[Measurement of cellular activity with the MTT test. Optimization of the method]

Since a few years activity of mitochondrial dehydrogenases has been determined by MTT-test as alternative method to measurement of the cellular activity and proliferation by incorporation of tritiated thymidine. In this test the tetrazolium salt MTT is converted into blue, insoluble formazan dye crystals, which have to be dissolved by a suitable extraction mixture. The present paper describes a modified extraction method using an isopropanol-dimethylformamide mixture acidified to pH 5.5. The modified method enables an optimal, easy to handle, less time and work consuming MTT-assay. A MTT concentration of 1 mg/ml was found to be optimal. The extinction maximum was identified at 566 nm.