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Bae M, Roh JD, Kim Y, Kim SS, Han HM, Yang E, Kang H, Lee S, Kim JY, Kang R, Jung H, Yoo T, Kim H, Kim D, Oh H, Han S, Kim D, Han J, Bae YC, Kim H, Ahn S, Chan AM, Lee D, Kim JW, Kim E. SLC6A20 transporter: a novel regulator of brain glycine homeostasis and NMDAR function. EMBO Mol Med 2021; 13:e12632. [PMID: 33428810 PMCID: PMC7863395 DOI: 10.15252/emmm.202012632] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2020] [Revised: 10/22/2020] [Accepted: 11/19/2020] [Indexed: 12/25/2022] Open
Abstract
Glycine transporters (GlyT1 and GlyT2) that regulate levels of brain glycine, an inhibitory neurotransmitter with co‐agonist activity for NMDA receptors (NMDARs), have been considered to be important targets for the treatment of brain disorders with suppressed NMDAR function such as schizophrenia. However, it remains unclear whether other amino acid transporters expressed in the brain can also regulate brain glycine levels and NMDAR function. Here, we report that SLC6A20A, an amino acid transporter known to transport proline based on in vitro data but is understudied in the brain, regulates proline and glycine levels and NMDAR function in the mouse brain. SLC6A20A transcript and protein levels were abnormally increased in mice carrying a mutant PTEN protein lacking the C terminus through enhanced β‐catenin binding to the Slc6a20a gene. These mice displayed reduced extracellular levels of brain proline and glycine and decreased NMDAR currents. Elevating glycine levels back to normal ranges by antisense oligonucleotide‐induced SLC6A20 knockdown, or the competitive GlyT1 antagonist sarcosine, normalized NMDAR currents and repetitive climbing behavior observed in these mice. Conversely, mice lacking SLC6A20A displayed increased extracellular glycine levels and NMDAR currents. Lastly, both mouse and human SLC6A20 proteins mediated proline and glycine transports, and SLC6A20 proteins could be detected in human neurons. These results suggest that SLC6A20 regulates proline and glycine homeostasis in the brain and that SLC6A20 inhibition has therapeutic potential for brain disorders involving NMDAR hypofunction.
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Affiliation(s)
- Mihyun Bae
- Center for Synaptic Brain Dysfunctions, Institute for Basic Science (IBS), Daejeon, Korea
| | - Junyeop Daniel Roh
- Department of Biological Sciences, Korea Advanced Institute for Science and Technology (KAIST), Daejeon, Korea
| | - Youjoung Kim
- Department of Biological Sciences, Korea Advanced Institute for Science and Technology (KAIST), Daejeon, Korea
| | - Seong Soon Kim
- Therapeutics and Biotechnology Division, Korea Research Institute of Chemical Technology (KRICT), Daejeon, Korea
| | - Hye Min Han
- Department of Anatomy and Neurobiology, School of Dentistry, Kyungpook National University, Daegu, Korea
| | - Esther Yang
- Department of Anatomy and Division of Brain Korea 21, Biomedical Science, College of Medicine, Korea University, Seoul, Korea
| | - Hyojin Kang
- Division of National Supercomputing, KISTI, Daejeon, Korea
| | - Suho Lee
- Center for Synaptic Brain Dysfunctions, Institute for Basic Science (IBS), Daejeon, Korea
| | - Jin Yong Kim
- Department of Anatomy and Division of Brain Korea 21, Biomedical Science, College of Medicine, Korea University, Seoul, Korea
| | - Ryeonghwa Kang
- Department of Biological Sciences, Korea Advanced Institute for Science and Technology (KAIST), Daejeon, Korea
| | - Hwajin Jung
- Center for Synaptic Brain Dysfunctions, Institute for Basic Science (IBS), Daejeon, Korea
| | - Taesun Yoo
- Center for Synaptic Brain Dysfunctions, Institute for Basic Science (IBS), Daejeon, Korea
| | - Hyosang Kim
- Department of Biological Sciences, Korea Advanced Institute for Science and Technology (KAIST), Daejeon, Korea
| | - Doyoun Kim
- Center for Synaptic Brain Dysfunctions, Institute for Basic Science (IBS), Daejeon, Korea
| | - Heejeong Oh
- Department of Biological Sciences, Korea Advanced Institute for Science and Technology (KAIST), Daejeon, Korea
| | - Sungwook Han
- Department of Biological Sciences, Korea Advanced Institute for Science and Technology (KAIST), Daejeon, Korea
| | - Dayeon Kim
- Graduate School of Medical Science and Engineering, KAIST, Daejeon, Korea
| | - Jinju Han
- Graduate School of Medical Science and Engineering, KAIST, Daejeon, Korea
| | - Yong Chul Bae
- Department of Anatomy and Neurobiology, School of Dentistry, Kyungpook National University, Daegu, Korea
| | - Hyun Kim
- Department of Anatomy and Division of Brain Korea 21, Biomedical Science, College of Medicine, Korea University, Seoul, Korea
| | - Sunjoo Ahn
- Therapeutics and Biotechnology Division, Korea Research Institute of Chemical Technology (KRICT), Daejeon, Korea
| | - Andrew M Chan
- School of Biomedical Sciences, The Chinese University of Hong Kong, Hong Kong, Hong Kong SAR, China
| | - Daeyoup Lee
- Department of Biological Sciences, Korea Advanced Institute for Science and Technology (KAIST), Daejeon, Korea
| | - Jin Woo Kim
- Department of Biological Sciences, Korea Advanced Institute for Science and Technology (KAIST), Daejeon, Korea
| | - Eunjoon Kim
- Center for Synaptic Brain Dysfunctions, Institute for Basic Science (IBS), Daejeon, Korea.,Department of Biological Sciences, Korea Advanced Institute for Science and Technology (KAIST), Daejeon, Korea
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Annecchino LA, Schultz SR. Progress in automating patch clamp cellular physiology. Brain Neurosci Adv 2018; 2:2398212818776561. [PMID: 32166142 PMCID: PMC7058203 DOI: 10.1177/2398212818776561] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2018] [Accepted: 04/19/2018] [Indexed: 12/30/2022] Open
Abstract
Patch clamp electrophysiology has transformed research in the life sciences over the last few decades. Since their inception, automatic patch clamp platforms have evolved considerably, demonstrating the capability to address both voltage- and ligand-gated channels, and showing the potential to play a pivotal role in drug discovery and biomedical research. Unfortunately, the cell suspension assays to which early systems were limited cannot recreate biologically relevant cellular environments, or capture higher order aspects of synaptic physiology and network dynamics. In vivo patch clamp electrophysiology has the potential to yield more biologically complex information and be especially useful in reverse engineering the molecular and cellular mechanisms of single-cell and network neuronal computation, while capturing important aspects of human disease mechanisms and possible therapeutic strategies. Unfortunately, it is a difficult procedure with a steep learning curve, which has restricted dissemination of the technique. Luckily, in vivo patch clamp electrophysiology seems particularly amenable to robotic automation. In this review, we document the development of automated patch clamp technology, from early systems based on multi-well plates through to automated planar-array platforms, and modern robotic platforms capable of performing two-photon targeted whole-cell electrophysiological recordings in vivo.
