FFN206 (FFN= False Fluorescent Neurotrasmitter) is a fluorescent assay developed in intact cells for monoamine uptake. Compound FFN206 is a fluorescent SLC18A1/SLC18A2 substrate which was developed and allowed functional examination of VMAT1 and VMAT2 in cell culture, using fluorescence microscopy or microplate reader. It crosses the plasma membrane and accumulates into vesicles by SLC18A1 or SLC18A2 transport. SLC18A1 is a transporter protein expressed on vesicular membranes for the monoamines (dopamine, serotonin, norepinephrine, and histamine). While the SLC18A2 isoform is expressed in the monoaminergic neurons throughout the CNS, the SLC18A1 isoform is only expressed in endocrine/paracrine cells associated with the stomach, intestine, and sympathetic nervous system. It functions as antiporter (2H+ out/1 monoamine in) essential for monoamine uptake into vesicles.