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Luque MA, Morcuende S, Torres B, Herrero L. Kv7/M channel dysfunction produces hyperexcitability in hippocampal CA1 pyramidal cells of Fmr1 knockout mice. J Physiol 2024; 602:3769-3791. [PMID: 38976504 DOI: 10.1113/jp285244] [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: 07/04/2023] [Accepted: 06/18/2024] [Indexed: 07/10/2024] Open
Abstract
Fragile X syndrome (FXS), the most frequent monogenic form of intellectual disability, is caused by transcriptional silencing of the FMR1 gene that could render neuronal hyperexcitability. Here we show that pyramidal cells (PCs) in the dorsal CA1 region of the hippocampus elicited a larger action potential (AP) number in response to suprathreshold stimulation in juvenile Fmr1 knockout (KO) than wild-type (WT) mice. Because Kv7/M channels modulate CA1 PC excitability in rats, we investigated if their dysfunction produces neuronal hyperexcitability in Fmr1 KO mice. Immunohistochemical and western blot analyses showed no differences in the expression of Kv7.2 and Kv7.3 channel subunits between genotypes; however, the current mediated by Kv7/M channels was reduced in Fmr1 KO mice. In both genotypes, bath application of XE991 (10 μM), a blocker of Kv7/M channels: produced an increased AP number, produced an increased input resistance, produced a decreased AP voltage threshold and shaped AP medium afterhyperpolarization by increasing mean velocities. Retigabine (10 μM), an opener of Kv7/M channels, produced opposite effects to XE991. Both XE991 and retigabine abolished differences in all these parameters found in control conditions between genotypes. Furthermore, a low concentration of retigabine (2.5 μM) normalized CA1 PC excitability of Fmr1 KO mice. Finally, ex vivo seizure-like events evoked by 4-aminopyiridine (200 μM) in the dorsal CA1 region were more frequent in Fmr1 KO mice, and were abolished by retigabine (5-10 μM). We conclude that CA1 PCs of Fmr1 KO mice exhibit hyperexcitability, caused by Kv7/M channel dysfunction, and increased epileptiform activity, which were abolished by retigabine. KEY POINTS: Dorsal pyramidal cells of the hippocampal CA1 region of Fmr1 knockout mice exhibit hyperexcitability. Kv7/M channel activity, but not expression, is reduced in pyramidal cells of the hippocampal CA1 region of Fmr1 knockout mice. Kv7/M channel dysfunction causes hyperexcitability in pyramidal cells of the hippocampal CA1 region of Fmr1 knockout mice by increasing input resistance, decreasing AP voltage threshold and shaping medium afterhyperpolarization. A Kv7/M channel opener normalizes neuronal excitability in pyramidal cells of the hippocampal CA1 region of Fmr1 knockout mice. Ex vivo seizure-like events evoked in the dorsal CA1 region were more frequent in Fmr1 KO mice, and such an epileptiform activity was abolished by a Kv7/M channel opener depending on drug concentration. Kv7/M channels may represent a therapeutic target for treating symptoms associated with hippocampal alterations in fragile X syndrome.
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Affiliation(s)
- M Angeles Luque
- Departamento Fisiología, Facultad de Biología, Universidad de Sevilla, Sevilla, Spain
| | - Sara Morcuende
- Departamento Fisiología, Facultad de Biología, Universidad de Sevilla, Sevilla, Spain
| | - Blas Torres
- Departamento Fisiología, Facultad de Biología, Universidad de Sevilla, Sevilla, Spain
| | - Luis Herrero
- Departamento Fisiología, Facultad de Biología, Universidad de Sevilla, Sevilla, Spain
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2
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Chen JJ, Kaufmann WA, Chen C, Arai I, Kim O, Shigemoto R, Jonas P. Developmental transformation of Ca 2+ channel-vesicle nanotopography at a central GABAergic synapse. Neuron 2024; 112:755-771.e9. [PMID: 38215739 DOI: 10.1016/j.neuron.2023.12.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2022] [Revised: 07/12/2023] [Accepted: 12/05/2023] [Indexed: 01/14/2024]
Abstract
The coupling between Ca2+ channels and release sensors is a key factor defining the signaling properties of a synapse. However, the coupling nanotopography at many synapses remains unknown, and it is unclear how it changes during development. To address these questions, we examined coupling at the cerebellar inhibitory basket cell (BC)-Purkinje cell (PC) synapse. Biophysical analysis of transmission by paired recording and intracellular pipette perfusion revealed that the effects of exogenous Ca2+ chelators decreased during development, despite constant reliance of release on P/Q-type Ca2+ channels. Structural analysis by freeze-fracture replica labeling (FRL) and transmission electron microscopy (EM) indicated that presynaptic P/Q-type Ca2+ channels formed nanoclusters throughout development, whereas docked vesicles were only clustered at later developmental stages. Modeling suggested a developmental transformation from a more random to a more clustered coupling nanotopography. Thus, presynaptic signaling developmentally approaches a point-to-point configuration, optimizing speed, reliability, and energy efficiency of synaptic transmission.