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Affiliation(s)
- Luca A. Annecchino
- Centre for Neurotechnology and Department of Bioengineering, Imperial College London, London, UK
| | - Simon R. Schultz
- Centre for Neurotechnology and Department of Bioengineering, Imperial College London, London, UK
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Bell DC, Dallas ML. Using automated patch clamp electrophysiology platforms in pain-related ion channel research: insights from industry and academia. Br J Pharmacol 2017. [PMID: 28622411 DOI: 10.1111/bph.13916] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Automated patch clamp (APC) technology was first developed at the turn of the millennium. The increased throughput it afforded promised a new paradigm in ion channel recordings, offering the potential to overcome the time-consuming, low-throughput bottleneck, arising from manual patch clamp investigations. This has relevance to the fast-paced development of novel therapies for chronic pain. This review highlights the advances in technology, using select examples that have facilitated APC usage in both industry and academia. It covers both first generation and the latest developments in second-generation platforms. In addition, it also provides an overview of the pain research field and how APC platforms have furthered our understanding of ion channel research and the development of pharmacological tools and therapeutics. APC platforms have much to offer to the ion channel research community, and this review highlights areas of best practice for both academia and industry. The impact of APC platforms and the prospects of ion channel research and improved therapeutics for chronic pain will be evaluated. LINKED ARTICLES This article is part of a themed section on Recent Advances in Targeting Ion Channels to Treat Chronic Pain. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.12/issuetoc.
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Affiliation(s)
| | - Mark L Dallas
- School of Pharmacy, University of Reading, Reading, UK
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The association of bacterial C 9-based TTX-like compounds with Prorocentrum minimum opens new uncertainties about shellfish seafood safety. Sci Rep 2017; 7:40880. [PMID: 28106083 PMCID: PMC5247728 DOI: 10.1038/srep40880] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2016] [Accepted: 12/12/2016] [Indexed: 12/23/2022] Open
Abstract
In 2012, Tetrodotoxin (TTX) was identified in mussels and linked to the presence of Prorocentrum minimum (P. minimum) in Greece. The connexion between TTX and P. minimum was further studied in this paper. First, the presence of TTX-producer bacteria, Vibrio and Pseudomonas spp, was confirmed in Greek mussels. In addition these samples showed high activity as inhibitors of sodium currents (INa). P. minimum was before associated with neurotoxic symptoms, however, the nature and structure of toxins produced by this dinoflagellate remains unknown. Three P. minimum strains, ccmp1529, ccmp2811 and ccmp2956, growing in different conditions of temperature, salinity and light were used to study the production of toxic compounds. Electrophysiological assays showed no effect of ccmp2811 strain on INa, while ccmp1529 and ccmp2956 strains were able to significantly reduce INa in the same way as TTX. In these samples two new compounds, m/z 265 and m/z 308, were identified and characterized by liquid chromatography tandem high-resolution mass spectrometry. Besides, two TTX-related bacteria, Roseobacter and Vibrio sp, were observed. These results show for the first time that P. minimum produce TTX-like compounds with a similar ion pattern and C9-base to TTX analogues and with the same effect on INa.
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Yuan NY, Poe MM, Witzigmann C, Cook JM, Stafford D, Arnold LA. Characterization of GABA A receptor ligands with automated patch-clamp using human neurons derived from pluripotent stem cells. J Pharmacol Toxicol Methods 2016; 82:109-114. [PMID: 27544543 DOI: 10.1016/j.vascn.2016.08.006] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2016] [Revised: 05/31/2016] [Accepted: 08/14/2016] [Indexed: 11/16/2022]
Abstract
INTRODUCTION Automated patch clamp is a recent but widely used technology to assess pre-clinical drug safety. With the availability of human neurons derived from pluripotent stem cells, this technology can be extended to determine CNS effects of drug candidates, especially those acting on the GABAA receptor. METHODS iCell Neurons (Cellular Dynamics International, A Fujifilm Company) were cultured for ten days and analyzed by patch clamp in the presence of agonist GABA or in combination with positive allosteric GABAA receptor modulators. Both efficacy and affinity were determined. In addition, mRNA of GABAA receptor subunits were quantified by qRT-PCR. RESULTS We have shown that iCell Neurons are compatible with the IonFlux microfluidic system of the automated patch clamp instrument. Resistance ranging from 15 to 25MΩ was achieved for each trap channel of patch clamped cells in a 96-well plate format. GABA induced a robust change of current with an EC50 of 0.43μM. Positive GABAA receptor modulators diazepam, HZ-166, and CW-04-020 exhibited EC50 values of 0.42μM, 1.56μM, and 0.23μM, respectively. The α2/α3/α5 selective compound HZ-166-induced the highest potentiation (efficacy) of 810% of the current induced by 100nM GABA. Quantification of GABAA receptor mRNA in iCell Neurons revealed high levels of α5 and β3 subunits and low levels of α1, which is similar to the configuration in human neonatal brain. DISCUSSION iCell Neurons represent a new cellular model to characterize GABAergic compounds using automated patch clamp. These cells have excellent representation of cellular GABAA receptor distribution that enable determination of total small molecule efficacy and affinity as measured by cell membrane current change.
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Affiliation(s)
- Nina Y Yuan
- Department of Chemistry and Biochemistry and Milwaukee Institute for Drug Discovery, University of Wisconsin - Milwaukee, 3210 N. Cramer Street, Milwaukee, WI 53211, United States.
| | - Michael M Poe
- Department of Chemistry and Biochemistry and Milwaukee Institute for Drug Discovery, University of Wisconsin - Milwaukee, 3210 N. Cramer Street, Milwaukee, WI 53211, United States.
| | - Christopher Witzigmann
- Department of Chemistry and Biochemistry and Milwaukee Institute for Drug Discovery, University of Wisconsin - Milwaukee, 3210 N. Cramer Street, Milwaukee, WI 53211, United States.
| | - James M Cook
- Department of Chemistry and Biochemistry and Milwaukee Institute for Drug Discovery, University of Wisconsin - Milwaukee, 3210 N. Cramer Street, Milwaukee, WI 53211, United States.
| | - Douglas Stafford
- Department of Chemistry and Biochemistry and Milwaukee Institute for Drug Discovery, University of Wisconsin - Milwaukee, 3210 N. Cramer Street, Milwaukee, WI 53211, United States.
| | - Leggy A Arnold
- Department of Chemistry and Biochemistry and Milwaukee Institute for Drug Discovery, University of Wisconsin - Milwaukee, 3210 N. Cramer Street, Milwaukee, WI 53211, United States.
