1
|
Fresquez AM, White C. Extracellular cysteines C226 and C232 mediate hydrogen sulfide-dependent inhibition of Orai3-mediated store-operated calcium entry. Am J Physiol Cell Physiol 2022; 322:C38-C48. [PMID: 34788146 PMCID: PMC8759961 DOI: 10.1152/ajpcell.00490.2019] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The gaseous signaling molecule hydrogen sulfide (H2S) physiologically regulates store-operated Ca2+ entry (SOCE). The SOCE machinery consists of the plasma membrane-localized Orai channels (Orai1-3) and endoplasmic reticulum-localized stromal interaction molecule (STIM)1 and STIM2 proteins. H2S inhibits Orai3- but not Orai1- or Orai2-mediated SOCE. The current objective was to define the mechanism by which H2S selectively modifies Orai3. We measured SOCE and STIM1/Orai3 dynamics and interactions in HEK293 cells exogenously expressing fluorescently tagged human STIM1 and Orai3 in the presence and absence of the H2S donor GYY4137. Two cysteines (C226 and C232) are present in Orai3 that are absent in the Orai1 and Orai2. When we mutated either of these cysteines to serine, alone or in combination, SOCE inhibition by H2S was abolished. We also established that inhibition was dependent on an interaction with STIM1. To further define the effects of H2S on STIM1/Orai3 interaction, we performed a series of fluorescence recovery after photobleaching (FRAP), colocalization, and fluorescence resonance energy transfer (FRET) experiments. Treatment with H2S did not affect the mobility of Orai3 in the membrane, nor did it influence STIM1/Orai3 puncta formation or STIM1-Orai3 protein-protein interactions. These data support a model in which H2S modification of Orai3 at cysteines 226 and 232 limits SOCE evoked upon store depletion and STIM1 engagement, by a mechanism independent of the interaction between Orai3 and STIM1.
Collapse
Affiliation(s)
- Adriana M. Fresquez
- 1Discipline of Physiology and Biophysics, Chicago Medical School, Rosalind Franklin University of Medicine and Science, North Chicago, Illinois,2Center for Cancer Cell Biology, Immunology, and Infection, Chicago Medical School, Rosalind Franklin University of Medicine and Science, North Chicago, Illinois
| | - Carl White
- 1Discipline of Physiology and Biophysics, Chicago Medical School, Rosalind Franklin University of Medicine and Science, North Chicago, Illinois,2Center for Cancer Cell Biology, Immunology, and Infection, Chicago Medical School, Rosalind Franklin University of Medicine and Science, North Chicago, Illinois
| |
Collapse
|
2
|
Kushnireva L, Korkotian E, Segal M. Calcium Sensors STIM1 and STIM2 Regulate Different Calcium Functions in Cultured Hippocampal Neurons. Front Synaptic Neurosci 2021; 12:573714. [PMID: 33469426 PMCID: PMC7813759 DOI: 10.3389/fnsyn.2020.573714] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2020] [Accepted: 12/07/2020] [Indexed: 12/20/2022] Open
Abstract
There are growing indications for the involvement of calcium stores in the plastic properties of neurons and particularly in dendritic spines of central neurons. The store-operated calcium entry (SOCE) channels are assumed to be activated by the calcium sensor stromal interaction molecule (STIM)which leads to activation of its associated Orai channel. There are two STIM species, and the differential role of the two in SOCE is not entirely clear. In the present study, we were able to distinguish between transfected STIM1, which is more mobile primarily in young neurons, and STIM2 which is less mobile and more prominent in older neurons in culture. STIM1 mobility is associated with spontaneous calcium sparks, local transient rise in cytosolic [Ca2+]i, and in the formation and elongation of dendritic filopodia/spines. In contrast, STIM2 is associated with older neurons, where it is mobile and moves into dendritic spines primarily when cytosolic [Ca2+]i levels are reduced, apparently to activate resident Orai channels. These results highlight a role for STIM1 in the regulation of [Ca2+]i fluctuations associated with the formation of dendritic spines or filopodia in the developing neuron, whereas STIM2 is associated with the maintenance of calcium entry into stores in the adult neuron.
Collapse
Affiliation(s)
- Liliya Kushnireva
- Department of Neurobiology, The Weizmann Institute, Rehovot, Israel.,Faculty of Biology, Perm State University, Perm, Russia
| | - Eduard Korkotian
- Department of Neurobiology, The Weizmann Institute, Rehovot, Israel.,Faculty of Biology, Perm State University, Perm, Russia
| | - Menahem Segal
- Department of Neurobiology, The Weizmann Institute, Rehovot, Israel
| |
Collapse
|
3
|
Chen H, Cross AC, Thakkar A, Xu H, Li A, Paull D, Noggle SA, Kruger L, Denton TT, Gibson GE. Selective linkage of mitochondrial enzymes to intracellular calcium stores differs between human-induced pluripotent stem cells, neural stem cells, and neurons. J Neurochem 2020; 156:867-879. [PMID: 32865230 DOI: 10.1111/jnc.15160] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2020] [Revised: 08/12/2020] [Accepted: 08/13/2020] [Indexed: 12/15/2022]
Abstract
Mitochondria and releasable endoplasmic reticulum (ER) calcium modulate neuronal calcium signaling, and both change in Alzheimer's disease (AD). The releasable calcium stores in the ER are exaggerated in fibroblasts from AD patients and in multiple models of AD. The activity of the alpha-ketoglutarate dehydrogenase complex (KGDHC), a key mitochondrial enzyme complex, is diminished in brains from AD patients, and can be plausibly linked to plaques and tangles. Our previous studies in cell lines and mouse neurons demonstrate that reductions in KGDHC increase the ER releasable calcium stores. The goal of these studies was to test whether the relationship was true in human iPSC-derived neurons. Inhibition of KGDHC for one or 24 hr increased the ER releasable calcium store in human neurons by 69% and 144%, respectively. The effect was mitochondrial enzyme specific because inhibiting the pyruvate dehydrogenase complex, another key mitochondrial enzyme complex, diminished the ER releasable calcium stores. The link of KGDHC to ER releasable calcium stores was cell type specific as the interaction was not present in iPSC or neural stem cells. Thus, these studies in human neurons verify a link between KGDHC and releasable ER calcium stores, and support the use of human neurons to examine mechanisms and potential therapies for AD.
Collapse
Affiliation(s)
- Huanlian Chen
- Burke Neurological Institute, Brain and Mind Research Institute, Weill Cornell Medicine, White Plains, NY, USA
| | - Abigail C Cross
- Burke Neurological Institute, Brain and Mind Research Institute, Weill Cornell Medicine, White Plains, NY, USA
| | - Ankita Thakkar
- Burke Neurological Institute, Brain and Mind Research Institute, Weill Cornell Medicine, White Plains, NY, USA
| | - Hui Xu
- Burke Neurological Institute, Brain and Mind Research Institute, Weill Cornell Medicine, White Plains, NY, USA
| | - Aiqun Li
- The New York Stem Cell Foundation Research Institute, New York, NY, USA.,Department of Genetics and Genomic Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Dan Paull
- The New York Stem Cell Foundation Research Institute, New York, NY, USA
| | - Scott A Noggle
- The New York Stem Cell Foundation Research Institute, New York, NY, USA
| | - Laken Kruger
- Department of Pharmaceutical Sciences, Washington State University, College of Pharmacy and Pharmaceutical Sciences, Spokane, WA, USA
| | - Travis T Denton
- Department of Pharmaceutical Sciences, Washington State University, College of Pharmacy and Pharmaceutical Sciences, Spokane, WA, USA
| | - Gary E Gibson
- Burke Neurological Institute, Brain and Mind Research Institute, Weill Cornell Medicine, White Plains, NY, USA
| |
Collapse
|
4
|
Bouron A. Transcriptomic Profiling of Ca2+ Transport Systems During the Formation of the Cerebral Cortex in Mice. Cells 2020; 9:E1800. [PMID: 32751129 DOI: 10.3390/cells9081800] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2020] [Revised: 07/20/2020] [Accepted: 07/24/2020] [Indexed: 01/05/2023] Open
Abstract
Cytosolic calcium (Ca2+) transients control key neural processes, including neurogenesis, migration, the polarization and growth of neurons, and the establishment and maintenance of synaptic connections. They are thus involved in the development and formation of the neural system. In this study, a publicly available whole transcriptome sequencing (RNA-Seq) dataset was used to examine the expression of genes coding for putative plasma membrane and organellar Ca2+-transporting proteins (channels, pumps, exchangers, and transporters) during the formation of the cerebral cortex in mice. Four ages were considered: embryonic days 11 (E11), 13 (E13), and 17 (E17), and post-natal day 1 (PN1). This transcriptomic profiling was also combined with live-cell Ca2+ imaging recordings to assess the presence of functional Ca2+ transport systems in E13 neurons. The most important Ca2+ routes of the cortical wall at the onset of corticogenesis (E11–E13) were TACAN, GluK5, nAChR β2, Cav3.1, Orai3, transient receptor potential cation channel subfamily M member 7 (TRPM7) non-mitochondrial Na+/Ca2+ exchanger 2 (NCX2), and the connexins CX43/CX45/CX37. Hence, transient receptor potential cation channel mucolipin subfamily member 1 (TRPML1), transmembrane protein 165 (TMEM165), and Ca2+ “leak” channels are prominent intracellular Ca2+ pathways. The Ca2+ pumps sarco/endoplasmic reticulum Ca2+ ATPase 2 (SERCA2) and plasma membrane Ca2+ ATPase 1 (PMCA1) control the resting basal Ca2+ levels. At the end of neurogenesis (E17 and onward), a more numerous and diverse population of Ca2+ uptake systems was observed. In addition to the actors listed above, prominent Ca2+-conducting systems of the cortical wall emerged, including acid-sensing ion channel 1 (ASIC1), Orai2, P2X2, and GluN1. Altogether, this study provides a detailed view of the pattern of expression of the main actors participating in the import, export, and release of Ca2+. This work can serve as a framework for further functional and mechanistic studies on Ca2+ signaling during cerebral cortex formation.