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Affiliation(s)
- Jing-Jing Chen
- Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria
| | - Walter A Kaufmann
- Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria
| | - Chong Chen
- Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria
| | - Itaru Arai
- Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria
| | - Olena Kim
- Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria
| | - Ryuichi Shigemoto
- Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria
| | - Peter Jonas
- Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria.
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3
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Eisner D, Neher E, Taschenberger H, Smith G. Physiology of intracellular calcium buffering. Physiol Rev 2023; 103:2767-2845. [PMID: 37326298 DOI: 10.1152/physrev.00042.2022] [Citation(s) in RCA: 18] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2022] [Revised: 05/08/2023] [Accepted: 06/11/2023] [Indexed: 06/17/2023] Open
Abstract
Calcium signaling underlies much of physiology. Almost all the Ca2+ in the cytoplasm is bound to buffers, with typically only ∼1% being freely ionized at resting levels in most cells. Physiological Ca2+ buffers include small molecules and proteins, and experimentally Ca2+ indicators will also buffer calcium. The chemistry of interactions between Ca2+ and buffers determines the extent and speed of Ca2+ binding. The physiological effects of Ca2+ buffers are determined by the kinetics with which they bind Ca2+ and their mobility within the cell. The degree of buffering depends on factors such as the affinity for Ca2+, the Ca2+ concentration, and whether Ca2+ ions bind cooperatively. Buffering affects both the amplitude and time course of cytoplasmic Ca2+ signals as well as changes of Ca2+ concentration in organelles. It can also facilitate Ca2+ diffusion inside the cell. Ca2+ buffering affects synaptic transmission, muscle contraction, Ca2+ transport across epithelia, and the killing of bacteria. Saturation of buffers leads to synaptic facilitation and tetanic contraction in skeletal muscle and may play a role in inotropy in the heart. This review focuses on the link between buffer chemistry and function and how Ca2+ buffering affects normal physiology and the consequences of changes in disease. As well as summarizing what is known, we point out the many areas where further work is required.
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Affiliation(s)
- David Eisner
- Division of Cardiovascular Sciences, University of Manchester, Manchester, United Kingdom
| | - Erwin Neher
- Membrane Biophysics Laboratory, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
- Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC), University of Göttingen, Göttingen, Germany
| | - Holger Taschenberger
- Department of Molecular Neurobiology, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
| | - Godfrey Smith
- School of Cardiovascular and Metabolic Health, College of Medical, Veterinary, and Life Sciences, University of Glasgow, Glasgow, United Kingdom
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4
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Ali Moussa HY, Park Y. Electrostatic regulation of the cis- and trans-membrane interactions of synaptotagmin-1. Sci Rep 2022; 12:22407. [PMID: 36575295 PMCID: PMC9794720 DOI: 10.1038/s41598-022-26723-9] [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: 09/15/2022] [Accepted: 12/19/2022] [Indexed: 12/28/2022] Open
Abstract
Synaptotagmin-1 is a vesicular protein and Ca2+ sensor for Ca2+-dependent exocytosis. Ca2+ induces synaptotagmin-1 binding to its own vesicle membrane, called the cis-interaction, thus preventing the trans-interaction of synaptotagmin-1 to the plasma membrane. However, the electrostatic regulation of the cis- and trans-membrane interaction of synaptotagmin-1 was poorly understood in different Ca2+-buffering conditions. Here we provide an assay to monitor the cis- and trans-membrane interactions of synaptotagmin-1 by using native purified vesicles and the plasma membrane-mimicking liposomes (PM-liposomes). Both ATP and EGTA similarly reverse the cis-membrane interaction of synaptotagmin-1 in free [Ca2+] of 10-100 μM. High PIP2 concentrations in the PM-liposomes reduce the Hill coefficient of vesicle fusion and synaptotagmin-1 membrane binding; this observation suggests that local PIP2 concentrations control the Ca2+-cooperativity of synaptotagmin-1. Our data provide evidence that Ca2+ chelators, including EGTA and polyphosphate anions such as ATP, ADP, and AMP, electrostatically reverse the cis-interaction of synaptotagmin-1.
