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Abbas F, Blömer LA, Millet H, Montnach J, De Waard M, Canepari M. Analysis of the effect of the scorpion toxin AaH-II on action potential generation in the axon initial segment. Sci Rep 2024; 14:4967. [PMID: 38424206 PMCID: PMC10904771 DOI: 10.1038/s41598-024-55315-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2023] [Accepted: 02/22/2024] [Indexed: 03/02/2024] Open
Abstract
The toxin AaH-II, from the scorpion Androctonus australis Hector venom, is a 64 amino acid peptide that targets voltage-gated Na+ channels (VGNCs) and slows their inactivation. While at macroscopic cellular level AaH-II prolongs the action potential (AP), a functional analysis of the effect of the toxin in the axon initial segment (AIS), where VGNCs are highly expressed, was never performed so far. Here, we report an original analysis of the effect of AaH-II on the AP generation in the AIS of neocortical layer-5 pyramidal neurons from mouse brain slices. After determining that AaH-II does not discriminate between Nav1.2 and Nav1.6, i.e. between the two VGNC isoforms expressed in this neuron, we established that 7 nM was the smallest toxin concentration producing a minimal detectable deformation of the somatic AP after local delivery of the toxin. Using membrane potential imaging, we found that, at this minimal concentration, AaH-II substantially widened the AP in the AIS. Using ultrafast Na+ imaging, we found that local application of 7 nM AaH-II caused a large increase in the slower component of the Na+ influx in the AIS. Finally, using ultrafast Ca2+ imaging, we observed that 7 nM AaH-II produces a spurious slow Ca2+ influx via Ca2+-permeable VGNCs. Molecules targeting VGNCs, including peptides, are proposed as potential therapeutic tools. Thus, the present analysis in the AIS can be considered a general proof-of-principle on how high-resolution imaging techniques can disclose drug effects that cannot be observed when tested at the macroscopic level.
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Affiliation(s)
- Fatima Abbas
- Univ. Grenoble Alpes, CNRS, LIPhy, 38000, Grenoble, France
- Laboratories of Excellence, Ion Channel Science and Therapeutics, 06560, Valbonne, France
| | - Laila Ananda Blömer
- Univ. Grenoble Alpes, CNRS, LIPhy, 38000, Grenoble, France
- Laboratories of Excellence, Ion Channel Science and Therapeutics, 06560, Valbonne, France
| | - Hugo Millet
- Laboratories of Excellence, Ion Channel Science and Therapeutics, 06560, Valbonne, France
- Nantes Université, CNRS, INSERM, l'institut du Thorax, 44000, Nantes, France
| | - Jérôme Montnach
- Laboratories of Excellence, Ion Channel Science and Therapeutics, 06560, Valbonne, France
- Nantes Université, CNRS, INSERM, l'institut du Thorax, 44000, Nantes, France
| | - Michel De Waard
- Laboratories of Excellence, Ion Channel Science and Therapeutics, 06560, Valbonne, France
- Nantes Université, CNRS, INSERM, l'institut du Thorax, 44000, Nantes, France
| | - Marco Canepari
- Univ. Grenoble Alpes, CNRS, LIPhy, 38000, Grenoble, France.
- Laboratories of Excellence, Ion Channel Science and Therapeutics, 06560, Valbonne, France.
- Institut National de la Santé et Recherche Médicale, Paris, France.
- Laboratoire Interdisciplinaire de Physique (UMR 5588), Bat. E45, 140 Avenue de la Physique, Domaine Univ., 38402, St Martin d'Hères Cedex, France.
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2
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Blömer LA, Giacalone E, Abbas F, Filipis L, Tegolo D, Migliore M, Canepari M. Kinetics and functional consequences of BK channels activation by N-type Ca 2+ channels in the dendrite of mouse neocortical layer-5 pyramidal neurons. Front Cell Neurosci 2024; 18:1353895. [PMID: 38419657 PMCID: PMC10899506 DOI: 10.3389/fncel.2024.1353895] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2023] [Accepted: 01/24/2024] [Indexed: 03/02/2024] Open
Abstract
The back-propagation of an action potential (AP) from the axon/soma to the dendrites plays a central role in dendritic integration. This process involves an intricate orchestration of various ion channels, but a comprehensive understanding of the contribution of each channel type remains elusive. In this study, we leverage ultrafast membrane potential recordings (Vm) and Ca2+ imaging techniques to shed light on the involvement of N-type voltage-gated Ca2+ channels (VGCCs) in layer-5 neocortical pyramidal neurons' apical dendrites. We found a selective interaction between N-type VGCCs and large-conductance Ca2+-activated K+ channels (BK CAKCs). Remarkably, we observe that BK CAKCs are activated within a mere 500 μs after the AP peak, preceding the peak of the Ca2+ current triggered by the AP. Consequently, when N-type VGCCs are inhibited, the early broadening of the AP shape amplifies the activity of other VGCCs, leading to an augmented total Ca2+ influx. A NEURON model, constructed to replicate and support these experimental results, reveals the critical coupling between N-type and BK channels. This study not only redefines the conventional role of N-type VGCCs as primarily involved in presynaptic neurotransmitter release but also establishes their distinct and essential function as activators of BK CAKCs in neuronal dendrites. Furthermore, our results provide original functional validation of a physical interaction between Ca2+ and K+ channels, elucidated through ultrafast kinetic reconstruction. This insight enhances our understanding of the intricate mechanisms governing neuronal signaling and may have far-reaching implications in the field.
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Affiliation(s)
- Laila Ananda Blömer
- LIPhy, CNRS, Université Grenoble Alpes, Grenoble, France
- Laboratories of Excellence, Ion Channel Science and Therapeutics, Valbonne, France
| | - Elisabetta Giacalone
- Institute of Biophysics, National Research Council, Palermo, Italy
- Dipartimento Matematica e Informatica, Universitá degli Studi di Palermo, Palermo, Italy
| | - Fatima Abbas
- LIPhy, CNRS, Université Grenoble Alpes, Grenoble, France
- Laboratories of Excellence, Ion Channel Science and Therapeutics, Valbonne, France
| | - Luiza Filipis
- LIPhy, CNRS, Université Grenoble Alpes, Grenoble, France
- Laboratories of Excellence, Ion Channel Science and Therapeutics, Valbonne, France
| | - Domenico Tegolo
- Dipartimento Matematica e Informatica, Universitá degli Studi di Palermo, Palermo, Italy
| | - Michele Migliore
- Institute of Biophysics, National Research Council, Palermo, Italy
| | - Marco Canepari
- LIPhy, CNRS, Université Grenoble Alpes, Grenoble, France
- Laboratories of Excellence, Ion Channel Science and Therapeutics, Valbonne, France
- Institut National de la Santé et Recherche Médicale, Paris, France
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3
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Canepari M, Ross WN. Spatial and temporal aspects of neuronal calcium and sodium signals measured with low-affinity fluorescent indicators. Pflugers Arch 2024; 476:39-48. [PMID: 37798555 DOI: 10.1007/s00424-023-02865-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2023] [Revised: 09/12/2023] [Accepted: 09/21/2023] [Indexed: 10/07/2023]
Abstract
Low-affinity fluorescent indicators for Ca2+ or Na+ allow measuring the dynamics of intracellular concentration of these ions with little perturbation from physiological conditions because they are weak buffers. When using synthetic indicators, which are small molecules with fast kinetics, it is also possible to extract spatial and temporal information on the sources of ion transients, their localization, and their disposition. This review examines these important aspects from the biophysical point of view, and how they have been recently exploited in neurophysiological studies. We first analyze the environment where Ca2+ and Na+ indicators are inserted, highlighting the interpretation of the two different signals. Then, we address the information that can be obtained by analyzing the rising phase and the falling phase of the Ca2+ and Na+ transients evoked by different stimuli, focusing on the kinetics of ionic currents and on the spatial interpretation of these measurements, especially on events in axons and dendritic spines. Finally, we suggest how Ca2+ or Na+ imaging using low-affinity synthetic fluorescent indicators can be exploited in future fundamental or applied research.
