A fluorescent redox dye. Influence of several substrates and electron carriers on the tetrazolium salt—formazan reaction of Ehrlich ascites tumour cells

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Abstract
This study was performed to elaborate the best conditions for measuring the redox activity of Ehrlich ascites tumour cells by using a new tetrazolium salt, cyantolyl tetrazolium chloride (CTC). This tetrazolium salt forms a fluorescent water-insoluble formazan on reduction on the surface of intact vital cells. The influences of fixation and of various substrates and electron carriers on the cellular reduction of CTC were investigated quantitatively using an elution technique. The amount of formazan obtained after incubating vital cells with Meldola Blue as electron carrier was greater than that obtained with Methylene Blue, menadione, 2,6-dichloroindophenol, 1-methoxyphenazine methosulphate or phenazine methosulphate. Using flow cytometry, the formazan production per cell and, after staining the nuclear DNA, the distribution of the redox activity in the cell population can be visualized with satisfactory resolution. We conclude from our findings that dehydrogenases are only partially involved in the reduction of tetrazolium salts by intact cells and that a redox activity, probably related to a cell membrane-bound NAD(P)H—oxidase system, is mainly measured.