Research on synthetic anionophores has the long-term perspective of therapeutic applications in human medicine, and the lipid composition of the liposomes as model system should thus reflect that of mammalian cells. Commonly used lipids are EYPC (egg yolk phosphatidylcholine), POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine), and POPC/cholesterol mixtures (for structures of lipids see Figure ). We prefer to use the mixture of POPC with cholesterol in a 7:3 molar ratio since this is a good mimic for epithelial membranes and the combination of POPC and cholesterol gives more stable membranes and better reproducibility than when POPC is used alone. solution should be filtered. The exact concentration of lucigenin is not crucial for the quantification of transport (in contrast to the concentration of NaCl and the transporter:lipid ratio).