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Affiliation(s)
- Houda Yasmine Ali Moussa
- grid.418818.c0000 0001 0516 2170Neurological Disorders Research Center, Qatar Biomedical Research Institute (QBRI), Hamad Bin Khalifa University (HBKU), Qatar Foundation, Doha, Qatar
| | - Yongsoo Park
- grid.418818.c0000 0001 0516 2170Neurological Disorders Research Center, Qatar Biomedical Research Institute (QBRI), Hamad Bin Khalifa University (HBKU), Qatar Foundation, Doha, Qatar ,grid.418818.c0000 0001 0516 2170College of Health and Life Sciences (CHLS), Hamad Bin Khalifa University (HBKU), Qatar Foundation, Doha, Qatar
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5
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Mendonça PRF, Tagliatti E, Langley H, Kotzadimitriou D, Zamora-Chimal CG, Timofeeva Y, Volynski KE. Asynchronous glutamate release is enhanced in low release efficacy synapses and dispersed across the active zone. Nat Commun 2022; 13:3497. [PMID: 35715404 PMCID: PMC9206079 DOI: 10.1038/s41467-022-31070-4] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2021] [Accepted: 05/31/2022] [Indexed: 11/09/2022] Open
Abstract
The balance between fast synchronous and delayed asynchronous release of neurotransmitters has a major role in defining computational properties of neuronal synapses and regulation of neuronal network activity. However, how it is tuned at the single synapse level remains poorly understood. Here, using the fluorescent glutamate sensor SF-iGluSnFR, we image quantal vesicular release in tens to hundreds of individual synaptic outputs from single pyramidal cells with 4 millisecond temporal and 75 nm spatial resolution. We find that the ratio between synchronous and asynchronous synaptic vesicle exocytosis varies extensively among synapses supplied by the same axon, and that the synchronicity of release is reduced at low release probability synapses. We further demonstrate that asynchronous exocytosis sites are more widely distributed within the release area than synchronous sites. Together, our results reveal a universal relationship between the two major functional properties of synapses - the timing and the overall efficacy of neurotransmitter release.
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Affiliation(s)
- Philipe R F Mendonça
- University College London Institute of Neurology, London, UK. .,Department of Physiology and Biophysics, Federal University of Minas Gerais, Gerais, Brazil.
| | - Erica Tagliatti
- University College London Institute of Neurology, London, UK
| | - Helen Langley
- University College London Institute of Neurology, London, UK
| | | | | | - Yulia Timofeeva
- University College London Institute of Neurology, London, UK. .,Department of Computer Science, University of Warwick, Coventry, UK.
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6
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Akaniro-Ejim NE, Smith PA. Intracellular Ca 2+ in Mouse White Fat Adipocytes: Effects of Extracellular Anions, Growth Hormone, and Their Interaction with Ca 2+ Influx. Bioelectricity 2021. [DOI: 10.1089/bioe.2021.0020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
| | - Paul A. Smith
- School of Life Sciences, University of Nottingham, Nottingham, United Kingdom
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7
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Robert V, Therreau L, Davatolhagh MF, Bernardo-Garcia FJ, Clements KN, Chevaleyre V, Piskorowski RA. The mechanisms shaping CA2 pyramidal neuron action potential bursting induced by muscarinic acetylcholine receptor activation. J Gen Physiol 2021; 152:133812. [PMID: 32069351 PMCID: PMC7141590 DOI: 10.1085/jgp.201912462] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2019] [Revised: 12/18/2019] [Accepted: 01/13/2020] [Indexed: 01/04/2023] Open
Abstract
Recent studies have revealed that hippocampal area CA2 plays an important role in hippocampal network function. Disruption of this region has been implicated in neuropsychiatric disorders. It is well appreciated that cholinergic input to the hippocampus plays an important role in learning and memory. While the effect of elevated cholinergic tone has been well studied in areas CA1 and CA3, it remains unclear how changes in cholinergic tone impact synaptic transmission and the intrinsic properties of neurons in area CA2. In this study, we applied the cholinergic agonist carbachol and performed on-cell, whole-cell, and extracellular recordings in area CA2. We observed that under conditions of high cholinergic tone, CA2 pyramidal neurons depolarized and rhythmically fired bursts of action potentials. This depolarization depended on the activation of M1 and M3 cholinergic receptors. Furthermore, we examined how the intrinsic properties and action-potential firing were altered in CA2 pyramidal neurons treated with 10 µM carbachol. While this intrinsic burst firing persisted in the absence of synaptic transmission, bursts were shaped by synaptic inputs in the intact network. We found that both excitatory and inhibitory synaptic transmission were reduced upon carbachol treatment. Finally, we examined the contribution of different channels to the cholinergic-induced changes in neuronal properties. We found that a conductance from Kv7 channels partially contributed to carbachol-induced changes in resting membrane potential and membrane resistance. We also found that D-type potassium currents contributed to controlling several properties of the bursts, including firing rate and burst kinetics. Furthermore, we determined that T-type calcium channels and small conductance calcium-activated potassium channels play a role in regulating bursting activity.
