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Bhat S, Niello M, Schicker K, Pifl C, Sitte HH, Freissmuth M, Sandtner W. Handling of intracellular K + determines voltage dependence of plasmalemmal monoamine transporter function. eLife 2021; 10:67996. [PMID: 34061030 PMCID: PMC8192120 DOI: 10.7554/elife.67996] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2021] [Accepted: 05/30/2021] [Indexed: 12/16/2022] Open
Abstract
The concentrative power of the transporters for dopamine (DAT), norepinephrine (NET), and serotonin (SERT) is thought to be fueled by the transmembrane Na+ gradient, but it is conceivable that they can also tap other energy sources, for example, membrane voltage and/or the transmembrane K+ gradient. We have addressed this by recording uptake of endogenous substrates or the fluorescent substrate APP+(4-(4-dimethylamino)phenyl-1-methylpyridinium) under voltage control in cells expressing DAT, NET, or SERT. We have shown that DAT and NET differ from SERT in intracellular handling of K+. In DAT and NET, substrate uptake was voltage-dependent due to the transient nature of intracellular K+ binding, which precluded K+ antiport. SERT, however, antiports K+ and achieves voltage-independent transport. Thus, there is a trade-off between maintaining constant uptake and harvesting membrane potential for concentrative power, which we conclude to occur due to subtle differences in the kinetics of co-substrate ion binding in closely related transporters.
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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 Vienna, Vienna, Austria
| | - Marco Niello
- 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
| | - Klaus Schicker
- Division of Neurophysiology and Neuropharmacology, Centre for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Christian Pifl
- Center for Brain Research, Medical University of Vienna, Vienna, Austria
| | - Harald H Sitte
- 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
| | - 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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Abstract
Products containing psychoactive synthetic cathinones, such as mephedrone and 3,4-methylenedioxypyrovalerone (MDPV) are prevalent in our society. Synthetic cathinones are structurally similar to methamphetamine, and numerous synthetics have biological activity at dopamine, serotonin, and norepinephrine transporters. Importantly, monoamine transporters co-transport sodium ions along with their substrate, and movement of substrates and ions through the transporter can generate measurable ionic currents. Here we review how electrophysiological information has enabled us to determine how synthetic cathinones affect transporter-mediated currents in cells that express these transporters. Specifically, drugs that act as transporter substrates induce inward depolarizing currents when cells are held near their resting membrane potential, whereas drugs that act as transporter blockers induce apparent outward currents by blocking an inherent inward leak current. We have employed the two-electrode voltage-clamp technique in Xenopus laevis oocytes overexpressing monoamine transporters to determine whether synthetic cathinones found in the so-called bath salts products behave as blockers or substrates. We also examined the structure-activity relationships for synthetic cathinone analogs related to the widely abused compound MDPV, a common constituent in "bath salts" possessing potent actions at the dopamine transporter.
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Affiliation(s)
- Ernesto Solis
- In Vivo Electrophysiology Unit, Behavioral Neuroscience Research Branch, National Institute on Drug Abuse - Intramural Research Program, National Institutes of Health, Triad Technology Center, 333 Cassell Drive, Suite 2200, Baltimore, MD, 21224, USA.
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Chloride requirement for monoamine transporters. Pflugers Arch 2016; 468:503-11. [PMID: 26794730 DOI: 10.1007/s00424-015-1783-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2015] [Revised: 12/20/2015] [Accepted: 12/22/2015] [Indexed: 12/18/2022]
Abstract
This review focuses on the Cl(-) requirement for dopamine, serotonin, and norepinephrine (DA, 5-HT, and NE) transport and induced current via the transporters for these transmitters, DAT, SERT, and NET. Indirect evidence exists for the passage of Cl(-) ions through monoamine transporters; however, direct evidence is sparse. An unanswered question is why in some preparations, notably native neurons, it appears that Cl(-) ions carry the current through DAT, whereas in heterologous expression systems Na(+) ions carry the current often referred to as the uncoupled current. It is suggested that different functional states in monoamine transporters represent conformational states that carry dominantly Cl(-) or Na(+). Structures of monoamine transporters contribute enormously to structure-function relationships; however, thus far no structural features support the functionally relevant ionic currents that are known to exist in monoamine transporters.