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Stead C, Brown A, Adams C, Nickolls SJ, Young G, Kammonen J, Pryde D, Cawkill D. Identification of Positive Allosteric Modulators of Glycine Receptors from a High-Throughput Screen Using a Fluorescent Membrane Potential Assay. ACTA ACUST UNITED AC 2016; 21:1042-1053. [PMID: 27412533 DOI: 10.1177/1087057116657779] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Glycine receptor 3 (GlyRα3) is a ligand-gated ion channel of the cys-loop family that plays a key role in mediating inhibitory neurotransmission and regulation of pain signaling in the dorsal horn. Potentiation of GlyRα3 function is therefore of interest as a putative analgesic mechanism with which to target new therapeutics. However, to date, positive allosteric modulators (PAMs) of this receptor with sufficient selectivity to enable target validation studies have not been described. To address this lack of pharmacological tools, we developed a suite of in vitro assays comprising a high-throughput fluorescent membrane potential screen and a medium-throughput electrophysiology assay using IonFlux HT together with conventional manual patch clamp. Using these assays, we conducted a primary screening campaign and report the structures of hit compounds identified as GlyR PAMs. Our functional characterization data reveal a hit compound with high efficacy relative to current known potentiators and selectivity over GABAAR, another major class of inhibitory neurotransmission receptors of importance to pain. These small-molecule GlyR PAMs have high potential both as early tool compounds to enable pharmacological studies of GlyR inhibitory neurotransmission and as a starting point for the development of potent, selective GlyRα3 PAMs as novel analgesics.
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Affiliation(s)
- Clara Stead
- 1 Neusentis (Pfizer Ltd.), Granta Park, Great Abington, Cambridgeshire, UK
| | - Adam Brown
- 1 Neusentis (Pfizer Ltd.), Granta Park, Great Abington, Cambridgeshire, UK
| | - Cathryn Adams
- 1 Neusentis (Pfizer Ltd.), Granta Park, Great Abington, Cambridgeshire, UK
| | - Sarah J Nickolls
- 1 Neusentis (Pfizer Ltd.), Granta Park, Great Abington, Cambridgeshire, UK
| | - Gareth Young
- 1 Neusentis (Pfizer Ltd.), Granta Park, Great Abington, Cambridgeshire, UK
| | - Juha Kammonen
- 1 Neusentis (Pfizer Ltd.), Granta Park, Great Abington, Cambridgeshire, UK
| | - David Pryde
- 1 Neusentis (Pfizer Ltd.), Granta Park, Great Abington, Cambridgeshire, UK
| | - Darren Cawkill
- 1 Neusentis (Pfizer Ltd.), Granta Park, Great Abington, Cambridgeshire, UK
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Danker T, Braun F, Silbernagl N, Guenther E. Catch and Patch: A Pipette-Based Approach for Automating Patch Clamp That Enables Cell Selection and Fast Compound Application. Assay Drug Dev Technol 2016; 14:144-55. [PMID: 26991363 DOI: 10.1089/adt.2015.696] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Manual patch clamp, the gold standard of electrophysiology, represents a powerful and versatile toolbox to stimulate, modulate, and record ion channel activity from membrane fragments and whole cells. The electrophysiological readout can be combined with fluorescent or optogenetic methods and allows for ultrafast solution exchanges using specialized microfluidic tools. A hallmark of manual patch clamp is the intentional selection of individual cells for recording, often an essential prerequisite to generate meaningful data. So far, available automation solutions rely on random cell usage in the closed environment of a chip and thus sacrifice much of this versatility by design. To parallelize and automate the traditional patch clamp technique while perpetuating the full versatility of the method, we developed an approach to automation, which is based on active cell handling and targeted electrode placement rather than on random processes. This is achieved through an automated pipette positioning system, which guides the tips of recording pipettes with micrometer precision to a microfluidic cell handling device. Using a patch pipette array mounted on a conventional micromanipulator, our automated patch clamp process mimics the original manual patch clamp as closely as possible, yet achieving a configuration where recordings are obtained from many patch electrodes in parallel. In addition, our implementation is extensible by design to allow the easy integration of specialized equipment such as ultrafast compound application tools. The resulting system offers fully automated patch clamp on purposely selected cells and combines high-quality gigaseal recordings with solution switching in the millisecond timescale.
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8
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Obergrussberger A, Bru ggemann A, Goetze TA, Rapedius M, Haarmann C, Rinke I, Becker N, Oka T, Ohtsuki A, Stengel T, Vogel M, Steindl J, Mueller M, Stiehler J, George M, Fertig N. Automated Patch Clamp Meets High-Throughput Screening: 384 Cells Recorded in Parallel on a Planar Patch Clamp Module. ACTA ACUST UNITED AC 2015; 21:779-793. [DOI: 10.1177/2211068215623209] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2015] [Indexed: 11/15/2022]
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9
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Berg B, Cortazar B, Tseng D, Ozkan H, Feng S, Wei Q, Chan RYL, Burbano J, Farooqui Q, Lewinski M, Di Carlo D, Garner OB, Ozcan A. Cellphone-Based Hand-Held Microplate Reader for Point-of-Care Testing of Enzyme-Linked Immunosorbent Assays. ACS NANO 2015; 9:7857-66. [PMID: 26159546 DOI: 10.1021/acsnano.5b03203] [Citation(s) in RCA: 212] [Impact Index Per Article: 23.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
Standard microplate based enzyme-linked immunosorbent assays (ELISA) are widely utilized for various nanomedicine, molecular sensing, and disease screening applications, and this multiwell plate batched analysis dramatically reduces diagnosis costs per patient compared to nonbatched or nonstandard tests. However, their use in resource-limited and field-settings is inhibited by the necessity for relatively large and expensive readout instruments. To mitigate this problem, we created a hand-held and cost-effective cellphone-based colorimetric microplate reader, which uses a 3D-printed opto-mechanical attachment to hold and illuminate a 96-well plate using a light-emitting-diode (LED) array. This LED light is transmitted through each well, and is then collected via 96 individual optical fibers. Captured images of this fiber-bundle are transmitted to our servers through a custom-designed app for processing using a machine learning algorithm, yielding diagnostic results, which are delivered to the user within ∼1 min per 96-well plate, and are visualized using the same app. We successfully tested this mobile platform in a clinical microbiology laboratory using FDA-approved mumps IgG, measles IgG, and herpes simplex virus IgG (HSV-1 and HSV-2) ELISA tests using a total of 567 and 571 patient samples for training and blind testing, respectively, and achieved an accuracy of 99.6%, 98.6%, 99.4%, and 99.4% for mumps, measles, HSV-1, and HSV-2 tests, respectively. This cost-effective and hand-held platform could assist health-care professionals to perform high-throughput disease screening or tracking of vaccination campaigns at the point-of-care, even in resource-poor and field-settings. Also, its intrinsic wireless connectivity can serve epidemiological studies, generating spatiotemporal maps of disease prevalence and immunity.