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Affiliation(s)
- Vincent Robert
- Université Paris Descartes, Inserm UMR1266, Institute of Psychiatry and Neuroscience of Paris, Team Synaptic Plasticity and Neural Networks, Paris, France
| | - Ludivine Therreau
- Université Paris Descartes, Inserm UMR1266, Institute of Psychiatry and Neuroscience of Paris, Team Synaptic Plasticity and Neural Networks, Paris, France
| | - M Felicia Davatolhagh
- Department of Neuroscience, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA
| | - F Javier Bernardo-Garcia
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, CA
| | | | - Vivien Chevaleyre
- Université Paris Descartes, Inserm UMR1266, Institute of Psychiatry and Neuroscience of Paris, Team Synaptic Plasticity and Neural Networks, Paris, France
| | - Rebecca A Piskorowski
- Université Paris Descartes, Inserm UMR1266, Institute of Psychiatry and Neuroscience of Paris, Team Synaptic Plasticity and Neural Networks, Paris, France
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8
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Otomo K, Perkins J, Kulkarni A, Stojanovic S, Roeper J, Paladini CA. In vivo patch-clamp recordings reveal distinct subthreshold signatures and threshold dynamics of midbrain dopamine neurons. Nat Commun 2020; 11:6286. [PMID: 33293613 PMCID: PMC7722714 DOI: 10.1038/s41467-020-20041-2] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2020] [Accepted: 11/06/2020] [Indexed: 01/19/2023] Open
Abstract
The in vivo firing patterns of ventral midbrain dopamine neurons are controlled by afferent and intrinsic activity to generate sensory cue and prediction error signals that are essential for reward-based learning. Given the absence of in vivo intracellular recordings during the last three decades, the subthreshold membrane potential events that cause changes in dopamine neuron firing patterns remain unknown. To address this, we established in vivo whole-cell recordings and obtained over 100 spontaneously active, immunocytochemically-defined midbrain dopamine neurons in isoflurane-anaesthetized adult mice. We identified a repertoire of subthreshold membrane potential signatures associated with distinct in vivo firing patterns. Dopamine neuron activity in vivo deviated from single-spike pacemaking by phasic increases in firing rate via two qualitatively distinct biophysical mechanisms: 1) a prolonged hyperpolarization preceding rebound bursts, accompanied by a hyperpolarizing shift in action potential threshold; and 2) a transient depolarization leading to high-frequency plateau bursts, associated with a depolarizing shift in action potential threshold. Our findings define a mechanistic framework for the biophysical implementation of dopamine neuron firing patterns in the intact brain.
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Affiliation(s)
- Kanako Otomo
- Institute of Neurophysiology, Neuroscience Center, Goethe University, Frankfurt, Germany
| | - Jessica Perkins
- University of Texas at San Antonio Neurosciences Institute, San Antonio, USA
| | - Anand Kulkarni
- University of Texas at San Antonio Neurosciences Institute, San Antonio, USA
| | - Strahinja Stojanovic
- Institute of Neurophysiology, Neuroscience Center, Goethe University, Frankfurt, Germany
| | - Jochen Roeper
- Institute of Neurophysiology, Neuroscience Center, Goethe University, Frankfurt, Germany.
| | - Carlos A Paladini
- University of Texas at San Antonio Neurosciences Institute, San Antonio, USA.
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9
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Herrmann AM, Cerina M, Bittner S, Meuth SG, Budde T. Intracellular fluoride influences TASK mediated currents in human T cells. J Immunol Methods 2020; 487:112875. [PMID: 33031794 DOI: 10.1016/j.jim.2020.112875] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2019] [Revised: 08/14/2020] [Accepted: 10/01/2020] [Indexed: 10/23/2022]
Abstract
The expression of Kv1.3 and KCa channels in human T cells is essential for maintaining cell activation, proliferation and migration during an inflammatory response. Recently, an additional residual current, sensitive to anandamide and A293, compounds specifically inhibiting currents mediated by TASK channels, was observed after complete pharmacological blockade of Kv1.3 and KCa channels. This finding was not consistently observed throughout different studies and, an in-depth review of the different recording conditions used for the electrophysiological analysis of K+ currents in T cells revealed fluoride as major anionic component of the pipette intracellular solutions in the initial studies. While fluoride is frequently used to stabilize electrophysiological recordings, it is known as G-protein activator and to influence the intracellular Ca2+ concentration, which are mechanisms known to modulate TASK channel functioning. Therefore, we systemically addressed different fluoride- and chloride-based pipette solutions in whole-cell patch-clamp experiments in human T cells and used specific blockers to identify membrane currents carried by TASK and Kv1.3 channels. We found that fluoride increased the decay time constant of K+ outward currents, reduced the degree of the sustained current component and diminished the effect of the specific TASK channels blocker A293. These findings indicate that the use of fluoride-based pipette solutions may hinder the identification of a functional TASK channel component in electrophysiological experiments.
