Fura-2-acetoxymethyl ester, often abbreviated Fura-2AM, is a man-made membrane-permeant derivative of the ratiometric calcium indicator Fura-2 used in the biochemistry laboratory to measure cellular calcium concentrations by fluorescence. When added to cells, Fura-2AM crosses cell membranes and once inside the cell, the acetoxymethyl groups are removed by cellular esterases. Removal of the acetoxymethyl esters regenerates "Fura-2", the pentacarboxylate calcium indicator. Measurement of Ca2+-induced fluorescence at both 340 nm and 380 nm allows for calculation of calcium concentrations based 340/380 ratios. The equation to complete these calculations is as follows: