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Mehrdel B, Villalba-Galea CA. Effect of a sensing charge mutation on the deactivation of KV7.2 channels. J Gen Physiol 2024; 156:e202213284. [PMID: 38236165 PMCID: PMC10796215 DOI: 10.1085/jgp.202213284] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2022] [Revised: 08/28/2023] [Accepted: 01/03/2024] [Indexed: 01/19/2024] Open
Abstract
Potassium-selective, voltage-gated channels of the KV7 family are critical regulators of electrical excitability in many cell types. Removing the outermost putative sensing charge (R198) of the human KV7.2 shifts its activation voltage dependence toward more negative potentials. This suggests that removing a charge "at the top" of the fourth (S4) segment of the voltage-sensing domain facilitates activation. Here, we hypothesized that restoring that charge would bring back the activation to its normal voltage range. We introduced the mutation R198H in KV7.2 with the idea that titrating the introduced histidine with protons would reinstate the sensing charge. As predicted, the mutant's activation voltage dependence changed as a function of the external pH (pHEXT) while modest changes in the activation voltage dependence were observed with the wild-type (WT) channel. On the other hand, the deactivation kinetics of the R198H mutant was remarkably sensitive to pHEXT changes, readily deactivating at pHEXT 6, while becoming slower to deactivate at pHEXT 8. In contrast, the KV7.2 WT displayed modest changes in the deactivation kinetics as a function of pHEXT. This suggested that the charge of residue 198 was critical for deactivation. However, in a surprising turn, the mutant R198Q-a non-titratable mutation-also displayed a high pHEXT sensitivity activity. We thus concluded that rather than the charge at position 198, the protonation status of the channel's extracellular face modulates the open channel stabilization and that the charge of residue 198 is required for the voltage sensor to effectively deactivate the channel, overcoming the stabilizing effect of high pHEXT.
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Affiliation(s)
- Baharak Mehrdel
- Department of Physiology and Pharmacology, Thomas J. Long School of Pharmacy, University of the Pacific, Stockton, CA, USA
| | - Carlos A. Villalba-Galea
- Department of Physiology and Pharmacology, Thomas J. Long School of Pharmacy, University of the Pacific, Stockton, CA, USA
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2
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Shogren IS, Gonzales JP, Boland LM. An affordable Three-Dimensional (3D) Printed Recording Chamber for Two-Electrode Voltage Clamp Electrophysiology. JOURNAL OF UNDERGRADUATE NEUROSCIENCE EDUCATION : JUNE : A PUBLICATION OF FUN, FACULTY FOR UNDERGRADUATE NEUROSCIENCE 2023; 21:A91-A96. [PMID: 37588644 PMCID: PMC10426821 DOI: 10.59390/vskd5667] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/19/2022] [Revised: 01/02/2023] [Accepted: 01/03/2023] [Indexed: 08/18/2023]
Abstract
Two electrode voltage-clamp (TEVC) electrophysiology in Xenopus oocytes is a common approach to studying the physiology and pharmacology of membrane transport proteins. Undergraduates may learn to use TEVC methodology in neuroscience or physiology courses and/or in faculty-mentored research experiences. Challenges with the methodology include the cost of commercially available recording chambers, especially when a lab needs multiple copies, and the additional time and expertise needed to use agar bridges and to stabilize solution flow and minimize noise from solution aspiration. Offering a low-cost and accessible recording chamber that overcomes these challenges would lower the barriers to success for undergraduates while also supporting publication-quality recordings. To address these issues, we developed a recording chamber using stereolithography, a 3D printing process. The physiology (PhISio) recording chamber features two options for solution aspiration that allow for individual preferences, optimizes placement of pre-made agar bridges to achieve laminar flow and reduce the time delays in initiating daily experiments, and minimizes the challenges of changing solution height and aspiration noise during perfusion. We compared the functionality of the PhISio chamber with a commercially available Warner Instruments RC-1Z chamber in electrophysiological recordings of inwardly rectifying potassium channels expressed in Xenopus oocytes. The PhISio chamber produced equivalent results to the RC-1Z chamber with respect to time-dependent solution changes and has several operational advantages for both new and experienced electrophysiologists, providing an affordable and convenient alternative to commercially available TEVC recording chambers.
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Affiliation(s)
- Ian Sk Shogren
- Biology Department, University of Richmond, Richmond, VA 23713
| | - Jean P Gonzales
- Biology Department, University of Richmond, Richmond, VA 23713
| | - Linda M Boland
- Biology Department, University of Richmond, Richmond, VA 23713
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3
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Chang ED, Owen SF, Hogstrand C, Bury NR. Active Pharmaceutical Ingredient Uptake by Zebrafish (Danio rerio) Oct2 (slc22a2) Transporter Expressed in Xenopus laevis Oocytes. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY 2022; 41:2993-2998. [PMID: 36102855 PMCID: PMC9827845 DOI: 10.1002/etc.5480] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/12/2022] [Revised: 07/05/2022] [Accepted: 09/07/2022] [Indexed: 06/15/2023]
Abstract
Uptake of active pharmaceutical ingredients (APIs) across the gill epithelium of fish is via either a passive or facilitated transport process, with the latter being more important at the lower concentrations more readily observed in the environment. The solute carrier (SLC) 22A family, which includes the organic cation transporter OCT2 (SLC22A2), has been shown in mammals to transport several endogenous chemicals and APIs. Zebrafish oct2 was expressed in Xenopus oocytes and the uptake of ranitidine, propranolol, and tetraethylammonium characterized. Uptake of ranitidine and propranolol was time- and concentration-dependent with a km and Vmax for ranitidine of 246 µM and 45 pmol/(oocyte × min) and for propranolol of 409 µM and 190 pmol/(oocyte × min), respectively. Uptake of tetraethylammonium (TEA) was inhibited by propranolol, amantadine, and cimetidine, known to be human OCT2 substrates, but not quinidine or ranitidine. At external media pH 7 and 8 propranolol uptake was 100-fold greater than at pH 6; pH did not affect ranitidine or TEA uptake. It is likely that cation uptake is driven by the electrochemical gradient across the oocyte. Uptake kinetics parameters, such as those derived in the present study, coupled with knowledge of transporter localization and abundance and API metabolism, can help derive pharmacokinetic models. Environ Toxicol Chem 2022;41:2993-2998. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.
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Affiliation(s)
- Elisabeth D. Chang
- Division of Diabetes and Nutritional SciencesKing's College LondonLondonUK
| | | | - Christer Hogstrand
- Division of Diabetes and Nutritional SciencesKing's College LondonLondonUK
| | - Nic R. Bury
- School of Ocean and Earth ScienceUniversity of SouthamptonSouthamptonUK
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Tanner GR, Tzingounis AV. The mammalian nodal action potential: new data bring new perspectives. ADVANCES IN PHYSIOLOGY EDUCATION 2022; 46:693-702. [PMID: 36173340 DOI: 10.1152/advan.00171.2021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/01/2021] [Revised: 09/19/2022] [Accepted: 09/19/2022] [Indexed: 06/16/2023]
Abstract
Since its discovery in the mid-20th century, the Hodgkin-Huxley biophysical model of the squid giant axon's (SGA's) neurophysiology has traditionally served as the basis for the teaching of action potential (AP) dynamics in the physiology classroom. This model teaches that leak conductances set membrane resting potential; that fast, inactivating, voltage-gated sodium channels effect the SGA AP upstroke; and that delayed, rectifying, noninactivating voltage-gated potassium channels carry AP repolarization and the early part of the afterhyperpolarization (AHP). This model serves well to introduce students to the fundamental ideas of resting potential establishment and maintenance, as well as basic principles of AP generation and propagation. Furthermore, the Hodgkin-Huxley SGA model represents an excellent and accessible starting point for discussion of the concept of AP threshold and the role of passive electrical properties of the neuron. Additionally, the introduction of the Hodgkin-Huxley model of the SGA AP permits the integration of physiological principles, as instructors ask students to apply previously studied principles of transporter and channel biophysics to the essential physiological phenomenon of electrical signal conduction. However, both some early observations as well as more recent evidence strongly suggest that this seminal invertebrate model of AP dynamics does not appropriately capture the full story for mammalian axons. We review recent evidence that mammalian axonal nodes of Ranvier repolarize largely (though not exclusively) through the activity of leak potassium-ion (K+) conductances carried through two-pore domain (K2P) channels. We call for changes to physiology textbooks and curricula to highlight this remarkable difference in invertebrate and mammalian AP repolarization mechanisms.NEW & NOTEWORTHY Historically, physiology courses have typically taught that action potential repolarization occurs exclusively due to the activation of delayed-rectifier voltage-gated potassium channels. Here, we review and highlight recent evidence that leak potassium channels of the two-pore domain (K2P) class may largely serve this repolarization role at mammalian nodes of Ranvier. We call for the inclusion of these ideas in physiology curricula at all levels, from high school to graduate school.
