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      Distinctive single-channel properties of α4β2-nicotinic acetylcholine receptor isoforms

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          Abstract

          Central nervous system nicotinic acetylcholine receptors (nAChR) are predominantly of the α4β2 subtype. Two isoforms exist, with high or low agonist sensitivity (HS-(α4β2) 2β2- and LS-(α4β2) 2α4-nAChR). Both isoforms exhibit similar macroscopic potency and efficacy values at low acetylcholine (ACh) concentrations, mediated by a common pair of high-affinity α4(+)/(-)β2 subunit binding interfaces. However LS-(α4β2) 2α4-nAChR also respond to higher concentrations of ACh, acting at a third α4(+)/(-)α4 subunit interface. To probe isoform functional differences further, HS- and LS-α4β2-nAChR were expressed in Xenopus laevis oocytes and single-channel responses were assessed using cell-attached patch-clamp. In the presence of a low ACh concentration, both isoforms produce low-bursting function. HS-(α4β2) 2β2-nAChR exhibit a single conductance state, whereas LS-(α4β2) 2α4-nAChR display two distinctive conductance states. A higher ACh concentration did not preferentially recruit either conductance state, but did result in increased LS-(α4β2) 2α4-nAChR bursting and reduced closed times. Introduction of an α4(+)/(-)α4-interface loss-of-function α4W182A mutation abolished these changes, confirming this site’s role in mediating LS-(α4β2) 2α4-nAChR responses. Small or large amplitude openings are highly-correlated within individual LS-(α4β2) 2α4-nAChR bursts, suggesting that they arise from distinct intermediate states, each of which is stabilized by α4(+)/(-)α4 site ACh binding. These findings are consistent with α4(+)/(-)α4 subunit interface occupation resulting in allosteric potentiation of agonist actions at α4(+)/(-)β2 subunit interfaces, rather than independent induction of high conductance channel openings.

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          Nicotinic acetylcholine receptors and nicotinic cholinergic mechanisms of the central nervous system.

          Subtypes of neuronal nicotinic acetylcholine receptors (nAChRs) are constructed from numerous subunit combinations that compose channel-receptor complexes with varied functional and pharmacological characteristics. Structural and functional diversity and the broad presynaptic, postsynaptic, and nonsynaptic locations of nAChRs underlie their mainly modulatory roles throughout the mammalian brain. Presynaptic and preterminal nicotinic receptors enhance neurotransmitter release, postsynaptic nAChRs contribute a small minority of fast excitatory transmission, and nonsynaptic nAChRs modulate many neurotransmitter systems by influencing neuronal excitability. Nicotinic receptors have roles in development and synaptic plasticity, and nicotinic mechanisms participate in learning, memory, and attention. Decline, disruption, or alterations of nicotinic cholinergic mechanisms contribute to dysfunctions such as epilepsy, schizophrenia, Parkinson's disease, autism, dementia with Lewy bodies, Alzheimer's disease, and addiction.
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            Estimating single-channel kinetic parameters from idealized patch-clamp data containing missed events.

            We present here a maximal likelihood algorithm for estimating single-channel kinetic parameters from idealized patch-clamp data. The algorithm takes into account missed events caused by limited time resolution of the recording system. Assuming a fixed dead time, we derive an explicit expression for the corrected transition rate matrix by generalizing the theory of Roux and Sauve (1985, Biophys. J. 48:149-158) to the case of multiple conductance levels. We use a variable metric optimizer with analytical derivatives for rapidly maximizing the likelihood. The algorithm is applicable to data containing substates and multiple identical or nonidentical channels. It allows multiple data sets obtained under different experimental conditions, e.g., concentration, voltage, and force, to be fit simultaneously. It also permits a variety of constraints on rate constants and provides standard errors for all estimates of model parameters. The algorithm has been tested extensively on a variety of kinetic models with both simulated and experimental data. It is very efficient and robust; rate constants for a multistate model can often be extracted in a processing time of approximately 1 min, largely independent of the starting values.
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              Structural and functional diversity of native brain neuronal nicotinic receptors.

              Neuronal nicotinic acetylcholine receptors (nAChRs) are a family of ligand-gated ion channels present in the central and peripheral nervous systems, that are permeable to mono- and divalent cations. They share a common basic structure but their pharmacological and functional properties arise from the wide range of different subunit combinations making up distinctive subtypes. nAChRs are involved in many physiological functions in the central and peripheral nervous systems, and are the targets of the widely used drug of abuse nicotine. In addition to tobacco dependence, changes in their number and/or function are associated with neuropsychiatric disorders, ranging from epilepsy to dementia. Although some of the neural circuits involved in the acute and chronic effects of nicotine have been identified, much less is known about which native nAChR subtypes are involved in specific physiological functions and pathophysiological conditions. We briefly review some recent findings concerning the structure and function of native nAChRs, focusing on the subtypes identified in the mesostriatal and habenulo-interpeduncular pathways, two systems involved in nicotine reinforcement and withdrawal. We also discuss recent findings concerning the effect of chronic nicotine on the expression of native subtypes.
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                Author and article information