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Affiliation(s)
- Marco Canepari
- LIPhy, CNRS, Univ. Grenoble Alpes, F-38000, Grenoble, France.
- Laboratories of Excellence, Ion Channel Science and Therapeutics, Valbonne, France.
- Institut National de la Santé et Recherche Médicale, Paris, France.
| | - William N Ross
- Department of Physiology, New York Medical College, Valhalla, NY, 10595, USA
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4
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Filipis L, Canepari M. Can neuron modeling constrained by ultrafast imaging data extract the native function of ion channels? Front Comput Neurosci 2023; 17:1192421. [PMID: 37293354 PMCID: PMC10244549 DOI: 10.3389/fncom.2023.1192421] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2023] [Accepted: 05/02/2023] [Indexed: 06/10/2023] Open
Affiliation(s)
- Luiza Filipis
- Univ Grenoble Alpes, CNRS, LIPhy, Grenoble, France
- Laboratories of Excellence, Ion Channel Science and Therapeutics, Valbonne, France
| | - Marco Canepari
- Univ Grenoble Alpes, CNRS, LIPhy, Grenoble, France
- Laboratories of Excellence, Ion Channel Science and Therapeutics, Valbonne, France
- Institut National de la Santé et Recherche Médicale, Paris, France
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5
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Fast Synaptically Activated Calcium and Sodium Kinetics in Hippocampal Pyramidal Neuron Dendritic Spines. eNeuro 2022; 9:ENEURO.0396-22.2022. [PMID: 36379712 PMCID: PMC9718353 DOI: 10.1523/eneuro.0396-22.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2022] [Revised: 10/31/2022] [Accepted: 11/02/2022] [Indexed: 11/16/2022] Open
Abstract
An accurate assessment of the time course, components, and magnitude of postsynaptic currents is important for a quantitative understanding of synaptic integration and signaling in dendritic spines. These parameters have been studied in some detail in previous experiments, primarily using two-photon imaging of [Ca2+]i changes and two-photon uncaging of glutamate. However, even with these revolutionary techniques, there are some missing pieces in our current understanding, particularly related to the time courses of synaptically evoked [Ca2+]i and [Na+]i changes. In new experiments, we used low-affinity, linear Na+ and Ca2+ indicators, laser fluorescence stimulation, and a sensitive camera-based detection system, combined with electrical stimulation and two-photon glutamate uncaging, to extend measurements of these spine parameters. We found that (1) almost all synaptically activated Na+ currents in CA1 hippocampal pyramidal neuron spines in slices from mice of either sex are through AMPA receptors with little Na+ entry through voltage-gated sodium channels (VGSCs) or NMDA receptor channels; (2) a spectrum of sodium transient decay times was observed, suggesting a spectrum of spine neck resistances, even on the same dendrite; (3) synaptically activated [Ca2+]i changes are very fast and are almost entirely because of Ca2+ entry through NMDA receptors at the time when the Mg2+ block is relieved by the fast AMPA-mediated EPSP; (4) the [Ca2+]i changes evoked by uncaging glutamate are slower than the changes evoked by synaptic release, suggesting that the relative contribution of Ca2+ entering through NMDA receptors at rest following uncaging is higher than following electrical stimulation.
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6
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An AIE-active probe for monitoring calcium-rich biological environment with high signal-to-noise and long-term retention in situ. Biomaterials 2022; 289:121778. [DOI: 10.1016/j.biomaterials.2022.121778] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2021] [Revised: 07/11/2022] [Accepted: 07/27/2022] [Indexed: 11/20/2022]
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7
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Montnach J, Blömer LA, Lopez L, Filipis L, Meudal H, Lafoux A, Nicolas S, Chu D, Caumes C, Béroud R, Jopling C, Bosmans F, Huchet C, Landon C, Canepari M, De Waard M. In vivo spatiotemporal control of voltage-gated ion channels by using photoactivatable peptidic toxins. Nat Commun 2022; 13:417. [PMID: 35058427 PMCID: PMC8776733 DOI: 10.1038/s41467-022-27974-w] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2021] [Accepted: 12/20/2021] [Indexed: 12/11/2022] Open
Abstract
Photoactivatable drugs targeting ligand-gated ion channels open up new opportunities for light-guided therapeutic interventions. Photoactivable toxins targeting ion channels have the potential to control excitable cell activities with low invasiveness and high spatiotemporal precision. As proof-of-concept, we develop HwTxIV-Nvoc, a UV light-cleavable and photoactivatable peptide that targets voltage-gated sodium (NaV) channels and validate its activity in vitro in HEK293 cells, ex vivo in brain slices and in vivo on mice neuromuscular junctions. We find that HwTxIV-Nvoc enables precise spatiotemporal control of neuronal NaV channel function under all conditions tested. By creating multiple photoactivatable toxins, we demonstrate the broad applicability of this toxin-photoactivation technology.
