FURA 2/AM is the cell-permeable ester form of FURA 2, which is a fluorescent chelator (Kd = 224 nM) selective for Ca2+ over other ions and offers 30 times greater fluorescence intensity than QUIN 2. FURA 2/AM is rapidly metabolized in the cell by cytoplasmic esterases; yielding the active dye FURA 2. FURA 2/AM can be used as a probe to determine calcium concentrations in many cellular systems, including: cardiac myocytes, vascular smooth muscle cells, and medullary collecting tubules. Spectral properties in the presence of low calcium concentrations (excitation max = 362 nm, emission max = 512 nm) differ from those during high calcium conditions (excitation max = 335 nm, emission max = 505 nm).