1
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Supplisson S. Dynamic role of GlyT1 as glycine sink or source: Pharmacological implications for the gain control of NMDA receptors. Neuroscience 2024:S0306-4522(24)00350-6. [PMID: 39059742 DOI: 10.1016/j.neuroscience.2024.07.037] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2024] [Revised: 07/03/2024] [Accepted: 07/22/2024] [Indexed: 07/28/2024]
Abstract
Glycine transporter 1 (GlyT1) mediates the termination of inhibitory glycinergic receptor signaling in the spinal cord and brainstem, and is also present diffusely in the forebrain. Here, it regulates the ambient glycine concentration and influences the 'glycine' site occupancy of N-methyl-d-aspartate receptors (NMDARs). GlyT1 is a reversible transporter with a substantial, but not excessive, sodium-motive force for uphill transport. This study investigates its role as a potential source of glycine supply, either by reverse uptake or heteroexchange. Indeed, glutamate alone does not induce NMDAR current in "naive" oocytes co-expressing GluN1/GluN2A and GlyT1, a previously characterized cellular model. However, after substantial intracellular glycine accumulation, GlyT1 reverses its transport mode, and begins to release glycine into the external compartment, allowing NMDAR activation by glutamate alone. These uptake-dependent glutamate currents were blocked by ALX-5407 and potentiated by sarcosine, a specific inhibitor and substrate of GlyT1, respectively, suggesting a higher occupancy of the co-agonist site when GlyT1 functions as a glycine source either by reversed-uptake or by heteroexchange. These two glycine release mechanisms can be distinguished by their voltage dependence, as the reversed-uptake cycle decreases at hyperpolarized potentials, whereas heteroexchange electroneutrality preserves glycine efflux and NMDAR activation at these potentials. These results establish GlyT1-mediated efflux as a positive regulator of NMDAR coagonist site occupancy, and demonstrate the efficacy of sarcosine heteroexchange in enhancing coagonist site occupancy. Because NMDAR facilitation by GlyT1-inhibitors and sarcosine relies on different transport mechanisms, their actions may be a source of variability in reversing NMDAR hypofunction in schizophrenia.
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Affiliation(s)
- Stéphane Supplisson
- Institut de Biologie de l'ENS (IBENS), Ecole normale supérieure, Université PSL, CNRS, INSERM, Paris, F-75005, France.
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2
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Alberto-Silva AS, Hemmer S, Bock HA, da Silva LA, Scott KR, Kastner N, Bhatt M, Niello M, Jäntsch K, Kudlacek O, Bossi E, Stockner T, Meyer MR, McCorvy JD, Brandt SD, Kavanagh P, Sitte HH. Bioisosteric analogs of MDMA: Improving the pharmacological profile? J Neurochem 2024. [PMID: 38898705 DOI: 10.1111/jnc.16149] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2023] [Revised: 03/26/2024] [Accepted: 05/29/2024] [Indexed: 06/21/2024]
Abstract
3,4-Methylenedioxymethamphetamine (MDMA, 'ecstasy') is re-emerging in clinical settings as a candidate for the treatment of specific neuropsychiatric disorders (e.g. post-traumatic stress disorder) in combination with psychotherapy. MDMA is a psychoactive drug, typically regarded as an empathogen or entactogen, which leads to transporter-mediated monoamine release. Despite its therapeutic potential, MDMA can induce dose-, individual-, and context-dependent untoward effects outside safe settings. In this study, we investigated whether three new methylenedioxy bioisosteres of MDMA improve its off-target profile. In vitro methods included radiotracer assays, transporter electrophysiology, bioluminescence resonance energy transfer and fluorescence-based assays, pooled human liver microsome/S9 fraction incubations, metabolic stability studies, isozyme mapping, and liquid chromatography coupled to high-resolution mass spectrometry. In silico methods included molecular docking. Compared with MDMA, all three MDMA bioisosteres (ODMA, TDMA, and SeDMA) showed similar pharmacological activity at human serotonin, dopamine, and norepinephrine transporters (hSERT, hDAT, and hNET, respectively) but decreased agonist activity at 5-HT2A/2B/2C receptors. Regarding their hepatic metabolism, they differed from MDMA, with N-demethylation being the only metabolic route shared, and without forming phase II metabolites. In addition, TDMA showed an enhanced intrinsic clearance in comparison to its congeners. Additional screening for their interaction with human organic cation transporters (hOCTs) and plasma membrane monoamine transporter (hPMAT) revealed a weaker interaction of the MDMA analogs with hOCT1, hOCT2, and hPMAT. Our findings suggest that these new MDMA bioisosteres might constitute appealing therapeutic alternatives to MDMA, sparing the primary pharmacological activity at hSERT, hDAT, and hNET, but displaying a reduced activity at 5-HT2A/2B/2C receptors and alternative hepatic metabolism. Whether these MDMA bioisosteres may pose lower risk alternatives to the clinically re-emerging MDMA warrants further studies.
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Affiliation(s)
- Ana Sofia Alberto-Silva
- Center for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Selina Hemmer
- Department of Experimental and Clinical Toxicology, Institute of Experimental and Clinical Pharmacology and Toxicology, Center for Molecular Signaling (PZMS), Saarland University, Homburg, Germany
| | - Hailey A Bock
- Department of Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
| | - Leticia Alves da Silva
- Center for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Kenneth R Scott
- Department of Pharmacology and Therapeutics, School of Medicine, Trinity Centre for Health Sciences, St James Hospital, Dublin, Ireland
| | - Nina Kastner
- Center for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Manan Bhatt
- Laboratory of Cellular and Molecular Physiology, Department of Biotechnology and Life Sciences, University of Insubria, Varese, Italy
| | - Marco Niello
- Center for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Kathrin Jäntsch
- Center for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Oliver Kudlacek
- Center for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Elena Bossi
- Laboratory of Cellular and Molecular Physiology, Department of Biotechnology and Life Sciences, University of Insubria, Varese, Italy
- Center for Research in Neuroscience, University of Insubria, Varese, Italy
| | - Thomas Stockner
- Center for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Markus R Meyer
- Department of Experimental and Clinical Toxicology, Institute of Experimental and Clinical Pharmacology and Toxicology, Center for Molecular Signaling (PZMS), Saarland University, Homburg, Germany
| | - John D McCorvy
- Department of Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
- Neuroscience Research Center, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
- Cancer Center, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
| | - Simon D Brandt
- School of Pharmacy and Biomolecular Sciences, Liverpool John Moores University, Liverpool, UK
| | - Pierce Kavanagh
- Department of Pharmacology and Therapeutics, School of Medicine, Trinity Centre for Health Sciences, St James Hospital, Dublin, Ireland
| | - Harald H Sitte
- Center for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, Vienna, Austria
- Hourani Center for Applied Scientific Research, Al-Ahliyya Amman University, Amman, Jordan
- Center for Addiction Research and Science, Medical University of Vienna, Vienna, Austria
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3
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Alberto-Silva AS, Hemmer S, Bock HA, Alves da Silva L, Scott KR, Kastner N, Bhatt M, Niello M, Jäntsch K, Kudlacek O, Bossi E, Stockner T, Meyer MR, McCorvy JD, Brandt SD, Kavanagh P, Sitte HH. Bioisosteric analogs of MDMA with improved pharmacological profile. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.04.08.588083. [PMID: 38645142 PMCID: PMC11030374 DOI: 10.1101/2024.04.08.588083] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/23/2024]
Abstract
3,4-Methylenedioxymethamphetamine (MDMA, ' ecstasy' ) is re-emerging in clinical settings as a candidate for the treatment of specific psychiatric disorders (e.g. post-traumatic stress disorder) in combination with psychotherapy. MDMA is a psychoactive drug, typically regarded as an empathogen or entactogen, which leads to transporter-mediated monoamine release. Despite its therapeutic potential, MDMA can induce dose-, individual-, and context-dependent untoward effects outside safe settings. In this study, we investigated whether three new methylenedioxy bioisosteres of MDMA improve its off-target profile. In vitro methods included radiotracer assays, transporter electrophysiology, bioluminescence resonance energy transfer and fluorescence-based assays, pooled human liver microsome/S9 fraction incubation with isozyme mapping, and liquid chromatography coupled to high-resolution mass spectrometry. In silico methods included molecular docking. Compared with MDMA, all three MDMA bioisosteres (ODMA, TDMA, and SeDMA) showed similar pharmacological activity at human serotonin and dopamine transporters (hSERT and hDAT, respectively) but decreased activity at 5-HT 2A/2B/2C receptors. Regarding their hepatic metabolism, they differed from MDMA, with N -demethylation being the only metabolic route shared, and without forming phase II metabolites. Additional screening for their interaction with human organic cation transporters (hOCTs) and plasma membrane transporter (hPMAT) revealed a weaker interaction of the MDMA analogs with hOCT1, hOCT2, and hPMAT. Our findings suggest that these new MDMA analogs might constitute appealing therapeutic alternatives to MDMA, sparing the primary pharmacological activity at hSERT and hDAT, but displaying a reduced activity at 5-HT 2A/2B/2C receptors and reduced hepatic metabolism. Whether these MDMA bioisosteres may pose lower risk alternatives to the clinically re-emerging MDMA warrants further studies.
