Membrane-permeant AM ester form of Fluo-4 that can enter into into cells via incubation. Fluo-4 AM ester itself does not bind Ca2 , but it is readily hydrolyzed to Fluo-4 by endogenous esterases once the dye is inside the cells. Fluo-4 AM ester is often used to measure intracellular calcium in high throughput drug screening.    Fluo-4 is an analog of Fluo-3 with the two chlorine substituents replaced by fluorines, which results in increased fluorescence excitation at 488 nm that gives higher fluorescence signal. Fluo-4 has its absorption maximum at 494 nm, thus making it excitable by the argon-ion laser. Fluo-4 is essentially nonfluorescent without Ca2 present, but the fluorescence increases at least 100 times on Ca2 binding. Also, because Fluo-4 binds Ca2 more weakly (higher Kd) than do fura-2 and indo-1, it is more useful for measuring high transient Ca2 concentration during Ca2 spikes.    Fluo-4 AM ester can be used to detect intracellular free calcium by fluorescence microscopy, flow cytometry, or fluorescence microplate reader.    We also sell Fluo-4 as a membrane-impermeant pentapotassium salt version.    Orange red solid soluble in DMSO  Store -20°C and protect from light, especially when in solution  Ex/Em of Ca2 €“bound form: 494/506 nm  Kd for Ca2  in buffer: ~335 nM  C51H50F2N2O23  MW: 1096.95  [273221-67-3]