Estimation of membrane potential by flow cytometry.

In most living cells, differences between interior and exterior concentrations of ions (e.g., Na(+), K(+), Cl(-)) generate an electrical potential across the cytoplasmic membrane. Membrane potential, like other cellular parameters, may change early in the course of surface receptor-mediated cell activation processes related to the development, differentiated function, and pathology of a large number of cell types. Changes in ionic environment may play a role in transmembrane signaling in response to cell surface ligand-receptor interactions. Thus, it is frequently of scientific interest to estimate membrane potential in individual cells. This unit provides methods for accomplishing this goal by flow or static cytometry using any of a number of cationic or anionic lipophilic fluorescent probes known as distributional dyes. The first of the two protocols is able to estimate the membrane potential of eukaryotic or bacterial cells. The second is more accurate, but can only be used with bacteria.