                Contributors
                Role: ConceptualizationRole: Data curationRole: Formal analysisRole: Funding acquisitionRole: InvestigationRole: MethodologyRole: Project administrationRole: ResourcesRole: VisualizationRole: Writing – original draftRole: Writing – review & editing
                Role: Funding acquisitionRole: MethodologyRole: VisualizationRole: Writing – review & editing
                Role: ResourcesRole: SupervisionRole: VisualizationRole: Writing – review & editing
                Role: ConceptualizationRole: Formal analysisRole: Funding acquisitionRole: Project administrationRole: ResourcesRole: SupervisionRole: VisualizationRole: Writing – original draftRole: Writing – review & editing
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, CA USA )
                1932-6203
                7 March 2019
                2019
                : 14
                : 3
                : e0213143
                Affiliations
                [001]Division of Neurobiology, Barrow Neurological Institute, Phoenix, Arizona, United States of America
                Universidade de Sao Paulo Instituto de Quimica, BRAZIL
                Author notes

                Competing Interests: The authors declare that they have no conflicts of interest with the contents of this article. The contents of this report are solely the responsibility of the authors and do not necessarily represent the official views of the aforementioned awarding agencies.

                [¤]

                Current address: University of Alaska Fairbanks, Department of Chemistry and Biochemistry, Fairbanks, Alaska, United States of America

                Author information
                http://orcid.org/0000-0001-9051-8150
                Article
                PONE-D-18-26985
                10.1371/journal.pone.0213143
                6405073
                30845161
                f6f9adc3-5a56-49a9-b41c-48d295e8e02a
                © 2019 Weltzin et al

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 14 September 2018
                : 17 February 2019
                Page count
                Figures: 12, Tables: 4, Pages: 35
                Funding
                Funded by: funder-id http://dx.doi.org/10.13039/100000002, National Institutes of Health;
                Award ID: R01 DA043567
                Award Recipient : Paul Whiteaker
                Funded by: funder-id http://dx.doi.org/10.13039/100000002, National Institutes of Health;
                Award ID: R21 DA026627
                Award Recipient : Paul Whiteaker
                Funded by: funder-id http://dx.doi.org/10.13039/100009797, Barrow Neurological Foundation;
                Award ID: 3032203
                Award Recipient :
                Funded by: funder-id http://dx.doi.org/10.13039/100009797, Barrow Neurological Foundation;
                Award ID: 3032206
                Award Recipient :
                Funded by: funder-id http://dx.doi.org/10.13039/100009797, Barrow Neurological Foundation;
                Award ID: 3031885
                Award Recipient :
                Funded by: Barrow Neurological Foundation
                Award ID: 3032203
                Award Recipient : Paul Whiteaker
                Research described in this article was supported by grants R01 DA043567 and R21 DA026627 to PW from the National Institutes of Health, and by funds from the Barrow Neurological Foundation to PW, MMW, AAG, and RJL. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
                Categories
                Research Article
                Biology and Life Sciences
                Biochemistry
                Proteins
                Transmembrane Receptors
                Acetylcholine Receptors
                Nicotinic Acetylcholine Receptors
                Biology and Life Sciences
                Cell Biology
                Signal Transduction
                Transmembrane Receptors
                Acetylcholine Receptors
                Nicotinic Acetylcholine Receptors
                Computer and Information Sciences
                Systems Science
                Dwell Time
                Physical Sciences
                Mathematics
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                Biology and Life Sciences
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                Animal Studies
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                Research and Analysis Methods
                Animal Studies
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                Xenopus
                Xenopus Oocytes
                Research and Analysis Methods
                Model Organisms
                Xenopus
                Xenopus Oocytes
                Research and Analysis Methods
                Animal Studies
                Experimental Organism Systems
                Animal Models
                Xenopus
                Xenopus Oocytes
                Biology and Life Sciences
                Organisms
                Eukaryota
                Animals
                Vertebrates
                Amphibians
                Frogs
                Xenopus
                Xenopus Oocytes
                Research and Analysis Methods
                Bioassays and Physiological Analysis
                Electrophysiological Techniques
                Membrane Electrophysiology
                Single Channel Recording
                Research and Analysis Methods
                Bioassays and Physiological Analysis
                Electrophysiological Techniques
                Membrane Electrophysiology
                Patch Clamp Techniques
                Biology and Life Sciences
                Anatomy
                Nervous System
                Central Nervous System
                Medicine and Health Sciences
                Anatomy
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