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Affiliation(s)
- Geoffrey R Tanner
- Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut
- Connecticut Institute for the Brain and Cognitive Sciences, University of Connecticut, Storrs, Connecticut
| | - Anastasios V Tzingounis
- Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut
- Connecticut Institute for the Brain and Cognitive Sciences, University of Connecticut, Storrs, Connecticut
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Chai Z, Tzingounis AV, Lykotrafitis G. The periodic axon membrane skeleton leads to Na nanodomains but does not impact action potentials. Biophys J 2022; 121:3334-3344. [PMID: 36029000 PMCID: PMC9515372 DOI: 10.1016/j.bpj.2022.08.027] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2022] [Revised: 07/07/2022] [Accepted: 08/19/2022] [Indexed: 11/20/2022] Open
Abstract
Recent work has established that axons have a periodic skeleton structure comprising of azimuthal actin rings connected via longitudinal spectrin tetramer filaments. This structure endows the axon with structural integrity and mechanical stability. Additionally, voltage-gated sodium channels follow the periodicity of the active-spectrin arrangement, spaced ∼190 nm segments apart. The impact of this periodic arrangement of sodium channels on the generation and propagation of action potentials is unknown. To address this question, we simulated an action potential using the Hodgkin-Huxley formalism in a cylindrical compartment, but instead of using a homogeneous distribution of voltage-gated sodium channels in the membrane, we applied the experimentally determined periodic arrangement. We found that the periodic distribution of voltage-gated sodium channels does not significantly affect the generation or propagation of action potentials but instead leads to large, localized sodium action currents caused by high-density sodium nanodomains. Additionally, our simulations show that the distance between periodic sodium channel strips could control axonal excitability, suggesting a previously underappreciated mechanism to regulate neuronal firing properties. Together, this work provides a critical new insight into the role of the periodic arrangement of sodium channels in axons, providing a foundation for future experimental studies.
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Affiliation(s)
- Zhaojie Chai
- Department of Mechanical Engineering, University of Connecticut, Storrs, Connecticut
| | | | - George Lykotrafitis
- Department of Mechanical Engineering, University of Connecticut, Storrs, Connecticut; Department of Biomedical Engineering, University of Connecticut, Storrs, Connecticut.
