Liposomes in the Study of Membrane Fusion in Neutrophils

Abstract

This chapter introduces lipid-mixing and content-mixing assays, which are useful for studying fusion in neutrophils. The advantages and disadvantages of both systems are also described. Lipid-mixing assays are easy to employ and can be used on any membrane. Lipid exchange could occur across apposed membrane surfaces. Attempts to label biological membranes with highly hydrophobic compounds could leave adherent micelles of the probe that, under suitable conditions, the membrane might dissolve or partition into available membranes, giving a false-positive signal. Membrane disruption due to lytic agents, added exogenously or generated endogenously also gives a false-positive signal. Thus, the action of a detergent might be interpreted as fusion, if viewed uncritically. The key to conducting unambiguous fusion studies is to use a content-mixing assay. In these assays, membrane vesicles (either natural or artificial) containing two different materials are allowed to fuse, such that the contents react within a single resulting vesicle. Devising a content-mixing assay is greatly simplified when endogenous vesicle contents can be manipulated.