorescence microplate reader. We also offer Fluo-4 as a membrane-impermeant pentapotassium salt version, Cat # 50019Features: Orange red solid soluble in DMSO; Store -20°C protected from light, especially in solution; Ex/Em nm (with Ca2+): 494/506 nm (after hydrolysis), excitable by the argon-ion laser; Kd for Ca2+ in buffer: ~335 nM (after hydrolysis); C51H50F2N2O23; MW: 1096.95; [273221-67-3]