1
|
Imrie G, Gray MB, Raghuraman V, Farhy-Tselnicker I. Gene Expression at the Tripartite Synapse: Bridging the Gap Between Neurons and Astrocytes. ADVANCES IN NEUROBIOLOGY 2024; 39:95-136. [PMID: 39190073 DOI: 10.1007/978-3-031-64839-7_5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/28/2024]
Abstract
Astrocytes, a major class of glial cells, are an important element at the synapse where they engage in bidirectional crosstalk with neurons to regulate numerous aspects of neurotransmission, circuit function, and behavior. Mutations in synapse-related genes expressed in both neurons and astrocytes are central factors in a vast number of neurological disorders, making the proteins that they encode prominent targets for therapeutic intervention. Yet, while the roles of many of these synaptic proteins in neurons are well established, the functions of the same proteins in astrocytes are largely unknown. This gap in knowledge must be addressed to refine therapeutic approaches. In this chapter, we integrate multiomic meta-analysis and a comprehensive overview of current literature to show that astrocytes express an astounding number of genes that overlap with the neuronal and synaptic transcriptomes. Further, we highlight recent reports that characterize the expression patterns and potential novel roles of these genes in astrocytes in both physiological and pathological conditions, underscoring the importance of considering both cell types when investigating the function and regulation of synaptic proteins.
Collapse
Affiliation(s)
- Gillian Imrie
- Department of Biology, Texas A&M University, College Station, TX, USA
| | - Madison B Gray
- Department of Biology, Texas A&M University, College Station, TX, USA
| | - Vishnuvasan Raghuraman
- Department of Biology, Texas A&M University, College Station, TX, USA
- Department of Computer Science and Engineering, Texas A&M University, College Station, TX, USA
| | - Isabella Farhy-Tselnicker
- Department of Biology, Texas A&M University, College Station, TX, USA.
- Texas A&M Institute for Neuroscience (TAMIN), Texas A&M University, College Station, TX, USA.
- Center for Biological Clocks Research, Texas A&M University, College Station, TX, USA.
| |
Collapse
|
2
|
Nicolazzo JA, Pan Y, Di Stefano I, Choy KHC, Reddiar SB, Low YL, Wai DCC, Norton RS, Jin L. Blockade of Microglial Kv1.3 Potassium Channels by the Peptide HsTX1[R14A] Attenuates Lipopolysaccharide-mediated Neuroinflammation. J Pharm Sci 2021; 111:638-647. [PMID: 34767826 DOI: 10.1016/j.xphs.2021.11.003] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Revised: 11/03/2021] [Accepted: 11/03/2021] [Indexed: 12/19/2022]
Abstract
The expression of voltage-gated potassium Kv1.3 channels is increased in activated microglia, with non-selective blockade reported to attenuate microglial-mediated neuroinflammation. In this study, we evaluated the impact of a potent and selective peptidic blocker of Kv1.3 channels, HsTX1[R14A], on microglial-mediated neuroinflammation in vitro and in vivo. Treatment with both 0.1 and 1 µg/mL lipopolysaccharide (LPS) significantly (p < 0.05) increased Kv1.3 abundance on the surface of BV-2 microglia in association with increased levels of mRNA for tumour necrosis factor-α (TNF-α) and interleukin-6 (IL-6). The increased transcription of TNF-α and IL-6 was significantly attenuated (by 24.9 and 20.2%, respectively) by HsTX1[R14A] (100 nM). The concomitant increase in TNF-α and IL-6 release from BV-2 microglia was significantly attenuated by HsTX1[R14A] by 10.7 and 12.6%, respectively. In LPS-treated primary mouse microglia, the levels of TNF-α and nitric oxide were also attenuated by HsTX1[R14A] (26.1 and 20.4%, respectively). In an LPS-induced mouse model of neuroinflammation, both an immediate and delayed subcutaneous dose of HsTX1[R14A] (2 mg/kg) significantly reduced plasma and brain levels of the pro-inflammatory mediators TNF-α, IL-1β and IL-6, with no impact on the anti-inflammatory IL-10. These results demonstrate that HsTX1[R14A] is a promising therapeutic candidate for the treatment of diseases with a neuroinflammatory component.
Collapse
Affiliation(s)
- Joseph A Nicolazzo
- Drug Delivery, Disposition and Dynamics, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria 3052, Australia
| | - Yijun Pan
- Drug Delivery, Disposition and Dynamics, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria 3052, Australia
| | - Ilenia Di Stefano
- Drug Delivery, Disposition and Dynamics, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria 3052, Australia
| | - Kwok H C Choy
- Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria 3052, Australia
| | - Sanjeevini Babu Reddiar
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria 3052, Australia
| | - Yi Ling Low
- Drug Delivery, Disposition and Dynamics, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria 3052, Australia
| | - Dorothy C C Wai
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria 3052, Australia
| | - Raymond S Norton
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria 3052, Australia; ARC Centre for Fragment-Based Design, Monash University, Parkville, Victoria 3052, Australia
| | - Liang Jin
- Drug Delivery, Disposition and Dynamics, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria 3052, Australia
| |
Collapse
|
3
|
Dynamic expression of homeostatic ion channels in differentiated cortical astrocytes in vitro. Pflugers Arch 2021; 474:243-260. [PMID: 34734327 PMCID: PMC8766406 DOI: 10.1007/s00424-021-02627-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2021] [Revised: 09/02/2021] [Accepted: 09/24/2021] [Indexed: 11/16/2022]
Abstract
The capacity of astrocytes to adapt their biochemical and functional features upon physiological and pathological stimuli is a fundamental property at the basis of their ability to regulate the homeostasis of the central nervous system (CNS). It is well known that in primary cultured astrocytes, the expression of plasma membrane ion channels and transporters involved in homeostatic tasks does not closely reflect the pattern observed in vivo. The individuation of culture conditions that promote the expression of the ion channel array found in vivo is crucial when aiming at investigating the mechanisms underlying their dynamics upon various physiological and pathological stimuli. A chemically defined medium containing growth factors and hormones (G5) was previously shown to induce the growth, differentiation, and maturation of primary cultured astrocytes. Here we report that under these culture conditions, rat cortical astrocytes undergo robust morphological changes acquiring a multi-branched phenotype, which develops gradually during the 2-week period of culturing. The shape changes were paralleled by variations in passive membrane properties and background conductance owing to the differential temporal development of inwardly rectifying chloride (Cl−) and potassium (K+) currents. Confocal and immunoblot analyses showed that morphologically differentiated astrocytes displayed a large increase in the expression of the inward rectifier Cl− and K+ channels ClC-2 and Kir4.1, respectively, which are relevant ion channels in vivo. Finally, they exhibited a large diminution of the intermediate filaments glial fibrillary acidic protein (GFAP) and vimentin which are upregulated in reactive astrocytes in vivo. Taken together the data indicate that long-term culturing of cortical astrocytes in this chemical-defined medium promotes a quiescent functional phenotype. This culture model could aid to address the regulation of ion channel expression involved in CNS homeostasis in response to physiological and pathological challenges.