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Affiliation(s)
- Jérôme Montnach
- l'institut du thorax, INSERM, CNRS, UNIV NANTES, F-44007, Nantes, France
- Laboratory of Excellence Ion Channels, Science & Therapeutics, F-06560, Valbonne, France
| | - Laila Ananda Blömer
- Laboratory of Excellence Ion Channels, Science & Therapeutics, F-06560, Valbonne, France
- Laboratoire Interdisciplinaire de Physique, Université Grenoble Alpes, CNRS UMR 5588, 38402, St Martin d'Hères, cedex, France
| | - Ludivine Lopez
- l'institut du thorax, INSERM, CNRS, UNIV NANTES, F-44007, Nantes, France
- Laboratory of Excellence Ion Channels, Science & Therapeutics, F-06560, Valbonne, France
- Smartox Biotechnology, 6 rue des Platanes, F-38120, Saint-Egrève, France
| | - Luiza Filipis
- Laboratory of Excellence Ion Channels, Science & Therapeutics, F-06560, Valbonne, France
- Laboratoire Interdisciplinaire de Physique, Université Grenoble Alpes, CNRS UMR 5588, 38402, St Martin d'Hères, cedex, France
| | - Hervé Meudal
- Center for Molecular Biophysics, CNRS, rue Charles Sadron, CS 80054, Orléans, 45071, France
| | - Aude Lafoux
- Therassay Platform, IRS2-Université de Nantes, Nantes, France
| | - Sébastien Nicolas
- l'institut du thorax, INSERM, CNRS, UNIV NANTES, F-44007, Nantes, France
- Laboratory of Excellence Ion Channels, Science & Therapeutics, F-06560, Valbonne, France
| | - Duong Chu
- Queen's University Faculty of Medicine, Kingston, ON, Canada
| | - Cécile Caumes
- Smartox Biotechnology, 6 rue des Platanes, F-38120, Saint-Egrève, France
| | - Rémy Béroud
- Smartox Biotechnology, 6 rue des Platanes, F-38120, Saint-Egrève, France
| | - Chris Jopling
- Institut de Génomique Fonctionnelle, 141 rue de la Cardonille, 34094, Montpellier, France
| | - Frank Bosmans
- Department of Basic and Applied Medical Sciences, Ghent University, Ghent, Belgium
| | - Corinne Huchet
- Therassay Platform, IRS2-Université de Nantes, Nantes, France
| | - Céline Landon
- Center for Molecular Biophysics, CNRS, rue Charles Sadron, CS 80054, Orléans, 45071, France
| | - Marco Canepari
- Laboratory of Excellence Ion Channels, Science & Therapeutics, F-06560, Valbonne, France
- Laboratoire Interdisciplinaire de Physique, Université Grenoble Alpes, CNRS UMR 5588, 38402, St Martin d'Hères, cedex, France
| | - Michel De Waard
- l'institut du thorax, INSERM, CNRS, UNIV NANTES, F-44007, Nantes, France.
- Laboratory of Excellence Ion Channels, Science & Therapeutics, F-06560, Valbonne, France.
- Smartox Biotechnology, 6 rue des Platanes, F-38120, Saint-Egrève, France.
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8
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Blömer LA, Filipis L, Canepari M. Cal-520FF is the Present Optimal Ca 2+ Indicator for Ultrafast Ca 2+ Imaging and Optical Measurement of Ca 2+ Currents. J Fluoresc 2021; 31:619-623. [PMID: 33606130 DOI: 10.1007/s10895-021-02701-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2020] [Accepted: 02/11/2021] [Indexed: 11/29/2022]
Abstract
Ultrafast Ca2+ imaging using low-affinity fluorescent indicators allows the precise measurement of the kinetics of fast Ca2+ currents mediated by voltage-gated Ca2+ channels. Thus far, only a few indicators provided fluorescence transients with sufficient signal-to-noise ratio necessary to achieve this measurement, with Oregon Green BAPTA-5N exhibiting the best performance. Here we evaluated the performance of the low-affinity Ca2+ indicator Cal-520FF to record fast Ca2+ signals and to measure the kinetics of Ca2+ currents. Compared to Oregon Green BAPTA-5N and to Fluo4FF, Cal-520FF offers a superior signal-to-noise-ratio providing the optimal characteristics for this important type of biophysical measurement. This ability is the result of a relatively high fluorescence at zero Ca2+, necessary to detect enough photons at short exposure windows, and a high dynamic range leading to large fluorescence transients associated with short Ca2+ influx periods. We conclude that Cal-520FF is at present the optimal commercial low-affinity Ca2+ indicator for ultrafast Ca2+ imaging applications.
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Affiliation(s)
- Laila Ananda Blömer
- University Grenoble Alpes, CNRS, LIPhy, F-38000, Grenoble, France
- Laboratories of Excellence, Ion Channel Science and Therapeutics, Valbonne, France
| | - Luiza Filipis
- University Grenoble Alpes, CNRS, LIPhy, F-38000, Grenoble, France
- Laboratories of Excellence, Ion Channel Science and Therapeutics, Valbonne, France
| | - Marco Canepari
- University Grenoble Alpes, CNRS, LIPhy, F-38000, Grenoble, France.
- Laboratories of Excellence, Ion Channel Science and Therapeutics, Valbonne, France.
- Institut National de la Santé et Recherche Médicale, Paris, France.
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9
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Blömer LA, Canepari M, Filipis L. Ultrafast Sodium Imaging of the Axon Initial Segment of Neurons in Mouse Brain Slices. Curr Protoc 2021; 1:e64. [PMID: 33657273 DOI: 10.1002/cpz1.64] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Monitoring Na+ influx in the axon initial segment (AIS) at high spatial and temporal resolution is fundamental to understanding the generation of an action potential (AP). Here, we present protocols to obtain this measurement, focusing on the AIS of layer 5 (L5) somatosensory cortex pyramidal neurons in mouse brain slices. We first outline how to prepare slices for this application, how to select and patch neurons, and how to optimize the image acquisition. Specifically, we describe the preparation of optimal slices, patching and loading of L5 pyramidal neurons with the Na+ indicator ING-2, and Na+ imaging at 100 µs temporal resolution with a pixel resolution of half a micron. Then, we present a data analysis strategy in order to extract information on the kinetics of activated voltage-gated Na+ channels by determining the change in Na+ by compensating for bleaching and calculating the time derivative of the resulting fit. In sum, this approach can be widely applied when investigating the function of Na+ channels during initiation of an AP and propagation under physiological or pathological conditions in neuronal subtypes. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Preparation of cortical slices Basic Protocol 2: Selection, patching, and Na+ fluorescence recording of a neuron Support Protocol: Calibrating Na+ fluorescence Basic Protocol 3: Data analysis.
