Zinquin ethyl ester is an analog of the widely used indicator TSQ. Although Zinquin ethyl ester itself is fluorescent, its fluorescence intensity is negligibly weak (1/30). Zinquin ethyl ester is membrane permeable, as are acetoxymethyl esters of calcium probes such as Fura 2-AM and Fluo 3-AM. Zinquin ethyl ester is thus useful to detect intracellular zinc ions. It forms a complex with a zinc ion with nitrogen atoms in the structure. This compound also forms a fluorescent complex with cadmium ion; however, detectable amounts of cadmium ions are not contained in normal living cells. Because the water solubility of Zinquin ethyl ester is poor, dimethylsulfoxide (DMSO) or ethanol is required as a solvent for preparing the stock solution.
2.4 mM Zinquin ethyl ester stock solution (1 mg Zinquin ethyl ester in 1 ml DMSO) Zinquin ethyl ester stock solution is stable for 1 month at -20ºC.
Suspend cells in Hanks Ebalanced salt solution (HBSS) to prepare 5-10 x 106 cells per ml medium.
Add Zinquin ethyl ester stock solution to the cell suspension to prepare 2.4 μM Zinquin ethyl ester (1/1000 vol of the cell suspension) as the final concentration.
Incubate the cell suspension at 37ºC for 30 min.
Wash the cells 3 times with HBSS and then prepare 2-5 x 106 cells per ml of cell suspension.
Determine the fluorescence intensity of each cell using a fluorescence microscope or a confocal laser microscope coupled with an image analyzer.
* Cell staining conditions depend on cell type, so it is necessary to optimize the conditions for each experiment.
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