Multi-modal antidepressant-like action of 6- and 7-chloro-2-aminodihydroquinazolines in the mouse tail suspension test.

Rationale: 2-Amino-6-chloro-3,4-dihydroquinazoline (e.g., A6CDQ) represents a novel putative antidepressant originally thought to act through a 5-HT serotonin receptor antagonist mechanism.

N-Alkylated Analogs of 4-Methylamphetamine (4-MA) Differentially Affect Monoamine Transporters and Abuse Liability.

Clandestine chemists synthesize novel stimulant drugs by exploiting structural templates known to target monoamine transporters for dopamine, norepinephrine, and serotonin (DAT, NET, and SERT, respectively). 4-Methylamphetamine (4-MA) is an emerging drug of abuse that interacts with transporters, but limited structure-activity data are available for its analogs. Here we employed uptake and release assays in rat brain synaptosomes, voltage-clamp current measurements in cells expressing transporters, and calcium flux assays in cells coexpressing transporters and calcium channels to study the effects of increasing N-alkyl chain length of 4-MA on interactions at DAT, NET, and SERT.

Monoamine Transporters as Ionotropic Receptors.

It is well established that glutamate and GABA signal through both ionotropic and metabotropic receptors. Conversely, it is thought that, with one exception, monoamines (dopamine, serotonin, and norepinephrine) signal via metabotropic receptors. Given their capacity to generate fast-acting currents, I suggest that the monoamine transporters should be considered as ionotropic receptors.

A current view of serotonin transporters.

Serotonin transporters (SERTs) are largely recognized for one aspect of their function-to transport serotonin back into the presynaptic terminal after its release. Another aspect of their function, however, may be to generate currents large enough to have physiological consequences. The standard model for electrogenic transport is the alternating access model, in which serotonin is transported with a fixed ratio of co-transported ions resulting in net charge per cycle.

Dissociable effects of the prodrug phendimetrazine and its metabolite phenmetrazine at dopamine transporters.

Phendimetrazine (PDM) is a clinically available anorectic and a candidate pharmacotherapy for cocaine addiction. PDM has been hypothesized to function as a prodrug that requires metabolism to the amphetamine-like monoamine transporter substrate phenmetrazine (PM) to produce its pharmacological effects; however, whether PDM functions as an inactive prodrug or has pharmacological activity on its own remains unclear. The study aim was to determine PDM pharmacological mechanisms using electrophysiological, neurochemical, and behavioral procedures.

Chloride requirement for monoamine transporters.

This review focuses on the Cl(-) requirement for dopamine, serotonin, and norepinephrine (DA, 5-HT, and NE) transport and induced current via the transporters for these transmitters, DAT, SERT, and NET. Indirect evidence exists for the passage of Cl(-) ions through monoamine transporters; however, direct evidence is sparse. An unanswered question is why in some preparations, notably native neurons, it appears that Cl(-) ions carry the current through DAT, whereas in heterologous expression systems Na(+) ions carry the current often referred to as the uncoupled current.

Amphetamine activates calcium channels through dopamine transporter-mediated depolarization.

Amphetamine (AMPH) and its more potent enantiomer S(+)AMPH are psychostimulants used therapeutically to treat attention deficit hyperactivity disorder and have significant abuse liability. AMPH is a dopamine transporter (DAT) substrate that inhibits dopamine (DA) uptake and is implicated in DA release. Furthermore, AMPH activates ionic currents through DAT that modify cell excitability presumably by modulating voltage-gated channel activity.

Structural analysis of dopamine- and amphetamine-induced depolarization currents in the human dopamine transporter.

Amphetamine (AMPH) induces depolarizing currents through the human dopamine transporter (hDAT). Recently we discovered that the S(+) enantiomer of AMPH induces a current through hDAT that persists long after its removal from the external milieu. The persistent current is less prominent for R(-)AMPH and essentially absent for dopamine (DA)-induced currents.

Electrical coupling between the human serotonin transporter and voltage-gated Ca(2+) channels.