Collapse
|
4
|
Studying Independent Kcna6 Knock-out Mice Reveals Toxicity of Exogenous LacZ to Central Nociceptor Terminals and Differential Effects of Kv1.6 on Acute and Neuropathic Pain Sensation. J Neurosci 2021; 41:9141-9162. [PMID: 34544832 DOI: 10.1523/jneurosci.0187-21.2021] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2021] [Revised: 08/19/2021] [Accepted: 08/20/2021] [Indexed: 11/21/2022] Open
Abstract
The potassium channel Kv1.6 has recently been implicated as a major modulatory channel subunit expressed in primary nociceptors. Furthermore, its expression at juxtaparanodes of myelinated primary afferents is induced following traumatic nerve injury as part of an endogenous mechanism to reduce hyperexcitability and pain-related hypersensitivity. In this study, we compared two mouse models of constitutive Kv1.6 knock-out (KO) achieved by different methods: traditional gene trap via homologous recombination and CRISPR-mediated excision. Both Kv1.6 KO mouse lines exhibited an unexpected reduction in sensitivity to noxious heat stimuli, to differing extents: the Kv1.6 mice produced via gene trap had a far more significant hyposensitivity. These mice (Kcna6lacZ ) expressed the bacterial reporter enzyme LacZ in place of Kv1.6 as a result of the gene trap mechanism, and we found that their central primary afferent presynaptic terminals developed a striking neurodegenerative phenotype involving accumulation of lipid species, development of "meganeurites," and impaired transmission to dorsal horn wide dynamic range neurons. The anatomic defects were absent in CRISPR-mediated Kv1.6 KO mice (Kcna6 -/-) but were present in a third mouse model expressing exogenous LacZ in nociceptors under the control of a Nav1.8-promoted Cre recombinase. LacZ reporter enzymes are thus intrinsically neurotoxic to sensory neurons and may induce pathologic defects in transgenic mice, which has confounding implications for the interpretation of gene KOs using lacZ Nonetheless, in Kcna6 -/- mice not affected by LacZ, we demonstrated a significant role for Kv1.6 regulating acute noxious thermal sensitivity, and both mechanical and thermal pain-related hypersensitivity after nerve injury.SIGNIFICANCE STATEMENT In recent decades, the expansion of technologies to experimentally manipulate the rodent genome has contributed significantly to the field of neuroscience. While introduction of enzymatic or fluorescent reporter proteins to label neuronal populations is now commonplace, often potential toxicity effects are not fully considered. We show a role of Kv1.6 in acute and neuropathic pain states through analysis of two mouse models lacking Kv1.6 potassium channels: one with additional expression of LacZ and one without. We show that LacZ reporter enzymes induce unintended defects in sensory neurons, with an impact on behavioral data outcomes. To summarize we highlight the importance of Kv1.6 in recovery of normal sensory function following nerve injury, and careful interpretation of data from LacZ reporter models.
Collapse
|
5
|
Boscia F, Elkjaer ML, Illes Z, Kukley M. Altered Expression of Ion Channels in White Matter Lesions of Progressive Multiple Sclerosis: What Do We Know About Their Function? Front Cell Neurosci 2021; 15:685703. [PMID: 34276310 PMCID: PMC8282214 DOI: 10.3389/fncel.2021.685703] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2021] [Accepted: 05/23/2021] [Indexed: 12/19/2022] Open
Abstract
Despite significant advances in our understanding of the pathophysiology of multiple sclerosis (MS), knowledge about contribution of individual ion channels to axonal impairment and remyelination failure in progressive MS remains incomplete. Ion channel families play a fundamental role in maintaining white matter (WM) integrity and in regulating WM activities in axons, interstitial neurons, glia, and vascular cells. Recently, transcriptomic studies have considerably increased insight into the gene expression changes that occur in diverse WM lesions and the gene expression fingerprint of specific WM cells associated with secondary progressive MS. Here, we review the ion channel genes encoding K+, Ca2+, Na+, and Cl- channels; ryanodine receptors; TRP channels; and others that are significantly and uniquely dysregulated in active, chronic active, inactive, remyelinating WM lesions, and normal-appearing WM of secondary progressive MS brain, based on recently published bulk and single-nuclei RNA-sequencing datasets. We discuss the current state of knowledge about the corresponding ion channels and their implication in the MS brain or in experimental models of MS. This comprehensive review suggests that the intense upregulation of voltage-gated Na+ channel genes in WM lesions with ongoing tissue damage may reflect the imbalance of Na+ homeostasis that is observed in progressive MS brain, while the upregulation of a large number of voltage-gated K+ channel genes may be linked to a protective response to limit neuronal excitability. In addition, the altered chloride homeostasis, revealed by the significant downregulation of voltage-gated Cl- channels in MS lesions, may contribute to an altered inhibitory neurotransmission and increased excitability.
