Elucidating the Cellular Effects of MDMA on the Serotonin Transporter (SERT)

Serotonin (5-HT) is a neurotransmitter with an integral role in regulating mood. Dysregulation of this system is implicated in disorders such as depression and withdrawal from drugs of abuse. 3,4- methylenedioxymethamphetamine (MDMA) or ‘Ecstasy’ is a commonly abused drug which primarily targets the serotonin transporter (SERT) and competes with 5-HT for uptake into the pre-synaptic neuron. This study focused on the cellular effects MDMA has on SERT, and how it is able to regulate SERT function. Previous studies have shown that MDMA is able to down-regulate SERT expression from the cell surface to intracellular vesicles, thereby decreasing 5-HT transport. How MDMA targets this regulatory pathway is unclear. Protein Kinase C (PKC) is a well-known regulator of SERT, and activation of PKC causes phosphorylation of SERT, targeting the transporter for internalization. Using rotating disc electrode voltammetry (RDEV) we show that MDMA causes a significant functional decrease of SERT in HEK-293 and N2A cells expressing GFP-hSERT. This MDMA-induced down-regulation was not observed when cells were pretreated with PKC inhibitor, Bis I. This data suggests that the MDMA-induced down-regulation of SERT occurs via PKC signaling pathways. Further investigations into the kinetics of the serotonin transporter did not show a change in the Vmax or Km values between the control and the MDMA-treated samples. This suggests that the functional down-regulation observed after MDMA treatment was not due to a decrease in SERT expression at the cell surface.