Inhibition of serotonin transport by (+)McN5652 is noncompetitive

IntroductionImaging of the serotonergic innervation of the brain using positron emission tomography (PET) with the serotonin transporter (SERT) ligand [11 C] (+)McN5652 might be affected by serotonin in the synaptic cleft if there is relevant interaction between [11C] (+)McN5652 and serotonin at the SERT. The aim of the present study therefore was to pharmacologically characterize the interaction of [11C] (+)McN5652 and serotonin at the SERT.MethodsIn vitro saturation analyses of [3H]serotonin uptake into HEK293 cells stably expressing the human SERT were performed in the absence and presence of unlabelled (+)McN5652. Data were evaluated assuming Michaelis–Menten kinetics.ResultsUnlabelled (+)McN5652 significantly reduced the maximal rate of serotonin transport Vmax of SERT without affecting the Michaelis–Menten constant KM.ConclusionsThis finding indicates that (+)McN5652 inhibits serotonin transport through the SERT in a noncompetitive manner. This might suggest that [11C] (+)McN5652 PET is not significantly affected by endogenous serotonin.