Collapse
Affiliation(s)
- Francesca Boscia
- Division of Pharmacology, Department of Neuroscience, Reproductive and Dentistry Sciences, School of Medicine, University of Naples "Federico II", Naples, Italy
| | - Maria Louise Elkjaer
- Neurology Research Unit, Department of Clinical Research, University of Southern Denmark, Odense, Denmark.,Department of Neurobiology Research, Institute of Molecular Medicine, University of Southern Denmark, Odense, Denmark
| | - Zsolt Illes
- Neurology Research Unit, Department of Clinical Research, University of Southern Denmark, Odense, Denmark.,Department of Neurobiology Research, Institute of Molecular Medicine, University of Southern Denmark, Odense, Denmark.,Department of Neurology, Odense University Hospital, Odense, Denmark
| | - Maria Kukley
- Achucarro Basque Center for Neuroscience, Leioa, Spain.,Ikerbasque Basque Foundation for Science, Bilbao, Spain
| |
Collapse
|
6
|
McNeill J, Rudyk C, Hildebrand ME, Salmaso N. Ion Channels and Electrophysiological Properties of Astrocytes: Implications for Emergent Stimulation Technologies. Front Cell Neurosci 2021; 15:644126. [PMID: 34093129 PMCID: PMC8173131 DOI: 10.3389/fncel.2021.644126] [Citation(s) in RCA: 35] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2020] [Accepted: 04/26/2021] [Indexed: 12/12/2022] Open
Abstract
Astrocytes comprise a heterogeneous cell population characterized by distinct morphologies, protein expression and function. Unlike neurons, astrocytes do not generate action potentials, however, they are electrically dynamic cells with extensive electrophysiological heterogeneity and diversity. Astrocytes are hyperpolarized cells with low membrane resistance. They are heavily involved in the modulation of K+ and express an array of different voltage-dependent and voltage-independent channels to help with this ion regulation. In addition to these K+ channels, astrocytes also express several different types of Na+ channels; intracellular Na+ signaling in astrocytes has been linked to some of their functional properties. The physiological hallmark of astrocytes is their extensive intracellular Ca2+ signaling cascades, which vary at the regional, subregional, and cellular levels. In this review article, we highlight the physiological properties of astrocytes and the implications for their function and influence of network and synaptic activity. Furthermore, we discuss the implications of these differences in the context of optogenetic and DREADD experiments and consider whether these tools represent physiologically relevant techniques for the interrogation of astrocyte function.
Collapse
Affiliation(s)
- Jessica McNeill
- Department of Neuroscience, Carleton University, Ottawa, ON, Canada
| | | | | | - Natalina Salmaso
- Department of Neuroscience, Carleton University, Ottawa, ON, Canada
| |
Collapse
|
7
|
Trosclair K, Dhaibar HA, Gautier NM, Mishra V, Glasscock E. Neuron-specific Kv1.1 deficiency is sufficient to cause epilepsy, premature death, and cardiorespiratory dysregulation. Neurobiol Dis 2020; 137:104759. [PMID: 31978607 DOI: 10.1016/j.nbd.2020.104759] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2019] [Revised: 01/03/2020] [Accepted: 01/20/2020] [Indexed: 12/14/2022] Open
Abstract
Sudden unexpected death in epilepsy (SUDEP) is the leading cause of epilepsy-related mortality, but the precise cellular substrates involved remain elusive. Epilepsy-associated ion channel genes with co-expression in brain and heart have been proposed as SUDEP candidate genes since they provide a singular unifying link between seizures and lethal cardiac arrhythmias. Here, we generated a conditional knockout (cKO) mouse with neuron-specific deletion of Kcna1, a SUDEP-associated gene with brain-heart co-expression, to test whether seizure-evoked cardiac arrhythmias and SUDEP require the absence of Kv1.1 in both brain and heart or whether ablation in neurons is sufficient. To obtain cKO mice, we developed a floxed Kcna1 mouse which we crossed to mice with the Synapsin1-Cre transgene, which selectively deletes Kcna1 in most neurons. Molecular analyses confirmed neuron-specific Kcna1 deletion in cKO mice and corresponding loss of Kv1.1 except in cerebellum where Synapsin1-Cre is not highly expressed. Survival studies and electroencephalography, electrocardiography, and plethysmography recordings showed that cKO mice exhibit premature death, epilepsy, and cardiorespiratory dysregulation but to a lesser degree than global knockouts. Heart rate variability (HRV) was increased in cKO mice with peaks during daytime suggesting disturbed diurnal HRV patterns as a SUDEP biomarker. Residual Kv1.1 expression in cKO cerebellum suggests it may play an unexpected role in regulating ictal cardiorespiratory dysfunction and SUDEP risk. This work demonstrates the principle that channelopathies with brain-heart expression patterns can increase death risk by brain-driven mechanisms alone without a functionally compromised heart, reinforcing seizure control as a primary clinical strategy for SUDEP prevention.
Collapse
Affiliation(s)
- Krystle Trosclair
- Department of Cellular Biology and Anatomy, Louisiana State University Health Sciences Center Shreveport, LA 71103, United States of America.
| | - Hemangini A Dhaibar
- Department of Cellular Biology and Anatomy, Louisiana State University Health Sciences Center Shreveport, LA 71103, United States of America.
| | - Nicole M Gautier
- Department of Cellular Biology and Anatomy, Louisiana State University Health Sciences Center Shreveport, LA 71103, United States of America.
| | - Vikas Mishra
- Department of Cellular Biology and Anatomy, Louisiana State University Health Sciences Center Shreveport, LA 71103, United States of America.
| | - Edward Glasscock
- Department of Cellular Biology and Anatomy, Louisiana State University Health Sciences Center Shreveport, LA 71103, United States of America; Department of Biological Sciences, Southern Methodist University, Dallas, TX 75275, United States of America.
