The Impedance-based ‘transporter activity through receptor activation (TRACT) assay detects transport activity of the dopamine transporter (DAT, SLC6A3) via GPCR-mediated changes in cell morphology. The assay is based on the principal that Co-expressed GPCR-SLC pair share a common agonist/substrate. Activation of a GPCR will result in changes in cell morphology that are detected as changes in cellular impedance using the xCELLigence RTCA system. Active SLCs transport part of the substrate into the cell leaving a lower extracellular concentration of agonist to activate the GPCR and consequently an attenuated GPCR-mediated response can be observed which reflects SLC activity (Fig. 1). Treatment with DAT inhibitors will enhance the GPCR response which is a measure of SLC inhibition. The TRACT assay can be used to determine the potency (EC50) of (endogenous) G protein-coupled receptor (GPCR) agonists on JumpIn-DAT cells and enables the determination of inhibitory potency (IC50) of DAT inhibitors.