SEARCH · PubMed Health

Results for “Membrane Transport Modulators”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5Linked to original sources

PubMed2004

Synthesis of 8-thiabicyclo[3.2.1]oct-2-enes and their binding affinity for the dopamine and serotonin transporters.

The reinforcing and stimulant properties of cocaine have been primarily associated with its propensity to bind to monoamine transport systems, in particular the dopamine transporter. Inhibition of the dopamine transporter then leads to an increase of synaptic dopamine with substantial pharmacological consequences. The search for medications for cocaine abuse has had a particular focus on tropane analogs of cocaine, and the interchange of nitrogen for oxygen in this class has led to potent and selective inhibitors of monoamine transport. Herein we report that 8-thiatrop-2-enes are highly potent and quite selective inhibitors of the dopamine transporter. The 3,4-dichlorophenyl-8-thiabicyclo[3.2.1]oct-2-ene (4f) is particularly potent (IC50=4.5 nM) and selective (800-fold) with respect to inhibition of the serotonin transporter.

Alkenes↗

PubMed2005

Vinylogous amide analogs of methylphenidate.

In an effort to produce compounds with longer durations of action, we attempted to synthesize ketone analogs of methylphenidate which, however, appear to be highly unstable due to a highly acidic proton alpha to the ketone and phenyl groups. Nevertheless, vinylogous amide by products have been synthesized and tested for activity at dopamine, norepinephrine, and serotonin transporters. The compounds were found to be weak inhibitors of monoamine reuptake despite rigid three dimensional structures that are quite similar to the global minimum of threo-(R,R)-methylphenidate. The structures were confirmed by X-ray crystallography.

Amides↗

PubMed2005

Quantitative analysis of immunolabeling for serotonin and for glutamate transporters after administration of imipramine and citalopram.

Serotonin (5-hydroxytryptamine, 5-HT) is an amine neurotransmitter derived from tryptophan and is important in brain systems regulating mood, emotional behavior, and sleep. Selective serotonin reuptake inhibitor (SSRI) drugs are used to treat disorders such as depression, stress, eating disorders, autism, and schizophrenia. It is thought that these drugs act to prolong the action of 5-HT by blocking reuptake. This may lead to decreased 5-HT content in the nerve fibers themselves; however, this has not previously been directly demonstrated. We have studied the effects of administration of two drugs, imipramine and citalopram, on levels of 5-HT in nerve fibers in the murine brain. Quantitative analysis of the areal density of 5-HT fibers throughout the brain was performed using ImageJ software. While a high density of fibers was observed in mid- and hind-brain regions and areas such as thalamus and hypothalamus, densities were far lower in areas such as cortex, where SSRIs might be thought to exert their actions. As anticipated, imipramine and citalopram produced a decline in 5-HT levels in nerve fibers, but the result was not uniform. Areas such as inferior colliculus showed significant reduction whereas little, if any, change was observed in the adjacent superior colliculus. The reason for, and significance of, this regionality is unclear. It has been proposed that serotonin effects in the brain might be linked to changes in glutamatergic transmission. Extracellular glutamate levels are regulated primarily by glial glutamate transporters. Qualitative evaluation of glutamate transporter immunolabeling in cortex of control and drug-treated mice revealed no discernable difference in intensity of glutamate transporter immunoreactivity. These data suggest that changes in intracellular and extracellular levels of serotonin do not cause concomitant changes in astroglial glutamate transporter expression, and thus cannot represent a mechanism for the delayed efficacy of antidepressants when administered clinically.

Amino Acid Transport System X-AG↗

PubMed2005

Synthesis and biological evaluation of new GABA-uptake inhibitors derived from proline and from pyrrolidine-2-acetic acid.

Several synthetic approaches to N-alkylated derivatives of 4-hydroxypyrrolidine-2-carboxylic acid and 4-hydroxypyrrolidine-2-acetic acid are described. The final compounds have been evaluated as potential inhibitors of the GABA transport proteins GAT-1 and GAT-3. The biological assays used were based on bovine material or porcine brain. As compared to the corresponding 4-unsubstituted compounds, the 4-hydroxypyrrolidine-2-carboxylic acid and 4-hydroxypyrrolidine-2-acetic acid derivatives showed a significant decrease in the inhibitory potency at both GAT-1 and GAT-3 with only four compounds having reasonable affinity to GAT-1 (IC(50): 5.1, 6.6 and 9.4 microM) or GAT-3 (IC(50): 19.9 microM), respectively. The biological data of the 4-hydroxypyrrolidine-2-acetic acid derivatives indicates that (2S)-configuration at the C-2 position for potent inhibition of GAT-1 and (4R)-configuration at the C-4 position for potent inhibition of GAT-3 may be crucial.