| |
Collapse
|
8
|
Nabel AL, Callan AR, Gleiss SA, Kladisios N, Leibold C, Felmy F. Distinct Distribution Patterns of Potassium Channel Sub-Units in Somato-Dendritic Compartments of Neurons of the Medial Superior Olive. Front Cell Neurosci 2019; 13:38. [PMID: 30837841 PMCID: PMC6390502 DOI: 10.3389/fncel.2019.00038] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2018] [Accepted: 01/23/2019] [Indexed: 12/17/2022] Open
Abstract
Coincidence detector neurons of the medial superior olive (MSO) are sensitive to interaural time differences in the range of a few tens of microseconds. The biophysical basis for this remarkable acuity is a short integration time constant of the membrane, which is achieved by large low voltage-activated potassium and hyperpolarization-activated inward cation conductances. Additional temporal precision is thought to be achieved through a sub-cellular distribution of low voltage-activated potassium channel expression biased to the soma. To evaluate the contribution of potassium channels, we investigated the presence and sub-cellular distribution profile of seven potassium channel sub-units in adult MSO neurons of gerbils. We find that low- and high voltage-activated potassium channels are present with distinct sub-cellular distributions. Overall, low voltage-activated potassium channels appear to be biased to the soma while high voltage-activated potassium channels are more evenly distributed and show a clear expression at distal dendrites. Additionally, low voltage-activated potassium channel sub-units co-localize with glycinergic inputs while HCN1 channels co-localize more with high voltage-activated potassium channels. Functionally, high voltage-activated potassium currents are already active at low voltages near the resting potential. We describe a possible role of high voltage-activated potassium channels in modulating EPSPs in a computational model and contributing to setting the integration time window of coincidental inputs. Our data shows that MSO neurons express a large set of different potassium channels with distinct functional relevance.
Collapse
Affiliation(s)
- Alisha L Nabel
- Division of Neurobiology, Department Biology II, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany.,Graduate School for Systemic Neurosciences, Ludwig-Maximilians-Universität München, Munich, Germany
| | - Alexander R Callan
- Division of Neurobiology, Department Biology II, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany.,Graduate School for Systemic Neurosciences, Ludwig-Maximilians-Universität München, Munich, Germany
| | - Sarah A Gleiss
- Division of Neurobiology, Department Biology II, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany.,Graduate School for Systemic Neurosciences, Ludwig-Maximilians-Universität München, Munich, Germany
| | - Nikolaos Kladisios
- Institute of Zoology, University of Veterinary Medicine Hannover, Hanover, Germany
| | - Christian Leibold
- Computational Neuroscience, Department Biology II, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany
| | - Felix Felmy
- Division of Neurobiology, Department Biology II, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany.,Institute of Zoology, University of Veterinary Medicine Hannover, Hanover, Germany
| |
Collapse
|
9
|
Price BR, Norris CM, Sompol P, Wilcock DM. An emerging role of astrocytes in vascular contributions to cognitive impairment and dementia. J Neurochem 2018; 144:644-650. [PMID: 29222909 DOI: 10.1111/jnc.14273] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2017] [Revised: 10/30/2017] [Accepted: 11/23/2017] [Indexed: 01/15/2023]
Abstract
Vascular contributions to cognitive impairment and dementia (VCID) is understood to be the second most common cause of dementia after Alzheimer's disease, and is also a frequent comorbidity with Alzheimer's disease. While VCID is widely acknowledged as a key contributor to dementia, the mechanistic underpinnings of VCID remain poorly understood. In this review, we address the potential role of astrocytes in the pathophysiology of VCID. The vast majority of the blood vessels in the brain are surrounded by astrocytic end-feet. Given that astrocytes make up a significant proportion of the cells in the brain, and that astrocytes are usually passively connected to one another through gap junctions, we hypothesize that astrocytes are key mediators of cognitive impairment because of cerebrovascular disease. In this review, we discuss the existing body of literature regarding the role of astrocytes at the vasculature in the brain, and the known consequences of their dysfunction, as well as our hypotheses regarding the role astrocytes play in VCID. This article is part of the Special Issue "Vascular Dementia".
Collapse
Affiliation(s)
- Brittani R Price
- Department of Physiology, Sanders-Brown Center on Aging, University of Kentucky, Lexington, Kentucky, USA
| | - Christopher M Norris
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, Kentucky, USA
| | - Pradoldej Sompol
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, Kentucky, USA
| | - Donna M Wilcock
- Department of Physiology, Sanders-Brown Center on Aging, University of Kentucky, Lexington, Kentucky, USA
| |
Collapse
|
10
|
Jiménez-Vargas JM, Possani LD, Luna-Ramírez K. Arthropod toxins acting on neuronal potassium channels. Neuropharmacology 2017; 127:139-160. [PMID: 28941737 DOI: 10.1016/j.neuropharm.2017.09.025] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2017] [Revised: 09/13/2017] [Accepted: 09/15/2017] [Indexed: 01/01/2023]
Abstract
Arthropod venoms are a rich mixture of biologically active compounds exerting different physiological actions across diverse phyla and affecting multiple organ systems including the central nervous system. Venom compounds can inhibit or activate ion channels, receptors and transporters with high specificity and affinity providing essential insights into ion channel function. In this review, we focus on arthropod toxins (scorpions, spiders, bees and centipedes) acting on neuronal potassium channels. A brief description of the K+ channels classification and structure is included and a compendium of neuronal K+ channels and the arthropod toxins that modify them have been listed. This article is part of the Special Issue entitled 'Venom-derived Peptides as Pharmacological Tools.'