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Affiliation(s)
- Brandon Berg
- Electrical Engineering Department, University of California , Los Angeles, California 90095, United States
- Physics and Astronomy Department, University of California , Los Angeles, California 90095, United States
| | - Bingen Cortazar
- Electrical Engineering Department, University of California , Los Angeles, California 90095, United States
| | - Derek Tseng
- Electrical Engineering Department, University of California , Los Angeles, California 90095, United States
- Bioengineering Department, University of California , Los Angeles, California 90095, United States
| | - Haydar Ozkan
- Electrical Engineering Department, University of California , Los Angeles, California 90095, United States
- Bioengineering Department, University of California , Los Angeles, California 90095, United States
- Biomedical Engineering Department, Fatih Sultan Mehmet Vakif University , Istanbul 34445, Turkey
| | - Steve Feng
- Electrical Engineering Department, University of California , Los Angeles, California 90095, United States
| | - Qingshan Wei
- Electrical Engineering Department, University of California , Los Angeles, California 90095, United States
- Bioengineering Department, University of California , Los Angeles, California 90095, United States
| | - Raymond Yan-Lok Chan
- Electrical Engineering Department, University of California , Los Angeles, California 90095, United States
| | - Jordi Burbano
- Electrical Engineering Department, University of California , Los Angeles, California 90095, United States
| | - Qamar Farooqui
- Electrical Engineering Department, University of California , Los Angeles, California 90095, United States
| | - Michael Lewinski
- Bioengineering Department, University of California , Los Angeles, California 90095, United States
- Roche Molecular Systems, Inc. , Pleasanton, California 94588, United States
| | - Dino Di Carlo
- Bioengineering Department, University of California , Los Angeles, California 90095, United States
- California NanoSystems Institute (CNSI), University of California , Los Angeles, California 90095, United States
- Jonsson Comprehensive Cancer Center, University of California , Los Angeles, California 90095, United States
| | - Omai B Garner
- Department of Pathology and Laboratory Medicine, David Geffen School of Medicine, University of California , Los Angeles, California 90095, United States
| | - Aydogan Ozcan
- Electrical Engineering Department, University of California , Los Angeles, California 90095, United States
- Bioengineering Department, University of California , Los Angeles, California 90095, United States
- California NanoSystems Institute (CNSI), University of California , Los Angeles, California 90095, United States
- Department of Surgery, David Geffen School of Medicine, University of California , Los Angeles, California 90095, United States
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Auzmendi JA, Smoler M, Moffatt L. Dynamics of T-Junction Solution Switching Aimed at Patch Clamp Experiments. PLoS One 2015; 10:e0133187. [PMID: 26177538 PMCID: PMC4503516 DOI: 10.1371/journal.pone.0133187] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2014] [Accepted: 06/23/2015] [Indexed: 11/29/2022] Open
Abstract
Solutions exchange systems are responsible for the timing of drug application on patch clamp experiments. There are two basic strategies for generating a solution exchange. When slow exchanges are bearable, it is easier to perform the exchange inside the tubing system upstream of the exit port. On the other hand, fast, reproducible, exchanges are usually performed downstream of the exit port. As both strategies are combinable, increasing the performance of upstream exchanges is desirable. We designed a simple method for manufacturing T-junctions (300 μm I.D.) and we measured the time profile of exchange of two saline solutions using a patch pipette with an open tip. Three factors were found to determine the timing of the solution switching: pressure, travelled distance and off-center distance. A linear relationship between the time delay and the travelled distance was found for each tested pressure, showing its dependence to the fluid velocity, which increased with pressure. The exchange time was found to increase quadratically with the delay, although a sizeable variability remains unexplained by this relationship. The delay and exchange times increased as the recording pipette moved away from the center of the stream. Those increases became dramatic as the pipette was moved close to the stream borders. Mass transport along the travelled distance between the slow fluid at the border and the fast fluid at the center seems to contribute to the time course of the solution exchange. This effect would be present in all tubing based devices. Present results might be of fundamental importance for the adequate design of serial compound exchangers which would be instrumental in the discovery of drugs that modulate the action of the physiological agonists of ion channels with the purpose of fine tuning their physiology.
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Affiliation(s)
- Jerónimo A. Auzmendi
- Instituto de Química Física de los Materiales, Medio Ambiente y Energía. Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina
| | - Mariano Smoler
- Instituto de Química Física de los Materiales, Medio Ambiente y Energía. Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina
| | - Luciano Moffatt
- Instituto de Química Física de los Materiales, Medio Ambiente y Energía. Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina
- * E-mail:
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Wong LW, Tae HS, Cromer BA. Assembly, trafficking and function of α1β2γ2 GABAA receptors are regulated by N-terminal regions, in a subunit-specific manner. J Neurochem 2015; 134:819-32. [PMID: 26016529 DOI: 10.1111/jnc.13175] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2015] [Revised: 04/16/2015] [Accepted: 05/09/2015] [Indexed: 02/01/2023]
Abstract
GABAA receptors are pentameric ligand-gated ion channels that mediate inhibitory fast synaptic transmission in the central nervous system. Consistent with recent pentameric ligand-gated ion channels structures, sequence analysis predicts an α-helix near the N-terminus of each GABAA receptor subunit. Preceding each α-helix are 8-36 additional residues, which we term the N-terminal extension. In homomeric GABAC receptors and nicotinic acetylcholine receptors, the N-terminal α-helix is functionally essential. Here, we determined the role of the N-terminal extension and putative α-helix in heteromeric α1β2γ2 GABAA receptors. This role was most prominent in the α1 subunit, with deletion of the N-terminal extension or further deletion of the putative α-helix both dramatically reduced the number of functional receptors at the cell surface. Conversely, deletion of the β2 or γ2 N-terminal extension had little effect on the number of functional cell surface receptors. Additional deletion of the putative α-helix in the β2 or γ2 subunits did, however, decrease both functional cell surface receptors and incorporation of the γ2 subunit into mature receptors. In the β2 subunit only, α-helix deletions affected GABA sensitivity and desensitization. Our findings demonstrate that N-terminal extensions and α-helices make key subunit-specific contributions to assembly, consistent with both regions being involved in inter-subunit interactions. N-terminal α-helices and preceding sequences of eukaryotic pentameric ligand-gated ion channels are absent in prokaryotic homologues, suggesting they may not be functionally essential. Here, we show that in heteropentameric α1β2γ2 GABAA receptors, the role of these segments is highly subunit dependent. The extension preceding the α-helix in the α subunit is crucial for assembly and trafficking, but is of little importance in β and γ subunits. Indeed, robust receptor levels remain when the extension and α-helix are removed in β or γ subunits.
