-An observed downward slope of lucigenin fluorescence intensity over time after addition of the chloride pulse during transport experiments in absence of anionophores suggests a poor quality of the liposomal membrane or the presence of an anionophore as pollution. The latter can be picked up from the extrusion kit or a size-exclusion column previously used for the preparation of liposomes with a high concentration of highly active transporter pre-incorporated (see Section 4.2) after insufficient cleaning. Alternatively, in some cases the membrane is not completely impermeable to the chloride ions. A lower membrane quality is usually caused by a poor lipid quality, arising from using too old lipids, poor storage, not using freshly deacidified chloroform for lipid stock solution preparation, or inadequate handling of the lipids. Figure shows examples of poor 'blank' transport curves due to problems with the lipids. Preparing new lipid solutions and replacing the size-exclusion column are recommended in this case.