Collapse
Affiliation(s)
- Juana María Jiménez-Vargas
- Departamento de Medicina Molecular y Bioprocesos, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Avenida Universidad, 2001, Colonia Chamilpa, Apartado Postal 510-3, Cuernavaca 62210, Mexico
| | - Lourival D Possani
- Departamento de Medicina Molecular y Bioprocesos, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Avenida Universidad, 2001, Colonia Chamilpa, Apartado Postal 510-3, Cuernavaca 62210, Mexico
| | - Karen Luna-Ramírez
- Illawarra Health and Medical Research Institute, University of Wollongong, Northfields Avenue, Wollongong, NSW 2522, Australia.
| |
Collapse
|
11
|
Seifert G, Henneberger C, Steinhäuser C. Diversity of astrocyte potassium channels: An update. Brain Res Bull 2016; 136:26-36. [PMID: 27965079 DOI: 10.1016/j.brainresbull.2016.12.002] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2016] [Revised: 12/08/2016] [Accepted: 12/09/2016] [Indexed: 01/08/2023]
Abstract
Astrocyte K+ channels and the K+ currents they mediate dwarf all other transmembrane conductances in these cells. This defining feature of astrocytes and its functional implications have been investigated intensely over the past decades. Nonetheless, many aspects of astrocyte K+ handling and signaling remain incompletely understood. In this review, we provide an update on the diversity of K+ channels expressed by astrocytes and new functional implications. We focus on inwardly-rectifying K+ channels (particularly Kir4.1), two-pore K+ channels and voltage and Ca2+-dependent K+ channels. We further discuss new insights into the involvement of these K+ channels in K+ buffering, control of synaptic transmission, regulation of the vasculature and in diseases of the central nervous system.
Collapse
Affiliation(s)
- Gerald Seifert
- Institute of Cellular Neurosciences, University of Bonn Medical School, Bonn, Germany.
| | - Christian Henneberger
- Institute of Cellular Neurosciences, University of Bonn Medical School, Bonn, Germany; German Center of Neurodegenerative Diseases (DZNE), Bonn, Germany; Institute of Neurology, University College London, London, United Kingdom
| | - Christian Steinhäuser
- Institute of Cellular Neurosciences, University of Bonn Medical School, Bonn, Germany.
| |
Collapse
|
12
|
Schrödl-Häußel M, Theparambil SM, Deitmer JW, Roussa E. Regulation of functional expression of the electrogenic sodium bicarbonate cotransporter 1, NBCe1 (SLC4A4), in mouse astrocytes. Glia 2015; 63:1226-39. [DOI: 10.1002/glia.22814] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2014] [Revised: 02/17/2015] [Accepted: 02/18/2015] [Indexed: 12/25/2022]
Affiliation(s)
- Magdalena Schrödl-Häußel
- Department of Molecular Embryology; Institute for Anatomy and Cell Biology, University of Freiburg; Freiburg Germany
| | - Shefeeq M. Theparambil
- Department of General Zoology; FB Biology, University of Kaiserslautern; Kaiserslautern Germany
| | - Joachim W. Deitmer
- Department of General Zoology; FB Biology, University of Kaiserslautern; Kaiserslautern Germany
| | - Eleni Roussa
- Department of Molecular Embryology; Institute for Anatomy and Cell Biology, University of Freiburg; Freiburg Germany
- Department of Neuroanatomy; University of Freiburg; Freiburg Germany
| |
Collapse
|
13
|
Jukkola P, Gu C. Regulation of neurovascular coupling in autoimmunity to water and ion channels. Autoimmun Rev 2015; 14:258-67. [PMID: 25462580 PMCID: PMC4303502 DOI: 10.1016/j.autrev.2014.11.010] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2014] [Accepted: 11/15/2014] [Indexed: 12/27/2022]
Abstract
Much progress has been made in understanding autoimmune channelopathies, but the underlying pathogenic mechanisms are not always clear due to broad expression of some channel proteins. Recent studies show that autoimmune conditions that interfere with neurovascular coupling in the central nervous system (CNS) can lead to neurodegeneration. Cerebral blood flow that meets neuronal activity and metabolic demand is tightly regulated by local neural activity. This process of reciprocal regulation involves coordinated actions of a number of cell types, including neurons, glia, and vascular cells. In particular, astrocytic endfeet cover more than 90% of brain capillaries to assist blood-brain barrier (BBB) function, and wrap around synapses and nodes of Ranvier to communicate with neuronal activity. In this review, we highlight four types of channel proteins that are expressed in astrocytes, regarding their structures, biophysical properties, expression and distribution patterns, and related diseases including autoimmune disorders. Water channel aquaporin 4 (AQP4) and inwardly rectifying potassium (Kir4.1) channels are concentrated in astrocytic endfeet, whereas some voltage-gated Ca(2+) and two-pore domain K(+) channels are expressed throughout the cell body of reactive astrocytes. More channel proteins are found in astrocytes under normal and abnormal conditions. This research field will contribute to a better understanding of pathogenic mechanisms underlying autoimmune disorders.
Collapse
Affiliation(s)
- Peter Jukkola
- Biomedical Sciences Graduate Program, The Ohio State University, Columbus, OH 43210, USA
| | - Chen Gu
- Biomedical Sciences Graduate Program, The Ohio State University, Columbus, OH 43210, USA; Department of Neuroscience, The Ohio State University, Columbus, OH 43210, USA.
| |
Collapse
|
14
|
Zhu J, Yan J, Thornhill WB. The Kv1.3 potassium channel is localized to the cis-Golgi and Kv1.6 is localized to the endoplasmic reticulum in rat astrocytes. FEBS J 2014; 281:3433-45. [PMID: 24924920 DOI: 10.1111/febs.12871] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2014] [Revised: 05/23/2014] [Accepted: 06/06/2014] [Indexed: 12/11/2022]
Abstract
The functions of voltage-gated potassium (Kv) channels in neurons have been well defined, whereas their roles in glial cells are not fully understood. Kv1.1, Kv1.3 and Kv1.6 are endogenously expressed in C6 astrocytoma cells, but their trafficking and subcellular localization have not been well studied. In C6 cells, Kv1.1 was localized to the cell surface, Kv1.3 was predominantly localized in the cis-Golgi, and Kv1.6 was enriched in the endoplasmic reticulum. Disruption of the Golgi stacks with brefeldin A treatment redirected Kv1.3 to the endoplasmic reticulum, further confirming that Kv1.3 was localized in the Golgi. Denaturing and reducing immunoblot analysis identified an expected Kv1.3 monomer and an unexpected Kv1.3 dimer/aggregate. These two forms had different protein half-lives: that of the monomer form T1/2 was 5.1 h, whereas the dimer/aggregate form was stable over the 8-h measurement period. The Kv1.3 dimer/aggregate form on immunoblots appeared to be correlated with its Golgi retention, based on examination with several cell types that expressed Kv1.3. Glycosidase treatment showed that Kv1.3 contained complex-type N-glycans terminated with sialic acids, suggesting that Kv1.3 had traveled to the trans-Golgi network for sialylation before it was recycled to the cis-Golgi for retention. Inhibition of N-glycosylation did not affect Kv1.3 localization, indicating that N-glycans did not play a role in its Golgi retention. Thus, Kv1.3 appears to be distributed to the cis-Golgi membrane of rat astrocytes in a similar way as a Golgi resident protein, and this unusual distribution appears to be correlated with its SDS/2-mercaptoethanol-resistant dimer/aggregate forms on immunoblots.
