Fura-2, pentapotassium salt is a ratiometric fluorescent dye that binds to free intracellular calcium. It is membrane-impermeant and may be loaded into cells via microinjection or scrape loading.    A major use of Fura-2 is in drug discovery, for measuring intracellular calcium mobilization after activation of G protein-coupled receptors (GPCRs) and calcium channels. Upon calcium binding, the fluorescent excitation maximum of the indicator undergoes a blue shift from 363 nm (Ca2-free) to 335 nm (Ca2-saturated), while the fluorescence emission maximum is relatively unchanged at ~510 nm.    Light yellow solid soluble in DMSO  Store at 4°C and protect from light, especially in solution  Kd: 145 nM (22°C in pH 7.2 buffer)  &lamba; Ex/&lamba;Em (no Ca2) = 363/512 nm; &lamba; Ex/&lamba; Em (high Ca2) = 335/505 nm  ε (363 nm, no Ca2) = 27,000 M-1cm-1; ε (335 nm, high Ca2) = 35,000 M-1cm-1  C29H22K5N3O14  MW: 832  [113694-64-7]