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4
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Bukowski L, Strøm ME, Andersen JL, Maesen JB, Tian L, Sinning S. 5-HT_FAsTR: a versatile, label-free, high-throughput, fluorescence-based microplate assay to quantify serotonin transport and release. Sci Rep 2024; 14:6541. [PMID: 38504103 PMCID: PMC10951269 DOI: 10.1038/s41598-024-56712-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2023] [Accepted: 03/09/2024] [Indexed: 03/21/2024] Open
Abstract
The neurotransmitter serotonin plays a pivotal role in mood and depression. It also acts as a vasoconstrictor within blood vessels and is the main neurotransmitter in the gastrointestinal system. In neurotransmission, released serotonin is taken up by serotonin transporters, which are principal targets of antidepressants and the psychostimulant, ecstasy. The investigation of serotonin transporters have relied almost exclusively on the use of radiolabeled serotonin in heterogenous end-point assays. Here we adapt the genetically encoded fluorescent biosensor, iSeroSnFR, to establish and validate the Serotonin (5-HT) Fluorescence Assay for Transport and Release (5-HT_FAsTR) for functional and pharmacological studies of serotonin transport and release. We demonstrate the applicability of the method for the study of a neuronal, high-affinity, low-capacity serotonin transporter (SERT) as well as an extraneuronal low-affinity, high-capacity organic cation transporter and mutants thereof. 5HT_FAsTR offers an accessible, versatile and reliable semi-homogenous assay format that only relies on a fluorescence plate reader for repeated, real-time measurements of serotonin influx and efflux. 5HT_FAsTR accelerates and democratizes functional characterization and pharmacological studies of serotonin transporters and genetic variants thereof in disease states such as depression, anxiety and ADHD.
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Affiliation(s)
- Lina Bukowski
- Department of Forensic Medicine, Aarhus University, Palle Juul-Jensens Boulevard 99, 8200, Aarhus N, Denmark
| | - Markus Emanuel Strøm
- Department of Forensic Medicine, Aarhus University, Palle Juul-Jensens Boulevard 99, 8200, Aarhus N, Denmark
| | - Jens Lindengren Andersen
- Department of Forensic Medicine, Aarhus University, Palle Juul-Jensens Boulevard 99, 8200, Aarhus N, Denmark
| | - Jannick Bang Maesen
- Department of Forensic Medicine, Aarhus University, Palle Juul-Jensens Boulevard 99, 8200, Aarhus N, Denmark
| | - Lin Tian
- Department of Biochemistry and Molecular Medicine, University of California, Davis, CA, 95616-8635, USA
- Max Planck Florida Institute for Neuroscience, Jupiter, FL, 33458, USA
| | - Steffen Sinning
- Department of Forensic Medicine, Aarhus University, Palle Juul-Jensens Boulevard 99, 8200, Aarhus N, Denmark.
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5
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Mayer FP, Niello M, Bulling S, Zhang YW, Li Y, Kudlacek O, Holy M, Kooti F, Sandtner W, Rudnick G, Schmid D, Sitte HH. Mephedrone induces partial release at human dopamine transporters but full release at human serotonin transporters. Neuropharmacology 2023; 240:109704. [PMID: 37703919 DOI: 10.1016/j.neuropharm.2023.109704] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2022] [Revised: 07/07/2023] [Accepted: 08/31/2023] [Indexed: 09/15/2023]
Abstract
Mephedrone (4-methylmethcathinone) is a cathinone derivative that is recreationally consumed for its energizing and empathogenic effects. The stimulating properties are believed to arise from the ability of mephedrone to interact with the high-affinity transporters for dopamine (DA) (DAT) and norepinephrine (NET), whereas the entactogenic effect presumably relies on its activity at the serotonin (5-HT) transporter (SERT). Early studies found that mephedrone acts as a releaser at NET, DAT and SERT, and thus promotes efflux of the respective monoamines. Evidence linked drug-induced reverse transport of 5-HT via SERT to prosocial effects, whereas activity at DAT is strongly correlated with abuse liability. Consequently, we sought to evaluate the pharmacology of mephedrone at human (h) DAT and SERT, heterologously expressed in human embryonic kidney 293 cells, in further detail. In line with previous studies, we report that mephedrone evokes carrier-mediated release via hDAT and hSERT. We found this effect to be sensitive to the protein kinase C inhibitor GF109203X. Electrophysiological recordings revealed that mephedrone is actively transported by hDAT and hSERT. However, mephedrone acts as a full substrate of hSERT but as a partial substrate of hDAT. Furthermore, when compared to fully efficacious releasing agents at hDAT and hSERT (i.e. S(+)-amphetamine and para-chloroamphetamine, respectively) mephedrone displays greater efficacy as a releaser at hSERT than at hDAT. In summary, this study provides additional insights into the molecular mechanism of action of mephedrone at hDAT and hSERT.