Collapse
Affiliation(s)
- Jing Zhu
- Department of Biological Sciences and Center for Cancer, Genetic Diseases, and Gene Regulation, Fordham University, Bronx, NY, USA
| | | | | |
Collapse
|
15
|
Benfenati V, Martino N, Antognazza MR, Pistone A, Toffanin S, Ferroni S, Lanzani G, Muccini M. Photostimulation of whole-cell conductance in primary rat neocortical astrocytes mediated by organic semiconducting thin films. Adv Healthc Mater 2014; 3:392-9. [PMID: 23966220 DOI: 10.1002/adhm.201300179] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2013] [Indexed: 12/19/2022]
Abstract
Astroglial ion channels are fundamental molecular targets in the study of brain physiology and pathophysiology. Novel tools and devices intended for stimulation and control of astrocytes ion channel activity are therefore highly desirable. The study of the interactions between astrocytes and biomaterials is also essential to control and minimize reactive astrogliosis, in view of the development of implantable functional devices. Here, the growth of rat primary neocortical astrocytes on the top of a light sensitive, organic polymer film is reported; by means of patch-clamp analyses, the effect of the visible light stimulation on membrane conductance is then determined. Photoexcitation of the active material causes a significant depolarization of the astroglial resting membrane potential: the effect is associated to an increase in whole-cell conductance at negative potentials. The magnitude of the evoked inward current density is proportional to the illumination intensity. Biophysical and pharmacological characterization suggests that the ion channel mediating the photo-transduction mechanism is a chloride channel, the ClC-2 channel. These results open interesting perspectives for the selective manipulation of astrocyte bioelectrical activity by non-invasive, label-free, organic-based, photostimulation approaches.
Collapse
Affiliation(s)
- Valentina Benfenati
- Consiglio Nazionale delle Ricerche (CNR), Istituto per la Sintesi Organica e la Fotoreattività (ISOF); Via Gobetti 101 40129 Bologna Italy
| | - Nicola Martino
- Center for Nanoscience and Technology @PoliMi, Istituto Italiano di Tecnologia; Via Pascoli 70/3 20133 Milano Italy
- Politecnico di Milano, Dip. di Fisica; Piazza L. Da Vinci 32 20133 Milano Italy
| | - Maria Rosa Antognazza
- Center for Nanoscience and Technology @PoliMi, Istituto Italiano di Tecnologia; Via Pascoli 70/3 20133 Milano Italy
| | - Assunta Pistone
- Consiglio Nazionale delle Ricerche (CNR), Istituto per la Sintesi Organica e la Fotoreattività (ISOF); Via Gobetti 101 40129 Bologna Italy
| | - Stefano Toffanin
- Consiglio Nazionale delle Ricerche (CNR), Istituto per lo Studio dei Materiali Nanostrutturati (ISMN); Via P. Gobetti 101 40129 Bologna Italy
| | - Stefano Ferroni
- Department of Pharmacy and Biotechnology; University of Bologna; Via S. Donato, 19/2 40127 Bologna Italy
| | - Guglielmo Lanzani
- Center for Nanoscience and Technology @PoliMi, Istituto Italiano di Tecnologia; Via Pascoli 70/3 20133 Milano Italy
- Politecnico di Milano, Dip. di Fisica; Piazza L. Da Vinci 32 20133 Milano Italy
| | - Michele Muccini
- Consiglio Nazionale delle Ricerche (CNR), Istituto per lo Studio dei Materiali Nanostrutturati (ISMN); Via P. Gobetti 101 40129 Bologna Italy
- E. T. C. s.r.l.; via P. Gobetti 101 I-40129 Bologna Italy
| |
Collapse
|
16
|
Wang W, Kim HJ, Lv P, Tempel B, Yamoah EN. Association of the Kv1 family of K+ channels and their functional blueprint in the properties of auditory neurons as revealed by genetic and functional analyses. J Neurophysiol 2013; 110:1751-64. [PMID: 23864368 DOI: 10.1152/jn.00290.2013] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Developmental plasticity in spiral ganglion neurons (SGNs) ensues from profound alterations in the functional properties of the developing hair cell (HC). For example, prehearing HCs are spontaneously active. However, at the posthearing stage, HC membrane properties transition to graded receptor potentials. The dendrotoxin (DTX)-sensitive Kv1 channel subunits (Kv1.1, 1.2, and 1.6) shape the firing properties and membrane potential of SGNs, and the expression of the channel undergoes developmental changes. Because of the stochastic nature of Kv subunit heteromultimerization, it has been difficult to determine physiologically relevant subunit-specific interactions and their functions in the underlying mechanisms of Kv1 channel plasticity in SGNs. Using Kcna2 null mutant mice, we demonstrate a surprising paradox in changes in the membrane properties of SGNs. The resting membrane potential of Kcna2(-/-) SGNs was significantly hyperpolarized compared with that of age-matched wild-type (WT) SGNs. Analyses of outward currents in the mutant SGNs suggest an apparent approximately twofold increase in outward K(+) currents. We show that in vivo and in vitro heteromultimerization of Kv1.2 and Kv1.4 α-subunits underlies the striking and unexpected alterations in the properties of SGNs. The results suggest that heteromeric interactions of Kv1.2 and Kv1.4 dominate the defining features of Kv1 channels in SGNs.