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6
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Boukens BJD, Joyce W, Kristensen DL, Hooijkaas I, Jongejan A, Wang T, Jensen B. Catecholamines are key modulators of ventricular repolarization patterns in the ball python (Python regius). J Gen Physiol 2022; 154:212914. [PMID: 34910097 PMCID: PMC8679508 DOI: 10.1085/jgp.202012761] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2020] [Revised: 10/28/2021] [Accepted: 11/19/2021] [Indexed: 12/13/2022] Open
Abstract
Ectothermic vertebrates experience daily changes in body temperature, and anecdotal observations suggest these changes affect ventricular repolarization such that the T-wave in the ECG changes polarity. Mammals, in contrast, can maintain stable body temperatures, and their ventricular repolarization is strongly modulated by changes in heart rate and by sympathetic nervous system activity. The aim of this study was to assess the role of body temperature, heart rate, and circulating catecholamines on local repolarization gradients in the ectothermic ball python (Python regius). We recorded body-surface electrocardiograms and performed open-chest high-resolution epicardial mapping while increasing body temperature in five pythons, in all of which there was a change in T-wave polarity. However, the vector of repolarization differed between individuals, and only a subset of leads revealed T-wave polarity change. RNA sequencing revealed regional differences related to adrenergic signaling. In one denervated and Ringer's solution-perfused heart, heating and elevated heart rates did not induce change in T-wave polarity, whereas noradrenaline did. Accordingly, electrocardiograms in eight awake pythons receiving intra-arterial infusion of the β-adrenergic receptor agonists adrenaline and isoproterenol revealed T-wave inversion in most individuals. Conversely, blocking the β-adrenergic receptors using propranolol prevented T-wave change during heating. Our findings indicate that changes in ventricular repolarization in ball pythons are caused by increased tone of the sympathetic nervous system, not by changes in temperature. Therefore, ventricular repolarization in both pythons and mammals is modulated by evolutionary conserved mechanisms involving catecholaminergic stimulation.
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Affiliation(s)
- Bastiaan J D Boukens
- University of Amsterdam, Amsterdam UMC, Department of Medical Biology, Amsterdam Cardiovascular Sciences, Amsterdam, The Netherlands
| | - William Joyce
- Department of Biology, Zoophysiology, Aarhus University, Aarhus, Denmark
| | | | - Ingeborg Hooijkaas
- University of Amsterdam, Amsterdam UMC, Department of Medical Biology, Amsterdam Cardiovascular Sciences, Amsterdam, The Netherlands
| | - Aldo Jongejan
- University of Amsterdam, Amsterdam UMC, Department of Epidemiology & Data Science, Amsterdam, The Netherlands
| | - Tobias Wang
- Department of Biology, Zoophysiology, Aarhus University, Aarhus, Denmark
| | - Bjarke Jensen
- University of Amsterdam, Amsterdam UMC, Department of Medical Biology, Amsterdam Cardiovascular Sciences, Amsterdam, The Netherlands
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Chou SM, Li KX, Huang MY, Chen C, Lin King YH, Li GG, Zhou W, Teo CF, Jan YN, Jan LY, Yang SB. Kv1.1 channels regulate early postnatal neurogenesis in mouse hippocampus via the TrkB signaling pathway. eLife 2021; 10:e58779. [PMID: 34018923 PMCID: PMC8208815 DOI: 10.7554/elife.58779] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2020] [Accepted: 05/20/2021] [Indexed: 12/20/2022] Open
Abstract
In the postnatal brain, neurogenesis occurs only within a few regions, such as the hippocampal sub-granular zone (SGZ). Postnatal neurogenesis is tightly regulated by factors that balance stem cell renewal with differentiation, and it gives rise to neurons that participate in learning and memory formation. The Kv1.1 channel, a voltage-gated potassium channel, was previously shown to suppress postnatal neurogenesis in the SGZ in a cell-autonomous manner. In this study, we have clarified the physiological and molecular mechanisms underlying Kv1.1-dependent postnatal neurogenesis. First, we discovered that the membrane potential of neural progenitor cells is highly dynamic during development. We further established a multinomial logistic regression model for cell-type classification based on the biophysical characteristics and corresponding cell markers. We found that the loss of Kv1.1 channel activity causes significant depolarization of type 2b neural progenitor cells. This depolarization is associated with increased tropomyosin receptor kinase B (TrkB) signaling and proliferation of neural progenitor cells; suppressing TrkB signaling reduces the extent of postnatal neurogenesis. Thus, our study defines the role of the Kv1.1 potassium channel in regulating the proliferation of postnatal neural progenitor cells in mouse hippocampus.