Monoamine transporters have been implicated in dopamine or serotonin release in response to abused drugs such as methamphetamine or ecstasy (MDMA). In addition, monoamine transporters show substrate-induced inward currents that may modulate excitability and Ca(2+) mobilization, which could also contribute to neurotransmitter release. How monoamine transporters modulate Ca(2+) permeability is currently unknown.

Comments on 'A quantitative model of amphetamine action on the serotonin transporter', by Sandtner et al., Br J Pharmacol 171: 1007-1018.

This article is a Commentary on Sandtner W, Schmid D, Schicker K, Gerstbrein K, Koenig X, Mayer FP, Boehm S, Freissmuth M and Sitte HH (2014). A quantitative model of amphetamine action on the 5-HT transporter. Br J Pharmacol 171: 1007–1018.

An N-terminal threonine mutation produces an efflux-favorable, sodium-primed conformation of the human dopamine transporter.

The dopamine transporter (DAT) reversibly transports dopamine (DA) through a series of conformational transitions. Alanine (T62A) or aspartate (T62D) mutagenesis of Thr62 revealed T62D-human (h)DAT partitions in a predominately efflux-preferring conformation. Compared with wild-type (WT), T62D-hDAT exhibits reduced [(3)H]DA uptake and enhanced baseline DA efflux, whereas T62A-hDAT and WT-hDAT function in an influx-preferring conformation.

Synthetic cathinones: chemical phylogeny, physiology, and neuropharmacology.

This mini-review summarizes the history of cathinone and its synthesized derivatives from early records to the present day, including the appearance of synthetic cathinones in the drug combination known as bath salts. Bath salts may consist of one compound (MDPV) or combinations of MDPV and one or more other synthetic cathinones, which may also appear alone without MDPV. We briefly review recent in vitro studies of bath salts components alone or in combination, focusing on pharmacological and biophysical studies.

"Deconstruction" of the abused synthetic cathinone methylenedioxypyrovalerone (MDPV) and an examination of effects at the human dopamine transporter.

Synthetic cathinones, β-keto analogues of amphetamine (or, more correctly, of phenylalkylamines), represent a new and growing class of abused substances. Several such analogues have been demonstrated to act as dopamine (DA) releasing agents. Methylenedioxypyrovalerone (MDPV) was the first synthetic cathinone shown to act as a cocaine-like DA reuptake inhibitor.

Bath salts components mephedrone and methylenedioxypyrovalerone (MDPV) act synergistically at the human dopamine transporter.

Background And Purpose: Bath salts is the street name for drug combinations that contain synthetic cathinone analogues, among them possibly mephedrone (MEPH) and certainly methylenedioxypyrovalerone (MDPV). In animal studies, cathinone and certain cathinone analogues release dopamine (DA), similar to the action of amphetamine (AMPH) and methamphetamine (METH). AMPH and METH act on the human DA transporter (hDAT); thus, we investigated MEPH and MDPV acting at hDAT.

4-(4-(dimethylamino)phenyl)-1-methylpyridinium (APP+) is a fluorescent substrate for the human serotonin transporter.

Monoamine transporters terminate synaptic neurotransmission and are molecular targets for antidepressants and psychostimulants. Fluorescent reporters can monitor real-time transport and are amenable for high-throughput screening. However, until now, their use has mostly been successful to study the catecholamine transporters but not the serotonin (5HT) transporter.

S(+)amphetamine induces a persistent leak in the human dopamine transporter: molecular stent hypothesis.

Background And Purpose: Wherever they are located, dopamine transporters (DATs) clear dopamine (DA) from the extracellular milieu to help regulate dopaminergic signalling. Exposure to amphetamine (AMPH) increases extracellular DA in the synaptic cleft, which has been ascribed to DAT reverse transport. Increased extracellular DA prolongs postsynaptic activity and reinforces abuse and hedonic behaviour.

A fluorescence displacement assay for antidepressant drug discovery based on ligand-conjugated quantum dots.

