However, the lucigenin assay has certain limitations, as the lucigenin probe can slowly leak out of liposomes and because it is commercially available as the dinitrate salt. For these reasons, we have employed the more hydrophilic lucigenin analogue SPBA and demonstrated that this does not leak out of liposomes, making it suitable for transport studies over longer times. Furthermore, the absence of nitrate ions allows to study chloride uniport without interference from chloride/nitrate antiport.