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Cocaine is a naturally occurring and illicitly used psychostimulant drug. Cocaine acts at monoaminergic neurotransmitter transporters to block uptake of the monoamines, dopamine, serotonin and norepinephrine. The resulting increase of monoamines in the extracellular space underlies the positively reinforcing effects that cocaine users seek. In turn, this increase in monoamines underlies the development of addiction, and can also result in a number of severe side effects. Currently, cocaine is one of the most common illicit drugs available on the European market. However, cocaine is increasingly sold in impure forms. This trend is driven by cocaine dealers seeking to increase their profit margin by mixing ("cutting") cocaine with numerous other compounds ("adulterants"). Importantly, these undeclared compounds put cocaine consumers at risk, because consumers are not aware of the additional potential threats to their health. This review describes adulterants that have been identified in cocaine sold on the street market. Their typical pharmacological profile and possible reasons why these compounds can be used as cutting agents will be discussed. Since a subset of these adulterants has been found to exert effects similar to cocaine itself, we will discuss levamisole, the most frequently used cocaine cutting agent today, and its metabolite aminorex.

The human serotonin transporter (hSERT) mediates uptake of serotonin from the synaptic cleft and thereby terminates serotonergic signalling. We have previously found by single-molecule microscopy that SERT forms stable higher-order oligomers of differing stoichiometry at the plasma membrane of living cells. Here, we report that SERT oligomer assembly at the endoplasmic reticulum (ER) membrane follows a dynamic equilibration process, characterized by rapid exchange of subunits between different oligomers, and by a concentration dependence of the degree of oligomerization. After trafficking to the plasma membrane, however, the SERT stoichiometry is fixed. Stabilization of the oligomeric SERT complexes is mediated by the direct binding to phosphoinositide phosphatidylinositol-4,5-biphosphate (PIP2). The observed spatial decoupling of oligomer formation from the site of oligomer operation provides cells with the ability to define protein quaternary structures independent of protein density at the cell surface.

The human serotonin transporter (hSERT) mediates uptake of serotonin from the synaptic cleft and thereby terminates serotonergic signalling. We have previously found by single-molecule microscopy that SERT forms stable higher-order oligomers of differing stoichiometry at the plasma membrane of living cells. Here, we report that SERT oligomer assembly at the endoplasmic reticulum (ER) membrane follows a dynamic equilibration process, characterized by rapid exchange of subunits between different oligomers, and by a concentration dependence of the degree of oligomerization. After trafficking to the plasma membrane, however, the SERT stoichiometry is fixed. Stabilization of the oligomeric SERT complexes is mediated by the direct binding to phosphoinositide phosphatidylinositol-4,5-biphosphate (PIP2). The observed spatial decoupling of oligomer formation from the site of oligomer operation provides cells with the ability to define protein quaternary structures independent of protein density at the cell surface., The human serotonin transporter (SERT) mediates the uptake of neurotransmitters to terminate neuronal signalling. Here the authors use single-molecule imaging to get insight into the molecular origin of SERT oligomerization and their pre-set stoichiometry at the plasma membrane.

The eukaryotic secretory pathway allows synthesized proteins to leave the endoplasmic reticulum and makes its way to the cell surface where it carries out its individual functions. The intracellular pathway through the various cellular compartments comprises different coat protein complexes, namely coat protein complex II (COPII) and coat protein complex I (COPI). The excitatory amino acid transporter 3 (EAAT3) mediates the regulation of the synaptic transmission at the glutamatergic synapse by transporting the neurotransmitter glutamate. Our goal is to understand the key mediators of the secretory pathway who play a pivotal role in transporting the EAAT3 to the surface. The work focuses on looking at the EAAT3 as a cargo within the cells and following it through the anterograde pathway mediated by COPII. The knowledge gained from this work will be able to shed some light in the pathway of EAAT3 through the cell and can be further extrapolated to the other glutamate transporter family members. Furthermore...

Dopamine (DA) signaling is central to movement, cognition, and reward pathways in the CNS and presynaptic DA reuptake mediated by the DA transporter (DAT) terminates DA signaling. DAT is potently i...

Serotonin plays an important role as neurotransmitter in the brain in a number of circuits which can also be linked to reward and cognition. The transporters for these neurotransmitters are located...

The human serotonin transporter (hSERT) is responsible for the termination of synaptic serotonergic signaling. Using single molecule microscopy, we have shown previously that SERT forms higher oligomers at the plasma membrane of living cells; we found a variety of aggregation states of membrane-associated transporters, revealing molecular associations at least up to pentamers and demonstrating the coexistence of different degrees of oligomerization in a single cell. The oligomerization was found to be independent of SERT surface density, indicating a stable interaction of the subunits. We developed a special bleaching protocol to decipher the interaction kinetics of SERT oligomers; the complexes remained stable over several minutes in the live cell plasma membrane. Together, the results indicate kinetic trapping of SERT oligomers at the plasma membrane, subsequent to an equilibration which occurs at an unknown subcellular organelle.By evaluating the subunit stoichiometry of SERT in the endoplasmic reticulum (ER) we show here that the oligomerization is indeed chemically equilibrated at ER membranes; after trafficking to the plasma membrane, the SERT stoichiometry remains fixed. Furthermore, we show that the stabilization of the transporter complexes can be ascribed to the differences in the lipid composition of the plasma membrane and the ER. Upon alteration of the lipid composition the SERT complexes are liberated from kinetic trapping at the plasma membrane and their oligomeric size is significantly reduced. In conjunction with the use of SERT mutants exhibiting altered lipid binding capability, we could thus show that stable oligomerization of SERT at the plasma membrane is lipid-mediated.