The lucigenin assay is commonly used to study the exchange of chloride with another anion via an antiport mechanism, to avoid the build-up of a potential gradient across the membrane. For this reason, NaNO3 or other salts are encapsulated together with lucigenin (see Figure ), and the relatively high concentration of 225 mM is used to minimise differences in osmolality upon addition of 25 mM NaCl (a concentration that gives a strong quenching response, while avoiding full quenching). Figure shows the extent to which 25 mM NaCl causes additional quenching in NaNO3, NaHCO3, Na2SO4, and NaOAc solutions as used in transport studies. The additional quenching caused by the NaCl addition is lower when the KSV of the other anion is higher. The sensitivity of lucigenin to chloride is thus the best in NaNO3 and NO3 -is also considered relatively easy to transport.