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Affiliation(s)
- Lik-Wei Wong
- Health Innovation Research Institute, School of Medical Sciences, RMIT University, Melbourne, Vic., Australia.,Department of Pharmacology and Therapeutics, University of Melbourne, Melbourne, Vic., Australia
| | - Han-Shen Tae
- Health Innovation Research Institute, School of Medical Sciences, RMIT University, Melbourne, Vic., Australia
| | - Brett A Cromer
- Health Innovation Research Institute, School of Medical Sciences, RMIT University, Melbourne, Vic., Australia
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Vaidyanathan S, Anderson KB, Merzel RL, Jacobovitz B, Kaushik MP, Kelly CN, van Dongen MA, Dougherty CA, Orr BG, Banaszak Holl MM. Quantitative Measurement of Cationic Polymer Vector and Polymer-pDNA Polyplex Intercalation into the Cell Plasma Membrane. ACS NANO 2015; 9:6097-6109. [PMID: 25952271 PMCID: PMC4771022 DOI: 10.1021/acsnano.5b01263] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Cationic gene delivery agents (vectors) are important for delivering nucleotides, but are also responsible for cytotoxicity. Cationic polymers (L-PEI, jetPEI, and G5 PAMAM) at 1× to 100× the concentrations required for translational activity (protein expression) induced the same increase in plasma membrane current of HEK 293A cells (30-50 nA) as measured by whole cell patch-clamp. This indicates saturation of the cell membrane by the cationic polymers. The increased currents induced by the polymers are not reversible for over 15 min. Irreversibility on this time scale is consistent with a polymer-supported pore or carpet model and indicates that the cell is unable to clear the polymer from the membrane. For polyplexes, although the charge concentration was the same (at N/P ratio of 10:1), G5 PAMAM and jetPEI polyplexes induced a much larger current increase (40-50 nA) than L-PEI polyplexes (<20 nA). Both free cationic lipid and lipid polyplexes induced a lower increase in current than cationic polymers (<20 nA). To quantify the membrane bound material, partition constants were measured for both free vectors and polyplexes into the HEK 293A cell membrane using a dye influx assay. The partition constants of free vectors increased with charge density of the vectors. Polyplex partition constants did not show such a trend. The long lasting cell plasma permeability induced by exposure to the polymer vectors or the polyplexes provides a plausible mechanism for the toxicity and inflammatory response induced by exposure to these materials.
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Affiliation(s)
- Sriram Vaidyanathan
- †Departments of Biomedical Engineering, ‡Chemistry, and §Physics, and ∥the Programs in Applied Physics and ⊥Biophysics, University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Kevin B Anderson
- †Departments of Biomedical Engineering, ‡Chemistry, and §Physics, and ∥the Programs in Applied Physics and ⊥Biophysics, University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Rachel L Merzel
- †Departments of Biomedical Engineering, ‡Chemistry, and §Physics, and ∥the Programs in Applied Physics and ⊥Biophysics, University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Binyamin Jacobovitz
- †Departments of Biomedical Engineering, ‡Chemistry, and §Physics, and ∥the Programs in Applied Physics and ⊥Biophysics, University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Milan P Kaushik
- †Departments of Biomedical Engineering, ‡Chemistry, and §Physics, and ∥the Programs in Applied Physics and ⊥Biophysics, University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Christina N Kelly
- †Departments of Biomedical Engineering, ‡Chemistry, and §Physics, and ∥the Programs in Applied Physics and ⊥Biophysics, University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Mallory A van Dongen
- †Departments of Biomedical Engineering, ‡Chemistry, and §Physics, and ∥the Programs in Applied Physics and ⊥Biophysics, University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Casey A Dougherty
- †Departments of Biomedical Engineering, ‡Chemistry, and §Physics, and ∥the Programs in Applied Physics and ⊥Biophysics, University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Bradford G Orr
- †Departments of Biomedical Engineering, ‡Chemistry, and §Physics, and ∥the Programs in Applied Physics and ⊥Biophysics, University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Mark M Banaszak Holl
- †Departments of Biomedical Engineering, ‡Chemistry, and §Physics, and ∥the Programs in Applied Physics and ⊥Biophysics, University of Michigan, Ann Arbor, Michigan 48109, United States
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13
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Chevallier OP, Graham SF, Alonso E, Duffy C, Silke J, Campbell K, Botana LM, Elliott CT. New insights into the causes of human illness due to consumption of azaspiracid contaminated shellfish. Sci Rep 2015; 5:9818. [PMID: 25928256 PMCID: PMC4415421 DOI: 10.1038/srep09818] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2014] [Accepted: 03/18/2015] [Indexed: 12/29/2022] Open
Abstract
Azaspiracid (AZA) poisoning was unknown until 1995 when shellfish harvested in Ireland caused illness manifesting by vomiting and diarrhoea. Further in vivo/vitro studies showed neurotoxicity linked with AZA exposure. However, the biological target of the toxin which will help explain such potent neurological activity is still unknown. A region of Irish coastline was selected and shellfish were sampled and tested for AZA using mass spectrometry. An outbreak was identified in 2010 and samples collected before and after the contamination episode were compared for their metabolite profile using high resolution mass spectrometry. Twenty eight ions were identified at higher concentration in the contaminated samples. Stringent bioinformatic analysis revealed putative identifications for seven compounds including, glutarylcarnitine, a glutaric acid metabolite. Glutaric acid, the parent compound linked with human neurological manifestations was subjected to toxicological investigations but was found to have no specific effect on the sodium channel (as was the case with AZA). However in combination, glutaric acid (1mM) and azaspiracid (50nM) inhibited the activity of the sodium channel by over 50%. Glutaric acid was subsequently detected in all shellfish employed in the study. For the first time a viable mechanism for how AZA manifests itself as a toxin is presented.