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Affiliation(s)
- Laila Ananda Blömer
- Université Grenoble Alpes, CNRS, LIPhy, Grenoble, France.,Laboratories of Excellence, Ion Channel Science and Therapeutics, Valbone, France
| | - Marco Canepari
- Université Grenoble Alpes, CNRS, LIPhy, Grenoble, France.,Laboratories of Excellence, Ion Channel Science and Therapeutics, Valbone, France.,Institut National de la Santé et Recherche Médicale, Paris, France
| | - Luiza Filipis
- Université Grenoble Alpes, CNRS, LIPhy, Grenoble, France.,Laboratories of Excellence, Ion Channel Science and Therapeutics, Valbone, France
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10
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Filipis L, Canepari M. Optical measurement of physiological sodium currents in the axon initial segment. J Physiol 2020; 599:49-66. [PMID: 33094478 DOI: 10.1113/jp280554] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2020] [Accepted: 10/16/2020] [Indexed: 01/06/2023] Open
Abstract
KEY POINTS Τhe axonal Na+ fluorescence underlying an action potential in the axon initial segment was optically measured at unprecedented temporal resolution. The measurement allowed resolution of the kinetics of the Na+ current at different axonal locations. The distinct components of the Na+ current were correlated with the kinetics of the action potential. NEURON simulations from a modified published model qualitatively predicted the experimentally measured Na+ current. The present method permits the direct investigation of the kinetic behaviour of native Na+ channels under physiological and pathological conditions. ABSTRACT In most neurons of the mammalian central nervous system, the action potential (AP) is generated in the axon initial segment (AIS) by a fast Na+ current mediated by voltage-gated Na+ channels. While the axonal Na+ signal associated with the AP has been measured using fluorescent Na+ indicators, the insufficient resolution of these recordings has not allowed tracking the Na+ current kinetics underlying this fundamental event. In this article, we report the first optical measurement of Na+ currents in the AIS of pyramidal neurons of layer 5 of the somatosensory cortex from brain slices of the mouse. This measurement was obtained by achieving a temporal resolution of 100 μs in the Na+ imaging technique, with a pixel resolution of 0.5 μm, and by calculating the time-derivative of the Na+ change corrected for longitudinal diffusion. We identified a subthreshold current before the AP, a fast-inactivating current peaking during the rise of the AP and a non-inactivating current during the AP repolarization. We established a correlation between the kinetics of the non-inactivating current at different distances from the soma and the kinetics of the somatic AP. We quantitatively compared the experimentally measured Na+ current with the current obtained by computer simulation of published NEURON models, demonstrating how the present approach can lead to the correct estimate of the native behaviour of Na+ channels. Finally, we discuss how the present approach can be used to investigate the physiological or pathological function of different channel types during AP initiation and propagation.
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Affiliation(s)
- Luiza Filipis
- University of Grenoble Alpes, CNRS, LIPhy, Grenoble, F38000, France.,Laboratories of Excellence, Ion Channel Science and Therapeutics, France
| | - Marco Canepari
- University of Grenoble Alpes, CNRS, LIPhy, Grenoble, F38000, France.,Laboratories of Excellence, Ion Channel Science and Therapeutics, France.,Institut National de la Santé et Recherche Médicale, France
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11
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Hanemaaijer NA, Popovic MA, Wilders X, Grasman S, Pavón Arocas O, Kole MH. Ca 2+ entry through Na V channels generates submillisecond axonal Ca 2+ signaling. eLife 2020; 9:54566. [PMID: 32553116 PMCID: PMC7380941 DOI: 10.7554/elife.54566] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2019] [Accepted: 06/12/2020] [Indexed: 12/15/2022] Open
Abstract
Calcium ions (Ca2+) are essential for many cellular signaling mechanisms and enter the cytosol mostly through voltage-gated calcium channels. Here, using high-speed Ca2+ imaging up to 20 kHz in the rat layer five pyramidal neuron axon we found that activity-dependent intracellular calcium concentration ([Ca2+]i) in the axonal initial segment was only partially dependent on voltage-gated calcium channels. Instead, [Ca2+]i changes were sensitive to the specific voltage-gated sodium (NaV) channel blocker tetrodotoxin. Consistent with the conjecture that Ca2+ enters through the NaV channel pore, the optically resolved ICa in the axon initial segment overlapped with the activation kinetics of NaV channels and heterologous expression of NaV1.2 in HEK-293 cells revealed a tetrodotoxin-sensitive [Ca2+]i rise. Finally, computational simulations predicted that axonal [Ca2+]i transients reflect a 0.4% Ca2+ conductivity of NaV channels. The findings indicate that Ca2+ permeation through NaV channels provides a submillisecond rapid entry route in NaV-enriched domains of mammalian axons. Nerve cells communicate using tiny electrical impulses called action potentials. Special proteins termed ion channels produce these electric signals by allowing specific charged particles, or ions, to pass in or out of cells across its membrane. When a nerve cell ‘fires’ an action potential, specific ion channels briefly open to let in a surge of positively charged ions which electrify the cell. Action potentials begin in the same place in each nerve cell, at an area called the axon initial segment. The large number of sodium channels at this site kick-start the influx of positively charged sodium ions ensuring that every action potential starts from the same place. Previous research has shown that, when action potentials begin, the concentration of calcium ions at the axon initial segment also increases, but it was not clear which ion channels were responsible for this entry of calcium. Channels that are selective for calcium ions are the prime candidates for this process. However, research in squid nerve cells gave rise to an unexpected idea by suggesting that sodium channels may not exclusively let in sodium but also allow some calcium ions to pass through. Hanemaaijer, Popovic et al. therefore wanted to test the routes that calcium ions take and see whether the sodium channels in mammalian nerve cells are also permeable to calcium. Experiments using fluorescent dyes to track the concentration of calcium in rat and human nerve cells showed that calcium ions accumulated at the axon initial segment when action potentials fired. Most of this increase in calcium could be stopped by treating the neurons with a toxin that prevents sodium channels from opening. Electrical manipulations of the cells revealed that, in this context, the calcium ions were effectively behaving like sodium ions. Human kidney cells were then engineered to produce the sodium channel protein. This confirmed that calcium and sodium ions were indeed both passing through the same channel. These results shed new light on the relationship between calcium ions and sodium channels within the mammalian nervous system and that this interplay occurs at the axon initial segment of the cell. Genetic mutations that ‘nudge’ sodium channels towards favoring calcium entry are also found in patients with autism spectrum disorders, and so this new finding may contribute to our understanding of these conditions.