Collapse
Affiliation(s)
- Wenying Wang
- Program in Communication Science, Center for Neuroscience, University of California, Davis, School of Medicine, Davis, California
| | | | | | | | | |
Collapse
|
17
|
Clarkson C, Herrero-Turrión MJ, Merchán MA. Cortical Auditory Deafferentation Induces Long-Term Plasticity in the Inferior Colliculus of Adult Rats: Microarray and qPCR Analysis. Front Neural Circuits 2012; 6:86. [PMID: 23233834 PMCID: PMC3516126 DOI: 10.3389/fncir.2012.00086] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2012] [Accepted: 10/29/2012] [Indexed: 12/14/2022] Open
Abstract
The cortico-collicular pathway is a bilateral excitatory projection from the cortex to the inferior colliculus (IC). It is asymmetric and predominantly ipsilateral. Using microarrays and RT-qPCR we analyzed changes in gene expression in the IC after unilateral lesions of the auditory cortex, comparing the ICs ipsi- and contralateral to the lesioned side. At 15 days after surgery there were mainly changes in gene expression in the IC ipsilateral to the lesion. Regulation primarily involved inflammatory cascade genes, suggesting a direct effect of degeneration rather than a neuronal plastic reorganization. Ninety days after the cortical lesion the ipsilateral IC showed a significant up-regulation of genes involved in apoptosis and axonal regeneration combined with a down-regulation of genes involved in neurotransmission, synaptic growth, and gap junction assembly. In contrast, the contralateral IC at 90 days post-lesion showed an up-regulation in genes primarily related to neurotransmission, cell proliferation, and synaptic growth. There was also a down-regulation in autophagy and neuroprotection genes. These findings suggest that the reorganization in the IC after descending pathway deafferentation is a long-term process involving extensive changes in gene expression regulation. Regulated genes are involved in many different neuronal functions, and the number and gene rearrangement profile seems to depend on the density of loss of the auditory cortical inputs.
Collapse
Affiliation(s)
- Cheryl Clarkson
- Instituto de Neurociencias de Castilla y León, Universidad de Salamanca Salamanca, Spain
| | | | | |
Collapse
|
18
|
He S, Shao LR, Rittase WB, Bausch SB. Increased Kv1 channel expression may contribute to decreased sIPSC frequency following chronic inhibition of NR2B-containing NMDAR. Neuropsychopharmacology 2012; 37:1338-56. [PMID: 22218089 PMCID: PMC3327840 DOI: 10.1038/npp.2011.320] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/26/2011] [Revised: 10/21/2011] [Accepted: 11/29/2011] [Indexed: 12/20/2022]
Abstract
Numerous studies have documented the effects of chronic N-methyl-D-aspartate receptor (NMDAR) blockade on excitatory circuits, but the effects on inhibitory circuitry are not well studied. NR2A- and NR2B-containing NMDARs play differential roles in physiological processes, but the consequences of chronic NR2A- or NR2B-containing NMDAR inhibition on glutamatergic and GABAergic neurotransmission are unknown. We investigated altered GABAergic neurotransmission in dentate granule cells and interneurons following chronic treatment with the NR2B-selective antagonist, Ro25,6981, the NR2A-prefering antagonist, NVP-AAM077, or the non-subunit-selective NMDAR antagonist, D-APV, in organotypic hippocampal slice cultures. Electrophysiological recordings revealed large reductions in spontaneous inhibitory postsynaptic current (sIPSC) frequency in both granule cells and interneurons following chronic Ro25,6981 treatment, which was associated with minimally altered sIPSC amplitude, miniature inhibitory postsynaptic current (mIPSC) frequency, and mIPSC amplitude, suggesting diminished action potential-dependent GABA release. Chronic NVP-AAM077 or D-APV treatment had little effect on these measures. Reduced sIPSC frequency did not arise from downregulated GABA(A)R, altered excitatory or inhibitory drive to interneurons, altered interneuron membrane properties, increased failure rate, decreased action potential-dependent release probability, or mGluR/GABA(B) receptor modulation of GABA release. However, chronic Ro25,6981-mediated reductions in sIPSC frequency were occluded by the K+ channel blockers, dendrotoxin, margatoxin, and agitoxin, but not dendrotoxin-K or XE991. Immunohistochemistry also showed increased Kv1.2, Kv1.3, and Kv1.6 in the dentate molecular layer following chronic Ro25,6981 treatment. Our findings suggest that increased Kv1 channel expression/function contributed to diminished action potential-dependent GABA release following chronic NR2B-containing NMDAR inhibition and that these Kv1 channels may be heteromeric complexes containing Kv1.2, Kv1.3, and Kv1.6.
Collapse
Affiliation(s)
- Shuijin He
- Department of Pharmacology, Uniformed Services University School of Medicine, Bethesda, MD, USA
- Graduate Program in Neuroscience, Uniformed Services University School of Medicine, Bethesda, MD, USA
| | - Li-Rong Shao
- Department of Pharmacology, Uniformed Services University School of Medicine, Bethesda, MD, USA
| | - W Bradley Rittase
- Department of Pharmacology, Uniformed Services University School of Medicine, Bethesda, MD, USA
| | - Suzanne B Bausch
- Department of Pharmacology, Uniformed Services University School of Medicine, Bethesda, MD, USA
- Graduate Program in Neuroscience, Uniformed Services University School of Medicine, Bethesda, MD, USA
| |
Collapse
|
19
|
Yang SB, Mclemore KD, Tasic B, Luo L, Jan YN, Jan LY. Kv1.1-dependent control of hippocampal neuron number as revealed by mosaic analysis with double markers. J Physiol 2012; 590:2645-58. [PMID: 22411008 DOI: 10.1113/jphysiol.2012.228486] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Megencephaly, or mceph, is a spontaneous frame-shift mutation of the mouse Kv1.1 gene. This mceph mutation results in a truncated Kv1.1 channel α-subunit without the channel pore domain or the voltage sensor. Interestingly, mceph/mceph mouse brains are enlarged and – unlike wild-type mouse brains – they keep growing throughout adulthood, especially in the hippocampus and ventral cortex. We used mosaic analysis with double markers (MADM) to identify the underlying mechanism. In mceph-MADM6 mice with only a small fraction of neurons homozygous for the mceph mutation, those homozygous mceph/mceph neurons in the hippocampus are more abundant than wild-type neurons produced by sister neural progenitors. In contrast, neither mceph/mceph astrocytes, nor neurons in the adjacent dorsal cortex (including the entorhinal and parietal cortex) exhibited overgrowth in the adult brain. The sizes of mceph/mceph hippocampal neurons were comparable to mceph/+ or wild-type neurons. Our mosaic analysis reveals that loss of Kv1.1 function causes an overproduction of hippocampal neurons, leading to an enlarged brain phenotype.