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He X, Ma Y, Li M, Zhang P, Li Y, Zhang Z. Quantifying and imaging engineered nanomaterials in vivo: challenges and techniques. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2013; 9:1482-1491. [PMID: 23027545 DOI: 10.1002/smll.201201502] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2012] [Revised: 07/24/2012] [Indexed: 06/01/2023]
Abstract
Quantifying and imaging the engineered nanomaterials (ENMs) in vivo can provide information on the bio-distribution and fate of ENMs in living systems. A necessary amount of in vivo quantitative data is indispensable to verify the extrapolation from in vitro tests, to modify the predictive models of ENM exposure, and to underpin the risk management strategy for ENMs. However, it remains a challenge to quantitatively assess the bio-distribution of ENMs under realistic exposure, their long-term deposition (especially in non-targeted tissues), their passage across the natural barriers, and the impacts of nano-bio interactions on their in vivo behaviors. Some commonly used techniques for in vivo ENM quantification, such as electron microscopy, fluorescence-based detection, atomic spectroscopy, radiotracing, and techniques basing on synchrotron radiation are reviewed, and their technical characteristics, the state of the art, limitations, and future prospects are addressed.
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Affiliation(s)
- Xiao He
- CAS Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety and CAS Key Laboratory of Nuclear Analytical Techniques, Institute of High Energy Physics, Chinese Academy of Sciences (CAS), Beijing 100049, China.
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Oz M, Isaev D, Lorke DE, Hasan M, Petroianu G, Shippenberg TS. Methylene blue inhibits function of the 5-HT transporter. Br J Pharmacol 2012; 166:168-76. [PMID: 21542830 DOI: 10.1111/j.1476-5381.2011.01462.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
BACKGROUND AND PURPOSE Methylene blue (MB) is commonly employed as a treatment for methaemoglobinaemia, malaria and vasoplegic shock. An increasing number of studies indicate that MB can cause 5-HT toxicity when administered with a 5-HT reuptake inhibitor. MB is a potent inhibitor of monoamine oxidases, but other targets that may contribute to MB toxicity have not been identified. Given the role of the 5-HT transporter (SERT) in the regulation of extracellular 5-HT concentrations, the present study aimed to characterize the effect of MB on SERT. EXPERIMENTAL APPROACH Live cell imaging, in conjunction with the fluorescent SERT substrate 4-(4-(dimethylamino)-styryl)-N-methylpyridinium (ASP(+) ), [(3) H]5-HT uptake and whole-cell patch-clamp techniques were employed to examine the effects of MB on SERT function. KEY RESULTS In EM4 cells expressing GFP-tagged human SERT (hSERT), MB concentration-dependently inhibited ASP(+) accumulation (IC(50) : 1.4 ± 0.3 µM). A similar effect was observed in N2A cells. Uptake of [(3) H]5-HT was decreased by MB pretreatment. Furthermore, patch-clamp studies in hSERT expressing cells indicated that MB significantly inhibited 5-HT-evoked ion currents. Pretreatment with 8-Br-cGMP did not alter the inhibitory effect of MB on hSERT activity, and intracellular Ca(2+) levels remained unchanged during MB application. Further experiments revealed that ASP(+) binding to cell surface hSERT was reduced after MB treatment. In whole-cell radioligand experiments, exposure to MB (10 µM; 10 min) did not alter surface binding of the SERT ligand [(125) I]RTI-55. CONCLUSIONS AND IMPLICATIONS MB modulated SERT function and suggested that SERT may be an additional target upon which MB acts to produce 5-HT toxicity.
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Affiliation(s)
- Murat Oz
- Department of Pharmacology, UAE University, Al Ain, UAE.