Collapse
|
5
|
Furlan S, Campione M, Murgia M, Mosole S, Argenton F, Volpe P, Nori A. Calsequestrins New Calcium Store Markers of Adult Zebrafish Cerebellum and Optic Tectum. Front Neuroanat 2020; 14:15. [PMID: 32372920 PMCID: PMC7188384 DOI: 10.3389/fnana.2020.00015] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2019] [Accepted: 03/18/2020] [Indexed: 12/26/2022] Open
Abstract
Calcium stores in neurons are heterogeneous in compartmentalization and molecular composition. Danio rerio (zebrafish) is an animal model with a simply folded cerebellum similar in cellular organization to that of mammals. The aim of the study was to identify new endoplasmic reticulum (ER) calcium store markers in zebrafish adult brain with emphasis on cerebellum and optic tectum. By quantitative polymerase chain reaction, we found three RNA transcripts coding for the intra-ER calcium binding protein calsequestrin: casq1a, casq1b, and casq2. In brain homogenates, two isoforms were detected by mass spectrometry and western blotting. Fractionation experiments of whole brain revealed that Casq1a and Casq2 were enriched in a heavy fraction containing ER microsomes and synaptic membranes. By in situ hybridization, we found the heterogeneous expression of casq1a and casq2 mRNA to be compatible with the cellular localization of calsequestrins investigated by immunofluorescence. Casq1 was expressed in neurogenic differentiation 1 expressing the granule cells of the cerebellum and the periventricular zone of the optic tectum. Casq2 was concentrated in parvalbumin expressing Purkinje cells. At a subcellular level, Casq1 was restricted to granular cell bodies, and Casq2 was localized in cell bodies, dendrites, and axons. Data are discussed in relation to the differential cellular and subcellular distribution of other cerebellum calcium store markers and are evaluated with respect to the putative relevance of calsequestrins in the neuron-specific functional activity.
Collapse
Affiliation(s)
- Sandra Furlan
- Consiglio Nazionale delle Ricerche, Institute of Neuroscience, Padova, Italy
| | - Marina Campione
- Consiglio Nazionale delle Ricerche, Institute of Neuroscience, Padova, Italy
| | - Marta Murgia
- Department of Biomedical Sciences, University of Padova, Istituto Interuniversitario di Miologia, Padova, Italy.,Department of Proteomics and Signal Transduction, Max-Planck-Institute of Biochemistry, Martinsried, Germany
| | - Simone Mosole
- Institute of Oncology Research (IOR), Bellinzona, Switzerland
| | | | - Pompeo Volpe
- Department of Biomedical Sciences, University of Padova, Istituto Interuniversitario di Miologia, Padova, Italy
| | - Alessandra Nori
- Department of Biomedical Sciences, University of Padova, Istituto Interuniversitario di Miologia, Padova, Italy
| |
Collapse
|
6
|
Fernández de Sevilla D, Núñez A, Buño W. Muscarinic Receptors, from Synaptic Plasticity to its Role in Network Activity. Neuroscience 2020; 456:60-70. [PMID: 32278062 DOI: 10.1016/j.neuroscience.2020.04.005] [Citation(s) in RCA: 32] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2019] [Revised: 03/27/2020] [Accepted: 04/01/2020] [Indexed: 12/13/2022]
Abstract
Acetylcholine acting via metabotropic receptors plays a key role in learning and memory by regulating synaptic plasticity and circuit activity. However, a recent overall view of the effects of muscarinic acetylcholine receptors (mAChRs) on excitatory and inhibitory long-term synaptic plasticity and on circuit activity is lacking. This review focusses on specific aspects of the regulation of synaptic plasticity and circuit activity by mAChRs in the hippocampus and cortex. Acetylcholine increases the excitability of pyramidal neurons, facilitating the generation of dendritic Ca2+-spikes, NMDA-spikes and action potential bursts which provide the main source of Ca2+ influx necessary to induce synaptic plasticity. The activation of mAChRs induced Ca2+ release from intracellular IP3-sensitive stores is a major player in the induction of a NMDA independent long-term potentiation (LTP) caused by an increased expression of AMPA receptors in hippocampal pyramidal neuron dendritic spines. In the neocortex, activation of mAChRs also induces a long-term enhancement of excitatory postsynaptic currents. In addition to effects on excitatory synapses, a single brief activation of mAChRs together with short repeated membrane depolarization can induce a long-term enhancement of GABA A type (GABAA) inhibition through an increased expression of GABAA receptors in hippocampal pyramidal neurons. By contrast, a long term depression of GABAA inhibition (iLTD) is induced by muscarinic receptor activation in the absence of postsynaptic depolarizations. This iLTD is caused by an endocannabinoid-mediated presynaptic inhibition that reduces the GABA release probability at the terminals of inhibitory interneurons. This bidirectional long-term plasticity of inhibition may dynamically regulate the excitatory/inhibitory balance depending on the quiescent or active state of the postsynaptic pyramidal neurons. Therefore, acetylcholine can induce varied effects on neuronal activity and circuit behavior that can enhance sensory detection and processing through the modification of circuit activity leading to learning, memory and behavior.
Collapse
Affiliation(s)
- D Fernández de Sevilla
- Departamento de Anatomía, Histología y Neurociencia, Facultad de Medicina, Universidad Autónoma de Madrid, Madrid 28029, Spain.
| | - A Núñez
- Departamento de Anatomía, Histología y Neurociencia, Facultad de Medicina, Universidad Autónoma de Madrid, Madrid 28029, Spain
| | - W Buño
- Instituto Cajal, Consejo Superior de Investigaciones Científicas, Madrid 28029, Spain
| |
Collapse
|
7
|
King CM, Bohmbach K, Minge D, Delekate A, Zheng K, Reynolds J, Rakers C, Zeug A, Petzold GC, Rusakov DA, Henneberger C. Local Resting Ca 2+ Controls the Scale of Astroglial Ca 2+ Signals. Cell Rep 2020; 30:3466-3477.e4. [PMID: 32160550 PMCID: PMC7068654 DOI: 10.1016/j.celrep.2020.02.043] [Citation(s) in RCA: 32] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2018] [Revised: 12/21/2019] [Accepted: 02/06/2020] [Indexed: 02/07/2023] Open
Abstract
Astroglia regulate neurovascular coupling while engaging in signal exchange with neurons. The underlying cellular machinery is thought to rely on astrocytic Ca2+ signals, but what controls their amplitude and waveform is poorly understood. Here, we employ time-resolved two-photon excitation fluorescence imaging in acute hippocampal slices and in cortex in vivo to find that resting [Ca2+] predicts the scale (amplitude) and the maximum (peak) of astroglial Ca2+ elevations. We bidirectionally manipulate resting [Ca2+] by uncaging intracellular Ca2+ or Ca2+ buffers and use ratiometric imaging of a genetically encoded Ca2+ indicator to establish that alterations in resting [Ca2+] change co-directionally the peak level and anti-directionally the amplitude of local Ca2+ transients. This relationship holds for spontaneous and for induced (for instance by locomotion) Ca2+ signals. Our findings uncover a basic generic rule of Ca2+ signal formation in astrocytes, thus also associating the resting Ca2+ level with the physiological "excitability" state of astroglia.
Collapse
Affiliation(s)
- Claire M King
- Institute of Neurology, University College London, London, UK
| | - Kirsten Bohmbach
- Institute of Cellular Neurosciences, Medical Faculty, University of Bonn, Bonn, Germany
| | - Daniel Minge
- Institute of Cellular Neurosciences, Medical Faculty, University of Bonn, Bonn, Germany
| | - Andrea Delekate
- German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany
| | - Kaiyu Zheng
- Institute of Neurology, University College London, London, UK
| | - James Reynolds
- Institute of Neurology, University College London, London, UK
| | - Cordula Rakers
- German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany
| | - Andre Zeug
- Cellular Neurophysiology, Hannover Medical School, Hannover, Germany
| | - Gabor C Petzold
- German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany; Department of Neurology, University Hospital Bonn, Bonn, Germany
| | | | - Christian Henneberger
- Institute of Neurology, University College London, London, UK; Institute of Cellular Neurosciences, Medical Faculty, University of Bonn, Bonn, Germany; German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany.
| |
Collapse
|
8
|
Schäffer DE, Iyer LM, Burroughs AM, Aravind L. Functional Innovation in the Evolution of the Calcium-Dependent System of the Eukaryotic Endoplasmic Reticulum. Front Genet 2020; 11:34. [PMID: 32117448 PMCID: PMC7016017 DOI: 10.3389/fgene.2020.00034] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2019] [Accepted: 01/10/2020] [Indexed: 01/30/2023] Open
Abstract
The origin of eukaryotes was marked by the emergence of several novel subcellular systems. One such is the calcium (Ca2+)-stores system of the endoplasmic reticulum, which profoundly influences diverse aspects of cellular function including signal transduction, motility, division, and biomineralization. We use comparative genomics and sensitive sequence and structure analyses to investigate the evolution of this system. Our findings reconstruct the core form of the Ca2+-stores system in the last eukaryotic common ancestor as having at least 15 proteins that constituted a basic system for facilitating both Ca2+ flux across endomembranes and Ca2+-dependent signaling. We present evidence that the key EF-hand Ca2+-binding components had their origins in a likely bacterial symbiont other than the mitochondrial progenitor, whereas the protein phosphatase subunit of the ancestral calcineurin complex was likely inherited from the asgard archaeal progenitor of the stem eukaryote. This further points to the potential origin of the eukaryotes in a Ca2+-rich biomineralized environment such as stromatolites. We further show that throughout eukaryotic evolution there were several acquisitions from bacteria of key components of the Ca2+-stores system, even though no prokaryotic lineage possesses a comparable system. Further, using quantitative measures derived from comparative genomics we show that there were several rounds of lineage-specific gene expansions, innovations of novel gene families, and gene losses correlated with biological innovation such as the biomineralized molluscan shells, coccolithophores, and animal motility. The burst of innovation of new genes in animals included the wolframin protein associated with Wolfram syndrome in humans. We show for the first time that it contains previously unidentified Sel1, EF-hand, and OB-fold domains, which might have key roles in its biochemistry.
Collapse
Affiliation(s)
- Daniel E Schäffer
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD, United States.,Science, Mathematics, and Computer Science Magnet Program, Montgomery Blair High School, Silver Spring, MD, United States
| | - Lakshminarayan M Iyer
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD, United States
| | - A Maxwell Burroughs
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD, United States
| | - L Aravind
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD, United States
| |
Collapse
|
9
|
Abstract
The physical continuity of axons over long cellular distances poses challenges for their maintenance. One organelle that faces this challenge is endoplasmic reticulum (ER); unlike other intracellular organelles, this forms a physically continuous network throughout the cell, with a single membrane and a single lumen. In axons, ER is mainly smooth, forming a tubular network with occasional sheets or cisternae and low amounts of rough ER. It has many potential roles: lipid biosynthesis, glucose homeostasis, a Ca2+ store, protein export, and contacting and regulating other organelles. This tubular network structure is determined by ER-shaping proteins, mutations in some of which are causative for neurodegenerative disorders such as hereditary spastic paraplegia (HSP). While axonal ER shares many features with the tubular ER network in other contexts, these features must be adapted to the long and narrow dimensions of axons. ER appears to be physically continuous throughout axons, over distances that are enormous on a subcellular scale. It is therefore a potential channel for long-distance or regional communication within neurons, independent of action potentials or physical transport of cargos, but involving its physiological roles such as Ca2+ or organelle homeostasis. Despite its apparent stability, axonal ER is highly dynamic, showing features like anterograde and retrograde transport, potentially reflecting continuous fusion and breakage of the network. Here we discuss the transport processes that must contribute to this dynamic behavior of ER. We also discuss the model that these processes underpin a homeostatic process that ensures both enough ER to maintain continuity of the network and repair breaks in it, but not too much ER that might disrupt local cellular physiology. Finally, we discuss how failure of ER organization in axons could lead to axon degenerative diseases, and how a requirement for ER continuity could make distal axons most susceptible to degeneration in conditions that disrupt ER continuity.
Collapse
Affiliation(s)
| | - Cahir J. O’Kane
- Department of Genetics, University of Cambridge, Cambridge, United Kingdom
| | | |
Collapse
|
10
|
Abstract
Extracellular calcium ions support synaptic activity but also reduce excitability of central neurons. In the present study, the effect of calcium on excitability was explored in cultured hippocampal neurons. CaCl2 injected by pressure in the vicinity of a neuron that is bathed only in MgCl2 as the main divalent cation caused a depolarizing shift in action potential threshold and a reduction in excitability. This effect was not seen if the intracellular milieu consisted of Cs+ instead of K-gluconate as the main cation or when it contained ruthenium red, which blocks release of calcium from stores. The suppression of excitability by calcium was mimicked by caffeine, and calcium store antagonists cyclopiazonic acid or thapsigargin blocked this action. Neurons taken from synaptopodin-knockout mice show significantly reduced efficacy of calcium modulation of action potential threshold. Likewise, in Orai1 knockdown cells, calcium is less effective in modulating excitability of neurons. Activation of small-conductance K (SK) channels increased action potential threshold akin to that produced by calcium ions, whereas blockade of SK channels but not big K channels reduced the threshold for action potential discharge. These results indicate that calcium released from stores may suppress excitability of central neurons. NEW & NOTEWORTHY Extracellular calcium reduces excitability of cultured hippocampal neurons. This effect is mediated by calcium-gated potassium currents, possibly small-conductance K channels. Release of calcium from internal stores mimics the effect of extracellular calcium. It is proposed that calcium stores modulate excitability of central neurons.
Collapse
Affiliation(s)
- Menahem Segal
- Department of Neurobiology, The Weizmann Institute , Rehovot , Israel
| |
Collapse
|
11
|
Kabbani N, Nichols RA. Beyond the Channel: Metabotropic Signaling by Nicotinic Receptors. Trends Pharmacol Sci 2018; 39:354-366. [PMID: 29428175 DOI: 10.1016/j.tips.2018.01.002] [Citation(s) in RCA: 112] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2017] [Revised: 01/05/2018] [Accepted: 01/08/2018] [Indexed: 01/01/2023]
Abstract
The α7 nicotinic acetylcholine receptor (nAChR) is a ligand-gated ion channel (LGIC) that plays an important role in cellular calcium signaling and contributes to several neurological diseases. Agonist binding to the α7 nAChR induces fast channel activation followed by inactivation and prolonged desensitization while triggering long-lasting calcium signaling. These activities foster neurotransmitter release, synaptic plasticity, and somatodendritic regulation in the brain. We discuss here the ability of α7 nAChRs to operate in ionotropic (α7i) and metabotropic (α7m) modes, leading to calcium-induced calcium release (CICR) and G protein-associated inositol trisphosphate (IP3)-induced calcium release (IICR), respectively. Metabotropic activity extends the spatial and temporal aspects of calcium signaling by the α7 channel beyond its ionotropic limits, persisting into the desensitized state. Delineation of the ionotropic and metabotropic properties of the α7 nAChR will provide definitive indicators of moment-to-moment receptor functional status that will, in turn, spearhead new drug development.