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Affiliation(s)
- Naomi Ak Hanemaaijer
- Department of Axonal Signaling, Netherlands Institute for Neuroscience (NIN), Royal Netherlands Academy of Arts and Sciences (KNAW), Amsterdam, Netherlands.,Cell Biology, Neurobiology and Biophysics, Department of Biology, Faculty of Science, Utrecht University, Utrecht, Netherlands
| | - Marko A Popovic
- Department of Axonal Signaling, Netherlands Institute for Neuroscience (NIN), Royal Netherlands Academy of Arts and Sciences (KNAW), Amsterdam, Netherlands
| | - Xante Wilders
- Department of Axonal Signaling, Netherlands Institute for Neuroscience (NIN), Royal Netherlands Academy of Arts and Sciences (KNAW), Amsterdam, Netherlands
| | - Sara Grasman
- Department of Axonal Signaling, Netherlands Institute for Neuroscience (NIN), Royal Netherlands Academy of Arts and Sciences (KNAW), Amsterdam, Netherlands
| | - Oriol Pavón Arocas
- Department of Axonal Signaling, Netherlands Institute for Neuroscience (NIN), Royal Netherlands Academy of Arts and Sciences (KNAW), Amsterdam, Netherlands
| | - Maarten Hp Kole
- Department of Axonal Signaling, Netherlands Institute for Neuroscience (NIN), Royal Netherlands Academy of Arts and Sciences (KNAW), Amsterdam, Netherlands.,Cell Biology, Neurobiology and Biophysics, Department of Biology, Faculty of Science, Utrecht University, Utrecht, Netherlands
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12
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The Origin of Physiological Local mGluR1 Supralinear Ca 2+ Signals in Cerebellar Purkinje Neurons. J Neurosci 2020; 40:1795-1809. [PMID: 31969470 DOI: 10.1523/jneurosci.2406-19.2020] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2019] [Revised: 01/09/2020] [Accepted: 01/11/2020] [Indexed: 11/21/2022] Open
Abstract
In mouse cerebellar Purkinje neurons (PNs), the climbing fiber (CF) input provides a signal to parallel fiber (PF) synapses, triggering PF synaptic plasticity. This signal is given by supralinear Ca2+ transients, associated with the CF synaptic potential and colocalized with the PF Ca2+ influx, occurring only when PF activity precedes the CF input. Here, we unravel the biophysical determinants of supralinear Ca2+ signals associated with paired PF-CF synaptic activity. We used membrane potential (V m) and Ca2+ imaging to investigate the local CF-associated Ca2+ influx following a train of PF synaptic potentials in two cases: (1) when the dendritic V m is hyperpolarized below the resting V m, and (2) when the dendritic V m is at rest. We found that supralinear Ca2+ signals are mediated by type-1 metabotropic glutamate receptors (mGluR1s) when the CF input is delayed by 100-150 ms from the first PF input in both cases. When the dendrite is hyperpolarized only, however, mGluR1s boost neighboring T-type channels, providing a mechanism for local coincident detection of PF-CF activity. The resulting Ca2+ elevation is locally amplified by saturation of endogenous Ca2+ buffers produced by the PF-associated Ca2+ influx via the mGluR1-mediated nonselective cation conductance. In contrast, when the dendritic V m is at rest, mGluR1s increase dendritic excitability by inactivating A-type K+ channels, but this phenomenon is not restricted to the activated PF synapses. Thus, V m is likely a crucial parameter in determining PF synaptic plasticity, and the occurrence of hyperpolarization episodes is expected to play an important role in motor learning.SIGNIFICANCE STATEMENT In Purkinje neurons, parallel fiber synaptic plasticity, determined by coincident activation of the climbing fiber input, underlies cerebellar learning. We unravel the biophysical mechanisms allowing the CF input to produce a local Ca2+ signal exclusively at the sites of activated parallel fibers. We show that when the membrane potential is hyperpolarized with respect to the resting membrane potential, type-1 metabotropic glutamate receptors locally enhance Ca2+ influx mediated by T-type Ca2+ channels, and that this signal is amplified by saturation of endogenous buffer also mediated by the same receptors. The combination of these two mechanisms is therefore capable of producing a Ca2+ signal at the activated parallel fiber sites, suggesting a role of Purkinje neuron membrane potential in cerebellar learning.
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Antic SD, Baker BJ, Canepari M. Editorial: New Insights on Neuron and Astrocyte Function From Cutting-Edge Optical Techniques. Front Cell Neurosci 2019; 13:463. [PMID: 31680872 PMCID: PMC6803618 DOI: 10.3389/fncel.2019.00463] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2019] [Accepted: 09/30/2019] [Indexed: 11/13/2022] Open
Affiliation(s)
- Srdjan D Antic
- Department of Neuroscience, Institute for Systems Genomics, Stem Cell Institute, UConn Health, Farmington, CT, United States
| | - Bradley James Baker
- The Center for Functional Connectomics, Korea Institute of Science and Technology, Seoul, South Korea
| | - Marco Canepari
- Division of Bio-Medical Science and Technology, KIST School, Korea University of Science and Technology (UST), Seoul, South Korea.,Laboratories of Excellence, Ion Channel Science and Therapeutics, Valbonne, France.,Institut National de la Santé et Recherche Médicale, Paris, France
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14
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Abstract
Imaging techniques may overcome the limitations of electrode techniques to measure locally not only membrane potential changes, but also ionic currents. Here, we review a recently developed approach to image native neuronal Ca2+ currents from brain slices. The technique is based on combined fluorescence recordings using low-affinity Ca2+ indicators possibly in combination with voltage sensitive dyes. We illustrate how the kinetics of a Ca2+ current can be estimated from the Ca2+ fluorescence change and locally correlated with the change of membrane potential, calibrated on an absolute scale, from the voltage fluorescence change. We show some representative measurements from the dendrites of CA1 hippocampal pyramidal neurons, from olfactory bulb mitral cells and from cerebellar Purkinje neurons. We discuss the striking difference in data analysis and interpretation between Ca2+ current measurements obtained using classical electrode techniques and the physiological currents obtained using this novel approach. Finally, we show how important is the kinetic information on the native Ca2+ current to explore the potential molecular targets of the Ca2+ flux from each individual Ca2+ channel.
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15
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Battefeld A, Popovic MA, van der Werf D, Kole MHP. A Versatile and Open-Source Rapid LED Switching System for One-Photon Imaging and Photo-Activation. Front Cell Neurosci 2019; 12:530. [PMID: 30705622 PMCID: PMC6344383 DOI: 10.3389/fncel.2018.00530] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2018] [Accepted: 12/21/2018] [Indexed: 01/12/2023] Open
Abstract
Combining fluorescence and transmitted light sources for microscopy is an invaluable method in cellular neuroscience to probe the molecular and cellular mechanisms of cells. This approach enables the targeted recording from fluorescent reporter protein expressing neurons or glial cells in brain slices and fluorescence-assisted electrophysiological recordings from subcellular structures. However, the existing tools to mix multiple light sources in one-photon microscopy are limited. Here, we present the development of several microcontroller devices that provide temporal and intensity control of light emitting diodes (LEDs) for computer controlled microscopy illumination. We interfaced one microcontroller with μManager for rapid and dynamic overlay of transmitted and fluorescent images. Moreover, on the basis of this illumination system we implemented an electronic circuit to combine two pulsed LED light sources for fast (up to 1 kHz) ratiometric calcium (Ca2+) imaging. This microcontroller enabled the calibration of intracellular Ca2+ concentration and furthermore the combination of Ca2+ imaging with optogenetic activation. The devices are based on affordable components and open-source hardware and software. Integration into existing bright-field microscope systems will take ∼1 day. The microcontroller based LED imaging substantially advances conventional illumination methods by limiting light exposure and adding versatility and speed.
