Changes of plasma membrane permeability in neutrophils treated with polycations

The effects of the polycations poly-L-arginine, poly-L-lysine, and poly-ethyleneimine on rabbit neutrophil membrane permeability were compared. LDH release, quin2 release from quin2-loaded cells, and increase of indo 1 fluorescence were considered as measures for changes in membrane permeability. All polycations cause abundant LDH release. Quin2 release occurs more rapidly than LDH release, and the increase of indo 1 fluorescence is even faster. Apparently polycation-induced permeability changes occur gradually, allowing the influx (or efflux) of small molecules more rapidly than larger ones. A number of divalent and trivalent cations inhibit polycation-induced LDH and quin2 release in a way that resembles the inhibition of other cytotoxic agents described in literature. In the absence of extracellular Ca2+, the polycations induce little lysozyme release. In the presence of extracellular Ca2+, there is abundant lysozyme release, indicating that the influx of Ca2+ causes exocytosis. Exocytosis still occurs when Ca2+ is added some time after polycation addition, indicating that polycation treatment leaves the cells largely intact. All polycations tested have in common that they cause gradual changes in the permeability of the plasma membrane only, which opens the possibility to use them as membrane-permeabilizing agents for the study of Ca(2+)-induced exocytosis.