Animals↗

PubMed2003

Inhibition by arachidonic acid and other fatty acids of dopamine uptake at the human dopamine transporter.

It is known that arachidonic acid, in addition to promoting release of dopamine, can inhibit its transport. The present study provides preliminary information on structure-activity relationships for uptake inhibition by rotating disk voltammetry in human embryonic kidney-293 cells expressing the human dopamine transporter. Except for anandamide, all other fatty acids studied at a pretreatment concentration of 80 microM caused significant reductions in Vmax but not Km. Increasing saturation of the hydrocarbon tails (partial saturation: oleic acid, linoleic acid; full saturation: arachidic acid, stearic acid, stearic acid ethyl ester) removed inhibitory activity incrementally, suggesting a role for cis-unsaturation (folding/bending of hydrocarbon tails). The relative lack of effect of 5,8,11,14-eicosatetraynoic acid also supports the idea that less linear structures are less inhibitory on dopamine uptake. Esterification of the free carboxylic group (arachidonic acid ethyl ester) prevented most of the inhibitory activity, arguing against mere membrane lipid disruption. Finally, the endogenous cannabinoid anandamide greatly reduced uptake Vmax accompanied by a small decrease in Km, a potentially important effect on dopaminergic neurotransmission.

Arachidonic Acid↗

PubMed2003

Non-amine-based dopamine transporter (reuptake) inhibitors retain properties of amine-based progenitors.

Without exception, therapeutic and addictive drugs that produce their primary effects by blocking monoamine transporters in brain contain an amine nitrogen in their structure. This fundamental canon of drug design was based on a prevailing premise that an amine nitrogen is required to mimic the structures of monoamine neurotransmitters and other natural products. Non-amines, a novel class of compounds that contain no amine nitrogen, block monoamine transporters in the nM range and display markedly high selectivity for monoamine transporters, but not for receptors. Non-amines retain the spectrum of biochemical and pharmacological properties characteristic of amine-bearing counterparts. These novel drugs compel a revision of current concepts of drug-monoamine transporter complex formation and open avenues for discovery of a new generation of therapeutic drugs.

Animals↗

PubMed2003

Dopamine transporter as target for drug development of cocaine dependence medications.

Because much evidence implicates the dopamine transporter in the reinforcing effects of cocaine, development of potential medications for cocaine dependence has included the dopamine transporter as a target. The present overview covers progress in the drug development area regarding several classes of dopamine uptake inhibitors, with an emphasis on structure-activity relationships that enhance potency and selectivity at transporters for dopamine compared with those for serotonin or norepinephrine. The following categories of compounds are covered: tropane, benztropine, 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)piperazine (GBR), methylphenidate, mazindol, and phencyclidine analogs. Activity at transporters as well as on behavior is highlighted.

Animals↗

PubMed2003

Rapid regulation of dopamine transporter function by substrates, blockers and presynaptic receptor ligands.

The extracellular actions of dopamine are terminated primarily through its binding to dopamine transporters and translocation back into dopamine neurons. The transporter thereby serves as an optimal target to regulate dopamine neurotransmission. Although acute pharmacological blockade of dopamine transporters is known to reversibly inhibit transporter function by preventing the binding of its endogenous substrate dopamine, it recently has become clear that dopamine transporter substrates, such as amphetamines, and blockers, such as cocaine, also have the ability to rapidly and persistently regulate transporter function after their direct pharmacological effect has subsided. Presynaptic receptor ligands can also regulate dopamine transporter function. This has been investigated most extensively for dopamine D2 receptors, but there is also evidence for regulation by gamma-aminobutyric acid (GABA) GABAB receptors, metabotropic glutamate, nicotinic acetylcholine, serotonin, sigma2- and kappa-opioid receptors. The focus of this review is the rapid, typically reversible, regulation of dopamine transporter velocity by substrates, blockers and presynaptic receptor ligands. The research discussed here suggests that a common mechanism through which these different classes of compounds regulate transporter activity is by altering the cell surface expression of dopamine transporters.

