Dopamine Transport by the Serotonin Transporter: A Mechanistically Distinct Mode of Substrate Translocation

Abstract

The serotonin transporter (SERT) is the principal mechanism for terminating serotonin (5HT) signals in the nervous system and is a site of action for a variety of psychoactive drugs including antidepressants, amphetamines, and cocaine. Here we show that human SERTs (hSERTs) and rat SERTs are capable of robust dopamine (DA) uptake through a process that differs mechanistically from 5HT transport in several unanticipated ways. DA transport by hSERT has a higher maximum velocity than 5HT transport, requires significantly higher Na+ and Cl− concentrations to sustain transport, is inhibited non-competitively by 5HT and is more sensitive to SERT inhibitors, including selective serotonin reuptake inhibitors (SSRIs). We use a thiol reactive methane thiosulfonate (MTS) reagent to modify a conformationally-sensitive cysteine residue to demonstrate that hSERT spends more time in an outward facing conformation when transporting DA than when transporting 5HT. Co-transfection of an inactive or an MTS-sensitive SERT with wild type SERT subunits reveals an absence of cooperative interactions between subunits during DA, but not 5HT transport. To establish the physiological relevance of this mechanism for DA clearance, we show using in vivo high-speed chronoamperometry that SERT has the capacity to clear extracellularly applied DA in the hippocampal CA3 region of anesthetized rats. Together, these observations suggest the possibility that SERT serves as a DA transporter in vivo and highlight the idea that there can be distinct modes of transport of alternative physiological substrates by SERT.

Stimulation of Dopamine Receptor D5 Expressed on Dendritic Cells Potentiates Th17-Mediated Immunity

“…2D) were detected in DCs. The human and rat SERT were recently described to mediate DA uptake (41). Notably, SERT mRNA expression was found in both iDCs and mDCs (Fig.…”

Drosophila melanogaster as a genetic model system to study neurotransmitter transporters

“…However, some processes in the adult brain, including those in the MB lobes, express dSERT but do not detectably label for 5HT. The function of dSERT at these sites is not clear but could conceivably involve uptake of a transmitter other than 5HT (Larsen et al, 2011), and perhaps the substrate of prt (see above).…”

Enhanced dopamine detection sensitivity by PEDOT/graphene oxide coating on in vivo carbon fiber electrodes

“…Observing the real-time kinetics of in vivo neurochemical signaling is paramount to uncovering these functionalities and furthering our understanding of brain function and dysfunction. Electrochemical methods, such as fast scan cyclic voltammetry (FSCV) and chronoamperometry, have been widely employed for the sub second detection of electroactive neurochemicals such as dopamine (Jones et al 1995; Kawagoe et al 1992; Larsen et al 2011; Taylor et al 2013; Taylor et al 2015; Wightman et al 1988), ascorbic acid (Cofan and Radovan 2008; Yoshimi and Weitemier 2014), norepinephrine (Park et al 2011), adenosine (Nguyen et al 2014; Ross et al 2014) and serotonin (Hashemi et al 2012; Hashemi et al 2009; Hashemi et al 2011). The high temporal resolution afforded by these electrochemical detection techniques allows for in vivo concentration monitoring of neurochemicals on a physiologically relevant timescale (Robinson et al 2011).…”