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Affiliation(s)
- Felix P Mayer
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Waehringer Strasse 13a, A-1090, Vienna, Austria
| | - Marco Niello
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Waehringer Strasse 13a, A-1090, Vienna, Austria
| | - Simon Bulling
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Waehringer Strasse 13a, A-1090, Vienna, Austria
| | - Yuan-Wei Zhang
- Department of Pharmacology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT, 06520-8066, USA
| | - Yang Li
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Waehringer Strasse 13a, A-1090, Vienna, Austria
| | - Oliver Kudlacek
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Waehringer Strasse 13a, A-1090, Vienna, Austria
| | - Marion Holy
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Waehringer Strasse 13a, A-1090, Vienna, Austria
| | - Fatemeh Kooti
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Waehringer Strasse 13a, A-1090, Vienna, Austria
| | - Walter Sandtner
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Waehringer Strasse 13a, A-1090, Vienna, Austria
| | - Gary Rudnick
- Department of Pharmacology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT, 06520-8066, USA
| | - Diethart Schmid
- Institute for Physiology, Center for Physiology and Pharmacology, Medical University of Vienna, Waehringer Strasse 13a, A-1090, Vienna, Austria
| | - Harald H Sitte
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Waehringer Strasse 13a, A-1090, Vienna, Austria; Hourani Center for Applied Scientific Research, Al-Ahliyya Amman University, Amman, Jordan; Center for Addiction Research and Science - AddRess, Medical University of Vienna, Waehringer Strasse 13a, A-1090, Vienna, Austria.
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6
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Lofthouse EM, Cleal J, Lewis RM, Sengers BG. Computational Modelling of Paracellular Diffusion and OCT3 Mediated Transport of Metformin in the Perfused Human Placenta. J Pharm Sci 2023; 112:2570-2580. [PMID: 37211316 DOI: 10.1016/j.xphs.2023.05.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2023] [Revised: 05/15/2023] [Accepted: 05/15/2023] [Indexed: 05/23/2023]
Abstract
Metformin is an antidiabetic drug, increasingly prescribed in pregnancy and has been shown to cross the human placenta. The mechanisms underlying placental metformin transfer remain unclear. This study investigated the roles of drug transporters and paracellular diffusion in the bidirectional transfer of metformin across the human placental syncytiotrophoblast using placental perfusion experiments and computational modelling. 14C-metformin transfer was observed in the maternal to fetal and fetal to maternal directions and was not competitively inhibited by 5 mM unlabelled metformin. Computational modelling of the data was consistent with overall placental transfer via paracellular diffusion. Interestingly, the model also predicted a transient peak in fetal 14C-metformin release due to trans-stimulation of OCT3 by unlabelled metformin at the basal membrane. To test this hypothesis a second experiment was designed. OCT3 substrates (5 mM metformin, 5 mM verapamil and 10 mM decynium-22) added to the fetal artery trans-stimulated release of 14C-metformin from the placenta into the fetal circulation, while 5 mM corticosterone did not. This study demonstrated activity of OCT3 transporters on the basal membrane of the human syncytiotrophoblast. However, we did not detect a contribution of either OCT3 or apical membrane transporters to overall materno-fetal transfer, which could be represented adequately by paracellular diffusion in our system.
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Affiliation(s)
- Emma M Lofthouse
- Faculty of Medicine, University of Southampton, UK; Institute for Life Sciences, University of Southampton, UK
| | - Jane Cleal
- Faculty of Medicine, University of Southampton, UK; Institute for Life Sciences, University of Southampton, UK
| | - Rohan M Lewis
- Faculty of Medicine, University of Southampton, UK; Institute for Life Sciences, University of Southampton, UK
| | - Bram G Sengers
- Faculty of Engineering and Physical Sciences, University of Southampton, UK; Institute for Life Sciences, University of Southampton, UK.
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7
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Niello M, Sideromenos S, Gradisch R, O´Shea R, Schwazer J, Maier J, Kastner N, Sandtner W, Jäntsch K, Lupica CR, Hoffman AF, Lubec G, Loland CJ, Stockner T, Pollak DD, Baumann MH, Sitte HH. Persistent binding at dopamine transporters determines sustained psychostimulant effects. Proc Natl Acad Sci U S A 2023; 120:e2114204120. [PMID: 36730201 PMCID: PMC9963675 DOI: 10.1073/pnas.2114204120] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2021] [Accepted: 12/28/2022] [Indexed: 02/03/2023] Open
Abstract
Psychostimulants interacting with the dopamine transporter (DAT) can be used illicitly or for the treatment of specific neuropsychiatric disorders. However, they can also produce severe and persistent adverse events. Often, their pharmacological properties in vitro do not fully correlate to their pharmacological profile in vivo. Here, we investigated the pharmacological effects of enantiomers of pyrovalerone, α-pyrrolidinovalerophenone, and 3,4-methylenedioxypyrovalerone as compared to the traditional psychostimulants cocaine and methylphenidate, using a variety of in vitro, computational, and in vivo approaches. We found that in vitro drug-binding kinetics at DAT correlate with the time-course of in vivo psychostimulant action in mice. In particular, a slow dissociation (i.e., slow koff) of S-enantiomers of pyrovalerone analogs from DAT predicts their more persistent in vivo effects when compared to cocaine and methylphenidate. Overall, our findings highlight the critical importance of drug-binding kinetics at DAT for determining the in vivo profile of effects produced by psychostimulant drugs.
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Affiliation(s)
- Marco Niello
- Center for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, 1090Vienna, Austria
| | - Spyridon Sideromenos
- Center for Physiology and Pharmacology, Department of Neurophysiology and Neuropharmacology, Medical University of Vienna, 1090Vienna, Austria
| | - Ralph Gradisch
- Center for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, 1090Vienna, Austria
| | - Ronan O´Shea
- Electrophysiology Research Section, National Institute on Drug Abuse, NIH, Baltimore, MD21224
| | - Jakob Schwazer
- Center for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, 1090Vienna, Austria
| | - Julian Maier
- Center for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, 1090Vienna, Austria
| | - Nina Kastner
- Center for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, 1090Vienna, Austria
| | - Walter Sandtner
- Center for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, 1090Vienna, Austria
| | - Kathrin Jäntsch
- Center for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, 1090Vienna, Austria
| | - Carl R. Lupica
- Electrophysiology Research Section, National Institute on Drug Abuse, NIH, Baltimore, MD21224
| | - Alexander F. Hoffman
- Electrophysiology Research Section, National Institute on Drug Abuse, NIH, Baltimore, MD21224
| | - Gert Lubec
- Department of Neuroproteomics, Paracelsus Medical University, 5020Salzburg, Austria
| | - Claus J. Loland
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, 2200Copenhagen, Denmark
| | - Thomas Stockner
- Center for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, 1090Vienna, Austria
| | - Daniela D. Pollak
- Center for Physiology and Pharmacology, Department of Neurophysiology and Neuropharmacology, Medical University of Vienna, 1090Vienna, Austria
| | - Michael H. Baumann
- Designer Drug Research Unit, Intramural Research Program, National Institute on Drug Abuse, NIH, Baltimore, MD21224
| | - Harald H. Sitte
- Center for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, 1090Vienna, Austria
- AddRess, Center for Addiction Research and Science, Medical University of Vienna, 1090Vienna, Austria
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8
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Bhat S, El-Kasaby A, Kasture A, Boytsov D, Reichelt JB, Hummel T, Sucic S, Pifl C, Freissmuth M, Sandtner W. A mechanism of uncompetitive inhibition of the serotonin transporter. eLife 2023; 12:e82641. [PMID: 36648438 PMCID: PMC9883013 DOI: 10.7554/elife.82641] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2022] [Accepted: 01/17/2023] [Indexed: 01/18/2023] Open
Abstract
The serotonin transporter (SERT/SLC6A4) is arguably the most extensively studied solute carrier (SLC). During its eponymous action - that is, the retrieval of serotonin from the extracellular space - SERT undergoes a conformational cycle. Typical inhibitors (antidepressant drugs and cocaine), partial and full substrates (amphetamines and their derivatives), and atypical inhibitors (ibogaine analogues) bind preferentially to different states in this cycle. This results in competitive or non-competitive transport inhibition. Here, we explored the action of N-formyl-1,3-bis (3,4-methylenedioxyphenyl)-prop-2-yl-amine (ECSI#6) on SERT: inhibition of serotonin uptake by ECSI#6 was enhanced with increasing serotonin concentration. Conversely, the KM for serotonin was lowered by augmenting ECSI#6. ECSI#6 bound with low affinity to the outward-facing state of SERT but with increased affinity to a potassium-bound state. Electrophysiological recordings showed that ECSI#6 preferentially interacted with the inward-facing state. Kinetic modeling recapitulated the experimental data and verified that uncompetitive inhibition arose from preferential binding of ECSI#6 to the K+-bound, inward-facing conformation of SERT. This binding mode predicted a pharmacochaperoning action of ECSI#6, which was confirmed by examining its effect on the folding-deficient mutant SERT-PG601,602AA: preincubation of HEK293 cells with ECSI#6 restored export of SERT-PG601,602AA from the endoplasmic reticulum and substrate transport. Similarly, in transgenic flies, the administration of ECSI#6 promoted the delivery of SERT-PG601,602AA to the presynaptic specialization of serotonergic neurons. To the best of our knowledge, ECSI#6 is the first example of an uncompetitive SLC inhibitor. Pharmacochaperones endowed with the binding mode of ECSI#6 are attractive, because they can rescue misfolded transporters at concentrations, which cause modest transport inhibition.
