FLIPR(R) membrane potential dye measures changes of charges across the cell membrane, upon activation of SLC6A12. 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. SLC6A12 is a Na+ and Cl- dependent GABA/betaine transporter that mediates an electrogenic transport with the stoichiometry of 3 Na+, 1 Cl-, 1 GABA/betaine. As GABA transporter, it facilitates the termination of GABAergic signaling by transporting GABA together with sodium and chloride from the synaptic cleft into presynaptic neurons and surrounding glial cells; but it also plays an important role in osmoprotection of renal medullary cells as it facilitates the accumulation of the osmolyte betain.