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Affiliation(s)
- Arne Battefeld
- Department of Axonal Signaling, Netherlands Institute for Neuroscience, Royal Netherlands Academy of Arts and Sciences, Amsterdam, Netherlands.,Grass Laboratory, Marine Biological Laboratory, Woods Holem, MA, United States
| | - Marko A Popovic
- Department of Axonal Signaling, Netherlands Institute for Neuroscience, Royal Netherlands Academy of Arts and Sciences, Amsterdam, Netherlands
| | - Dirk van der Werf
- Department of Mechatronics, Netherlands Institute for Neuroscience, Royal Netherlands Academy of Arts and Sciences, Amsterdam, Netherlands
| | - Maarten H P Kole
- Department of Axonal Signaling, Netherlands Institute for Neuroscience, Royal Netherlands Academy of Arts and Sciences, Amsterdam, Netherlands.,Cell Biology, Faculty of Science, Utrecht University, Utrecht, Netherlands
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16
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Two Distinct Sets of Ca 2+ and K + Channels Are Activated at Different Membrane Potentials by the Climbing Fiber Synaptic Potential in Purkinje Neuron Dendrites. J Neurosci 2019; 39:1969-1981. [PMID: 30630881 DOI: 10.1523/jneurosci.2155-18.2018] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2018] [Revised: 12/14/2018] [Accepted: 12/23/2018] [Indexed: 11/21/2022] Open
Abstract
In cerebellar Purkinje neuron dendrites, the transient depolarization associated with a climbing fiber (CF) EPSP activates voltage-gated Ca2+ channels (VGCCs), voltage-gated K+ channels (VGKCs), and Ca2+-activated SK and BK K+ channels. The resulting membrane potential (V m) and Ca2+ transients play a fundamental role in dendritic integration and synaptic plasticity of parallel fiber inputs. Here we report a detailed investigation of the kinetics of dendritic Ca2+ and K+ channels activated by CF-EPSPs, based on optical measurements of V m and Ca2+ transients and on a single-compartment NEURON model reproducing experimental data. We first measured V m and Ca2+ transients associated with CF-EPSPs at different initial V m, and we analyzed the changes in the Ca2+ transients produced by the block of each individual VGCCs, of A-type VGKCs and of SK and BK channels. Then, we constructed a model that includes six active ion channels to accurately match experimental signals and extract the physiological kinetics of each channel. We found that two different sets of channels are selectively activated. When the dendrite is hyperpolarized, CF-EPSPs mainly activate T-type VGCCs, SK channels, and A-type VGKCs that limit the transient V m ∼ <0 mV. In contrast, when the dendrite is depolarized, T-type VGCCs and A-type VGKCs are inactivated and CF-EPSPs activate P/Q-type VGCCs, high-voltage activated VGKCs, and BK channels, leading to Ca2+ spikes. Thus, the potentially activity-dependent regulation of A-type VGKCs, controlling the activation of this second set of channels, is likely to play a crucial role in signal integration and plasticity in Purkinje neuron dendrites.SIGNIFICANCE STATEMENT The climbing fiber synaptic input transiently depolarizes the dendrite of cerebellar Purkinje neurons generating a signal that plays a fundamental role in dendritic integration. This signal is mediated by two types of Ca2+ channels and four types of K+ channels. Thus, understanding the kinetics of all of these channels is crucial for understanding PN function. To obtain this information, we used an innovative strategy that merges ultrafast optical membrane potential and Ca2+ measurements, pharmacological analysis, and computational modeling. We found that, according to the initial membrane potential, the climbing fiber depolarizing transient activates two distinct sets of channels. Moreover, A-type K+ channels limit the activation of P/Q-type Ca2+ channels and associated K+ channels, thus preventing the generation of Ca2+ spikes.
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Filipis L, Ait Ouares K, Moreau P, Tanese D, Zampini V, Latini A, Bleau C, Bleau C, Graham J, Canepari M. A novel multisite confocal system for rapid Ca 2+ imaging from submicron structures in brain slices. JOURNAL OF BIOPHOTONICS 2018; 11. [PMID: 29165917 DOI: 10.1002/jbio.201700197] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/29/2017] [Accepted: 11/13/2017] [Indexed: 05/14/2023]
Abstract
In brain slices, resolving fast Ca2+ fluorescence signals from submicron structures is typically achieved using 2-photon or confocal scanning microscopy, an approach that limits the number of scanned points. The novel multiplexing confocal system presented here overcomes this limitation. This system is based on a fast spinning disk, a multimode diode laser and a novel high-resolution CMOS camera. The spinning disk, running at 20 000 rpm, has custom-designed spiral pattern that maximises light collection, while rejecting out-of-focus fluorescence to resolve signals from small neuronal compartments. Using a 60× objective, the camera permits acquisitions of tens of thousands of pixels at resolutions of ~250 nm per pixel in the kHz range with 14 bits of digital depth. The system can resolve physiological Ca2+ transients from submicron structures at 20 to 40 μm below the slice surface, using the low-affinity Ca2+ indicator Oregon Green BAPTA-5N. In particular, signals at 0.25 to 1.25 kHz were resolved in single trials, or through averages of a few recordings, from dendritic spines and small parent dendrites in cerebellar Purkinje neurons. Thanks to an unprecedented combination of temporal and spatial resolution with relatively simple implementation, it is expected that this system will be widely adopted for multisite monitoring of Ca2+ signals.
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Affiliation(s)
- Luiza Filipis
- Laboratory for Interdisciplinary Physics, UMR 5588 CNRS and Université Grenoble Alpes, Saint Martin d'Hères Cedex, France
- Laboratories of Excellence, Ion Channel Science and Therapeutics, France
| | - Karima Ait Ouares
- Laboratory for Interdisciplinary Physics, UMR 5588 CNRS and Université Grenoble Alpes, Saint Martin d'Hères Cedex, France
- Laboratories of Excellence, Ion Channel Science and Therapeutics, France
| | - Philippe Moreau
- Laboratory for Interdisciplinary Physics, UMR 5588 CNRS and Université Grenoble Alpes, Saint Martin d'Hères Cedex, France
| | - Dimitrii Tanese
- Wavefront-Engineering Microscopy Group, Neurophotonics Laboratory, UMR8250 CNRS and Paris Descartes University, Paris, France
| | - Valeria Zampini
- Wavefront-Engineering Microscopy Group, Neurophotonics Laboratory, UMR8250 CNRS and Paris Descartes University, Paris, France
| | | | | | | | | | - Marco Canepari
- Laboratory for Interdisciplinary Physics, UMR 5588 CNRS and Université Grenoble Alpes, Saint Martin d'Hères Cedex, France
- Laboratories of Excellence, Ion Channel Science and Therapeutics, France
- Institut National de la Santé et Recherche Médicale (INSERM), France
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18
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Antic SD. Simultaneous recordings of voltage and current waveforms from dendrites. J Physiol 2017; 594:2557-8. [PMID: 27173019 DOI: 10.1113/jp271966] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2015] [Accepted: 01/15/2016] [Indexed: 11/08/2022] Open
Affiliation(s)
- Srdjan D Antic
- University of Connecticut Health, Rm L-3052, 263 Farmington Avenue, Farmington, CT, 06030, USA
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19
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Ait Ouares K, Jaafari N, Canepari M. A generalised method to estimate the kinetics of fast Ca(2+) currents from Ca(2+) imaging experiments. J Neurosci Methods 2016; 268:66-77. [PMID: 27163479 DOI: 10.1016/j.jneumeth.2016.05.005] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2016] [Revised: 05/04/2016] [Accepted: 05/05/2016] [Indexed: 10/21/2022]
Abstract
BACKGROUND Fast Ca(2+) imaging using low-affinity fluorescent indicators allows tracking Ca(2+) neuronal influx at high temporal resolution. In some systems, where the Ca(2+)-bound indicator is linear with Ca(2+) entering the cell, the Ca(2+) current has same kinetics of the fluorescence time derivative. In other systems, like cerebellar Purkinje neuron dendrites, the time derivative strategy fails since fluorescence kinetics is affected by Ca(2+) binding proteins sequestering Ca(2+) from the indicator. NEW METHOD Our novel method estimates the kinetics of the Ca(2+) current in cells where the time course of fluorescence is not linear with Ca(2+) influx. The method is based on a two-buffer and two-indicator model, with three free parameters, where Ca(2+) sequestration from the indicator is mimicked by Ca(2+)-binding to the slower buffer. We developed a semi-automatic protocol to optimise the free parameters and the kinetics of the input current to match the experimental fluorescence change with the simulated curve of the Ca(2+)-bound indicator. RESULTS We show that the optimised input current is a good estimate of the real Ca(2+) current by validating the method both using computer simulations and data from real neurons. We report the first estimates of Ca(2+) currents associated with climbing fibre excitatory postsynaptic potentials in Purkinje neurons. COMPARISON WITH EXISTING METHODS The present method extends the possibility of studying Ca(2+) currents in systems where the existing time derivative approach fails. CONCLUSIONS The information available from our technique allows investigating the physiological behaviour of Ca(2+) channels under all possible conditions.