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Affiliation(s)
- Alexander M Herrmann
- Department of Neurology with Institute of Translational Neurology, Münster University Hospital, Münster, Germany.
| | - Manuela Cerina
- Department of Neurology with Institute of Translational Neurology, Münster University Hospital, Münster, Germany
| | - Stefan Bittner
- Department of Neurology, University of Mainz, Mainz, Germany
| | - Sven G Meuth
- Department of Neurology with Institute of Translational Neurology, Münster University Hospital, Münster, Germany
| | - Thomas Budde
- Institute of Physiology I, Westfälische-Wilhems Universität Münster, Münster, Germany.
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10
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Bornschein G, Eilers J, Schmidt H. Neocortical High Probability Release Sites Are Formed by Distinct Ca 2+ Channel-to-Release Sensor Topographies during Development. Cell Rep 2020; 28:1410-1418.e4. [PMID: 31390556 DOI: 10.1016/j.celrep.2019.07.008] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2019] [Revised: 05/29/2019] [Accepted: 06/28/2019] [Indexed: 01/10/2023] Open
Abstract
Coupling distances between Ca2+ channels and release sensors regulate vesicular release probability (pv). Tight coupling is thought to provide a framework for high pv and loose coupling for high plasticity at low pv. At synapses investigated during development, coupling distances decrease, thereby increasing pv and transmission fidelity. We find that neocortical high-fidelity synapses deviate from these rules. Paired recordings from pyramidal neurons with "slow" and "fast" Ca2+ chelators combined with experimentally constrained simulations suggest that coupling tightens significantly during development. However, fluctuation analysis revealed that neither pv (∼0.63) nor the number of release sites (∼8) changes concomitantly. Moreover, the amplitude and time course of presynaptic Ca2+ transients are not different between age groups. These results are explained by high-pv release sites with Ca2+ microdomains in young synapses and nanodomains in mature synapses. Thus, at neocortical synapses, a developmental reorganization of the active zone leaves pv unaffected, emphasizing developmental and functional synaptic diversity.
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Affiliation(s)
- Grit Bornschein
- Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, Liebigstrasse 27a, 04103 Leipzig, Germany.
| | - Jens Eilers
- Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, Liebigstrasse 27a, 04103 Leipzig, Germany
| | - Hartmut Schmidt
- Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, Liebigstrasse 27a, 04103 Leipzig, Germany.
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11
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Sánchez-Gómez L, Guerrero-Hernández A, Santillán M. Polymerization of sarcoplasmic-reticulum calcium-binding proteins might explain observed reticulum kinetics-on-demand behavior. J Theor Biol 2019; 482:109986. [PMID: 31465729 DOI: 10.1016/j.jtbi.2019.08.017] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2019] [Revised: 08/20/2019] [Accepted: 08/26/2019] [Indexed: 11/20/2022]
Abstract
Reported experimental results, in which transient elevations of sarcoplasmic calcium levels are induced by caffeine in smooth muscle cells, apparently contradict the principle of mass conservation. The commonly accepted model assumes that the total number of Ca2+ binding sites is fixed. A former work dealing with this problem proved that assuming the presence within the reticulum of calcium sequestering proteins whose total number of calcium binding sites increases as the existent sites get occupied, is enough to explain the above referred counter-intuitive experimental results. However, no chemical explanation was given to account for this binding-site count increase. In the present work, we propose a chemical-kinetics scheme for the binding of calcium to calsequestrin (a protein found within the reticulum) and the polymerization of this protein. On the one hand, this scheme is in agreement with reported results on calsequestrin binding kinetics, but it is also fully capable of explaining the observed intriguing performance of the sarcoplasmic reticulum. We further explore the behavior of the resulting nonlinear dynamic system and discuss possible physiological implications of the proposed scheme.
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Affiliation(s)
- Laura Sánchez-Gómez
- Centro de Investigación y de Estudios Avanzados del IPN, Unidad Monterrey, Vía del Conocimiento 201, Apodaca, NL 66600, México
| | - Agustín Guerrero-Hernández
- Centro de Investigación y de Estudios Avanzados del IPN, Unidad Zacatenco, Departamento de Bioquímica, Av. Instituto Politécnico Nacional 2508, Ciudad de México, 07000, México
| | - Moisés Santillán
- Centro de Investigación y de Estudios Avanzados del IPN, Unidad Monterrey, Vía del Conocimiento 201, Apodaca, NL 66600, México.
