A-23187, also known as Calcimycin or Calcium Ionophore III, is a calcium ionophore that rapidly equilibrates intracellular and extracellular calcium concentrations. It is commonly used for in situ calibrations of fluorescent calcium indicators. The ionophore allows Mn2 to enter the cells and quench intracellular fluorescence of calcium indicators.    White solid soluble in DMSO  Store at 4°C and protect from light  C29H37N3O6  MW: 523.6  [52665-69-7]    Also see 4-bromo A-23187. Because 4-bromo A-23187 is nonfluorescent, it is preferred over the blue fluorescent A-23187 for calibrations of UV-excited Ca2 indicators such as Indo-1 and Fura-2 in order to keep background fluorescence to a minimum.