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Affiliation(s)
- Shu-Min Chou
- Institute of Biomedical Sciences, Academia SinicaTaipeiTaiwan
| | - Ke-Xin Li
- Howard Hughes Medical Institute, Departments of Physiology, Biochemistry and Biophysics, University of California, San FranciscoSan FranciscoUnited States
| | | | - Chao Chen
- Howard Hughes Medical Institute, Departments of Physiology, Biochemistry and Biophysics, University of California, San FranciscoSan FranciscoUnited States
| | - Yuan-Hung Lin King
- Howard Hughes Medical Institute, Departments of Physiology, Biochemistry and Biophysics, University of California, San FranciscoSan FranciscoUnited States
- Neuroscience Graduate Program, University of California, San FranciscoSan FranciscoUnited States
| | | | - Wei Zhou
- Department of Anesthesia and Perioperative Care, University of California, San FranciscoSan FranciscoUnited States
| | - Chin Fen Teo
- Howard Hughes Medical Institute, Departments of Physiology, Biochemistry and Biophysics, University of California, San FranciscoSan FranciscoUnited States
| | - Yuh Nung Jan
- Howard Hughes Medical Institute, Departments of Physiology, Biochemistry and Biophysics, University of California, San FranciscoSan FranciscoUnited States
| | - Lily Yeh Jan
- Howard Hughes Medical Institute, Departments of Physiology, Biochemistry and Biophysics, University of California, San FranciscoSan FranciscoUnited States
| | - Shi-Bing Yang
- Institute of Biomedical Sciences, Academia SinicaTaipeiTaiwan
- Neuroscience Program of Academia Sinica, Academia SinicaTaipeiTaiwan
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8
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Kawai T, Hashimoto M, Eguchi N, Nishino JM, Jinno Y, Mori-Kreiner R, Aspåker M, Chiba D, Ohtsuka Y, Kawanabe A, Nishino AS, Okamura Y. Heterologous functional expression of ascidian Nav1 channels and close relationship with the evolutionary ancestor of vertebrate Nav channels. J Biol Chem 2021; 296:100783. [PMID: 34000300 PMCID: PMC8192821 DOI: 10.1016/j.jbc.2021.100783] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2021] [Revised: 05/01/2021] [Accepted: 05/10/2021] [Indexed: 02/09/2023] Open
Abstract
Voltage-gated sodium channels (Nav1s) are responsible for the initiation and propagation of action potentials in neurons, muscle, and endocrine cells. Many clinically used drugs such as local anesthetics and antiarrhythmics inhibit Nav1s, and a variety of inherited human disorders are caused by mutations in Nav1 genes. Nav1s consist of the main α subunit and several auxiliary β subunits. Detailed information on the structure–function relationships of Nav1 subunits has been obtained through heterologous expression experiments and analyses of protein structures. The basic properties of Nav1s, including their gating and ion permeation, were classically described in the squid giant axon and other invertebrates. However, heterologous functional expression of Nav1s from marine invertebrates has been unsuccessful. Ascidians belong to the Urochordata, a sister group of vertebrates, and the larval central nervous system of ascidians shows a similar plan to that of vertebrates. Here, we report the biophysical properties of ascidian Ciona Nav1 (CiNav1a) heterologously expressed in Xenopus oocytes. CiNav1a exhibited tetrodotoxin-insensitive sodium currents with rapid gating kinetics of activation and inactivation. Furthermore, consistent with the fact that the Ciona genome lacks orthologous genes to vertebrate β subunits, the human β1 subunit did not influence the gating properties when coexpressed with CiNav1a. Interestingly, CiNav1a contains an ankyrin-binding motif in the II–III linker, which can be targeted to the axon initial segment of mammalian cortical neurons. Our findings provide a platform to gain insight into the evolutionary and biophysical properties of Nav1s, which are important for the development of targeted therapeutics.