Collapse
Affiliation(s)
- Nadine Kabbani
- School of Systems Biology, George Mason University, Manassas, VA 20110, USA.
| | - Robert A Nichols
- Department of Cell and Molecular Biology, University of Hawai'i at Manoa, Honolulu, HI 96813, USA
| |
Collapse
|
12
|
Williams HL, Mansell S, Alasmari W, Brown SG, Wilson SM, Sutton KA, Miller MR, Lishko PV, Barratt CLR, Publicover SJ, Martins da Silva S. Specific loss of CatSper function is sufficient to compromise fertilizing capacity of human spermatozoa. Hum Reprod 2015; 30:2737-46. [PMID: 26453676 PMCID: PMC4643530 DOI: 10.1093/humrep/dev243] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2015] [Accepted: 09/07/2015] [Indexed: 12/26/2022] Open
Abstract
STUDY QUESTION Are significant abnormalities of CatSper function present in IVF patients with normal sperm concentration and motility and if so what is their functional significance for fertilization success? SUMMARY ANSWER Sperm with a near absence of CatSper current failed to respond to activation of CatSper by progesterone and there was fertilization failure at IVF. WHAT IS KNOWN ALREADY In human spermatozoa, Ca2+ influx induced by progesterone is mediated by CatSper, a sperm-specific Ca2+ channel. A suboptimal Ca2+ influx is significantly associated with, and more prevalent in, men with abnormal semen parameters, and is associated with reduced fertilizing capacity. However, abnormalities in CatSper current can only be assessed directly using electrophysiology. There is only one report of a CatSper-deficient man who showed no progesterone potentiated CatSper current. A CatSper 2 genetic abnormality was present but there was no information on the [Ca2+]i response to CatSper activation by progesterone. Additionally, the semen samples had indicating significant abnormalities (oligoasthenoteratozoospermia) multiple suboptimal functional responses in the spermatozoon. As such it cannot be concluded that impaired CatSper function alone causes infertility or that CatSper blockade is a potential safe target for contraception. STUDY DESIGN, SIZE, DURATION Spermatozoa were obtained from donors and subfertile IVF patients attending a hospital assisted reproductive techniques clinic between January 2013 and December 2014. In total 134 IVF patients, 28 normozoospermic donors and 10 patients recalled due to a history of failed/low fertilization at IVF took part in the study. PARTICIPANTS/MATERIALS, SETTING, METHODS Samples were primarily screened using the Ca2+ influx induced by progesterone and, if cell number was sufficient, samples were also assessed by hyperactivation and penetration into viscous media. A defective Ca2+ response to progesterone was defined using the 99% confidence interval from the distribution of response amplitudes in normozoospermic donors. Samples showing a defective Ca2+ response were further examined in order to characterize the potential CatSper abnormalities. In men where there was a consistent and robust failure of calcium signalling, a direct assessment of CatSper function was performed using electrophysiology (patch clamping), and a blood sample was obtained for genetic analysis. MAIN RESULTS AND THE ROLE OF CHANCE A total of 101/102 (99%) IVF patients and 22/23 (96%) donors exhibited a normal Ca2+ response. The mean (±SD) normalized peak response did not differ between donors and IVF patients (2.57 ± 0.68 [n = 34 ejaculates from 23 different donors] versus 2.66 ± 0.68 [n = 102 IVF patients], P = 0.63). In recall patients, 9/10 (90%) showed a normal Ca2+ response. Three men were initially identified with a defective Ca2+ influx. However, only one (Patient 1) had a defective response in repeat semen samples. Electrophysiology experiments on sperm from Patient 1 showed a near absence of CatSper current and exon screening demonstrated no mutations in the coding regions of the CatSper complex. There was no increase in penetration of viscous media when the spermatozoa were stimulated with progesterone and importantly there was failed fertilization at IVF. LIMITATIONS, REASONS FOR CAUTION A key limitation relates to working with a specific functional parameter (Ca2+ influx induced by progesterone) in fresh sperm samples from donors and patients that have limited viability. Therefore, for practical, technical and logistical reasons, some men (∼22% of IVF patients) could not be screened. As such the incidence of significant Ca2+ abnormalities induced by progesterone may be higher than the ∼1% observed here. Additionally, we used a strict definition of a defective Ca2+ influx such that only substantial abnormalities were selected for further study. Furthermore, electrophysiology was only performed on one patient with a robust and repeatable defective calcium response. This man had negligible CatSper current but more subtle abnormalities (e.g. currents present but significantly smaller) may have been present in men with either normal or below normal Ca2+ influx. WIDER IMPLICATIONS OF THE FINDINGS These data add significantly to the understanding of the role of CatSper in human sperm function and its impact on male fertility. Remarkably, these findings provide the first direct evidence that CatSper is a suitable and specific target for human male contraception. STUDY FUNDING/COMPETING INTEREST(S) Initial funding was from NHS Tayside, Infertility Research Trust, TENOVUS, Chief Scientist Office NRS Fellowship, the Wellcome Trust, University of Abertay. The majority of the data were obtained using funding from a MRC project grant (# 4190). The authors declare that there is no conflict of interest. TRIAL REGISTRATION NUMBER Not applicable.
Collapse
Affiliation(s)
- Hannah L Williams
- Reproductive and Developmental Biology, Medical School, Ninewells Hospital, University of Dundee, Dundee DD1 9SY, UK Assisted Conception Unit, NHS Tayside, Ninewells Hospital, Dundee DD1 9SY, UK
| | - Steven Mansell
- Reproductive and Developmental Biology, Medical School, Ninewells Hospital, University of Dundee, Dundee DD1 9SY, UK Department of Molecular and Cell Biology, University of California, Berkeley, USA
| | - Wardah Alasmari
- Reproductive and Developmental Biology, Medical School, Ninewells Hospital, University of Dundee, Dundee DD1 9SY, UK
| | | | - Stuart M Wilson
- Reproductive and Developmental Biology, Medical School, Ninewells Hospital, University of Dundee, Dundee DD1 9SY, UK Wolfson Research Institute, School of Medicine, Pharmacy and Health, Queen's Campus, University Of Durham, Stockton on Tees TS17 6BH, UK
| | - Keith A Sutton
- Reproductive and Developmental Biology, Medical School, Ninewells Hospital, University of Dundee, Dundee DD1 9SY, UK
| | - Melissa R Miller
- Department of Molecular and Cell Biology, University of California, Berkeley, USA
| | - Polina V Lishko
- Department of Molecular and Cell Biology, University of California, Berkeley, USA
| | - Christopher L R Barratt
- Reproductive and Developmental Biology, Medical School, Ninewells Hospital, University of Dundee, Dundee DD1 9SY, UK Assisted Conception Unit, NHS Tayside, Ninewells Hospital, Dundee DD1 9SY, UK
| | | | - Sarah Martins da Silva
- Reproductive and Developmental Biology, Medical School, Ninewells Hospital, University of Dundee, Dundee DD1 9SY, UK Assisted Conception Unit, NHS Tayside, Ninewells Hospital, Dundee DD1 9SY, UK
| |
Collapse
|
13
|
Gantz SC, Robinson BG, Buck DC, Bunzow JR, Neve RL, Williams JT, Neve KA. Distinct regulation of dopamine D2S and D2L autoreceptor signaling by calcium. eLife 2015; 4. [PMID: 26308580 PMCID: PMC4575989 DOI: 10.7554/elife.09358] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2015] [Accepted: 08/25/2015] [Indexed: 11/29/2022] Open
Abstract
D2 autoreceptors regulate dopamine release throughout the brain. Two isoforms of the D2 receptor, D2S and D2L, are expressed in midbrain dopamine neurons. Differential roles of these isoforms as autoreceptors are poorly understood. By virally expressing the isoforms in dopamine neurons of D2 receptor knockout mice, this study assessed the calcium-dependence and drug-induced plasticity of D2S and D2L receptor-dependent G protein-coupled inwardly rectifying potassium (GIRK) currents. The results reveal that D2S, but not D2L receptors, exhibited calcium-dependent desensitization similar to that exhibited by endogenous autoreceptors. Two pathways of calcium signaling that regulated D2 autoreceptor-dependent GIRK signaling were identified, which distinctly affected desensitization and the magnitude of D2S and D2L receptor-dependent GIRK currents. Previous in vivo cocaine exposure removed calcium-dependent D2 autoreceptor desensitization in wild type, but not D2S-only mice. Thus, expression of D2S as the exclusive autoreceptor was insufficient for cocaine-induced plasticity, implying a functional role for the co-expression of D2S and D2L autoreceptors. DOI:http://dx.doi.org/10.7554/eLife.09358.001 Dopamine is an important component of the brain's reward system and is commonly referred to as a ‘feel-good’ chemical. It is mainly released from neurons in the brain in response to natural rewards, such as food or sex, and following exposure to, or in anticipation of, certain drugs of abuse (including cocaine). Dopamine-releasing neurons also sense dopamine, and just like someone can change the volume of their voice by hearing themselves speak, dopamine neurons regulate how much dopamine is released based on how much dopamine they sense. This feedback system is known as autoinhibition. These neurons sense dopamine when it binds to, and activates, so-called ‘dopamine D2 receptors’ on their cell surface. But not all D2 receptors are alike. Instead there are two variants called D2S and D2L. Previous studies have shown that D2 receptor signaling in