The serotonin (5-hydroxytryptamine, 5-HT) transporter (SERT) protein plays a central role in terminating 5-HT neurotransmission and is the most important therapeutic target for the treatment of major depression and anxiety disorders. We report an innovative, versatile, and target-selective quantum dot (QD) labeling approach for SERT in single Xenopus oocytes that can be adopted as a drug-screening platform. Our labeling approach employs a custom-made, QD-tagged indoleamine derivative ligand, IDT318, that is structurally similar to 5-HT and accesses the primary binding site with enhanced human SERT selectivity.

A conserved asparagine residue in transmembrane segment 1 (TM1) of serotonin transporter dictates chloride-coupled neurotransmitter transport.

Na(+)- and Cl(-)-dependent uptake of neurotransmitters via transporters of the SLC6 family, including the human serotonin transporter (SLC6A4), is critical for efficient synaptic transmission. Although residues in the human serotonin transporter involved in direct Cl(-) coordination of human serotonin transport have been identified, the role of Cl(-) in the transport mechanism remains unclear. Through a combination of mutagenesis, chemical modification, substrate and charge flux measurements, and molecular modeling studies, we reveal an unexpected role for the highly conserved transmembrane segment 1 residue Asn-101 in coupling Cl(-) binding to concentrative neurotransmitter uptake.

Amphetamine and methamphetamine differentially affect dopamine transporters in vitro and in vivo.

The psychostimulants d-amphetamine (AMPH) and methamphetamine (METH) release excess dopamine (DA) into the synaptic clefts of dopaminergic neurons. Abnormal DA release is thought to occur by reverse transport through the DA transporter (DAT), and it is believed to underlie the severe behavioral effects of these drugs. Here we compare structurally similar AMPH and METH on DAT function in a heterologous expression system and in an animal model.

Dopamine transporter/syntaxin 1A interactions regulate transporter channel activity and dopaminergic synaptic transmission.

The Caenorhabditis elegans (C. elegans) dopamine (DA) transporter (DAT-1) regulates DA signaling through efficient DA reuptake following synaptic release. In addition to its DA transport function, DAT-1 generates detectable DA-gated currents that may influence neuronal excitability.

Targeting the human serotonin transporter (hSERT) with quantum dots.

In this paper we report our work on the development of a human serotonin transporter (hSERT) antagonist that can be conjugated to quantum dots. This approach has been used to target and visualize the human serotonin transporter protein (hSERT). We demonstrate that labeling is blocked by the addition of high affinity hSERT antagonists such as paroxetine.

All aglow about presynaptic receptor regulation of neurotransmitter transporters.

Mounting evidence supports the idea that neurotransmitter transporters are subject to many forms of post-translational regulation typically associated with receptors and ion channels, including receptor and kinase-mediated changes in transporter phosphorylation, cell surface trafficking, and/or catalytic activation. Although hints of this regulation can be achieved with traditional radiolabeled substrate flux techniques, higher resolution methods are needed that can localize transporter function in situ as well as permit real-time monitoring of transport function without confounds associated with coincident receptor activation. The elegant study by Bolan et al.

Transporters as channels.

This review investigates some key aspects of transport mechanisms and recent advances in our understanding of this ubiquitous cellular process. The prevailing model of cotransport is the alternating access model, which suggests that large conformational changes in the transporter protein accompany cotransport. This model rests on decades of research and has received substantial support because many transporter characteristics are explained using its premises.

Na+, Cl-, and pH dependence of the human choline transporter (hCHT) in Xenopus oocytes: the proton inactivation hypothesis of hCHT in synaptic vesicles.

The recent cloning of the human choline transporter (hCHT) has allowed its expression in Xenopus laevis oocytes and the simultaneous measurement of choline transport and choline-induced current under voltage clamp. hCHT currents and choline transport are evident in cRNA-injected oocytes and significantly enhanced by the hCHT trafficking mutant L530A/V531A. The charge/choline ratio of hCHT varies from 10e/choline at -80 mV to 3e/choline at -20 mV, in contrast with the reported fixed stoichiometry of the Na+-coupled glucose transporter in the same gene family.