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12
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Tran V, Stricker C. Diffusion of Ca 2+ from Small Boutons en Passant into the Axon Shapes AP-Evoked Ca 2+ Transients. Biophys J 2018; 115:1344-1356. [PMID: 30103908 DOI: 10.1016/j.bpj.2018.07.018] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2018] [Revised: 07/01/2018] [Accepted: 07/16/2018] [Indexed: 01/16/2023] Open
Abstract
Not only the amplitude but also the time course of a presynaptic Ca2+ transient determine multiple aspects of synaptic transmission. In small bouton-type synapses, the mechanisms underlying the Ca2+ decay kinetics have not been fully investigated. Here, factors that shape an action-potential-evoked Ca2+ transient were quantitatively studied in synaptic boutons of neocortical layer 5 pyramidal neurons. Ca2+ transients were measured with different concentrations of fluorescent Ca2+ indicators and analyzed based on a single-compartment model. We found a small endogenous Ca2+-binding ratio (7 ± 2) and a high activity of Ca2+ transporters (0.64 ± 0.03 ms-1), both of which enable rapid clearance of Ca2+ from the boutons. However, contrary to predictions of the single-compartment model, the decay time course of the measured Ca2+ transients was biexponential and became prolonged during repetitive stimulation. Measurements of [Ca2+]i along the adjoining axon, together with an experimentally constrained model, showed that the initial fast decay of the Ca2+ transients predominantly arose from the diffusion of Ca2+ from the boutons into the axon. Therefore, for small boutons en passant, factors like terminal volume, axon diameter, and the concentration of mobile Ca2+-binding molecules are critical determinants of Ca2+ dynamics and thus Ca2+-dependent processes, including short-term synaptic plasticity.
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Affiliation(s)
- Van Tran
- Eccles Institute of Neuroscience, JCSMR.
| | - Christian Stricker
- Eccles Institute of Neuroscience, JCSMR; ANU Medical School, ANU, Acton, Australian Capital Territory, Australia
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13
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An improved measurement of the Ca2+-binding affinity of fluorescent Ca2+ indicators. Cell Calcium 2018; 71:86-94. [DOI: 10.1016/j.ceca.2018.01.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2017] [Revised: 12/11/2017] [Accepted: 01/07/2018] [Indexed: 01/18/2023]
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14
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Neef J, Urban NT, Ohn TL, Frank T, Jean P, Hell SW, Willig KI, Moser T. Quantitative optical nanophysiology of Ca 2+ signaling at inner hair cell active zones. Nat Commun 2018; 9:290. [PMID: 29348575 PMCID: PMC5773603 DOI: 10.1038/s41467-017-02612-y] [Citation(s) in RCA: 60] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2016] [Accepted: 12/14/2017] [Indexed: 12/17/2022] Open
Abstract
Ca2+ influx triggers the release of synaptic vesicles at the presynaptic active zone (AZ). A quantitative characterization of presynaptic Ca2+ signaling is critical for understanding synaptic transmission. However, this has remained challenging to establish at the required resolution. Here, we employ confocal and stimulated emission depletion (STED) microscopy to quantify the number (20-330) and arrangement (mostly linear 70 nm × 100-600 nm clusters) of Ca2+ channels at AZs of mouse cochlear inner hair cells (IHCs). Establishing STED Ca2+ imaging, we analyze presynaptic Ca2+ signals at the nanometer scale and find confined elongated Ca2+ domains at normal IHC AZs, whereas Ca2+ domains are spatially spread out at the AZs of bassoon-deficient IHCs. Performing 2D-STED fluorescence lifetime analysis, we arrive at estimates of the Ca2+ concentrations at stimulated IHC AZs of on average 25 µM. We propose that IHCs form bassoon-dependent presynaptic Ca2+-channel clusters of similar density but scalable length, thereby varying the number of Ca2+ channels amongst individual AZs.
