Flow cytometric analysis of cell cycle‐dependent changes in cell thiol level by combining a new laser dye with hoechst 33342

By halogenation of methylfluoresceindiacetate (MFDA) or eosin‐diacetate, two new dyes for cellular thiol compatible with visible laser excitation have become available. These probes circumvent the use of an ultraviolet (UV)‐excitation system as required by bimane‐based dyes and allow combination with probes for other cellular parameters. The thiol dyes attain maximal staining after 10 min at 37°C, and fluorescence is sensitive to pre‐treatment with diethylmaleate but not to buthionine sulfoximine. In a dual‐laser system, analysis of the cellular thiol level as a function of cell cycle distribution can be achieved in viable cells by simultaneous staining with the bisbenzimidazole dye Hoechst 33342 and one of the halogenated dyes. Using this approach, we were able to show that cells in the G2 phase of the cell cycle were more sensitive to thiol depletion with diethylmaleate than were cells in the G1 compartment. The new thiol dyes allow a more flexible selection of wavelengths of excitation and emission for assessing changes in cellular thiol (glutathione and other thiol compounds) and allow this parameter to be examined as a function of cell cycle position.