FLIPR(R) membrane potential dye measures changes of charges across the cell membrane, upon activation of SLC15A2. The assay allows the detection of ion channel and transporter modulation by increasing or decreasing the fluorescent signal as cellular membrane potential changes. When cells are depolarized dye enters the cells, causing an increase in fluorescent signal, conversely, cells hyperpolarization results in dye exit and decreased fluorescence. SLC15A2 belongs to the proton-coupled oligopeptide transporters (POTs) family, it is an electrogenic transporter that mediates the cellular uptake of di/tripeptides and many peptide-like drugs such as cefadroxil, valacyclovir and others, utilizing an inwardly directed proton gradient.