3 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-C-3(3)) and 3,3'-dipropyloxaca rbocyanine iodide (diO-C-3(3)), were tested for their suitability as f luorescent indicators of membrane potential in Saccharomyces cerevisia e in studies performed by now cytometry. For all these dyes the intens ity of fluorescence of stained cells increased with probe concentratio n in the range of 60-3000 nmol/L. The optimum staining period was 15-2 0 min for diS-C-3(3). Depolarization of cells by increased extracellul ar potassium level and by valinomycin elicited with all probes a drop in fluorescence intensity. In some yeast batches this depolarization w as accompanied by a separation of subpopulations with different fluore scence properties.