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Affiliation(s)
- Shreyas Bhat
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of ViennaViennaAustria
| | - Ali El-Kasaby
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of ViennaViennaAustria
| | - Ameya Kasture
- Department of Neurobiology, University of ViennaViennaAustria
| | - Danila Boytsov
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of ViennaViennaAustria
| | - Julian B Reichelt
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of ViennaViennaAustria
| | - Thomas Hummel
- Department of Neurobiology, University of ViennaViennaAustria
| | - Sonja Sucic
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of ViennaViennaAustria
| | - Christian Pifl
- Center for Brain Research, Medical University of ViennaViennaAustria
| | - Michael Freissmuth
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of ViennaViennaAustria
| | - Walter Sandtner
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of ViennaViennaAustria
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9
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Farr CV, El-Kasaby A, Erdem FA, Sucic S, Freissmuth M, Sandtner W. Cooperative Binding of Substrate and Ions Drives Forward Cycling of the Human Creatine Transporter-1. Front Physiol 2022; 13:919439. [PMID: 35837012 PMCID: PMC9273935 DOI: 10.3389/fphys.2022.919439] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2022] [Accepted: 06/09/2022] [Indexed: 11/25/2022] Open
Abstract
Creatine serves as an ATP buffer and is thus an integral component of cellular energy metabolism. Most cells maintain their creatine levels via uptake by the creatine transporter (CRT-1, SLC6A8). The activity of CRT-1, therefore, is a major determinant of cytosolic creatine concentrations. We determined the kinetics of CRT-1 in real time by relying on electrophysiological recordings of transport-associated currents. Our analysis revealed that CRT-1 harvested the concentration gradient of NaCl and the membrane potential but not the potassium gradient to achieve a very high concentrative power. We investigated the mechanistic basis for the ability of CRT-1 to maintain the forward cycling mode in spite of high intracellular concentrations of creatine: this is achieved by cooperative binding of substrate and co-substrate ions, which, under physiological ion conditions, results in a very pronounced (i.e. about 500-fold) drop in the affinity of creatine to the inward-facing state of CRT-1. Kinetic estimates were integrated into a mathematical model of the transport cycle of CRT-1, which faithfully reproduced all experimental data. We interrogated the kinetic model to examine the most plausible mechanistic basis of cooperativity: based on this systematic exploration, we conclude that destabilization of binary rather than ternary complexes is necessary for CRT-1 to maintain the observed cytosolic creatine concentrations. Our model also provides a plausible explanation why neurons, heart and skeletal muscle cells must express a creatine releasing transporter to achieve rapid equilibration of the intracellular creatine pool.
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Affiliation(s)
| | | | | | | | - Michael Freissmuth
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
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10
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Schicker K, Farr CV, Boytsov D, Freissmuth M, Sandtner W. Optimizing the Substrate Uptake Rate of Solute Carriers. Front Physiol 2022; 13:817886. [PMID: 35185619 PMCID: PMC8850955 DOI: 10.3389/fphys.2022.817886] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2021] [Accepted: 01/10/2022] [Indexed: 11/16/2022] Open
Abstract
The diversity in solute carriers arose from evolutionary pressure. Here, we surmised that the adaptive search for optimizing the rate of substrate translocation was also shaped by the ambient extracellular and intracellular concentrations of substrate and co-substrate(s). We explored possible solutions by employing kinetic models, which were based on analytical expressions of the substrate uptake rate, that is, as a function of the microscopic rate constants used to parameterize the transport cycle. We obtained the defining terms for five reaction schemes with identical transport stoichiometry (i.e., Na+: substrate = 2:1). We then utilized an optimization algorithm to find the set of numeric values for the microscopic rate constants, which provided the largest value for the substrate uptake rate: The same optimized rate was achieved by different sets of numerical values for the microscopic rate constants. An in-depth analysis of these sets provided the following insights: (i) In the presence of a low extracellular substrate concentration, a transporter can only cycle at a high rate, if it has low values for both, the Michaelis-Menten constant (KM) for substrate and the maximal substrate uptake rate (Vmax). (ii) The opposite is true for a transporter operating at high extracellular substrate concentrations. (iii) Random order of substrate and co-substrate binding is superior to sequential order, if a transporter is to maintain a high rate of substrate uptake in the presence of accumulating intracellular substrate. Our kinetic models provide a framework to understand how and why the transport cycles of closely related transporters differ.
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Affiliation(s)
| | | | | | | | - Walter Sandtner
- Center of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
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11
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Szöllősi D, Stockner T. Sodium Binding Stabilizes the Outward-Open State of SERT by Limiting Bundle Domain Motions. Cells 2022; 11:cells11020255. [PMID: 35053371 PMCID: PMC8773566 DOI: 10.3390/cells11020255] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2021] [Revised: 12/23/2021] [Accepted: 12/29/2021] [Indexed: 11/16/2022] Open
Abstract
The human serotonin transporter (hSERT) removes the neurotransmitter serotonin from the synaptic cleft by reuptake into the presynaptic nerve terminal. A number of neurologic diseases are associated with dysfunction of the hSERT, and several medications for their treatment are hSERT blockers, including citalopram, fluoxetine, and paroxetine. The substrate transport is energized by the high concentration of external NaCl. We showed through molecular dynamics simulations that the binding of NaCl stabilized the hSERT in the substrate-binding competent conformation, which was characterized by an open access path to the substrate-binding site through the outer vestibule. Importantly, the binding of NaCl reduced the dynamics of the hSERT by decreasing the internal fluctuations of the bundle domain as well as the movement of the bundle domain relative to the scaffold domain. In contrast, the presence of only the bound chloride ion did not reduce the high domain mobility of the apo state.
