(Science: chemical) a fluorescent calcium chelating agent which is used to study intracellular calcium in many tissues.
The fluorescent and chelating properties of fura-2 aid in the quantitation of endothelial cell injury, in monitoring ATP-dependent calcium uptake by membrane vesicles, and in the determination of the relationship between cytoplasmic free calcium and oxidase activation in rat neutrophils.
Pharmacological action: chelating agents, fluorescent dyes.
chemical name: 5-Oxazolecarboxylic acid, 2-(6-(bis(carboxymethyl)amino)-5-(2-(2-(bis(carboxymethyl)amino)-5-methylphenoxy)ethoxy)-2-benzofuranyl)-5-oxazolecarboxylic acid.
Ca2+ imaging by fura-2
The development of fura-2 by Roger Tsien and collaborateurs in 1985 has been an important contribution to the better understanding of the role of calcium in cellular processes. Fura-2 (C44H47N3O24) is a Ca2+ indicator, a dye–molecule that binds Ca2+ with four carboxylgroups.
fura-2 molecule: the binding sites for calcium are the four carboxylgroups.
Its structure is derived from egta (Ethylen glycolbis(beta-amino-ethyl ether)) that has also 4 COOH-groups to bind calcium.
fura-2 is a calcium chelator which means that it is able to bind Ca2+ so that the ions are not able to perform a reaction with anything and easily can be transported.
This highly selective substance for calcium is nearly insensitive to slight fluctuations in the physiological range of the ph value.
The calcium affinity is very useful for physiological measurements, for having a diffusion constant of about 0,25 µM. This is in a range of cellular calcium signals (0,1-1 µM).
Advantages of fura-2
fura-2 is an improved fluorescent calcium probe to its precursor “Quin 2”: the first cell permeant calcium dye. The most interesting difference between fura-2 AM and other fluorescence dyes like Qin-2 is the ability of calcium to alter the wavelengths for quantitative meaning. Via fura-2 the intracellular calcium concentration can be displayed by using ratio values 340/380.
Rationing minimizes a number of negative effects which occur and disturb measurements like uneven dye loading, leakage of fura-2 and bleaching. Fura-2 dye provides the possibility to perform measurements for about 1 hour without significant bleaching.
even different thickness does not corrupt the result when using the ratio 340/380. With the help of the ratio values the exact intracellular calcium concentration of cells (single cells or mean value for cell population) can be easily calculated. But as it can be seen the sensitivity of fura-2 gets worse when calcium concentrations are above 1 µM.