To study the activity of different transporters or to compare activities of a transporter at different concentrations, it is convenient to do the experiments using a single large batch of liposomes. However, in the lucigenin assay, this is not possible due to gradual leaking of the dye from the liposomes (see Section 3.5). In order to avoid leakage from the liposomes, we propose the use of an alternative more hydrophilic bis-acridinium probe that would not partition into and diffuse through the lipid bilayers.