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Solis E, Zdravkovic I, Tomlinson ID, Noskov SY, Rosenthal SJ, De Felice LJ. 4-(4-(dimethylamino)phenyl)-1-methylpyridinium (APP+) is a fluorescent substrate for the human serotonin transporter. J Biol Chem 2012; 287:8852-63. [PMID: 22291010 DOI: 10.1074/jbc.m111.267757] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Monoamine transporters terminate synaptic neurotransmission and are molecular targets for antidepressants and psychostimulants. Fluorescent reporters can monitor real-time transport and are amenable for high-throughput screening. However, until now, their use has mostly been successful to study the catecholamine transporters but not the serotonin (5HT) transporter. Here, we use fluorescence microscopy, electrophysiology, pharmacology, and molecular modeling to compare fluorescent analogs of 1-methyl-4-phenylpyridinium (MPP(+)) as reporters for the human serotonin transporter (hSERT) in single cells. The fluorescent substrate 4-(4-(dimethylamino)phenyl)-1-methylpyridinium (APP(+)) exhibits superior fluorescence uptake in hSERT-expressing HEK293 cells than other MPP(+) analogs tested. APP(+) uptake is Na(+)- and Cl(-)-dependent, displaced by 5HT, and inhibited by fluoxetine, suggesting APP(+) specifically monitors hSERT activity. ASP(+), which was previously used to study catecholamine transporters, is 10 times less potent than APP(+) at inhibiting 5HT uptake and has minimal hSERT-mediated uptake. Furthermore, in hSERT-expressing oocytes voltage-clamped to -60 mV, APP(+) induced fluoxetine-sensitive hSERT-mediated inward currents, indicating APP(+) is a substrate, whereas ASP(+) induced hSERT-mediated outward currents and counteracted 5HT-induced hSERT currents, indicating ASP(+) possesses activity as an inhibitor. Extra-precise ligand receptor docking of APP(+) and ASP(+) in an hSERT homology model showed both ASP(+) and APP(+) docked favorably within the active region; accordingly, comparable concentrations are required to elicit their opposite electrophysiological responses. We conclude APP(+) is better suited than ASP(+) to study hSERT transport fluorometrically.
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Affiliation(s)
- Ernesto Solis
- Graduate Training Program in Neuroscience, Vanderbilt University School of Medicine, Nashville, Tennessee 23235, USA.
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Abstract
AbstractThe development of effective therapeutic interventions for neurodegeneration requires a better understanding of the early events that precede neuronal loss. Recent work in various disease models has begun to emphasize the significance of presynaptic dysfunction as an early event that occurs before manifestation of neurological disorders. Dysregulation of dopamine (DA) homeostasis is implicated in neurodegenerative diseases, drug addiction, and neuropsychiatric disorders. The neuronal plasma membrane dopamine transporter (DAT) is essential for the maintenance of DA homeostasis in the brain. α-synuclein is a 140-amino acid protein that forms a stable complex with DAT and is linked to the pathogenesis of neurodegenerative disease. In this review we will examine the prevailing hypotheses for α-synuclein-regulation of DAT biology.
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Swant J, Goodwin JS, North A, Ali AA, Gamble-George J, Chirwa S, Khoshbouei H. α-Synuclein stimulates a dopamine transporter-dependent chloride current and modulates the activity of the transporter. J Biol Chem 2011; 286:43933-43943. [PMID: 21990355 DOI: 10.1074/jbc.m111.241232] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Dysregulation of dopamine (DA) homeostasis is implicated in neurodegenerative diseases, drug addiction, and neuropsychiatric disorders. The neuronal plasma membrane dopamine transporter (DAT) is essential for the maintenance of DA homeostasis in the brain. α-Synuclein is a 140-amino acid protein that forms a stable complex with DAT and is linked to the pathogenesis of neurodegenerative disease. To elucidate the potential functional consequences of DAT/α-synuclein interaction, we explored α-synuclein modulation of DAT activity in midbrain dopaminergic neurons obtained from TH::RFP mice, immortalized DA neurons, and a heterologous system expressing DAT. We used dual pipette whole cell patch clamp recording to measure the DAT-mediated current before and after dialysis of recombinant α-synuclein into immortalized DA neurons. Our data suggest that intracellular α-synuclein induces a Na+ independent but Cl--sensitive inward current in DAT-expressing cells. This current is blocked by DAT blocker GBR12935 and is absent when heat-inactivated α-synuclein is dialyzed into these cells. The functional consequence of this interaction on DAT activity was further examined with real-time monitoring of transport function using a fluorescent substrate of DAT, 4-(4-(dimethylamino)styryl)-N-methylpyridinium (ASP+). Overexpression of α-synuclein in DAT-positive immortalized DA neurons and CHO cells expressing DAT decreased the magnitude and rate of DAT-mediated substrate uptake without a decrease in the initial binding of the substrate at the plasma membrane. Taken together our findings are consistent with the interpretation that DAT/α-synuclein interaction at the cell surface results in a DAT-dependent, Na+-insensitive, Cl-sensitive inward current with a decrease in substrate uptake, suggesting that DAT/α-synuclein interaction can modulate dopamine transmission and thus neuronal function.