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Affiliation(s)
- O P Chevallier
- Advanced Asset Technology Centre, Institute for Global Food Security, Queen's University Belfast, Stranmillis Road, Belfast, BT9 5AG, UK
| | - S F Graham
- Beaumont Research Institute, 3811 W Thirteen Mile Road, Royal Oak, MI, 48073
| | - E Alonso
- Department of Pharmacology, Faculty of Veterinary, Campus Lugo, USC, 27002 Lugo, Spain
| | - C Duffy
- Marine Institute, Rinville, Oranmore, Co. Galway, Ireland
| | - J Silke
- Marine Institute, Rinville, Oranmore, Co. Galway, Ireland
| | - K Campbell
- Advanced Asset Technology Centre, Institute for Global Food Security, Queen's University Belfast, Stranmillis Road, Belfast, BT9 5AG, UK
| | - L M Botana
- Department of Pharmacology, Faculty of Veterinary, Campus Lugo, USC, 27002 Lugo, Spain
| | - C T Elliott
- Advanced Asset Technology Centre, Institute for Global Food Security, Queen's University Belfast, Stranmillis Road, Belfast, BT9 5AG, UK
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14
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Evaluation of toxicity equivalent factors of paralytic shellfish poisoning toxins in seven human sodium channels types by an automated high throughput electrophysiology system. Arch Toxicol 2015; 90:479-88. [DOI: 10.1007/s00204-014-1444-y] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2014] [Accepted: 12/17/2014] [Indexed: 12/19/2022]
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15
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Martin NJ, Ferreiro SF, Barbault F, Nicolas M, Lecellier G, Paetz C, Gaysinski M, Alonso E, Thomas OP, Botana LM, Raharivelomanana P. Indole alkaloids from the Marquesan plant Rauvolfia nukuhivensis and their effects on ion channels. PHYTOCHEMISTRY 2015; 109:84-95. [PMID: 25468537 DOI: 10.1016/j.phytochem.2014.10.026] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/03/2014] [Revised: 10/12/2014] [Accepted: 10/20/2014] [Indexed: 06/04/2023]
Abstract
In addition to the already reported nukuhivensiums 1 and 2, 11 indole alkaloids were isolated from the bark of the plant Rauvolfia nukuhivensis, growing in the Marquesas archipelago. The known sandwicine (3), isosandwicine (4), spegatrine (8), lochneram (9), flavopereirine (13) have been found in this plant together with the norsandwicine (5), isonorsandwicine (6), Nb-methylisosandwicine (7), 10-methoxypanarine (10), nortueiaoine (11), tueiaoine (12). The structure elucidation was performed on the basis of a deep exploration of the NMR and HRESIMS data as well as comparison with literature data for similar compounds. Norsandwicine, 10-methoxypanarine, tueiaoine, and more importantly nukuhivensiums, were shown to significantly induce a reduction of IKr amplitude (HERG current). Molecular modelling through docking was performed in order to illustrate this result.
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Affiliation(s)
- Nicolas J Martin
- Laboratoire EIMS UMR 241 EIO, Université de la Polynésie française, BP 6570, 98702 Faa'a, Tahiti, French Polynesia.
| | - Sara F Ferreiro
- Departamento de Farmacología, Facultad de Veterinaria, Universidad de Santiago de Compostela, Lugo, Spain.
| | - Florent Barbault
- Laboratoire ITODYS UMR CNRS 7086, Université Paris Diderot, Sorbonne Paris Cité, 15 rue J.-A. de Baïf, 75013 Paris, France.
| | - Mael Nicolas
- Laboratoire EIMS UMR 241 EIO, Université de la Polynésie française, BP 6570, 98702 Faa'a, Tahiti, French Polynesia.
| | - Gaël Lecellier
- Université de Versailles Saint Quentin en Yvelines, 55 Avenue des Etats-Unis, 78035 Versailles Cedex, France; Laboratoire d'Excellence "CORAIL" - Centre de Recherches Insulaires et Observatoire de l'Environnement (CRIOBE), BP 1013 - 98729, Papetoai, Moorea, French Polynesia.
| | - Christian Paetz
- MPI for Chemical Ecology, Hans-Knöll-Strasse 8, 07745 Jena, Germany.
| | - Marc Gaysinski
- Institut de Chimie de Nice-PCRE, UMR 7272 CNRS, Université de Nice-Sophia Antipolis, Parc Valrose, 06108 Nice, France.
| | - Eva Alonso
- Departamento de Farmacología, Facultad de Veterinaria, Universidad de Santiago de Compostela, Lugo, Spain.
| | - Olivier P Thomas
- Institut de Chimie de Nice-PCRE, UMR 7272 CNRS, Université de Nice-Sophia Antipolis, Parc Valrose, 06108 Nice, France; Institut Méditerranéen de Biodiversité et d́Ecologie marine et continentale, UMR 7263 CNRS - IRD - Aix-Marseille Université - UAPV, Station Marine d́Endoume, Rue de la Batterie des Lions, 13007 Marseille, France.
| | - Luis M Botana
- Departamento de Farmacología, Facultad de Veterinaria, Universidad de Santiago de Compostela, Lugo, Spain.
| | - Phila Raharivelomanana
- Laboratoire EIMS UMR 241 EIO, Université de la Polynésie française, BP 6570, 98702 Faa'a, Tahiti, French Polynesia.
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16
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Wong LW, Tae HS, Cromer BA. Role of the ρ1 GABA(C) receptor N-terminus in assembly, trafficking and function. ACS Chem Neurosci 2014; 5:1266-77. [PMID: 25347026 DOI: 10.1021/cn500220t] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
The GABAC receptor and closely related GABAA receptor are members of the pentameric ligand-gated ion channels (pLGICs) superfamily and mediate inhibitory fast synaptic transmission in the nervous system. Each pLGIC subunit comprises an N-terminal extracellular agonist-binding domain followed by a channel domain and a variable intracellular domain. Available structural information shows that the core of the agonist-binding domain is a β sandwich of ten β-strands, which form the agonist-binding pocket at the subunit interface. This β-sandwich is preceded by an N-terminal α-helix in eukaryotic structures but not in prokaryotic structures. The N-terminal α-helix has been shown to be functionally essential in α7 nicotinic acetylcholine receptors. Sequence analysis of GABAC and GABAA receptors predicts an α-helix in a similar position but preceded by 8 to 46 additional residues, of unknown function, which we term the N-terminal extension. To test the functional role of both the N-terminal extension and the putative N-terminal α-helix in the ρ1 GABAC receptor, we created a series of deletions from the N-terminus. The N-terminal extension was not functionally essential, but its removal did reduce both cell surface expression and cooperativity of agonist-gated channel function. Further deletion of the putative N-terminal α-helix abolished receptor function by preventing cell-surface expression. Our results further demonstrate the essential role of the N-terminal α-helix in the assembly and trafficking of eukaryotic pLGICs. They also provide evidence that the N-terminal extension, although not essential, contributes to receptor assembly, trafficking and conformational changes associated with ligand gating.
