Estimation of membrane potentials of individual lymphocytes by flow cytometry

The membrane potentials of individual cells can be estimated by flow cytometric quantitation of the cells' uptake of the fluorescent lipophilic cationic dye 3,3'-dihexyloxacarbocyanine iodide. Human lymphocytes separated from peripheral blood on Hypaque-Ficoll gradients are uniformly depolarized by gramicidin and hyperpolarized by valinomycin. Concanavalin A and phytohemagglutinin depolarize only a fraction of the lymphocytes. The flow cytometric technique allows precise detection of heterogeneous membrane potential responses to stimuli such as lectins; it could also provide a basis for sorting cells that respond differently to a given stimulus.