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

Biologically active substance-induced changes in the permeability of two di fferent liposomes mimicking bacterial and eukaryotic cell membranes were me asured using K+- and Cs+-Selective electrodes simultaneously. Our method in volves the loading of K+ in liposomes composed of egg phosphatidylcholine ( PC)/cholesterol and of Cs+ in liposomes composed of egg phosphatidylethanol amine (PE)/egg phosphatidylglycerol (PG), and the release of K+ and Cs+ upo n addition of a biologically active substance was monitored with both ion-s elective electrodes. We analyzed the selective permeability-increasing abil ity of amphotericin B, a polyene antibiotic, on liposomes composed of egg P C/cholesterol and that of magainin, an amphiphilic peptide, on liposomes co mposed of egg PE/egg PG. The present method enabled us to precisely measure changes in the permeability of two different liposomes and to directly eva luate differences in the action of biologically active substances in situ.