Animals↗

PubMed2003

Interactions of cations and anions with the binding of uptake blockers to the dopamine transporter.

Uptake blockers and substrates are likely to recognise a common binding domain on the dopamine neuronal transporter (DAT). Among cations that form ionic gradients at the level of the cellular plasma membrane, Na+ is the only one that can stimulate their binding. The binding stimulation appears over Na+ concentrations ranging from 0 to 10-60 mM; at higher Na+ concentrations, binding reaches a plateau or decreases, according to the uptake blocker that is studied. The majority of the other cations, including K+, Ca2+, Mg2+ and Tris+, inhibit the binding of uptake blockers. Several metals impair binding to the DAT and/or the dopamine transport, but, under specific conditions, some of them, and chiefly Zn2+, stimulate binding. The complex relationships between cations, uptake blockers and the DAT suggest that cations recognise at least three different sites: the first one, site 1, is for cation-induced binding inhibition; the second one, site 2, is for Na+-induced binding stimulation; and the third one, site 3, is for Zn2+-induced binding stimulation. Modelling of the interactions between Na+, K+ and radioligands allows a better understanding of the effects of cations at sites 1 and 2, and of uptake blockers at site 1. Some anions also facilitate the binding of uptake blockers to the DAT, as far as they are associated with Na+. The dependence of the binding of dopamine on ions could be involved in its preferential inward transport and used by uptake blockers for their own binding to the DAT.

Animals↗

PubMed2003

Transporter-mediated actions of R-(-)-1-(benzofuran-2-yl)-2-propylaminopentane.

R-(-)-1-(Benzofuran-2-yl)-2-propylaminopentane [(-)-BPAP] is a catecholaminergic and serotonergic activity enhancer that increases impulse-evoked catecholamine and serotonin release from nerve terminals, and is a candidate for symptomatic treatment of early Parkinson's disease. We now report the catecholamine and serotonin transporter-mediated actions of (-)-BPAP. The effects of (-)-BPAP on inhibition of neurotransmitter uptake and radioligand binding were assessed using human embryonic kidney 293 cells (HEK 293 cells) expressing cDNA for the human dopamine transporter (hDAT), norepinephrine transporter (hNET), and serotonin transporter (hSERT). The IC(50) values for the effects of (-)-BPAP on [3H]dopamine, [3H]norepinephrine, and [3H]serotonin uptake were 42+/-9, 52+/-19, and 640+/-120 nM, respectively. The IC(50) values for the effects of (-)-BPAP on [125I]3 beta-(4-iodophenyl)tropane-2 beta-carboxylic acid methyl ester ([125I]RTI-55) binding to hDAT, hNET, and hSERT were 16+/-2, 211+/-61, and 638+/-63 nM, respectively. The effects of (-)-BPAP on spontaneous and tyramine-induced norepinephrine and dopamine release from rat brain synaptosomes using a superfusion system were also assessed. Tyramine but not (-)-BPAP potentiated norepinephrine release. Furthermore, (-)-BPAP inhibited tyramine-induced norepinephrine release. Thus, (-)-BPAP may block tyramine-induced adverse effects such as hypertensive crisis. The actions of (-)-BPAP on the spontaneous and tyramine-induced dopamine release resembled its effects on norepinephrine release. We conclude that (-)-BPAP is not only catecholaminergic and serotonergic activity enhancer, but also a norepinephrine and dopamine uptake inhibitor and a weak serotonin uptake inhibitor that does not possess a tyramine-like action on catecholamine release, and is an inhibitor of tyramine-induced release of norepinephrine.

Animals↗

PubMed2005

Novel parent structures for inhibitors of the murine GABA transporters mGAT3 and mGAT4.

Searching for potent and subtype selective parent structures of the murine gamma-aminobutyric acid (GABA) transporter subtypes mGAT3 and mGAT4 a series of amino acids was characterised in a uniform [3H]GABA uptake test system based on transiently expressed mGAT1-4. From several potent inhibitors showing IC50 values at mGAT3 and mGAT4 in the low microM range cis-4-aminocrotonic acid and (RS)-2,3-diaminopropionic acid turned out to be most subtype selective for these transporters. With (RS)-isoserine--a compound unknown as GAT inhibitor until now--one of the most potent amino acids selectively inhibiting mGAT3 and mGAT4 was found. Furthermore, (2-amino-1,3-thiazol-4-yl)acetic acid was identified as the first parent structure exhibiting a clear, though still moderate, selective inhibition of GABA uptake at mGAT3.