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12
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Extracellular loops of the serotonin transporter act as a selectivity filter for drug binding. J Biol Chem 2021; 297:100863. [PMID: 34118233 PMCID: PMC8253976 DOI: 10.1016/j.jbc.2021.100863] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2021] [Revised: 06/04/2021] [Accepted: 06/07/2021] [Indexed: 11/24/2022] Open
Abstract
The serotonin transporter (SERT) shapes serotonergic neurotransmission by retrieving its eponymous substrate from the synaptic cleft. Ligands that discriminate between SERT and its close relative, the dopamine transporter DAT, differ in their association rate constant rather than their dissociation rate. The structural basis for this phenomenon is not known. Here we examined the hypothesis that the extracellular loops 2 (EL2) and 4 (EL4) limit access to the ligand-binding site of SERT. We employed an antibody directed against EL4 (residues 388–400) and the antibody fragments 8B6 scFv (directed against EL2 and EL4) and 15B8 Fab (directed against EL2) and analyzed their effects on the transport cycle of and inhibitor binding to SERT. Electrophysiological recordings showed that the EL4 antibody and 8B6 scFv impeded the initial substrate-induced transition from the outward to the inward-facing conformation but not the forward cycling mode of SERT. In contrast, binding of radiolabeled inhibitors to SERT was enhanced by either EL4- or EL2-directed antibodies. We confirmed this observation by determining the association and dissociation rate of the DAT-selective inhibitor methylphenidate via electrophysiological recordings; occupancy of EL2 with 15B8 Fab enhanced the affinity of SERT for methylphenidate by accelerating its binding. Based on these observations, we conclude that (i) EL4 undergoes a major movement during the transition from the outward to the inward-facing state, and (ii) EL2 and EL4 limit access of inhibitors to the binding of SERT, thus acting as a selectivity filter. This insight has repercussions for drug development.
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13
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Szöllősi D, Stockner T. Investigating the Mechanism of Sodium Binding to SERT Using Direct Simulations. Front Cell Neurosci 2021; 15:673782. [PMID: 34040506 PMCID: PMC8141550 DOI: 10.3389/fncel.2021.673782] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2021] [Accepted: 04/14/2021] [Indexed: 11/13/2022] Open
Abstract
The serotonin transporter (SERT) terminates neurotransmission by transporting serotonin from the synapse into the pre-synaptic nerve terminal. Altered SERT function leads to several neurological diseases including depression, anxiety, mood disorders, and attention deficit hyperactivity disorders (ADHD). Accordingly SERT is the target for their pharmacological treatments, but also targeted by multiple drugs of abuse. Transport of serotonin by SERT is energized by the transmembrane electrochemical gradient of sodium. We used extensive molecular dynamics simulations to investigate the process of sodium binding to SERT, which is the first step in the transport cycle that leads to serotonin uptake. Comparing data from 51 independent simulations, we find a remarkably well-defined path for sodium entry and could identify two transient binding sites, while observing binding kinetics that are comparable to experimental data. Importantly, the structure and dynamics of the sodium binding sites indicate that sodium binding is accompanied by an induced-fit mechanism that leads to new conformations and reduces local dynamics.
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Affiliation(s)
- Dániel Szöllősi
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Thomas Stockner
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
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14
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Hong YK, Kim YH, Lee JM, Yoo HH, Choi SO, Kang MS. Characterization of in vitro phase I metabolites of methamnetamine in human liver microsomes by liquid chromatography-quadrupole time-of-flight mass spectrometry. Int J Legal Med 2021; 135:1471-1476. [PMID: 33928430 DOI: 10.1007/s00414-021-02594-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2020] [Accepted: 04/01/2021] [Indexed: 11/24/2022]
Abstract
N-Methyl-1-(naphthalen-2-yl)propan-2-amine (methamnetamine, PAL-1046) is an amphetamine-based new psychoactive substance (NPS). Methamnetamine has been reported to cause excessive release of serotonin, and it is classified as an empathogen or entactogen. It is not regulated as a controlled substance in most countries, and there are no studies on its metabolism. In this study, in vitro phase I metabolism of methamnetamine in human liver microsomes (HLM) and flavin-containing monooxygenase (FMO) was investigated by liquid chromatography-quadrupole time-of-flight mass spectrometry (LC-Q-TOF/MS). Eight metabolites of methamnetamine were identified and were structurally characterized achieved by a combination of accurate mass analysis and tandem mass spectrometry. The identified metabolic processes include N-demethylation, N-hydroxylation, aromatic hydroxylation, and a combination of these processes. N-Hydroxylated metabolites were confirmed based on expressed FMOs. The major metabolite was formed from methamnetamine via hydroxylation of the naphthalene ring after the in vitro phase I process. These results could help detect methamnetamine ingestion by NPS abusers.
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Affiliation(s)
- Young-Ki Hong
- Pharmacological Research Division, Toxicological and Research Department, National Institute of Food and Drug Safety Evaluation, Ministry of Food and Drug Safety, 187 Osong Saengmyeong 2-ro, Heungdeok-gu, Chungju-shi, 28159, Chungccheongbuk-do, Republic of Korea
| | - Young-Hoon Kim
- Pharmacological Research Division, Toxicological and Research Department, National Institute of Food and Drug Safety Evaluation, Ministry of Food and Drug Safety, 187 Osong Saengmyeong 2-ro, Heungdeok-gu, Chungju-shi, 28159, Chungccheongbuk-do, Republic of Korea
| | - Jin-Moo Lee
- Pharmacological Research Division, Toxicological and Research Department, National Institute of Food and Drug Safety Evaluation, Ministry of Food and Drug Safety, 187 Osong Saengmyeong 2-ro, Heungdeok-gu, Chungju-shi, 28159, Chungccheongbuk-do, Republic of Korea
| | - Hye Hyun Yoo
- Institute of Pharmaceutical Science and Technology and College of Pharmacy, Hanyang University, Ansan, Gyeonggi-do, 15588, Republic of Korea
| | - Sun-Ok Choi
- Pharmacological Research Division, Toxicological and Research Department, National Institute of Food and Drug Safety Evaluation, Ministry of Food and Drug Safety, 187 Osong Saengmyeong 2-ro, Heungdeok-gu, Chungju-shi, 28159, Chungccheongbuk-do, Republic of Korea
| | - Mi Sun Kang
- Pharmacological Research Division, Toxicological and Research Department, National Institute of Food and Drug Safety Evaluation, Ministry of Food and Drug Safety, 187 Osong Saengmyeong 2-ro, Heungdeok-gu, Chungju-shi, 28159, Chungccheongbuk-do, Republic of Korea.