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Affiliation(s)
- Lik-Wei Wong
- Health
Innovation Research Institute, School of Medical Sciences, RMIT University, Bundoora, Victoria 3083, Australia
- Department
of Pharmacology and Therapeutics, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Han-Shen Tae
- Health
Innovation Research Institute, School of Medical Sciences, RMIT University, Bundoora, Victoria 3083, Australia
| | - Brett A. Cromer
- Health
Innovation Research Institute, School of Medical Sciences, RMIT University, Bundoora, Victoria 3083, Australia
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17
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Saez NJ, Nozach H, Blemont M, Vincentelli R. High throughput quantitative expression screening and purification applied to recombinant disulfide-rich venom proteins produced in E. coli. J Vis Exp 2014:e51464. [PMID: 25146501 PMCID: PMC4692350 DOI: 10.3791/51464] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Escherichia coli (E. coli) is the most widely used expression system for the production of recombinant proteins for structural and functional studies. However, purifying proteins is sometimes challenging since many proteins are expressed in an insoluble form. When working with difficult or multiple targets it is therefore recommended to use high throughput (HTP) protein expression screening on a small scale (1-4 ml cultures) to quickly identify conditions for soluble expression. To cope with the various structural genomics programs of the lab, a quantitative (within a range of 0.1-100 mg/L culture of recombinant protein) and HTP protein expression screening protocol was implemented and validated on thousands of proteins. The protocols were automated with the use of a liquid handling robot but can also be performed manually without specialized equipment. Disulfide-rich venom proteins are gaining increasing recognition for their potential as therapeutic drug leads. They can be highly potent and selective, but their complex disulfide bond networks make them challenging to produce. As a member of the FP7 European Venomics project (www.venomics.eu), our challenge is to develop successful production strategies with the aim of producing thousands of novel venom proteins for functional characterization. Aided by the redox properties of disulfide bond isomerase DsbC, we adapted our HTP production pipeline for the expression of oxidized, functional venom peptides in the E. coli cytoplasm. The protocols are also applicable to the production of diverse disulfide-rich proteins. Here we demonstrate our pipeline applied to the production of animal venom proteins. With the protocols described herein it is likely that soluble disulfide-rich proteins will be obtained in as little as a week. Even from a small scale, there is the potential to use the purified proteins for validating the oxidation state by mass spectrometry, for characterization in pilot studies, or for sensitive micro-assays.
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Affiliation(s)
- Natalie J Saez
- Architecture et Fonction des Macromolécules Biologiques (AFMB), Aix-Marseille Université
| | - Hervé Nozach
- iBiTec-S, Service d'Ingénierie Moléculaire des Protéines (SIMOPRO), Commissariat à l'énergie atomique et aux énergies alternatives (CEA) Saclay, France
| | - Marilyne Blemont
- Architecture et Fonction des Macromolécules Biologiques (AFMB), Aix-Marseille Université
| | - Renaud Vincentelli
- Architecture et Fonction des Macromolécules Biologiques (AFMB), Aix-Marseille Université;
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18
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Abstract
This unit provides an overview of the principal electrophysiological techniques commonly used for the study of ionic currents and the ion channels that mediate them. These techniques include electroencephalograms (EEGs), electrocardiograms (ECGs), single- and multiunit extracellular recording, multielectrode arrays, transepithelial recording, impedance measurements, and current-clamp, voltage-clamp, patch-clamp, and lipid bilayer recording. The unit also discusses recent advances in high-throughput, automated electrophysiological techniques for drug discovery and the use of stem cells as a tissue source.
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19
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Vaidyanathan S, Orr BG, Banaszak Holl MM. Detergent induction of HEK 293A cell membrane permeability measured under quiescent and superfusion conditions using whole cell patch clamp. J Phys Chem B 2014; 118:2112-23. [PMID: 24548291 PMCID: PMC3983356 DOI: 10.1021/jp4124315] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
![]()
Detergents have several biological
applications but present cytotoxicity
concerns, since they can solubilize cell membranes. Using the IonFlux
16, an ensemble whole cell planar patch clamp, we observed that anionic
sodium dodecyl sulfate (SDS), cationic cetyltrimethylammonium bromide
(CTAB), and cationic, fluorescent octadecyl rhodamine B (ORB) increased
the membrane permeability of cells substantially within a second of
exposure, under superfusion conditions. Increased permeability was
irreversible for 15 min. At subsolubilizing detergent concentrations,
patched cells showed increased membrane currents that reached a steady
state and were intact when imaged using fluorescence microscopy. SDS
solubilized cells at concentrations of 2 mM (2× CMC), while CTAB
did not solubilize cells even at concentrations of 10 mM (1000×
CMC). The relative activity for plasma membrane current induction
was 1:20:14 for SDS, CTAB, and ORB, respectively. Under quiescent
conditions, the relative ratio of lipid to detergent in cell membranes
at the onset of membrane permeability was 1:7:5 for SDS, CTAB, and
ORB, respectively. The partition constants (K) for
SDS, CTAB, and ORB were 23000, 55000, and 39000 M–1, respectively. Combining the whole cell patch clamp data and XTT
viability data, SDS ≤ 0.2 mM and CTAB and ORB ≤ 1 mM
induced cell membrane permeability without causing acute toxicity.
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Affiliation(s)
- Sriram Vaidyanathan
- Departments of Biomedical Engineering, ‡Chemistry, and §Physics, ∥the Program in Applied Physics, and ⊥the Michigan Nanotechnology Institute for Medicine and Biological Sciences, University of Michigan , Ann Arbor, Michigan 48109, United States
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20
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Raphemot R, Kadakia RJ, Olsen ML, Banerjee S, Days E, Smith SS, Weaver CD, Denton JS. Development and validation of fluorescence-based and automated patch clamp-based functional assays for the inward rectifier potassium channel Kir4.1. Assay Drug Dev Technol 2013; 11:532-43. [PMID: 24266659 DOI: 10.1089/adt.2013.544] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The inward rectifier potassium (Kir) channel Kir4.1 plays essential roles in modulation of neurotransmission and renal sodium transport and may represent a novel drug target for temporal lobe epilepsy and hypertension. The molecular pharmacology of Kir4.1 is limited to neurological drugs, such as fluoxetine (Prozac(©)), exhibiting weak and nonspecific activity toward the channel. The development of potent and selective small-molecule probes would provide critically needed tools for exploring the integrative physiology and therapeutic potential of Kir4.1. A fluorescence-based thallium (Tl(+)) flux assay that utilizes a tetracycline-inducible T-Rex-HEK293-Kir4.1 cell line to enable high-throughput screening (HTS) of small-molecule libraries was developed. The assay is dimethyl sulfoxide tolerant and exhibits robust screening statistics (Z'=0.75±0.06). A pilot screen of 3,655 small molecules and lipids revealed 16 Kir4.1 inhibitors (0.4% hit rate). 3,3-Diphenyl-N-(1-phenylethyl)propan-1-amine, termed VU717, inhibits Kir4.1-mediated thallium flux with an IC50 of ∼6 μM. An automated patch clamp assay using the IonFlux HT workbench was developed to facilitate compound characterization. Leak-subtracted ensemble "loose patch" recordings revealed robust tetracycline-inducible and Kir4.1 currents that were inhibited by fluoxetine (IC50=10 μM), VU717 (IC50=6 μM), and structurally related calcium channel blocker prenylamine (IC50=6 μM). Finally, we demonstrate that VU717 inhibits Kir4.1 channel activity in cultured rat astrocytes, providing proof-of-concept that the Tl(+) flux and IonFlux HT assays can enable the discovery of antagonists that are active against native Kir4.1 channels.