Acetates↗

PubMed2005

Repeated swim stress leads to down-regulation of vesicular monoamine transporter 2 in rat brain nucleus accumbens and striatum.

We assessed the impact of chronic swim stress in rats (daily for 3 weeks) on vesicular monoamine transporter 2 (VMAT2) in the nucleus accumbens and striatum. Exposure to repeated swim stress resulted in significant reduction in VMAT2 density in nucleus accumbens (20%, p<0.01) and striatum subregions (21-38%, p<0.001). The down-regulation of VMAT2 in this dopaminergic regions may serve as an adaptatory mechanism in the response to prolonged stress, and may be relevant to chronic stress-induced depression.

Animals↗

PubMed2005

Decreased platelet vesicular monoamine transporter density in habitual smokers.

The brain vesicular monoamine transporter (VMAT2) is part of the re-uptake mechanism which regulates monoaminergic neurotransmission. We demonstrated previously a high degree of similarity between the pharmacodynamic characteristics of platelet and brain VMAT2. Nicotine induced increase of dopamine and serotonin neurotransmission in limbic structures may alter the expression of VMAT2 in brains of smokers. In this study we measured the VMAT2 pharmacodynamic characteristics using high-affinity [3H]dihydrotetrabenazine (TBZOH) binding to platelets of smokers (n=15) compared to sex and age matched healthy nonsmokers controls (n=14). A significant decrease (17%, P=0.02) in VMAT2 density (Bmax) was observed in platelets of smokers compared to nonsmokers. There was no significant difference in the affinity of [3H]TBZOH to its platelet binding site and the VMAT2 density did not correlate with the heaviness of smoking. The decreased density of the VMAT2 in the platelets of smokers may reflect nicotine induced desensitization of VMAT2, a phenomenon that may be relevant to the addictive properties of nicotine.

Adult↗

PubMed2005

Molecular cloning and functional characterization of a neuronal choline transporter from Trichoplusia ni.

A cDNA encoding a high-affinity Na(+)-dependent choline transporter (TrnCHT) was isolated from the CNS of the cabbage looper Trichoplusia ni using an RT-PCR-based approach. The deduced amino acid sequence of the CHT cDNA predicts a 594 amino acid protein of 64.74 kDa prior to glycosylation. TrnCHT has 80%, 79%, 76%, and 58% amino acid identity to putative CHTs from Anopheles gambiae, Drosophila melanogaster and Apis mellifera, and a cloned CHT from Limulus polyphemus, respectively. In situ hybridization of TrnCHT cRNA in whole-mount preparations of caterpillar CNS revealed that TrnCHT mRNA is expressed by hundreds of presumably cholinergic neurons present in both the brain and cortex of all segmental ganglia. Na(+)-dependent [(3)H]-choline uptake was induced in Sf9 cells in vitro following infection with a TrnCHT-expressing recombinant baculovirus. Virally induced [(3)H]-choline uptake was found to approximately equal the endogenous rate of choline uptake in insect cells, seen either after infection with a control virus or in TrnCHT-infected cells exposed to [(3)H]-choline in the absence of Na(+). The Na(+)-dependent component of [(3)H]-choline uptake by TrnCHT-infected cells was saturable with a K(m) for choline transport of 8.4 microM. Several compounds reported to be potent blockers of [(3)H]-choline uptake by cloned vertebrate choline transporters proved to be relatively weak inhibitors of choline uptake by Sf9 cells expressing TrnCHT. Hemicholinium-3 (K(i)=4.1 microM) and two oxoquinuclidium analogues of choline, quireston-A (K(i) approximately 10 microM) and quireston (K(i) approximately 100 microM) inhibited 50% of control uptake only at micromolar concentrations. The endogenous low-affinity Na(+)-independent uptake of [(3)H]-choline was also inhibited by high micromolar concentrations of hemicholinium-3.

Amino Acid Sequence↗

PubMed2004

Relative contribution of target gene mutation and efflux to fluoroquinolone and erythromycin resistance, in French poultry and pig isolates of Campylobacter coli.

