Simultaneous determination of changes in the permeability of two different liposomes mimicking bacterial and eukaryotic cell membranes using ion-selective electrodes

Biologically active substance-induced changes in the permeability of two different liposomes mimicking bacterial and eukaryotic cell membranes were measured using K+- and Cs+-Selective electrodes simultaneously. Our method involves the loading of K+ in liposomes composed of egg phosphatidylcholine (PC)/cholesterol and of Cs+ in liposomes composed of egg phosphatidylethanolamine (PE)/egg phosphatidylglycerol (PG), and the release of K+ and Cs+ upon addition of a biologically active substance was monitored with both ion-selective electrodes. We analyzed the selective permeability-increasing ability of amphotericin B, a polyene antibiotic, on liposomes composed of egg PC/cholesterol and that of magainin, an amphiphilic peptide, on liposomes composed of egg PE/egg PG. The present method enabled us to precisely measure changes in the permeability of two different liposomes and to directly evaluate differences in the action of biologically active substances in situ.