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Affiliation(s)
- Jakob Neef
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, 37099, Göttingen, Germany.,Collaborative Research Center 889, University of Göttingen, 37075 Göttingen, Germany.,Bernstein Focus for Neurotechnology, University of Göttingen, 37075 Göttingen, Germany.,Synaptic Nanophysiology Group, Max Planck Institute for Biophysical Chemistry, 37077, Göttingen, Germany
| | - Nicolai T Urban
- Department of Nanobiophotonics, Max Planck Institute for Biophysical Chemistry, 37077, Göttingen, Germany. .,Center for Nanoscale Microscopy and Molecular Physiology of the Brain, University Medical Center Göttingen, 37099 Göttingen, Germany.
| | - Tzu-Lun Ohn
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, 37099, Göttingen, Germany.,Collaborative Research Center 889, University of Göttingen, 37075 Göttingen, Germany.,Bernstein Focus for Neurotechnology, University of Göttingen, 37075 Göttingen, Germany
| | - Thomas Frank
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, 37099, Göttingen, Germany.,Friedrich Miescher Institute for Biomedical Research, 4058, Basel, Switzerland
| | - Philippe Jean
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, 37099, Göttingen, Germany
| | - Stefan W Hell
- Department of Nanobiophotonics, Max Planck Institute for Biophysical Chemistry, 37077, Göttingen, Germany.,Center for Nanoscale Microscopy and Molecular Physiology of the Brain, University Medical Center Göttingen, 37099 Göttingen, Germany
| | - Katrin I Willig
- Collaborative Research Center 889, University of Göttingen, 37075 Göttingen, Germany. .,Department of Nanobiophotonics, Max Planck Institute for Biophysical Chemistry, 37077, Göttingen, Germany. .,Center for Nanoscale Microscopy and Molecular Physiology of the Brain, University Medical Center Göttingen, 37099 Göttingen, Germany. .,Optical Nanoscopy in Neuroscience, University Medical Center Göttingen, 37099, Göttingen, Germany.
| | - Tobias Moser
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, 37099, Göttingen, Germany. .,Collaborative Research Center 889, University of Göttingen, 37075 Göttingen, Germany. .,Bernstein Focus for Neurotechnology, University of Göttingen, 37075 Göttingen, Germany. .,Synaptic Nanophysiology Group, Max Planck Institute for Biophysical Chemistry, 37077, Göttingen, Germany. .,Center for Nanoscale Microscopy and Molecular Physiology of the Brain, University Medical Center Göttingen, 37099 Göttingen, Germany. .,Bernstein Center for Computational Neuroscience, University of Göttingen, 37075 Göttingen, Germany.
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15
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Age-dependent regulation of GABA transmission by kappa opioid receptors in the basolateral amygdala of Sprague-Dawley rats. Neuropharmacology 2017; 117:124-133. [PMID: 28163104 DOI: 10.1016/j.neuropharm.2017.01.036] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2016] [Revised: 01/26/2017] [Accepted: 01/29/2017] [Indexed: 12/17/2022]
Abstract
Anxiety disorders are one of the most common and debilitating mental illnesses worldwide. Growing evidence indicates an age-dependent rise in the incidence of anxiety disorders from adolescence through adulthood, suggestive of underlying neurodevelopmental mechanisms. Kappa opioid receptors (KORs) are known to contribute to the development and expression of anxiety; however, the functional role of KORs in the basolateral amygdala (BLA), a brain structure critical in mediating anxiety, particularly across ontogeny, are unknown. Using whole-cell patch-clamp electrophysiology in acute brain slices from adolescent (postnatal day (P) 30-45) and adult (P60+) male Sprague-Dawley rats, we found that the KOR agonist, U69593, increased the frequency of GABAA-mediated spontaneous inhibitory postsynaptic currents (sIPSCs) in the adolescent BLA, without an effect in the adult BLA or on sIPSC amplitude at either age. The KOR effect was blocked by the KOR antagonist, nor-BNI, which alone did not alter GABA transmission at either age, and the effect of the KOR agonist was TTX-sensitive. Additionally, KOR activation did not alter glutamatergic transmission in the BLA at either age. In contrast, U69593 inhibited sIPSC frequency in the central amygdala (CeA) at both ages, without altering sIPSC amplitude. Western blot analysis of KOR expression indicated that KOR levels were not different between the two ages in either the BLA or CeA. This is the first study to provide compelling evidence for a novel and unique neuromodulatory switch in one of the primary brain regions involved in initiating and mediating anxiety that may contribute to the ontogenic rise in anxiety disorders.
