Chapter 4 Cell Membrane Potential Analysis

Abstract

Cytoplasmic and mitochondrial membrane potential (MP) changes may occur during the early stages of surface recepior-mediated activation processes related to the development, differentiated function, and pathology of a large number of cell types and are thought to play a role in signal transduction between the cell surface and the interior. Investigations have been facilitated by the development of methods for the flow cytometric (FCM) estimation of MP in single cells. This chapter discusses the principles, practical aspects, and limitations of such methods. The limits of accuracy and precision with which cell membrane potentials and changes can be measured by FCM are largely due to the population variance of fluorescence intensity, presumably reflecting cell-to-cell differences in numbers of dye-binding sites. This problem is largely eliminated when the repeated measurements of the fluorescence of a cyanine dye or other distributional probe of MP are made of the same cell at intervals using a static low-resolution or image cytometer. Bacterial membrane potentials are primarily dependent on metabolic activity, of which they are a sensitive indicator. Membrane potential changes substantially and rapidly in response to the availability or lack of suitable energy sources and is rapidly dissipated when the organism is killed by drugs or other agents.