Three fluorescent probes for the flow-cytometric assessment of membrane potential in Saccharomyces cerevisiae.

Three fluorescent probes, tetramethyl rhodamine ethyl ester (TMRE), 3,3'-dipropylthiacarbocyanine iodide (diS-C3(3)) and 3,3'-dipropyloxacarbocyanine iodide (diO-C3(3)), were tested for their suitability as fluorescent indicators of membrane potential in Saccharomyces cerevisiae in studies performed by flow cytometry. For all these dyes the intensity of fluorescence of stained cells increased with probe concentration in the range of 60-3000 nmol/L. The optimum staining period was 15-20 min for diS-C3(3). Depolarization of cells by increased extracellular potassium level and by valinomycin elicited with all probes a drop in fluorescence intensity. In some yeast batches this depolarization was accompanied by a separation of subpopulations with different fluorescence properties.