dopamine neurons is altered by the concentration of calcium ions inside these cells. Furthermore, exposure to cocaine and other drugs is known to change how these calcium ions regulate D2 receptor signaling. Now, Gantz et al. have used mice that produce only a single variant of the D2 receptor (either D2S or D2L) in their dopamine neurons to uncover similarities and differences between the two variants. The experiments show that localized increases in calcium ion concentration make D2S less capable of autoinhibition, like D2 receptors in neurons from wild type mice, without affecting autoinhibition by D2L. In further experiments, some of these mice were given cocaine before D2 receptor signaling was assessed. In dopamine neurons from wild type mice, a single exposure to cocaine eliminates the calcium-dependent regulation; thus, cocaine treatment causes a D2L-like response. In contrast, cocaine treatment did not affect the calcium-dependent regulation when only one variant of the D2 receptor was present. This implies that dopamine neurons must have both D2S and D2L receptors before the drug can induce changes in D2 receptor signaling. These findings also challenge the long-held view that the D2S receptor is the predominant form involved in autoinhibition. The next challenge is to determine how cocaine induces an apparent switch from D2S to D2L and the implications of this switch for the development of cocaine addiction. DOI:http://dx.doi.org/10.7554/eLife.09358.002
Collapse
Affiliation(s)
- Stephanie C Gantz
- Vollum Institute, Oregon Health & Science University, Portland, United States
| | - Brooks G Robinson
- Vollum Institute, Oregon Health & Science University, Portland, United States
| | - David C Buck
- Research Service, VA Portland Health Care System, United States Department of Veterans Affairs, Portland, United States
| | - James R Bunzow
- Vollum Institute, Oregon Health & Science University, Portland, United States
| | - Rachael L Neve
- Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, United States
| | - John T Williams
- Vollum Institute, Oregon Health & Science University, Portland, United States
| | - Kim A Neve
- Research Service, VA Portland Health Care System, United States Department of Veterans Affairs, Portland, United States
| |
Collapse
|
14
|
Abstract
The role of synaptopodin (SP), an actin-binding protein residing in dendritic spines, in synaptic plasticity was studied in dissociated cultures of hippocampus taken from control and SP knock-out (SPKO) mice. Unlike controls, SPKO cultures were unable to express changes in network activity or morphological plasticity after intense activation of their NMDA receptors. SPKO neurons were transfected with SP-GFP, such that the only SP resident in these neurons is the fluorescent species. The localization and intensity of the transfected SP were similar to that of the native one. Because less than half of the spines in the transfected neurons contained SP, comparisons were made between SP-containing (SP(+)) and SP lacking (SP(-)) spines in the same dendritic segments. Synaptic plasticity was induced either in the entire network by facilitation of the activation of the NMDA receptor, or specifically by local flash photolysis of caged glutamate. After activation, spines that were endowed with SP puncta were much more likely to expand than SP(-) spines. The spine expansion was suppressed by thapsigargin, which disables calcium stores. The mechanism through which SP may promote plasticity is indicated by the observations that STIM-1, the sensor of calcium concentration in stores, and Orai-1, the calcium-induced calcium entry channel, are colocalized with SP, in the same dendritic spines. The structural basis of SP is likely to be the spine apparatus, found in control but not in SPKO cells. These results indicate that SP has an essential, calcium store-related role in regulating synaptic plasticity in cultured hippocampal neurons.
Collapse
|
15
|
Abstract
Rise in Ca(2+) concentration in the nucleus affects gene transcription and has been implicated in neuroprotection, transcription-dependent neuronal plasticity, and pain modulation, but the mechanism of regulation of nuclear Ca(2+) remains poorly understood. The nuclear envelope is a part of the endoplasmic reticulum and may be one of the sources of nuclear Ca(2+) . Here, we studied ion channels in the nuclear membrane of hippocampal neurons using the patch-clamp technique. We have found that the nuclear membrane of CA1 pyramidal and dentate gyrus granule (DG), but not CA3 pyramidal neurons, was enriched in functional inositol 1,4,5-trisphosphate receptors/Ca(2+) -release channels (IP3 Rs) localized mainly in the inner nuclear membrane. A single nuclear ryanodine receptor (RyR) has been detected only in DG granule neurons. Nuclei of the hippocampal neurons also expressed a variety of spontaneously active cation and anion channels specific for each type of neuron. In particular, large-conductance ion channels selective for monovalent cations (LCC) were coexpressed with IP3 Rs. These data suggest that: (1) the nuclear membranes of hippocampal neurons contain distinct sets of ion channels, which are specific for each type of neuron; (2) IP3 Rs, but not RyRs are targeted to the inner nuclear membrane of CA1 pyramidal and DG granule, but they were not found in the nuclear membranes of CA3 pyramidal neurons; (3) the nuclear envelope of these neurons is specialized to release Ca(2+) into the nucleoplasm which may amplify Ca(2+) signals entering the nucleus from the cytoplasm or generate Ca(2+) transients on its own; (4) LCC channels are an integral part the of Ca(2+) -releasing machinery providing a route for counterflow of К(+) and thereby facilitating Ca(2+) movement in and out of the Ca(2+) store.
Collapse
Affiliation(s)
- Olena A Fedorenko
- Bogomoletz Institute of Physiology, Department of Brain Physiology, 4 Bogomoletz Street, Kiev, 01024, Ukraine; State Key Laboratory of Molecular and Cellular Biology, 4 Bogomoletz Street, Kiev, 01024, Ukraine
| | | |
Collapse
|
16
|
Nordman JC, Kabbani N. Microtubule dynamics at the growth cone are mediated by α7 nicotinic receptor activation of a Gαq and IP3 receptor pathway. FASEB J 2014; 28:2995-3006. [PMID: 24687992 DOI: 10.1096/fj.14-251439] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The α7 nicotinic receptor (α7) plays an important role in neuronal growth and structural plasticity in the developing brain. We have recently characterized a G-protein-signaling pathway regulated by α7 that directs the growth of neurites in developing neural cells. Now we show that choline activation of α7 promotes a rise in intracellular calcium from local ER stores via Gαq signaling, leading to IP3 receptor (IP3R) activation at the growth cone of differentiating PC12 cells. A mutant α7 significantly attenuated in calcium conductance (D44A; P<0.001) was found to be unable to promote IP3R signaling and calcium store release. In addition, calcium elevation via α7 correlates with a significant attenuation in the rate of microtubule invasion of the growth cone (P<0.001). This process was also attenuated in the D44A mutant and blocked by an inhibitor of the IP3R, suggesting that calcium flow through the α7 channel and activation of the Gαq pathway are necessary for growth. Taken together, the findings reveal an inhibitory mechanism of α7 on cytoskeletal growth via the intracellular calcium activity of the receptor channel and the Gαq signaling pathway at the growth cone.-Nordman, J. C., Kabbani, N. Microtubule dynamics at the growth cone are mediated by α7 nicotinic receptor activation of a Gαq and IP3 receptor pathway.
Collapse
Affiliation(s)
- Jacob C Nordman
- Department of Molecular Neuroscience, Krasnow Institute for Advanced Study, George Mason University, Fairfax, Virginia, USA
| | - Nadine Kabbani
- Department of Molecular Neuroscience, Krasnow Institute for Advanced Study, George Mason University, Fairfax, Virginia, USA
| |
Collapse
|
17
|
Clemens AM, Johnston D. Age- and location-dependent differences in store depletion-induced h-channel plasticity in hippocampal pyramidal neurons. J Neurophysiol 2013; 111:1369-82. [PMID: 24381027 DOI: 10.1152/jn.00839.2013] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Disruptions of endoplasmic reticulum (ER) Ca(2+) homeostasis are heavily linked to neuronal pathology. Depletion of ER Ca(2+) stores can result in cellular dysfunction and potentially cell death, although adaptive processes exist to aid in survival. We examined the age and region dependence of one postulated, adaptive response to ER store-depletion (SD), hyperpolarization-activated cation-nonspecific (h)-channel plasticity in neurons of the dorsal and ventral hippocampus (DHC and VHC, respectively) from adolescent and adult rats. With the use of whole-cell patch-clamp recordings from the soma and dendrites of CA1 pyramidal neurons, we observed a change in h-sensitive measurements in response to SD, induced by treatment with cyclopiazonic acid, a sarcoplasmic reticulum/ER Ca(2+)-ATPase blocker. We found that whereas DHC and VHC neurons in adolescent animals respond to SD with a perisomatic expression of SD h plasticity, adult animals express SD h plasticity with a dendritic and somatodendritic locus of plasticity in DHC and VHC neurons, respectively. Furthermore, SD h plasticity in adults was dependent on membrane potential and on the activation of L-type voltage-gated Ca(2+) channels. These results suggest that cellular responses to the impairment of ER function, or ER stress, are dependent on brain region and age and that the differential expression of SD h plasticity could provide a neural basis for region- and age-dependent disease vulnerabilities.