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Affiliation(s)
- Karima Ait Ouares
- Laboratory for Interdisciplinary Physics, UMR 5588, Université Grenoble Alpes and CNRS, 38402 Saint Martin d'Hères, France; Laboratories of Excellence, Ion Channel Science and Therapeutics, France
| | - Nadia Jaafari
- Laboratory for Interdisciplinary Physics, UMR 5588, Université Grenoble Alpes and CNRS, 38402 Saint Martin d'Hères, France; Laboratories of Excellence, Ion Channel Science and Therapeutics, France
| | - Marco Canepari
- Laboratory for Interdisciplinary Physics, UMR 5588, Université Grenoble Alpes and CNRS, 38402 Saint Martin d'Hères, France; Laboratories of Excellence, Ion Channel Science and Therapeutics, France; Institut National de la Santé et Recherche Médicale (INSERM), France.
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20
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Jaafari N, Canepari M. Functional coupling of diverse voltage-gated Ca(2+) channels underlies high fidelity of fast dendritic Ca(2+) signals during burst firing. J Physiol 2016; 594:967-83. [PMID: 26634988 DOI: 10.1113/jp271830] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2015] [Accepted: 11/27/2015] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS In neurons, the Ca(2+) signal associated with the dendritic back-propagating action potential codes a chemical message to the different dendritic sites, playing a crucial role in electrical signalling, synaptic transmission and synaptic plasticity. The study of the underlying Ca(2+) current, mediated by different types of voltage-gated Ca(2+) channels, cannot be achieved by using the patch clamp technique. In this article, we used a recently developed cutting-edge optical technique to investigate the physiological behaviour of local Ca(2+) currents along the apical dendrite of CA1 hippocampal pyramidal neurons. We directly measure, for the first time, the synergistic activation and deactivation of the diverse dendritic voltage-gated Ca(2+) channels operating during bursts of back-propagating action potentials to precisely control the Ca(2+) signal. We demonstrate that the Ca(2+) loss via high-voltage-activated channels is compensated by the Ca(2+) entry via the other channels translating in high fidelity of Ca(2+) signalling. ABSTRACT In CA1 hippocampal pyramidal neurons, the dendritic Ca(2+) signal associated with somatic firing represents a fundamental activation code for several proteins. This signal, mediated by voltage-gated Ca(2+) channels (VGCCs), varies along the dendrites. In this study, using a recent optical technique based on the low-affinity indicator Oregon Green 488 BAPTA-5N, we analysed how activation and deactivation of VGCCs produced by back-propagating action potentials (bAPs) along the apical dendrite shape the Ca(2+) signal at different locations in CA1 hippocampal pyramidal neurons of the mouse. We measured, at multiple dendritic sites, the Ca(2+) transients and the changes in membrane potential associated with bAPs at 50 μs temporal resolution and we estimated the kinetics of the Ca(2+) current. We found that during somatic bursts, the bAPs decrease in amplitude along the apical dendrite but the amplitude of the associated Ca(2+) signal in the initial 200 μm dendritic segment does not change. Using a detailed pharmacological analysis, we demonstrate that this effect is due to the perfect compensation of the loss of Ca(2+) via high-voltage-activated (HVA) VGCCs by a larger Ca(2+) component via low-voltage-activated (LVA) VGCCs, revealing a mechanism coupling the two VGCC families of K(+) channels. More distally, where the bAP does not activate HVA-VGCCs, the Ca(2+) signal is variable during the burst. Thus, we demonstrate that HVA- and LVA-VGCCs operate synergistically to stabilise Ca(2+) signals associated with bAPs in the most proximal 200 μm dendritic segment.
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Affiliation(s)
- Nadia Jaafari
- Laboratory for Interdisciplinary Physics, UMR 5588, Université Grenoble Alpes and CNRS, 38402, Saint Martin d'Hères, France.,Institut National de la Santé et Recherche Médicale (INSERM), France.,Laboratories of Excellence, Ion Channel Science and Therapeutics, France
| | - Marco Canepari
- Laboratory for Interdisciplinary Physics, UMR 5588, Université Grenoble Alpes and CNRS, 38402, Saint Martin d'Hères, France.,Institut National de la Santé et Recherche Médicale (INSERM), France.,Laboratories of Excellence, Ion Channel Science and Therapeutics, France
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21
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Rama S. Shift and Mean Algorithm for Functional Imaging with High Spatio-Temporal Resolution. Front Cell Neurosci 2015; 9:446. [PMID: 26635526 PMCID: PMC4647111 DOI: 10.3389/fncel.2015.00446] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2015] [Accepted: 10/26/2015] [Indexed: 12/20/2022] Open
Abstract
Understanding neuronal physiology requires to record electrical activity in many small and remote compartments such as dendrites, axon or dendritic spines. To do so, electrophysiology has long been the tool of choice, as it allows recording very subtle and fast changes in electrical activity. However, electrophysiological measurements are mostly limited to large neuronal compartments such as the neuronal soma. To overcome these limitations, optical methods have been developed, allowing the monitoring of changes in fluorescence of fluorescent reporter dyes inserted into the neuron, with a spatial resolution theoretically only limited by the dye wavelength and optical devices. However, the temporal and spatial resolutive power of functional fluorescence imaging of live neurons is often limited by a necessary trade-off between image resolution, signal to noise ratio (SNR) and speed of acquisition. Here, I propose to use a Super-Resolution Shift and Mean (S&M) algorithm previously used in image computing to improve the SNR, time sampling and spatial resolution of acquired fluorescent signals. I demonstrate the benefits of this methodology using two examples: voltage imaging of action potentials (APs) in soma and dendrites of CA3 pyramidal cells and calcium imaging in the dendritic shaft and spines of CA3 pyramidal cells. I show that this algorithm allows the recording of a broad area at low speed in order to achieve a high SNR, and then pick the signal in any small compartment and resample it at high speed. This method allows preserving both the SNR and the temporal resolution of the signal, while acquiring the original images at high spatial resolution.