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Affiliation(s)
- Takafumi Kawai
- Integrative Physiology, Department of Physiology, Graduate School of Medicine, Osaka University, Suita, Japan
| | - Masaki Hashimoto
- Graduate School of Frontier Bioscience, Osaka University, Suita, Japan
| | | | - Junko M Nishino
- Department of Biology, Faculty of Agriculture and Life Science, Hirosaki University, Hirosaki, Japan; Department of Bioresources Science, United Graduate School of Agricultural Sciences, Iwate University, Hirosaki, Japan
| | - Yuka Jinno
- Integrative Physiology, Department of Physiology, Graduate School of Medicine, Osaka University, Suita, Japan
| | - Risa Mori-Kreiner
- Integrative Physiology, Department of Physiology, Graduate School of Medicine, Osaka University, Suita, Japan
| | | | - Daijiro Chiba
- Department of Biology, Faculty of Agriculture and Life Science, Hirosaki University, Hirosaki, Japan
| | - Yukio Ohtsuka
- Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan
| | - Akira Kawanabe
- Integrative Physiology, Department of Physiology, Graduate School of Medicine, Osaka University, Suita, Japan
| | - Atsuo S Nishino
- Department of Biology, Faculty of Agriculture and Life Science, Hirosaki University, Hirosaki, Japan; Department of Bioresources Science, United Graduate School of Agricultural Sciences, Iwate University, Hirosaki, Japan
| | - Yasushi Okamura
- Integrative Physiology, Department of Physiology, Graduate School of Medicine, Osaka University, Suita, Japan; Graduate School of Frontier Bioscience, Osaka University, Suita, Japan.
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Rivero-Echeto MC, Perissinotti PP, González-Inchauspe C, Kargieman L, Bisagno V, Urbano FJ. Simultaneous administration of cocaine and caffeine dysregulates HCN and T-type channels. Psychopharmacology (Berl) 2021; 238:787-810. [PMID: 33241481 PMCID: PMC7688300 DOI: 10.1007/s00213-020-05731-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/06/2020] [Accepted: 11/18/2020] [Indexed: 12/13/2022]
Abstract
RATIONALE The abuse of psychostimulants has adverse consequences on the physiology of the central nervous system. In Argentina, and other South American countries, coca paste or "PACO" (cocaine and caffeine are its major components) is massively consumed with deleterious clinical consequences for the health and well-being of the general population. A scant number of studies have addressed the consequences of stimulant combination of cocaine and caffeine on the physiology of the somatosensory thalamocortical (ThCo) system. OBJECTIVES Our aim was to study ion conductances that have important implications regulating sleep-wake states 24-h after an acute or chronic binge-like administration of a cocaine and caffeine mixture following previously analyzed pasta base samples ("PACO"-like binge") using mice. METHODS We randomly injected (i.p.) male C57BL/6JFcen mice with a binge-like psychostimulants regimen during either 1 day (acute) or 1 day on/1 day off during 13 days for a total of 7 binges (chronic). Single-cell patch-clamp recordings of VB neurons were performed in thalamocortical slices 24 h after the last psychostimulant injection. We also recorded EEG/EMG from mice 24 h after being systemically treated with chronic administration of cocaine + caffeine versus saline, vehicle. RESULTS Our results showed notorious changes in the intrinsic properties of the VB nucleus neurons that persist after 24-h of either acute or chronic binge administrations of combined cocaine and caffeine ("PACO"-like binge). Functional dysregulation of HCN (hyperpolarization-activated cyclic nucleotide-gated) and T-type VGC (voltage-gated calcium) channels was described 24-h after acute/chronic "PACO"-like administrations. Furthermore, intracellular basal [Ca2+] disturbances resulted a key factor that modulated the availability and the activation of T-type channels, altering T-type "window currents." As a result, all these changes ultimately shaped the low-threshold spikes (LTS)-associated Ca2+ transients, regulated the membrane excitability, and altered sleep-wake transitions. CONCLUSION Our results suggest that deleterious consequences of stimulants cocaine and caffeine combination on the thalamocortical physiology as a whole might be related to potential neurotoxic effects of soaring intracellular [Ca2+].