Collapse
Affiliation(s)
- Ann M Clemens
- The Institute for Neuroscience and Center for Learning and Memory, The University of Texas at Austin, Austin, Texas; and
| | | |
Collapse
|
18
|
McKeown L, Moss NK, Turner P, Li J, Heath N, Burke D, O’Regan D, Gilthorpe MS, Porter KE, Beech DJ. Platelet-derived growth factor maintains stored calcium through a nonclustering Orai1 mechanism but evokes clustering if the endoplasmic reticulum is stressed by store depletion. Circ Res 2012; 111:66-76. [PMID: 22556336 PMCID: PMC3605802 DOI: 10.1161/circresaha.111.263616] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
RATIONALE Calcium entry through Orai1 channels drives vascular smooth muscle cell migration and neointimal hyperplasia. The channels are activated by the important growth factor platelet-derived growth factor (PDGF). Channel activation is suggested to depend on store depletion, which redistributes and clusters stromal interaction molecule 1 (STIM1), which then coclusters and activates Orai1. OBJECTIVE To determine the relevance of STIM1 and Orai1 redistribution in PDGF responses. METHODS AND RESULTS Vascular smooth muscle cells were cultured from human saphenous vein. STIM1 and Orai1 were tagged with green and red fluorescent proteins to track them in live cells. Under basal conditions, the proteins were mobile but mostly independent of each other. Inhibition of sarco-endoplasmic reticulum calcium ATPase led to store depletion and dramatic redistribution of STIM1 and Orai1 into coclusters. PDGF did not evoke redistribution, even though it caused calcium release and Orai1-mediated calcium entry in the same time period. After chemical blockade of Orai1-mediated calcium entry, however, PDGF caused redistribution. Similarly, mutagenic disruption of calcium flux through Orai1 caused PDGF to evoke redistribution, showing that calcium flux through the wild-type channels had been filling the stores. Acidification of the extracellular medium to pH 6.4 caused inhibition of Orai1-mediated calcium entry and conferred capability for PDGF to evoke complete redistribution and coclustering. CONCLUSIONS The data suggest that PDGF has a nonclustering mechanism by which to activate Orai1 channels and maintain calcium stores replete. Redistribution and clustering become important, however, when the endoplasmic reticulum stress signal of store depletion arises, for example when acidosis inhibits Orai1 channels.
Collapse
MESH Headings
- Bacterial Proteins/genetics
- Bacterial Proteins/metabolism
- Calcium/metabolism
- Calcium Channels/metabolism
- Cells, Cultured
- Endoplasmic Reticulum/drug effects
- Endoplasmic Reticulum/metabolism
- Green Fluorescent Proteins/genetics
- Green Fluorescent Proteins/metabolism
- Humans
- Hydrogen-Ion Concentration
- Luminescent Proteins/genetics
- Luminescent Proteins/metabolism
- Membrane Proteins/genetics
- Membrane Proteins/metabolism
- Microscopy, Fluorescence
- Microscopy, Video
- Muscle, Smooth, Vascular/drug effects
- Muscle, Smooth, Vascular/metabolism
- Mutation
- Myocytes, Smooth Muscle/drug effects
- Myocytes, Smooth Muscle/metabolism
- Neoplasm Proteins/genetics
- Neoplasm Proteins/metabolism
- ORAI1 Protein
- Platelet-Derived Growth Factor/metabolism
- Protein Transport
- Recombinant Fusion Proteins/metabolism
- Saphenous Vein/metabolism
- Stress, Physiological
- Stromal Interaction Molecule 1
- Thapsigargin/pharmacology
- Time Factors
- Transfection
- Red Fluorescent Protein
Collapse
Affiliation(s)
- Lynn McKeown
- Multidisciplinary Cardiovascular Research Centre, University of Leeds, Leeds, LS2 9JT, UK
- Faculty of Biological Sciences, University of Leeds, Leeds, LS2 9JT, UK
| | - Nicholas K Moss
- Multidisciplinary Cardiovascular Research Centre, University of Leeds, Leeds, LS2 9JT, UK
- Faculty of Biological Sciences, University of Leeds, Leeds, LS2 9JT, UK
| | - Paul Turner
- Multidisciplinary Cardiovascular Research Centre, University of Leeds, Leeds, LS2 9JT, UK
- Faculty of Biological Sciences, University of Leeds, Leeds, LS2 9JT, UK
| | - Jing Li
- Multidisciplinary Cardiovascular Research Centre, University of Leeds, Leeds, LS2 9JT, UK
- Faculty of Biological Sciences, University of Leeds, Leeds, LS2 9JT, UK
| | - Nikki Heath
- Multidisciplinary Cardiovascular Research Centre, University of Leeds, Leeds, LS2 9JT, UK
- Faculty of Biological Sciences, University of Leeds, Leeds, LS2 9JT, UK
| | - Dermot Burke
- Leeds Teaching Hospitals, General Infirmary, Great George Street, Leeds, LS1 3EX
| | - David O’Regan
- Leeds Teaching Hospitals, General Infirmary, Great George Street, Leeds, LS1 3EX
| | - Mark S Gilthorpe
- Faculty of Medicine & Health, University of Leeds, Leeds, LS2 9JT, UK
| | - Karen E Porter
- Multidisciplinary Cardiovascular Research Centre, University of Leeds, Leeds, LS2 9JT, UK
- Faculty of Medicine & Health, University of Leeds, Leeds, LS2 9JT, UK
| | - David J Beech
- Multidisciplinary Cardiovascular Research Centre, University of Leeds, Leeds, LS2 9JT, UK
- Faculty of Biological Sciences, University of Leeds, Leeds, LS2 9JT, UK
- Faculty of Medicine & Health, University of Leeds, Leeds, LS2 9JT, UK
| |
Collapse
|
19
|
Abstract
Cell death and dysfunction after traumatic brain injury (TBI) is caused by a primary phase, related to direct mechanical disruption of the brain, and a secondary phase which consists of delayed events initiated at the time of the physical insult. Arguably, the calcium ion contributes greatly to the delayed cell damage and death after TBI. A large, sustained influx of calcium into cells can initiate cell death signaling cascades, through activation of several degradative enzymes, such as proteases and endonucleases. However, a sustained level of intracellular free calcium is not necessarily lethal, but the specific route of calcium entry may couple calcium directly to cell death pathways. Other sources of calcium, such as intracellular calcium stores, can also contribute to cell damage. In addition, calcium-mediated signal transduction pathways in neurons may be perturbed following injury. These latter types of alterations may contribute to abnormal physiology in neurons that do not necessarily die after a traumatic episode. This review provides an overview of experimental evidence that has led to our current understanding of the role of calcium signaling in death and dysfunction following TBI.
Collapse
Affiliation(s)
- John T. Weber
- School of Pharmacy and Division of BioMedical Sciences, Faculty of Medicine, Memorial University of NewfoundlandSt. John’s, NL, Canada
| |
Collapse
|
20
|
Abstract
Among the diverse physiological functions exerted by calcium signaling in living cells, its role in the regulation of protein biogenesis and trafficking remains incompletely understood. In cystic fibrosis (CF) disease the most common CF transmembrane conductance regulator (CFTR) mutation, F508del-CFTR generates a misprocessed protein that is abnormally retained in the endoplasmic reticulum (ER) compartment, rapidly degraded by the ubiquitin/proteasome pathway and hence absent at the plasma membrane of CF epithelial cells. Recent studies have demonstrated that intracellular calcium signals consequent to activation of apical G-protein-coupled receptors by different agonists are increased in CF airway epithelia. Moreover, the regulation of various intracellular calcium storage compartments, such as ER is also abnormal in CF cells. Although the molecular mechanism at the origin of this increase remains puzzling in epithelial cells, the F508del-CFTR mutation is proposed to be the onset of abnormal Ca2+ influx linking the calcium signaling to CFTR pathobiology. This article reviews the relationships between CFTR and calcium signaling in the context of the genetic disease CF.
