The Ca²⁺ ionophore A-23187 is commonly used for in situ calibrations of fluorescent Ca²⁺ indicators, to equilibrate intracellular and extracellular Ca²⁺ concentrations and to permit Mn²⁺ to enter the cell to quench intracellular dye fluorescence. Although the intrinsic fluorescence of A-23197 is too high for use with UV-excitable calcium indicators like fura-2, indo-1 and quin-2 it is suitable for use with the visible light-excitable indicators, including fluo-4, fluo-3, Calcium Green and rhod-2. A-23187 can also be used to equilibrate extracelular and intrcellular Mg²⁺ concentrations, making it useful for calibrating Mg²⁺ indicators.

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