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Affiliation(s)
- María Celeste Rivero-Echeto
- grid.7345.50000 0001 0056 1981CONICET-Universidad de Buenos Aires, Instituto de Fisiología, Biología Molecular y Neurociencias (IFIBYNE), Ciudad de Buenos Aires, Argentina
| | - Paula P. Perissinotti
- grid.7345.50000 0001 0056 1981CONICET-Universidad de Buenos Aires, Instituto de Fisiología, Biología Molecular y Neurociencias (IFIBYNE), Ciudad de Buenos Aires, Argentina
| | - Carlota González-Inchauspe
- grid.7345.50000 0001 0056 1981CONICET-Universidad de Buenos Aires, Instituto de Fisiología, Biología Molecular y Neurociencias (IFIBYNE), Ciudad de Buenos Aires, Argentina
| | - Lucila Kargieman
- grid.7345.50000 0001 0056 1981CONICET-Universidad de Buenos Aires, Instituto de Fisiología, Biología Molecular y Neurociencias (IFIBYNE), Ciudad de Buenos Aires, Argentina
| | - Verónica Bisagno
- grid.7345.50000 0001 0056 1981CONICET-Universidad de Buenos Aires, Instituto de Investigaciones Farmacológicas (ININFA), Ciudad de Buenos Aires, Argentina
| | - Francisco J. Urbano
- grid.7345.50000 0001 0056 1981CONICET-Universidad de Buenos Aires, Instituto de Fisiología, Biología Molecular y Neurociencias (IFIBYNE), Ciudad de Buenos Aires, Argentina ,grid.7345.50000 0001 0056 1981Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Fisiología, Biología Molecular y Celular “Dr. Héctor Maldonado”, Ciudad de Buenos Aires, Argentina ,grid.7345.50000 0001 0056 1981IFIBYNE (UBA-CONICET), Intendente Güiraldes 2160, Ciudad Universitaria, C1428EGA Ciudad Autónoma de Buenos Aires, Argentina
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10
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Walther F, Feind D, Vom Dahl C, Müller CE, Kukaj T, Sattler C, Nagel G, Gao S, Zimmer T. Action potentials in Xenopus oocytes triggered by blue light. J Gen Physiol 2020; 152:151581. [PMID: 32211871 PMCID: PMC7201882 DOI: 10.1085/jgp.201912489] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2019] [Accepted: 02/24/2020] [Indexed: 11/20/2022] Open
Abstract
Voltage-gated sodium (Na+) channels are responsible for the fast upstroke of the action potential of excitable cells. The different α subunits of Na+ channels respond to brief membrane depolarizations above a threshold level by undergoing conformational changes that result in the opening of the pore and a subsequent inward flux of Na+. Physiologically, these initial membrane depolarizations are caused by other ion channels that are activated by a variety of stimuli such as mechanical stretch, temperature changes, and various ligands. In the present study, we developed an optogenetic approach to activate Na+ channels and elicit action potentials in Xenopus laevis oocytes. All recordings were performed by the two-microelectrode technique. We first coupled channelrhodopsin-2 (ChR2), a light-sensitive ion channel of the green alga Chlamydomonas reinhardtii, to the auxiliary β1 subunit of voltage-gated Na+ channels. The resulting fusion construct, β1-ChR2, retained the ability to modulate Na+ channel kinetics and generate photosensitive inward currents. Stimulation of Xenopus oocytes coexpressing the skeletal muscle Na+ channel Nav1.4 and β1-ChR2 with 25-ms lasting blue-light pulses resulted in rapid alterations of the membrane potential strongly resembling typical action potentials of excitable cells. Blocking Nav1.4 with tetrodotoxin prevented the fast upstroke and the reversal of the membrane potential. Coexpression of the voltage-gated K+ channel Kv2.1 facilitated action potential repolarization considerably. Light-induced action potentials were also obtained by coexpressing β1-ChR2 with either the neuronal Na+ channel Nav1.2 or the cardiac-specific isoform Nav1.5. Potential applications of this novel optogenetic tool are discussed.