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Affiliation(s)
- Jarod Swant
- Department of Biomedical Sciences, Meharry Medical College, Nashville, Tennessee 37208
| | - J Shawn Goodwin
- Department of Biomedical Sciences, Meharry Medical College, Nashville, Tennessee 37208
| | - Ashley North
- Department of Biomedical Sciences, Meharry Medical College, Nashville, Tennessee 37208
| | | | - Joyonna Gamble-George
- Department of Biomedical Sciences, Meharry Medical College, Nashville, Tennessee 37208
| | - Sanika Chirwa
- Department of Biomedical Sciences, Meharry Medical College, Nashville, Tennessee 37208
| | - Habibeh Khoshbouei
- Department of Biomedical Sciences, Meharry Medical College, Nashville, Tennessee 37208.
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Oz M, Jaligam V, Galadari S, Petroianu G, Shuba YM, Shippenberg TS. The endogenous cannabinoid, anandamide, inhibits dopamine transporter function by a receptor-independent mechanism. J Neurochem 2009; 112:1454-64. [PMID: 20050977 DOI: 10.1111/j.1471-4159.2009.06557.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The endocannabinoid, anandamide (AEA), modulates the activity of the dopamine transporter (DAT) in heterologous cells and synaptosomal preparations. The cellular mechanisms mediating this effect are unknown. The present studies employed live cell imaging techniques and the fluorescent, high affinity DAT substrate, 4-(4-(dimethylamino)-styryl)-N-methylpyridinium (ASP(+)), to address this issue. AEA addition to EM4 cells expressing yellow fluorescent protein-tagged human DAT (hDAT) produced a concentration-dependent inhibition of ASP(+) accumulation (IC(50): 3.2 +/- 0.8 microM). This effect occurred within 1 min after AEA addition and persisted for 10 min thereafter. Pertussis toxin did not attenuate the effects of AEA suggesting a mechanism independent of G(i)/G(o) coupled receptors. The amidohydrolase inhibitor, phenylmethylsulfonyl fluoride (0.2 mM), failed to alter the AEA-evoked inhibition of ASP(+) accumulation. Methanandamide (10 microM), a metabolically stable analogue of AEA inhibited accumulation but arachidonic acid (10 microM) was without effect suggesting that the effects of AEA are not mediated by its metabolic products. The extent of AEA inhibition of ASP(+) accumulation was not altered in cells pre-treated with 1 microM URB597, a specific and potent fatty acid amide hydrolase inhibitor, and the cyclooxygenase inhibitor, indomethacin (5 microM) Live cell imaging revealed a significant redistribution of hDAT from the membrane to the cytosol in response to AEA treatment (10 microM; 10 min). Similarly biotinylation experiments revealed that the decrease in DAT function was associated with a reduction in hDAT cell surface expression. These results demonstrate that AEA modulates DAT function via a cannabinoid receptor-independent mechanism and suggest that AEA may produces this effect, in part, by modulating DAT trafficking.
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Affiliation(s)
- Murat Oz
- Integrative Neuroscience Section, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, US Department of Health and Human Services, Baltimore, Maryland 21224, USA
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Chapter 12 Reflections on FRET imaging. ACTA ACUST UNITED AC 2009. [DOI: 10.1016/s0075-7535(08)00012-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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Blakely RD, DeFelice LJ. All aglow about presynaptic receptor regulation of neurotransmitter transporters. Mol Pharmacol 2007; 71:1206-8. [PMID: 17329498 DOI: 10.1124/mol.107.035493] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Mounting evidence supports the idea that neurotransmitter transporters are subject to many forms of post-translational regulation typically associated with receptors and ion channels, including receptor and kinase-mediated changes in transporter phosphorylation, cell surface trafficking, and/or catalytic activation. Although hints of this regulation can be achieved with traditional radiolabeled substrate flux techniques, higher resolution methods are needed that can localize transporter function in situ as well as permit real-time monitoring of transport function without confounds associated with coincident receptor activation. The elegant study by Bolan et al. (p. 1222) capitalizes on the fluorescent properties of a recently introduced substrate for the dopamine (DA) transporter (DAT), termed 4-(4-(dimethylamino)styryl)-N-methylpyridinium (ASP+), to illuminate a pertussis toxin-sensitive, extracellular signal-regulated kinase (ERK1/2)-dependent pathway by which presynaptic DA D(2) receptors regulate DATs.
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Affiliation(s)
- Randy D Blakely
- Department of Pharmacology, Center for Molecular Neuroscience, Vanderbilt University School of Medicine, Nashville, TN 37232-8548, USA.
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