Collapse
Affiliation(s)
- Fabrice Antigny
- Institut de Physiologie et de Biologie Cellulaires, Université de Poitiers, CNRS Poitiers, France
| | | | | | | |
Collapse
|
21
|
López J, Camello-Almaraz C, Pariente J, Salido G, Rosado J. Ca2+ accumulation into acidic organelles mediated by Ca2+- and vacuolar H+-ATPases in human platelets. Biochem J 2005; 390:243-52. [PMID: 15847604 PMCID: PMC1188269 DOI: 10.1042/bj20050168] [Citation(s) in RCA: 102] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2005] [Revised: 04/19/2005] [Accepted: 04/22/2005] [Indexed: 11/17/2022]
Abstract
Most physiological agonists increase cytosolic free [Ca2+]c (cytosolic free Ca2+ concentration) to regulate a variety of cellular processes. How different stimuli evoke distinct spatiotemporal Ca2+ responses remains unclear, and the presence of separate intracellular Ca2+ stores might be of great functional relevance. Ca2+ accumulation into intracellular compartments mainly depends on the activity of Ca2+- and H+-ATPases. Platelets present two separate Ca2+ stores differentiated by the distinct sensitivity to thapsigargin and TBHQ [2,5-di-(t-butyl)-1,4-hydroquinone]. Although one store has long been identified as the dense tubular system, the nature of the TBHQ-sensitive store remains uncertain. Treatment of platelets with GPN (glycylphenylalanine-2-naphthylamide) impaired Ca2+ release by TBHQ and reduced that evoked by thrombin. In contrast, GPN did not modify Ca2+ mobilization stimulated by ADP or AVP ([arginine]vasopressin). Treatment with nigericin, a proton carrier, and bafilomycin A1, an inhibitor of the vacuolar H+-ATPase, to dissipate the proton gradient into acidic organelles induces a transient increase in [Ca2+]c that was abolished by previous treatment with the SERCA (sarcoplasmic/endoplasmic-reticulum Ca2+-ATPase) 3 inhibitor TBHQ. Depleted acidic stores after nigericin or bafilomycin A1 were refilled by SERCA 3. Thrombin, but not ADP or AVP, reduces the rise in [Ca2+]c evoked by nigericin and bafilomycin A1. Our results indicate that the TBHQ-sensitive store in human platelets is an acidic organelle whose Ca2+ accumulation is regulated by both Ca2+- and vacuolar H+-ATPases.
Collapse
Key Words
- acidic organelles
- bafilomycin
- calcium stores
- nigericin
- platelets
- thrombin
- avp, [arginine]vasopressin
- [ca2+]c, cytosolic free calcium concentration
- er, endoplasmic reticulum
- gpn, glycylphenylalanine 2-naphthylamide
- hbs, hepes-buffered saline
- pmca, plasma-membrane ca2+ atpase
- serca 3, sarcoplasmic/endoplasmic-reticulum ca2+-atpase
- tbhq, 2,5-di-(t-butyl)-1,4-hydroquinone
- tg, thapsigargin
Collapse
Affiliation(s)
- José J. López
- Department of Physiology, University of Extremadura, 10071 Cáceres, Spain
| | | | - José A. Pariente
- Department of Physiology, University of Extremadura, 10071 Cáceres, Spain
| | - Ginés M. Salido
- Department of Physiology, University of Extremadura, 10071 Cáceres, Spain
| | - Juan A. Rosado
- Department of Physiology, University of Extremadura, 10071 Cáceres, Spain
| |
Collapse
|
22
|
Abstract
1. In this study, we determined a pharmacological profile of store-operated channels (SOCs) in smooth muscle cells of rabbit pial arterioles. Ca(2+)-indicator dyes, fura-PE3 or fluo-4, were used to track [Ca(2+)](i) and 10 micro M methoxyverapamil (D600) was present in all experiments on SOCs to prevent voltage-dependent Ca(2+) entry. Store depletion was induced using thapsigargin or cyclopiazonic acid. 2. SOC-mediated Ca(2+) entry was inhibited concentration dependently by Gd(3+) (IC(50) 101 nM). It was also inhibited by 10 micro M La(3+) (70% inhibition, N=5), 100 micro M Ni(2+) (57% inhibition, N=5), 75 micro M 2-aminoethoxydiphenylborate (66% inhibition, N=4), 100 micro M capsaicin (12% inhibition, N=3) or preincubation with 10 micro M wortmannin (76% inhibition, N=4). It was completely resistant to 1 micro M nifedipine (N=5), 10 micro M SKF96365 (N=6), 10 micro M LOE908 (N=14), 10-100 micro M ruthenium red (N=1+2), 100 micro M sulindac (N=4), 0.5 mM streptomycin (N=3) or 1 : 10,000 dilution Grammostolla spatulata venom (N=4). 3. RT-PCR experiments on isolated arteriolar fragments showed expression of mRNA species for TRPC1, 3, 4, 5 and 6. 4. The pharmacological profile of SOC-mediated Ca(2+) entry in arterioles supports the hypothesis that these SOCs are distinct from tonically active background channels and several store-operated and other nonselective cation channels described in other cells. Similarities with the pharmacology of TRPC1 support the hypothesis that TRPC1 is a subunit of the arteriolar smooth muscle SOC.
Collapse
Affiliation(s)
- R Flemming
- School of Biomedical Sciences, University of Leeds, Leeds, LS2 9JT
| | - S Z Xu
- School of Biomedical Sciences, University of Leeds, Leeds, LS2 9JT
| | - D J Beech
- School of Biomedical Sciences, University of Leeds, Leeds, LS2 9JT
- Author for correspondence:
| |
Collapse
|
23
|
Fiorillo CD, Williams JT. Cholinergic inhibition of ventral midbrain dopamine neurons. J Neurosci 2000; 20:7855-60. [PMID: 11027251 PMCID: PMC6772848] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/17/2023] Open
Abstract
Muscarinic acetylcholine receptors are common throughout the CNS. The predominant subtypes in the brain are positively coupled to phosphoinositide hydrolysis and have been found to modulate multiple conductances. Muscarinic receptor activation is most often observed to be excitatory because of suppression of various potassium conductances. Here it is reported that three distinct effects of muscarinic receptor activation can be observed in isolation from one another, depending on the duration of receptor activation and the concentration of agonist. Brief activation of muscarinic receptors, as is likely to occur with normal synaptic transmission, hyperpolarized dopamine neurons of the ventral midbrain through a calcium-activated potassium conductance. With repeated or persistent activation of muscarinic receptors, the hyperpolarizing response was entirely desensitized in the absence of any change in resting membrane potential. With sustained activation by higher concentrations of agonist, dopamine neurons were depolarized. This demonstrates that muscarinic receptors can mediate very diverse, and even opposing, postsynaptic effects on neurons depending on the pattern of acetylcholine release.
Collapse
Affiliation(s)
- C D Fiorillo
- Vollum Institute, L474, Oregon Health Sciences University, Portland, Oregon 97201, USA
| | | |
Collapse
|
24
|
Abstract
Cerebellar Purkinje neurons demonstrate a form of synaptic plasticity that, in acutely prepared brain slices, has been shown to require calcium release from the intracellular calcium stores through inositol trisphosphate (InsP(3)) receptors. Similar studies performed in cultured Purkinje cells, however, find little evidence for the involvement of InsP(3) receptors. To address this discrepancy, the properties of InsP(3)- and caffeine-evoked calcium release in cultured Purkinje cells were directly examined. Photorelease of InsP(3) (up to 100 microM) from its photolabile caged analogue produced no change in calcium levels in 70% of cultured Purkinje cells. In the few cells where a calcium increase was detected, the response was very small and slow to peak. In contrast, the same concentration of InsP(3) resulted in large and rapidly rising calcium responses in all acutely dissociated Purkinje cells tested. Similar to InsP(3), caffeine also had little effect on calcium levels in cultured Purkinje cells, yet evoked large calcium transients in all acutely dissociated Purkinje cells tested. The results demonstrate that calcium release from intracellular calcium stores is severely impaired in Purkinje cells when they are maintained in culture. Our findings suggest that cultured Purkinje cells are an unfaithful experimental model for the study of the role of calcium release in the induction of cerebellar long term depression.