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Affiliation(s)
- Sylvain Rama
- INSERM, UMR_S 1072 Marseille, France ; Unité de Neurobiologie des canaux Ioniques et de la Synapse (UNIS) Marseille, France ; Department is UNIS, Unité de Neurobiologie des canaux Ioniques et de la Synapse, Aix-Marseille University Marseille, France
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22
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Jousset F, Rohr S. Optical recording of calcium currents during impulse conduction in cardiac tissue. NEUROPHOTONICS 2015; 2:021011. [PMID: 26158001 PMCID: PMC4478756 DOI: 10.1117/1.nph.2.2.021011] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/16/2014] [Accepted: 01/08/2015] [Indexed: 06/04/2023]
Abstract
We explore the feasibility of obtaining a spatially resolved picture of [Formula: see text] inward currents ([Formula: see text]) in multicellular cardiac tissue by differentiating optically recorded [Formula: see text] transients that accompany propagating action potentials. Patterned growth strands of neonatal rat ventricular cardiomyocytes were stained with the [Formula: see text] indicators Fluo-4 or Fluo-4FF. Preparations were stimulated at 1 Hz, and [Formula: see text] transients were recorded with high spatiotemporal resolution ([Formula: see text], 2 kHz analog bandwidth) with a photodiode array. Signals were differentiated after appropriate digital filtering. Differentiation of [Formula: see text] transients resulted in optically recorded calcium currents (ORCCs) that carried the temporal and pharmacological signatures of L-type [Formula: see text] inward currents: the time to peak amounted to [Formula: see text] (Fluo-4FF) and [Formula: see text] (Fluo-4), full-width at half-maximum was [Formula: see text], and ORCCs were completely suppressed by [Formula: see text][Formula: see text]. Also, and as reported before from patch-clamp studies, caffeine reversibly depressed the amplitude of ORCCs. The results demonstrate that the differentiation of [Formula: see text] transients can be used to obtain a spatially resolved picture of the initial phase of [Formula: see text] in cardiac tissue and to assess relative changes of activation/fast inactivation of [Formula: see text] following pharmacological interventions.
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Affiliation(s)
- Florian Jousset
- University of Bern, Department of Physiology, Bühlplatz 5, CH-3012 Bern, Switzerland
| | - Stephan Rohr
- University of Bern, Department of Physiology, Bühlplatz 5, CH-3012 Bern, Switzerland
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23
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Jaafari N, Marret E, Canepari M. Using simultaneous voltage and calcium imaging to study fast Ca(2+) channels. NEUROPHOTONICS 2015; 2:021010. [PMID: 26158000 PMCID: PMC4479034 DOI: 10.1117/1.nph.2.2.021010] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/17/2014] [Accepted: 01/06/2015] [Indexed: 05/27/2023]
Abstract
The combination of fluorescence measurements of membrane potential and intracellular [Formula: see text] concentration allows correlating the electrical and calcium activity of a cell with spatial precision. The technical advances allowing this type of measurement were achieved only recently and represent an important step in the progress of the voltage imaging approach pioneered over 40 years ago by Lawrence B. Cohen. Here, we show how this approach can be used to investigate the function of [Formula: see text] channels using the foreseen possibility to extract [Formula: see text] currents from imaging experiments. The kinetics of the [Formula: see text] current, mediated by voltage-gated [Formula: see text] channels, can be accurately derived from the [Formula: see text] fluorescence measurement using [Formula: see text] indicators with [Formula: see text] that equilibrate in [Formula: see text]. In this respect, the imaging apparatus dedicated to this application is described in detail. Next, we illustrate the mathematical procedure to extract the current from the [Formula: see text] fluorescence change, including a method to calibrate the signal to charge flux density. Finally, we show an example of simultaneous membrane potential and [Formula: see text] optical measurement associated with an action potential at a CA1 hippocampal pyramidal neuron from a mouse brain slice. The advantages and limitations of this approach are discussed.
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Affiliation(s)
- Nadia Jaafari
- Inserm U836, Grenoble Institute of Neuroscience, Team 3, Grenoble Cedex 09, France
- Université Joseph Fourier, Laboratoire Interdisciplinare de Physique (CNRS UMR 5588), F-38000 Grenoble, France
- Laboratories of Excellence, Ion Channel Science and Therapeutics, France
| | - Elodie Marret
- Inserm U836, Grenoble Institute of Neuroscience, Team 3, Grenoble Cedex 09, France
- Université Joseph Fourier, Laboratoire Interdisciplinare de Physique (CNRS UMR 5588), F-38000 Grenoble, France
- Laboratories of Excellence, Ion Channel Science and Therapeutics, France
| | - Marco Canepari
- Inserm U836, Grenoble Institute of Neuroscience, Team 3, Grenoble Cedex 09, France
- Université Joseph Fourier, Laboratoire Interdisciplinare de Physique (CNRS UMR 5588), F-38000 Grenoble, France
- Laboratories of Excellence, Ion Channel Science and Therapeutics, France
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24
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Jaafari N, Vogt KE, Saggau P, Leslie LM, Zecevic D, Canepari M. Combining Membrane Potential Imaging with Other Optical Techniques. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2015; 859:103-25. [PMID: 26238050 DOI: 10.1007/978-3-319-17641-3_4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Membrane potential imaging using voltage-sensitive dyes can be combined with other optical techniques for a variety of applications. Combining voltage imaging with Ca2+ imaging allows correlating membrane potential changes with intracellular Ca2+ signals or with Ca2+ currents. Combining voltage imaging with uncaging techniques allows analyzing electrical signals elicited by photorelease of a particular molecule. This approach is also a useful tool to calibrate the change in fluorescence intensity in terms of membrane potential changes from different sites permitting spatial mapping of electrical activity. Finally, combining voltage imaging with optogenetics, in particular with channelrhodopsin stimulation, opens the gate to novel investigations of brain circuitries by allowing measurements of synaptic signals mediated by specific sets of neurons. Here we describe in detail the methods of membrane potential imaging in combination with other optical techniques and discus some important applications.
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Affiliation(s)
- Nadia Jaafari
- Inserm U836, Grenoble Institute of Neuroscience, Team 3, Grenoble Cedex 09, France
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