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16
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Lin KH, Taschenberger H, Neher E. Dynamics of volume-averaged intracellular Ca 2+ in a rat CNS nerve terminal during single and repetitive voltage-clamp depolarizations. J Physiol 2017; 595:3219-3236. [PMID: 27957749 DOI: 10.1113/jp272773] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2016] [Accepted: 11/28/2016] [Indexed: 12/28/2022] Open
Abstract
KEY POINTS The intracellular concentration of free calcium ions ([Ca2+ ]i ) in a nerve terminal controls both transmitter release and synaptic plasticity. The rapid triggering of transmitter release depends on the local micro- or nanodomain of highly elevated [Ca2+ ]i in the vicinity of open voltage-gated Ca2+ channels, whereas short-term synaptic plasticity is often controlled by global changes in residual [Ca2+ ]i , averaged over the whole nerve terminal volume. Here we describe dynamic changes of such global [Ca2+ ]i in the calyx of Held - a giant mammalian glutamatergic nerve terminal, which is particularly suited for biophysical studies. We provide quantitative data on Ca2+ inflow, Ca2+ buffering and Ca2+ clearance. These data allow us to predict changes in [Ca2+ ]i in the nerve terminal in response to a wide range of stimulus protocols at high temporal resolution and provide a basis for the modelling of short-term plasticity of glutamatergic synapses. ABSTRACT Many aspects of short-term synaptic plasticity (STP) are controlled by relatively slow changes in the presynaptic intracellular concentration of free calcium ions ([Ca2+ ]i ) that occur in the time range of a few milliseconds to several seconds. In nerve terminals, [Ca2+ ]i equilibrates diffusionally during such slow changes, such that the globally measured, residual [Ca2+ ]i that persists after the collapse of local domains is often the appropriate parameter governing STP. Here, we study activity-dependent dynamic changes in global [Ca2+ ]i at the rat calyx of Held nerve terminal in acute brainstem slices using patch-clamp and microfluorimetry. We use low concentrations of a low-affinity Ca2+ indicator dye (100 μm Fura-6F) in order not to overwhelm endogenous Ca2+ buffers. We first study voltage-clamped terminals, dialysed with pipette solutions containing minimal amounts of Ca2+ buffers, to determine Ca2+ binding properties of endogenous fixed buffers as well as the mechanisms of Ca2+ clearance. Subsequently, we use pipette solutions including 500 μm EGTA to determine the Ca2+ binding kinetics of this chelator. We provide a formalism and parameters that allow us to predict [Ca2+ ]i changes in calyx nerve terminals in response to a wide range of stimulus protocols. Unexpectedly, the Ca2+ affinity of EGTA under the conditions of our measurements was substantially lower (KD = 543 ± 51 nm) than measured in vitro, mainly as a consequence of a higher than previously assumed dissociation rate constant (2.38 ± 0.20 s-1 ), which we need to postulate in order to model the measured presynaptic [Ca2+ ]i transients.
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Affiliation(s)
- Kun-Han Lin
- Emeritus Group Membrane Biophysics, Max Planck Institute for Biophysical Chemistry, 37077, Göttingen, Germany
| | - Holger Taschenberger
- Emeritus Group Membrane Biophysics, Max Planck Institute for Biophysical Chemistry, 37077, Göttingen, Germany.,Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075, Göttingen, Germany.,DFG-Research Centre for Nanoscale Microscopy and Molecular Physiology of the Brain (CNMPB), 37073, Göttingen, Germany
| | - Erwin Neher
- Emeritus Group Membrane Biophysics, Max Planck Institute for Biophysical Chemistry, 37077, Göttingen, Germany.,DFG-Research Centre for Nanoscale Microscopy and Molecular Physiology of the Brain (CNMPB), 37073, Göttingen, Germany
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17
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Abstract
Calcium influx during action potentials triggers neurotransmitter release at presynaptic active zones. Calcium buffers limit the spread of calcium and restrict neurotransmitter release to the vicinity of calcium channels. To sustain synchronous release during repetitive activity, rapid removal of calcium from the active zone is essential, but the underlying mechanisms are unclear. Therefore, we focused on cerebellar mossy fiber synapses, which are among the fastest synapses in the mammalian brain and found very weak presynaptic calcium buffering. One might assume that strong calcium buffering has the potential to efficiently remove calcium from active zones. In contrast, our results show that weak calcium buffering speeds active zone calcium clearance. Thus, the strength of presynaptic buffering limits the rate of synaptic transmission. Fast synchronous neurotransmitter release at the presynaptic active zone is triggered by local Ca2+ signals, which are confined in their spatiotemporal extent by endogenous Ca2+ buffers. However, it remains elusive how rapid and reliable Ca2+ signaling can be sustained during repetitive release. Here, we established quantitative two-photon Ca2+ imaging in cerebellar mossy fiber boutons, which fire at exceptionally high rates. We show that endogenous fixed buffers have a surprisingly low Ca2+-binding ratio (∼15) and low affinity, whereas mobile buffers have high affinity. Experimentally constrained modeling revealed that the low endogenous buffering promotes fast clearance of Ca2+ from the active zone during repetitive firing. Measuring Ca2+ signals at different distances from active zones with ultra-high-resolution confirmed our model predictions. Our results lead to the concept that reduced Ca2+ buffering enables fast active zone Ca2+ signaling, suggesting that the strength of endogenous Ca2+ buffering limits the rate of synchronous synaptic transmission.
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