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15
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Schicker K, Bhat S, Farr C, Burtscher V, Horner A, Freissmuth M, Sandtner W. Descriptors of Secondary Active Transporter Function and How They Relate to Partial Reactions in the Transport Cycle. MEMBRANES 2021; 11:178. [PMID: 33802510 PMCID: PMC8001282 DOI: 10.3390/membranes11030178] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/28/2021] [Revised: 02/25/2021] [Accepted: 02/27/2021] [Indexed: 12/19/2022]
Abstract
Plasmalemmal solute carriers (SLCs) gauge and control solute abundance across cellular membranes. By virtue of this action, they play an important role in numerous physiological processes. Mutations in genes encoding the SLCs alter amino acid sequence that often leads to impaired protein function and onset of monogenic disorders. To understand how these altered proteins cause disease, it is necessary to undertake relevant functional assays. These experiments reveal descriptors of SLC function such as the maximal transport velocity (Vmax), the Michaelis constant for solute uptake (KM), potencies for inhibition of transporter function (IC50/EC50), and many more. In several instances, the mutated versions of different SLC transporters differ from their wild-type counterparts in the value of these descriptors. While determination of these experimental parameters can provide conjecture as to how the mutation gives rise to disease, they seldom provide any definitive insights on how a variant differ from the wild-type transporter in its operation. This is because the experimental determination of association between values of the descriptors and several partial reactions a transporter undergoes is casual, but not causal, at best. In the present study, we employ kinetic models that allow us to derive explicit mathematical terms and provide experimental descriptors as a function of the rate constants used to parameterize the kinetic model of the transport cycle. We show that it is possible to utilize these mathematical expressions to deduce, from experimental outcomes, how the mutation has impinged on partial reactions in the transport cycle.
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Affiliation(s)
- Klaus Schicker
- Center for Physiology and Pharmacology, Division of Neurophysiology and Neuropharmacology, Medical University of Vienna, 1090 Vienna, Austria;
| | - Shreyas Bhat
- Center of Physiology and Pharmacology, Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Medical University of Vienna, 1090 Vienna, Austria; (S.B.); (C.F.); (V.B.); (M.F.)
| | - Clemens Farr
- Center of Physiology and Pharmacology, Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Medical University of Vienna, 1090 Vienna, Austria; (S.B.); (C.F.); (V.B.); (M.F.)
| | - Verena Burtscher
- Center of Physiology and Pharmacology, Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Medical University of Vienna, 1090 Vienna, Austria; (S.B.); (C.F.); (V.B.); (M.F.)
| | - Andreas Horner
- Institute of Biophysics, Johannes Kepler University Linz, 4040 Linz, Austria;
| | - Michael Freissmuth
- Center of Physiology and Pharmacology, Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Medical University of Vienna, 1090 Vienna, Austria; (S.B.); (C.F.); (V.B.); (M.F.)
| | - Walter Sandtner
- Center of Physiology and Pharmacology, Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Medical University of Vienna, 1090 Vienna, Austria; (S.B.); (C.F.); (V.B.); (M.F.)
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16
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Jayaraman K, Das AK, Luethi D, Szöllősi D, Schütz GJ, Reith MEA, Sitte HH, Stockner T. SLC6 transporter oligomerization. J Neurochem 2020; 157:919-929. [PMID: 32767560 PMCID: PMC8247324 DOI: 10.1111/jnc.15145] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2020] [Revised: 07/31/2020] [Accepted: 07/31/2020] [Indexed: 12/18/2022]
Abstract
Transporters of the solute carrier 6 (SLC6) family mediate the reuptake of neurotransmitters such as dopamine, norepinephrine, serotonin, GABA, and glycine. SLC6 family members are 12 transmembrane helix‐spanning proteins that operate using the transmembrane sodium gradient for transport. These transporters assume various quaternary arrangements ranging from monomers to complex stoichiometries with multiple subunits. Dopamine and serotonin transporter oligomerization has been implicated in trafficking of newly formed proteins from the endoplasmic reticulum to the plasma membrane with a pre‐fixed assembly. Once at the plasma membrane, oligomers are kept fixed in their quaternary assembly by interaction with phosphoinositides. While it remains unclear how oligomer formation precisely affects physiological transporter function, it has been shown that oligomerization supports the activity of release‐type psychostimulants. Most recently, single molecule microscopy experiments unveiled that the stoichiometry differs between individual members of the SLC6 family. The present overview summarizes our understanding of the influence of plasma membrane constituents on transporter oligomerization, describes the known interfaces between protomers and discusses open questions. ![]()
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Affiliation(s)
- Kumaresan Jayaraman
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Anand K Das
- Institute of Applied Physics, Vienna University of Technology, Vienna, Austria
| | - Dino Luethi
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria.,Institute of Applied Physics, Vienna University of Technology, Vienna, Austria
| | - Dániel Szöllősi
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Gerhard J Schütz
- Institute of Applied Physics, Vienna University of Technology, Vienna, Austria
| | - Maarten E A Reith
- Department of Psychiatry, New York University School of Medicine, New York City, NY, USA
| | - Harald H Sitte
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Thomas Stockner
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
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17
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Niello M, Gradisch R, Loland CJ, Stockner T, Sitte HH. Allosteric Modulation of Neurotransmitter Transporters as a Therapeutic Strategy. Trends Pharmacol Sci 2020; 41:446-463. [PMID: 32471654 PMCID: PMC7610661 DOI: 10.1016/j.tips.2020.04.006] [Citation(s) in RCA: 41] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2020] [Revised: 04/21/2020] [Accepted: 04/22/2020] [Indexed: 12/11/2022]
Abstract
Neurotransmitter transporters (NTTs) are involved in the fine-tuning of brain neurotransmitter homeostasis. As such, they are implicated in a plethora of complex behaviors, including reward, movement, and cognition. During recent decades, compounds that modulate NTT functions have been developed. Some of them are in clinical use for the management of different neuropsychiatric conditions. The majority of these compounds have been found to selectively interact with the orthosteric site of NTTs. Recently, diverse allosteric sites have been described in a number of NTTs, modulating their function. A more complex NTT pharmacology may be useful in the development of novel therapeutics. Here, we summarize current knowledge on such modulatory allosteric sites, with specific focus on their pharmacological and therapeutic potential.
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Affiliation(s)
- Marco Niello
- Centre for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Ralph Gradisch
- Centre for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Claus Juul Loland
- Laboratory for Membrane Protein Dynamics. Department of Neuroscience. University of Copenhagen, Copenhagen, Denmark
| | - Thomas Stockner
- Centre for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Harald H Sitte
- Centre for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, Vienna, Austria; AddRess, Centre for Addiction Research and Science, Medical University of Vienna, Vienna, Austria.