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Affiliation(s)
- Florian Walther
- Institute of Physiology II, University Hospital Jena, Friedrich Schiller University, Jena, Germany
| | - Dominic Feind
- Institute of Physiology II, University Hospital Jena, Friedrich Schiller University, Jena, Germany
| | - Christian Vom Dahl
- Institute of Physiology II, University Hospital Jena, Friedrich Schiller University, Jena, Germany
| | - Christoph Emanuel Müller
- Institute of Physiology II, University Hospital Jena, Friedrich Schiller University, Jena, Germany
| | - Taulant Kukaj
- Institute of Physiology II, University Hospital Jena, Friedrich Schiller University, Jena, Germany
| | - Christian Sattler
- Institute of Physiology II, University Hospital Jena, Friedrich Schiller University, Jena, Germany
| | - Georg Nagel
- Institute of Physiology-Neurophysiology, Biocentre, Julius-Maximilians-University, Wuerzburg, Germany
| | - Shiqiang Gao
- Institute of Physiology-Neurophysiology, Biocentre, Julius-Maximilians-University, Wuerzburg, Germany
| | - Thomas Zimmer
- Institute of Physiology II, University Hospital Jena, Friedrich Schiller University, Jena, Germany
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Vicente MC, Humphrey CM, Gargaglioni LH, Ostrowski TD. Decreased excitability of locus coeruleus neurons during hypercapnia is exaggerated in the streptozotocin-model of Alzheimer's disease. Exp Neurol 2020; 328:113250. [PMID: 32088169 DOI: 10.1016/j.expneurol.2020.113250] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2019] [Revised: 02/04/2020] [Accepted: 02/17/2020] [Indexed: 10/25/2022]
Abstract
The locus coeruleus (LC) is a pontine nucleus important for respiratory control and central chemoreception. It is affected in Alzheimer's disease (AD) and alteration of LC cell function may account for respiratory problems observed in AD patients. In the current study, we tested the electrophysiological properties and CO2/pH sensitivity of LC neurons in a model for AD. Sporadic AD was induced in rats by intracerebroventricular injection of 2 mg/kg streptozotocin (STZ), which induces behavioral and molecular impairments found in AD. LC neurons were recorded using the patch clamp technique and tested for responses to CO2 (10% CO2, pH = 7.0). The majority (~60%) of noradrenergic LC neurons in adult rats were inhibited by CO2 exposure as indicated by a significant decrease in action potential (AP) discharge to step depolarizations. The STZ-AD rat model had a greater sensitivity to CO2 than controls. The increased CO2-sensitivity was demonstrated by a significantly stronger inhibition of activity during hypercapnia that was in part due to hyperpolarization of the resting membrane potential. Reduction of AP discharge in both groups was generally accompanied by lower LC network activity, depolarized AP threshold, increased AP repolarization, and increased current through a subpopulation of voltage-gated K+ channels (KV). The latter was indicated by enhanced transient KV currents particularly in the STZ-AD group. Interestingly, steady-state KV currents were reduced under hypercapnia, a change that would favor enhanced AP discharge. However, the collective response of most LC neurons in adult rats, and particularly those in the STZ-AD group, was inhibited by CO2.
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Affiliation(s)
- Mariane C Vicente
- Department of Physiology, Kirksville College of Osteopathic Medicine, A.T. Still University of Health Sciences, Kirksville, MO, USA; Department of Animal Morphology and Physiology, Sao Paulo State University-UNESP/FCAV at Jaboticabal, SP, Brazil
| | - Chuma M Humphrey
- Department of Biology, Truman State University, Kirksville, MO, USA
| | - Luciane H Gargaglioni
- Department of Animal Morphology and Physiology, Sao Paulo State University-UNESP/FCAV at Jaboticabal, SP, Brazil
| | - Tim D Ostrowski
- Department of Physiology, Kirksville College of Osteopathic Medicine, A.T. Still University of Health Sciences, Kirksville, MO, USA.
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