Collapse
Affiliation(s)
- Mary D. Womack
- Department of Physiology & Biophysics, University of Colorado Health Sciences Center, Denver, Colorado 80262
| | - Jeffery W. Walker
- Department of Physiology, University of Wisconsin, Madison, Wisconsin 53706
| | - Kamran Khodakhah
- Department of Physiology & Biophysics, University of Colorado Health Sciences Center, Denver, Colorado 80262
| |
Collapse
|
25
|
Wayman CP, McFadzean I, Gibson A, Tucker JF. Cellular mechanisms underlying carbachol-induced oscillations of calcium-dependent membrane current in smooth muscle cells from mouse anococcygeus. Br J Pharmacol 1997; 121:1301-8. [PMID: 9257907 PMCID: PMC1564838 DOI: 10.1038/sj.bjp.0701279] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
1. At a holding potential of -40 mV, carbachol (50 microM) produced a complex pattern of inward currents in single smooth muscle cells freshly isolated from the mouse anococcygeus. Membrane currents were monitored by the whole-cell configuration of the patch-clamp technique. Previous work has identified the first, transient component as a calcium-activated chloride current (ICl(Ca)) and the second sustained component as a store depletion-operated non-selective cation current (I(DOC)). The object of the present study was to examine the cellular mechanisms underlying the third component, a series of inward current oscillations (I(oscil)) superimposed on I(DOC). 2. Carbachol-induced I(oscil) (amplitude 97 +/- 11 pA; frequency 0.26 +/- 0.02 Hz) was inhibited by the chloride channel blocker anthracene-9-carboxylic acid (A-9-C; 1 mM), and by inclusion of 1 mM EGTA in the patch-pipette filling solution. 3. In calcium-free extracellular medium (plus 1 mM EGTA), carbachol produced an initial burst of oscillatory current which lasted 94 s before decaying to zero; I(oscil) could be restored by re-admission of calcium. The frequency, but not the amplitude, of I(oscil) increased with increasing concentrations of extracellular calcium (0.5-10 mM). 4. Inclusion of the inositol triphosphate (IP3) receptor antagonist heparin (5 mg ml(-1) in the patch-pipette filling solution, or pretreatment of cells with the sarcoplasmic reticulum (SR) calcium ATPase inhibitor cyclopiazonic acid (CPA; 10 microM), prevented the activation of I(oscil) by carbachol. Caffeine (10 mM) activated both ICl(Ca) and I(DOC) and prevented the induction of I(oscil) by carbachol. Caffeine and CPA also abolished I(oscil) in the presence of carbachol, as did both a low (3 microM) and a high (30 microM) concentration of ryanodine. 5. Carbachol-induced I(oscil) was abolished by the general calcium entry blocker SKF 96365 (10 MM) and by Cd2+ (100 microM), but was unaffected by La3+ (400 microM). As found previously, I(DOC) was also blocked by SKF 96365 and Cd2+, but not La3+; the inhibition of I(DOC) preceded the abolition of I(oscil) by 27 s with SKF 96365 and by 30 s with Cd2+. Nifedipine (1 microM) produced a partial inhibition of the carbachol-induced I(oscil) frequency at holding potentials of -20 mV and -60 mV and, in addition, reduced I(DOC) at -60 mV by 18%. 6. It is concluded that carbachol-induced inward current oscillations in mouse anococcygeus cells are due to a calcium-activated chloride current, and reflect oscillatory changes in cytoplasmic calcium ion concentration. These calcium oscillations are derived primarily from the SR stores, but entry of calcium into the cell is necessary for store replenishment and maintenance of the oscillations. Capacitative calcium entry (via I(DOC) appears to be important not only for sustained contraction of this tissue, but also as a route for re-filling of the SR and, therefore, represents an important target for the development of novel and selective drugs.
Collapse
Affiliation(s)
- C P Wayman
- Division of Biomedical Sciences, King's College London, U.K
| | | | | | | |
Collapse
|
26
|
Korkotian E, Segal M. Calcium-containing organelles display unique reactivity to chemical stimulation in cultured hippocampal neurons. J Neurosci 1997; 17:1670-82. [PMID: 9030626 PMCID: PMC6573380] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Cultured rat hippocampal neurons grown on glass coverslips for 1-3 weeks were loaded with the calcium-sensitive fluorescent dye Fluo-3 and viewed with a confocal laser scanning microscope. Large pyramidal-shaped neurons were found to contain dye-accumulating organelles in their somata, primarily around nuclei and near the base of their primary dendrites. These organelles varied in size and increased in density over weeks in culture, and were not colocalized with the endoplasmic reticulum or with mitochondria. The Fluo-3 fluorescence in these calcium-containing organelles (CCOs) was transiently quenched by exposure to Mn2+, indicating that the dye is a genuine [Ca2+] reporter and is not just a site of accumulating Fluo-3 dye. Recovery of fluorescence in the CCOs after washout of Mn2+ involved activation of a thapsigargin-sensitive process. CCOs responded to stimuli that evoke a rise of cytosolic [Ca2+] ([Ca]i) in a unique manner; perfusion of caffeine caused a prolonged rise of [Ca] in the CCOs ([Ca]C), whereas it caused only a transient rise of [Ca]i. Pulse application of caffeine also caused a faster effect on [Ca]C than on [Ca]i. Glutamate caused a transient rise of both [Ca]i and [Ca]C, followed by a prolonged fall of only [Ca]C to below rest level. This fall was blocked by preincubation with thapsigargin. Ryanodine blocked the cytosolic effects of caffeine but not its effect on [C]C. A clear distinction between CCOs and the known calcium stores was seen in digitonin-permeabilized cells; in these, remaining Fluo-3 reported changes in store calcium, i.e., caffeine caused a reduction in Fluo-3 fluorescence in permeabilized cells, whereas it still caused an increase in [Ca]C. A possible role of CCOs in regulation of release of calcium from ryanodine-sensitive stores was indicated by the observation that CCO-containing cells exhibited a larger and faster response to caffeine than cells that did not have them. We propose that CCOs constitute a unique functional compartment involved in release of calcium from calcium-sensitive stores.
Collapse
Affiliation(s)
- E Korkotian
- Department of Neurobiology, The Weizmann Institute, Rehovot 76100, Israel
| | | |
Collapse
|
27
|
Gillo B, Chorna I, Cohen H, Cook B, Manistersky I, Chorev M, Arnon A, Pollock JA, Selinger Z, Minke B. Coexpression of Drosophila TRP and TRP-like proteins in Xenopus oocytes reconstitutes capacitative Ca2+ entry. Proc Natl Acad Sci U S A 1996; 93:14146-51. [PMID: 8943075 PMCID: PMC19508 DOI: 10.1073/pnas.93.24.14146] [Citation(s) in RCA: 87] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Capacitative Ca2+ entry is a component of the inositol-lipid signaling in which depletion of inositol 1,4,5-trisphosphate (InsP3)-sensitive Ca2+ stores activates Ca2+ influx by a mechanism that is still unknown. This pathway plays a central role in cellular signaling, which is mediated by many hormones, neurotransmitters, and growth factors. Studies of Drosophila photoreceptors provided the first putative capacitative Ca2+ entry mutant designated transient receptor potential (trp) and a Drosophila gene encoding TRP-like protein (trpl). It is not clear how the Ca2+ store depletion signal is relayed to the plasma membrane and whether both TRP and TRPL participate in this process. We report here that coexpressing Drosophila TRP and TRPL in Xenopus oocytes synergistically enhances the endogenous Ca(2+)-activated Cl- current and produces a divalent inward current. Both of these currents are activated by Ca2+ store depletion. In the absence of Ca2+, Mg2+ is the main charge carrier of the divalent current. This current is characterized by lanthanum sensitivity and a voltage-dependent blocking effect of Mg2+, which is relieved at both hyperpolarizing (inward rectification) and depolarizing (outward rectification) potentials. The store-operated divalent current is neither observed in native oocytes nor in oocytes expressing either TRP or TRPL alone. The production of this current implicates a cooperative action of TRP and TRPL in the depletion-activated current.
Collapse
Affiliation(s)
- B Gillo
- Department of Physiology, Hebrew University, Jerusalem, Israel
| | | | | | | | | | | | | | | | | | | |
Collapse
|
28
|
Prakriya M, Solaro CR, Lingle CJ. [Ca2+]i elevations detected by BK channels during Ca2+ influx and muscarine-mediated release of Ca2+ from intracellular stores in rat chromaffin cells. J Neurosci 1996; 16:4344-59. [PMID: 8699245 PMCID: PMC6578855] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Submembrane [Ca2+]i changes were examined in rat chromaffin cells by monitoring the activity of an endogenous Ca(2+)-dependent protein: the large conductance Ca(2+)-and voltage-activated K+ channel (also known as the BK channel). The Ca2+ and voltage dependence of BK current inactivation and conductance were calibrated first by using defined [Ca2+]i salines. This information was used to examine submembrane [Ca2+]i elevations arising out of Ca2+ influx and muscarine-mediated release of Ca2+ from intracellular stores. During Ca2+ influx, some BK channels are exposed to [Ca2+]i of at least 60 microM. However, the distribution of this [Ca2+]i elevation is highly nonuniform so that the average [Ca2+]i detected when all BK channels are activated is only approximately 10 microM. Intracellular dialysis with 1 mM or higher EGTA spares only the BK channels activated by the highest [Ca2+]i during influx, whereas dialysis with 1 mM or higher BAPTA blocks activation of all BK channels. Submembrane [Ca2+]i elevations fall rapidly after termination of short (5 msec) Ca2+ influx steps but persist above 1 microM for several hundred milliseconds after termination of long (200 msec) influx steps. In contrast to influx, the submembrane [Ca2+]i elevations produced by release of intracellular Ca2+ by muscarinic actetylcholine receptor (mAChR) activation are much more uniform and reach peak levels of 3-5 microM. Our results suggest that during normal action potential activity only 10-20% of BK channels in each chromaffin cell see sufficient [Ca2+]i to be activated.
Collapse
Affiliation(s)
- M Prakriya
- Washington University School of Medicine, Department of Anesthesiology, St. Louis, Missouri 63110, USA
| | | | | |
Collapse
|