FFN-102 is a fluorescent false neurotransmitter (FFN) that is a substrate for the dopamine transporter (DAT) and vesicular monoamine transporter 2 (VMAT2). It is a pH-dependent fluorescent probe that labels dopamine cell bodies, axons, and presynaptic terminals. It can also be used to monitor dopamine exocytosis. It has a pKa of 6.2 and displays pH-dependent excitation spectra of 340 and 370 nm at pH 5 and 7.4, respectively, which correspond to vesicular and cytoplasmic pH values. The emission spectrum of FFN-102 is pH-independent at 453 nm, but the intensity of emission is pH-dependent with a higher intensity at a pH of 7.4. FFN-102 inhibits DAT (13.6% at a concentration of 10 μM) and the serotonin (5-HT) receptor subtype 5-HT2c (Ki = ~3 μM) but does not bind to 37 other central nervous system receptors and transporters, including dopamine receptors, up to a concentration of 10 μM.