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Affiliation(s)
- Rene Raphemot
- 1 Department of Anesthesiology, Vanderbilt University School of Medicine , Nashville, Tennessee
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21
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Rattan R, Vaidyanathan S, Wu GSH, Shakya A, Orr BG, Banaszak Holl MM. Polyplex-induced cytosolic nuclease activation leads to differential transgene expression. Mol Pharm 2013; 10:3013-22. [PMID: 23834286 DOI: 10.1021/mp400103f] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Cytosolic nucleases have been proposed to play an important role in limiting the effectiveness of polyplex-based gene delivery agents. In order to explore the effect of cell membrane disruption on nuclease activation, nuclease activity upon polyplex uptake and localization, and nuclease activity upon gene expression, we employed an oligonucleotide molecular beacon (MB). The MB was incorporated as an integral part of the polymer/DNA polyplex, and two-color flow cytometry experiments were performed to explore the relationship of MB cleavage with propidium iodide (PI) uptake, protein expression, and polyplex uptake. In addition, confocal fluorescence microcopy was performed to examine both polyplex and cleaved MB localization. The impact of cell membrane disruption was also probed using whole-cell patch clamp measurement of the plasma membrane's electrical conductance. Differential activation of cytosolic nuclease was observed with substantial activity for B-PEI and G5 PAMAM dendrimer (G5), less cleavage for jetPEI, and little activity for L-PEI. jetPEI and L-PEI exhibited substantially greater transgene expression, consistent with the lower amounts of MB oligonucleotide cleavage observed. Cytosolic nuclease activity, although dependent on the choice of polymer employed, was not related to the degree of cell plasma membrane disruption that occurred as measured by PI uptake or whole-cell patch clamp.
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Affiliation(s)
- Rahul Rattan
- Department of Biomedical Engineering, Michigan Nanotechnology Institute for Medicine and Biological Sciences, University of Michigan , Ann Arbor, Michigan 48019, United States
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22
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Talwar S, Lynch JW, Gilbert DF. Fluorescence-based high-throughput functional profiling of ligand-gated ion channels at the level of single cells. PLoS One 2013; 8:e58479. [PMID: 23520514 PMCID: PMC3592791 DOI: 10.1371/journal.pone.0058479] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2012] [Accepted: 02/06/2013] [Indexed: 12/26/2022] Open
Abstract
Ion channels are involved in many physiological processes and are attractive targets for therapeutic intervention. Their functional properties vary according to their subunit composition, which in turn varies in a developmental and tissue-specific manner and as a consequence of pathophysiological events. Understanding this diversity requires functional analysis of ion channel properties in large numbers of individual cells. Functional characterisation of ligand-gated channels involves quantitating agonist and drug dose-response relationships using electrophysiological or fluorescence-based techniques. Electrophysiology is limited by low throughput and high-throughput fluorescence-based functional evaluation generally does not enable the characterization of the functional properties of each individual cell. Here we describe a fluorescence-based assay that characterizes functional channel properties at single cell resolution in high throughput mode. It is based on progressive receptor activation and iterative fluorescence imaging and delivers >100 dose-responses in a single well of a 384-well plate, using α1-3 homomeric and αβ heteromeric glycine receptor (GlyR) chloride channels as a model system. We applied this assay with transiently transfected HEK293 cells co-expressing halide-sensitive yellow fluorescent protein and different GlyR subunit combinations. Glycine EC50 values of different GlyR isoforms were highly correlated with published electrophysiological data and confirm previously reported pharmacological profiles for the GlyR inhibitors, picrotoxin, strychnine and lindane. We show that inter and intra well variability is low and that clustering of functional phenotypes permits identification of drugs with subunit-specific pharmacological profiles. As this method dramatically improves the efficiency with which ion channel populations can be characterized in the context of cellular heterogeneity, it should facilitate systems-level analysis of ion channel properties in health and disease and the discovery of therapeutics to reverse pathological alterations.
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Affiliation(s)
- Sahil Talwar
- Queensland Brain Institute, The University of Queensland, Brisbane, Queensland, Australia
| | - Joseph W. Lynch
- Queensland Brain Institute, The University of Queensland, Brisbane, Queensland, Australia
- School of Biomedical Sciences, The University of Queensland, Brisbane, Queensland, Australia
| | - Daniel F. Gilbert
- Queensland Brain Institute, The University of Queensland, Brisbane, Queensland, Australia
- Institute of Medical Biotechnology, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany
- * E-mail:
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23
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de Groot MWGDM, Westerink RHS, Dingemans MML. Don't judge a neuron only by its cover: neuronal function in in vitro developmental neurotoxicity testing. Toxicol Sci 2012; 132:1-7. [PMID: 22961093 DOI: 10.1093/toxsci/kfs269] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Classical cases of developmental neurotoxicity (DNT) in humans and advances in risk assessment methods did not prevent the emergence of new chemicals with (suspected) DNT potential. Exposure to these chemicals may be related to the increased worldwide incidence of learning and neurodevelopmental disorders in children. DNT is often investigated in a traditional manner (in vivo using large numbers of experimental animals), whereas development of in vitro methods for DNT reduces animal use and increases insight into cellular and molecular mechanisms of DNT. Several essential neurodevelopmental processes, including proliferation, migration, differentiation, formation of axons and dendrites, synaptogenesis, and apoptosis, are already being evaluated in vitro using biochemical and morphological endpoints. Yet, investigation of chemical-induced effects on the development of functional neuronal networks, including network formation, inter- and intracellular signaling and neuronal network function, is underrepresented in DNT testing. This view therefore focuses on in vitro models and innovative experimental approaches for functional DNT testing, ranging from optical and electrophysiological measurements of intra- and intercellular signaling in neural stem/progenitor cells to measurements of network activity in neuronal networks using multielectrode arrays. The development of functional DNT assays will strongly support the decision-making process for measures to prevent potential chemical-induced adverse effects on neurodevelopment and cognition in humans. We therefore argue that for risk assessment, biochemical and morphological approaches should be complemented with investigations of neuronal (network) functionality.
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