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18
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Barenys M, Reverte I, Masjosthusmann S, Gómez-Catalán J, Fritsche E. Developmental neurotoxicity of MDMA. A systematic literature review summarized in a putative adverse outcome pathway. Neurotoxicology 2019; 78:209-241. [PMID: 31812710 DOI: 10.1016/j.neuro.2019.12.007] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2019] [Revised: 11/11/2019] [Accepted: 12/04/2019] [Indexed: 12/14/2022]
Abstract
The increasing use of illegal drugs by pregnant women causes a public health concern because it is associated with health risks for mothers and their developing children. One of such drugs is MDMA (3,4-methylenedioxymethamphetamine) or ecstasy due to its high consumption in relevant age and sex groups and its adverse effects on human and rodent developing brains. To thoroughly review the current knowledge on the developmentally neurotoxic potential of MDMA we systematically collected and summarized articles investigating developmental neurotoxicity (DNT) of MDMA in humans and animals in vivo and in vitro. In addition, we summarized the findings in a putative adverse outcome pathway (AOP). From an initial 299 articles retrieved from the bibliographic databases Web of Science, PubMed and DART, we selected 39 articles according to inclusion/exclusion criteria for data collection after title/abstract and full text screening. Of these 3 where epidemiological studies, 34 where in vivo studies in mice and rats and 2 were in vitro studies. The three epidemiological studies reported from the same longitudinal study and suggested that MDMA exposure during pregnancy impairs neuromotor function in infants. In rat, postnatal exposure towards MDMA also caused locomotor deficits as well as impaired spatial learning that might be associated with decreased serotonin levels in the hippocampus. In vitro MDMA caused cytotoxicity at high concentrations and effects on the serotonergic and neuritogenic alterations at lower concentrations which are in line with some of the in vivo alterations observed. Considering the adverse outcomes of developmental MDMA described in humans and in rodents we summarized the first putative AOP on developmental compound exposure leading to impaired neuromotor function in children. For generation of this AOP, MDMA exposure was taken as a model compound. In addition, we hypothesized a second AOP involving developmental disturbance of the dopaminergic system. However, further in vitro mechanistic studies are needed to understand the molecular initiating event(s) (MIE) triggering the downstream cascades and obtain consistent evidences causally linking the adverse outcome to effects at the cellular, organ and organism level.
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Affiliation(s)
- Marta Barenys
- GRET, INSA-UB and Toxicology Unit, Pharmacology, Toxicology and Therapeutical Chemistry Department, Faculty of Pharmacy, University of Barcelona, 08028 Barcelona, Spain.
| | - Ingrid Reverte
- Department of Physiology and Pharmacology, Sapienza University of Rome, Rome, Italy; Santa Lucia Foundation (IRCCS Fondazione Santa Lucia), Rome, Italy
| | - Stefan Masjosthusmann
- IUF - Leibniz Research Institute for Environmental Medicine, 40225 Düsseldorf, Germany
| | - Jesús Gómez-Catalán
- GRET, INSA-UB and Toxicology Unit, Pharmacology, Toxicology and Therapeutical Chemistry Department, Faculty of Pharmacy, University of Barcelona, 08028 Barcelona, Spain
| | - Ellen Fritsche
- IUF - Leibniz Research Institute for Environmental Medicine, 40225 Düsseldorf, Germany; Heinrich-Heine University, 40225 Düsseldorf, Germany
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19
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Kinetic Models of Secondary Active Transporters. Int J Mol Sci 2019; 20:ijms20215365. [PMID: 31661895 PMCID: PMC6862442 DOI: 10.3390/ijms20215365] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2019] [Revised: 10/24/2019] [Accepted: 10/26/2019] [Indexed: 01/18/2023] Open
Abstract
Kinetic models have been employed to understand the logic of substrate transport through transporters of the Solute Carrier (SLC) family. All SLC transporters operate according to the alternate access model, which posits that substrate transport occurs in a closed loop of partial reactions (i.e., a transport cycle). Kinetic models can help to find realistic estimates for conformational transitions between individual states of the transport cycle. When constrained by experimental results, kinetic models can faithfully describe the function of a candidate transporter at a pre-steady state. In addition, we show that kinetic models can accurately predict the intra- and extracellular substrate concentrations maintained by the transporter at a steady state, even under the premise of loose coupling between the electrochemical gradient of the driving ion and of the substrate. We define the criteria for the design of a credible kinetic model of the SLC transporter. Parsimony is the guiding principle of kinetic modeling. We argue, however, that the level of acceptable parsimony is limited by the need to account for the substrate gradient established by a secondary active transporter, and for random order binding of co-substrates and substrate. Random order binding has consistently been observed in transporters of the SLC group.
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20
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Rudnick G, Sandtner W. Serotonin transport in the 21st century. J Gen Physiol 2019; 151:1248-1264. [PMID: 31570504 PMCID: PMC6829555 DOI: 10.1085/jgp.201812066] [Citation(s) in RCA: 43] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2019] [Accepted: 08/24/2019] [Indexed: 12/16/2022] Open
Abstract
Rudnick and Sandtner review the history of serotonin transporter research in light of structural and electrophysiological advances. Serotonin (5-hydroxytryptamine [5-HT]) is accumulated within nerve endings by the serotonin transporter (SERT), which terminates its extracellular action and provides cytoplasmic 5-HT for refilling of synaptic vesicles. SERT is the target for many antidepressant medications as well as psychostimulants such as cocaine and ecstasy (3,4-methylenedioxymethamphetamine). SERT belongs to the SLC6 family of ion-coupled transporters and is structurally related to several other transporter families. SERT was studied in the 1970s and 1980s using membrane vesicles isolated from blood platelets. These studies led to a proposed stoichiometry of transport that has been challenged by high-resolution structures of SERT and its homologues and by studies of SERT electrophysiology. Here, we review the original evidence alongside more recent structural and electrophysiological evidence. A self-consistent picture emerges with surprising insights into the ion fluxes that accompany 5-HT transport.
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Affiliation(s)
- Gary Rudnick
- Department of Pharmacology, Yale University School of Medicine, New Haven, CT
| | - Walter Sandtner
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
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21
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Erdem FA, Ilic M, Koppensteiner P, Gołacki J, Lubec G, Freissmuth M, Sandtner W. A comparison of the transport kinetics of glycine transporter 1 and glycine transporter 2. J Gen Physiol 2019; 151:1035-1050. [PMID: 31270129 PMCID: PMC6683666 DOI: 10.1085/jgp.201912318] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2019] [Revised: 04/16/2019] [Accepted: 06/17/2019] [Indexed: 12/20/2022] Open
Abstract
Erdem et al. compare the kinetics of the SLC6 family glycine transporters GlyT1 and GlyT2. Though the two transporters are rate-limited by distinct reaction steps, they both display high transport capacity, with the kinetics of GlyT1 sufficient to supply extracellular glycine to the NMDA receptor. Transporters of the solute carrier 6 (SLC6) family translocate their cognate substrate together with Na+ and Cl−. Detailed kinetic models exist for the transporters of GABA (GAT1/SLC6A1) and the monoamines dopamine (DAT/SLC6A3) and serotonin (SERT/SLC6A4). Here, we posited that the transport cycle of individual SLC6 transporters reflects the physiological requirements they operate under. We tested this hypothesis by analyzing the transport cycle of glycine transporter 1 (GlyT1/SLC6A9) and glycine transporter 2 (GlyT2/SLC6A5). GlyT2 is the only SLC6 family member known to translocate glycine, Na+, and Cl− in a 1:3:1 stoichiometry. We analyzed partial reactions in real time by electrophysiological recordings. Contrary to monoamine transporters, both GlyTs were found to have a high transport capacity driven by rapid return of the empty transporter after release of Cl− on the intracellular side. Rapid cycling of both GlyTs was further supported by highly cooperative binding of cosubstrate ions and substrate such that their forward transport mode was maintained even under conditions of elevated intracellular Na+ or Cl−. The most important differences in the transport cycle of GlyT1 and GlyT2 arose from the kinetics of charge movement and the resulting voltage-dependent rate-limiting reactions: the kinetics of GlyT1 were governed by transition of the substrate-bound transporter from outward- to inward-facing conformations, whereas the kinetics of GlyT2 were governed by Na+ binding (or a related conformational change). Kinetic modeling showed that the kinetics of GlyT1 are ideally suited for supplying the extracellular glycine levels required for NMDA receptor activation.