Thirty-eight avian and swine French isolates of Campylobacter coli were studied for their mechanisms of co-resistance to fluoroquinolones and erythromycin. A Thr86Ile modification of GyrA, responsible for fluoroquinolone resistance, was found in all the strains. Two different levels of resistance to erythromycin (MIC of 8-16 or >/=256 mg/l) were observed. A A2075G mutation in the 23S rRNA genes was found only in the highly-resistant strains. Phe-Arg-beta-naphthylamide, an efflux pump inhibitor, potentiated erythromycin in all the strains examined but restored susceptibility only in the strains with a low-level of resistance. This suggests the involvement of efflux in intrinsic and in acquired low-level of resistance to erythromycin in C. coli.

Amino Acid Substitution↗

PubMed2004

SecA folding kinetics: a large dimeric protein rapidly forms multiple native states.

SecA, a 202 kDa dimeric protein, is the ATPase for the Sec-dependent translocase of precursor proteins in vivo. SecA must undergo conformational changes, which may involve dissociation into a monomer, as it translocates the precursor protein across the inner membrane. To better understand the dynamics of SecA in vivo, protein folding studies to probe the native, intermediate, and unfolded species of SecA in vitro have been done. SecA folds through a stable dimeric intermediate and dimerizes in the dead-time of a manual-mixing kinetic experiment ( approximately 5-7 seconds). Here, stopped-flow fluorescence and CD, as well as ultra-rapid continuous flow fluorescence techniques, were used to further probe the rapid folding kinetics of SecA. In the absence of urea, rapid, near diffusion-limited ( approximately 10(9)M(-1)s(-1)) SecA dimerization occurs following a rate-limiting unimolecular rearrangement of a rapidly formed intermediate. Multiple kinetic folding and unfolding phases were observed and SecA was shown to have multiple native and unfolded states. Using sequential-mixing stopped-flow experiments, SecA was determined to fold via parallel channels with sequential intermediates. These results confirm that SecA is a highly dynamic protein, consistent with the rapid, major conformational changes it must undergo in vivo.

Adenosine Triphosphatases↗

PubMed2004

Novel fluorescence-based approaches for the study of biogenic amine transporter localization, activity, and regulation.

Pre-synaptic norepinephrine (NE) and dopamine (DA) transporters (NET and DAT) terminate catecholamine synaptic transmission through reuptake of released neurotransmitter. Recent studies reveal that NET and DAT are tightly regulated by receptor and second messenger-linked signaling pathways. Common approaches for studying these transporters involve use of radiolabeled substrates or antagonists, methods possessing limited spatial resolution and that bear limited opportunities for repeated monitoring of living preparations. To circumvent these issues, we have explored two novel assay platforms that permit temporally resolved quantitation of transport activity and transporter protein localization. To monitor the binding and transport function of NET and DAT in real-time, we have investigated the uptake of the fluorescent organic compound 4-(4-diethylaminostyryl)-N-methylpyridinium iodide (ASP+). We have extended our previous single cell level application of this substrate to monitor transport activity via high-throughput assay platforms. Compared to radiotracer uptake methods, acquisition of ASP+ fluorescence is non-isotopic and allows for continuous, repeated transport measurements on both transfected and native preparations. Secondly, we have extended our application of small-molecule-conjugated fluorescent CdSe/ZnS nanocrystals, or quantum dots (Qdots), to utilize antibody and peptide ligands that can identify surface expressed transporters, receptors and other membrane proteins in living cell systems. Unlike typical organic fluorophores, Qdots are highly resistant to bleaching and can be conjugated to multiple ligands. They can also be illuminated by conventional light sources, yet produce narrow, gaussian emission spectra compatible with multiple target visualization (multiplexing). Together, these approaches offer novel opportunities to investigate changes in transporter function and distribution in real-time with superior spatial and temporal resolution.

Antibodies↗

PubMed2004

Peritoneal macrophages express the serotonin transporter.

Although it is known that macrophages take up serotonin, a specific monoamine transporter has not been identified in macrophages. In this study, mRNA coding for the serotonin transporter (SERT) was detected with the reverse transcription-polymerase chain reaction (RT-PCR) in recruited mouse peritoneal macrophages. Sequencing confirmed the identity of the RT-PCR product to mouse SERT mRNA. SERT protein was detected by Western blotting. Macrophage activation with lipopolysaccharide had no effect on expression of SERT mRNA or protein. Consistent with expression of a functional SERT, specific uptake of (3)H-serotonin in macrophages was sodium dependent and inhibited by fluoxetine (IC(50) 6.9 nM) and desipramine (IC(50) 32 nM) but not by nisoxetine or reserpine.

Animals↗