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Affiliation(s)
- Fatma Asli Erdem
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Marija Ilic
- Department of Pharmaceutical Chemistry, Faculty of Life Sciences, University of Vienna, Vienna, Austria
| | | | - Jakub Gołacki
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Gert Lubec
- Neuroproteomics, Paracelsus Private Medical University, Salzburg, Austria
| | - Michael Freissmuth
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Walter Sandtner
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
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22
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How to rescue misfolded SERT, DAT and NET: targeting conformational intermediates with atypical inhibitors and partial releasers. Biochem Soc Trans 2019; 47:861-874. [PMID: 31064865 PMCID: PMC6599159 DOI: 10.1042/bst20180512] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2019] [Revised: 04/12/2019] [Accepted: 04/12/2019] [Indexed: 11/17/2022]
Abstract
Point mutations in the coding sequence for solute carrier 6 (SLC6) family members result in clinically relevant disorders, which are often accounted for by a loss-of-function phenotype. In many instances, the mutated transporter is not delivered to the cell surface because it is retained in the endoplasmic reticulum (ER). The underlying defect is improper folding of the transporter and is the case for many of the known dopamine transporter mutants. The monoamine transporters, i.e. the transporters for norepinephrine (NET/SLC6A2), dopamine (DAT/SLC6A3) and serotonin (SERT/SLC6A4), have a rich pharmacology; hence, their folding-deficient mutants lend themselves to explore the concept of pharmacological chaperoning. Pharmacochaperones are small molecules, which bind to folding intermediates with exquisite specificity and scaffold them to a folded state, which is exported from the ER and delivered to the cell surface. Pharmacochaperoning of mutant monoamine transporters, however, is not straightforward: ionic conditions within the ER are not conducive to binding of most typical monoamine transporter ligands. A collection of compounds exists, which are classified as atypical ligands because they trap monoamine transporters in unique conformational states. The atypical binding mode of some DAT inhibitors has been linked to their anti-addictive action. Here, we propose that atypical ligands and also compounds recently classified as partial releasers can serve as pharmacochaperones.
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Niello M, Cintulova D, Hellsberg E, Jäntsch K, Holy M, Ayatollahi LH, Cozzi NV, Freissmuth M, Sandtner W, Ecker GF, Mihovilovic MD, Sitte HH. para-Trifluoromethyl-methcathinone is an allosteric modulator of the serotonin transporter. Neuropharmacology 2019; 161:107615. [PMID: 31028773 DOI: 10.1016/j.neuropharm.2019.04.021] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2018] [Revised: 04/17/2019] [Accepted: 04/19/2019] [Indexed: 11/15/2022]
Abstract
The transporters for dopamine (DAT) and serotonin (SERT) are important targets in the treatment of psychiatric disorders including major depression, anxiety and attention-deficit hyperactivity disorder. Drugs acting at these transporters can act as inhibitors or as releasers. In addition, it has been recently appreciated that some compounds are less efficacious releasers than amphetamine. Thus, they are classified as partial releasers. Compounds can act on both SERT and DAT or display exquisite selectivity for either SERT or DAT, but the structural basis for selectivity is poorly understood. The trifluoromethyl-substitution of methcathinone in the para-position has been shown to dramatically shift the selectivity of methcathinone (MCAT) towards SERT. Here, we examined MCAT, para-trifluoromethyl-methcathinone (pCF3MCAT) and other analogues to understand (i) the determinants of selectivity and (ii) the effects of the para-CF3-substitution of MCAT on the transport cycle. We systematically tested different para-substituted MCATs by biochemical, computational and electrophysiological approaches: addition of the pCF3group, but not of other substituents with larger van der Waal's volume, lipophilicity or polarity, converted the DAT-selective MCAT into a SERT-selective partial releaser. Electrophysiological and superfusion experiments, together with kinetic modelling, showed that pCF3MCAT, but not MCAT, trapped a fraction of SERTs in an inactive state by occupying the S2-site. These findings define a new mechanism of action for partial releasers, which is distinct from the other two known binding modes underlying partial release. Our observations highlight the fact that the substrate permeation pathway of monoamine transporters supports multiple binding modes, which can be exploited for drug design. This article is part of the issue entitled 'Special Issue on Neurotransmitter Transporters'.
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Affiliation(s)
- Marco Niello
- Institute of Pharmacology, Medical University, Vienna, Austria
| | | | - Eva Hellsberg
- Department of Pharmaceutical Chemistry, University of Vienna, Vienna, Austria
| | - Kathrin Jäntsch
- Institute of Pharmacology, Medical University, Vienna, Austria
| | - Marion Holy
- Institute of Pharmacology, Medical University, Vienna, Austria
| | | | - Nicholas V Cozzi
- Department of Cell and Regenerative Biology, University of Wisconsin School of Medicine and Public Health, Madison, USA
| | | | - Walter Sandtner
- Institute of Pharmacology, Medical University, Vienna, Austria
| | - Gerhard F Ecker
- Department of Pharmaceutical Chemistry, University of Vienna, Vienna, Austria
| | | | - Harald H Sitte
- Institute of Pharmacology, Medical University, Vienna, Austria.
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Hasenhuetl PS, Bhat S, Freissmuth M, Sandtner W. Functional Selectivity and Partial Efficacy at the Monoamine Transporters: A Unified Model of Allosteric Modulation and Amphetamine-Induced Substrate Release. Mol Pharmacol 2018; 95:303-312. [PMID: 30567955 DOI: 10.1124/mol.118.114793] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2018] [Accepted: 12/13/2018] [Indexed: 12/13/2022] Open
Abstract
All clinically approved drugs targeting the plasmalemmal transporters for dopamine, norepinephrine, and serotonin act either as competitive uptake inhibitors or as amphetamine-like releasers. Monoamine transporter (MAT) ligands that allosterically affect MAT-mediated substrate uptake, release, or both were recently discovered. Their modes of action have not yet been explained in a unified framework. Here, we go beyond competitive inhibitors and classic amphetamines and introduce concepts for partial efficacy at and allosteric modulation of MATs. After we elaborate on a kinetic account for amphetamine action, we provide an explanation for partial release (i.e., the observation that some amphetamines are less efficacious than others in inducing monoamine efflux). We then elucidate mechanisms of allosteric inhibition and stimulation of MATs, which can be functionally selective for either substrate uptake or amphetamine-induced release. These concepts are integrated into a parsimonious kinetic framework, which relies exclusively on physiologic transport modes (without any deviation from an alternating access mechanism). The model posits cooperative substrate and Na+ binding and functional selectivity by conformational selection (i.e., preference of the allosteric modulators for the substrate-loaded or substrate-free states of the transporter). Thus, current knowledge about the kinetics of monoamine transport is sufficiently detailed to provide a quantitative description of the releasing action of amphetamines, of substrate uptake, and of selective modulation thereof by allosteric modulators.
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Affiliation(s)
- Peter S Hasenhuetl
- Institute of Pharmacology, Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Shreyas Bhat
- Institute of Pharmacology, Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Michael Freissmuth
- Institute of Pharmacology, Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Walter Sandtner
- Institute of Pharmacology, Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
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