Collapse
Affiliation(s)
- Shi-Bing Yang
- Howard Hughes Medical Institute, Department of Physiology, University of California–San Francisco, San Francisco, CA, USA
| | | | | | | | | | | |
Collapse
|
20
|
Han Y, Chen JD, Liu ZM, Zhou Y, Xia JH, Du XL, Jin MW. Functional ion channels in mouse cardiac c-kit(+) cells. Am J Physiol Cell Physiol 2010; 298:C1109-17. [PMID: 20130208 DOI: 10.1152/ajpcell.00207.2009] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Cardiac c-kit(+) cells are generally believed to be the major population of stem/progenitor cells in the heart and can be used as a cell source for cardiomyoplasty; however, the cellular electrophysiological properties are not understood in this type of cells. The present study was designed to investigate functional ion channels in undifferentiated mouse cardiac c-kit(+) cells using approaches of whole cell patch voltage clamp, RT-PCR, and cell proliferation assay. It was found that three types of ionic currents were present in mouse cardiac c-kit(+) cells, including a delayed rectifier K(+) current (IK(DR)) inhibited by 4-aminopyridine (4-AP), an inward rectifier K(+) current (I(Kir)) decreased by Ba(2+), and a volume-sensitive chloride current (I(Cl.vol)) inhibited by 5-nitro-1-(3-phenylpropylamino) benzoic acid (NPPB). RT-PCR revealed that the corresponding ion channel genes, Kv1.1, Kv1.2, and Kv1.6 (for IK(DR)), Kir.1.1, Kir2.1, and Kir2.2 (likely responsible for I(Kir)), and Clcn3 (for I(Cl.vol)), were significant in mouse cardiac c-kit(+) cells. The inhibition of I(Cl.vol) with NPPB and niflumic acid, but not IK(DR) with 4-AP and tetraethylammonium, reduced cell proliferation and accumulated the cell progression at G(0)/G(1) phase in mouse cardiac c-kit(+) cells. Our results demonstrate that three types of functional ion channel currents (i.e., IK(DR), I(Kir), and I(Cl.vol)) are present in mouse cardiac c-kit(+) cells, and I(Cl.vol) participates in regulating cell proliferation.
Collapse
Affiliation(s)
- Yi Han
- Dept. of Pharmacology, Tongji Medical College, Huazhong Univ. of Science and Technology, Wuhan, China
| | | | | | | | | | | | | |
Collapse
|
21
|
Vignali M, Benfenati V, Caprini M, Anderova M, Nobile M, Ferroni S. The endocannabinoid anandamide inhibits potassium conductance in rat cortical astrocytes. Glia 2009; 57:791-806. [PMID: 19031444 DOI: 10.1002/glia.20807] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Endocannabinoids are a family of endogenous signaling molecules that modulate neuronal excitability in the central nervous system (CNS) by interacting with cannabinoid (CB) receptors. In spite of the evidence that astroglial cells also possess CB receptors, there is no information on the role of endocannabinoids in regulating CNS function through the modulation of ion channel-mediated homeostatic mechanisms in astroglial cells. We provide electrophysiological evidence that the two brain endocannabinoids anandamide (AEA) and 2-arachidonylglycerol (2-AG) markedly depress outward conductance mediated by delayed outward rectifier potassium current (IK(DR)) in primary cultured rat cortical astrocytes. Pharmacological experiments suggest that the effect of AEA does not result from the activation of known CB receptors. Moreover, neither the production of AEA metabolites nor variations in free cytosolic calcium are involved in the negative modulation of IK(DR). We show that the action of AEA is mediated by its interaction with the extracellular leaflet of the plasma membrane. Similar experiments performed in situ in cortical slices indicate that AEA downregulates IK(DR) in complex and passive astroglial cells. Moreover, IK(DR) is also inhibited by AEA in NG2 glia. Collectively, these results support the notion that endocannabinoids may exert their modulation of CNS function via the regulation of homeostatic function of the astroglial syncytium mediated by ion channel activity.
Collapse
Affiliation(s)
- M Vignali
- Department of Human and General Physiology, University of Bologna, 40127 Bologna, Italy
| | | | | | | | | | | |
Collapse
|
22
|
Wilcock DM, Vitek MP, Colton CA. Vascular amyloid alters astrocytic water and potassium channels in mouse models and humans with Alzheimer's disease. Neuroscience 2009; 159:1055-69. [PMID: 19356689 DOI: 10.1016/j.neuroscience.2009.01.023] [Citation(s) in RCA: 189] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2008] [Revised: 01/13/2009] [Accepted: 01/14/2009] [Indexed: 11/17/2022]
Abstract
The neurovascular unit (NVU) comprises cerebral blood vessels and surrounding astrocytes, neurons, perivascular microglia and pericytes. Astrocytes associated with the NVU are responsible for maintaining cerebral blood flow and ionic and osmotic balances in the brain. A significant proportion of individuals with Alzheimer's disease (AD) have vascular amyloid deposits (cerebral amyloid angiopathy, CAA) that contribute to the heterogeneous nature of the disease. To determine whether NVU astrocytes are affected by the accumulation of amyloid at cerebral blood vessels we examined astrocytic markers in four transgenic mouse models of amyloid deposition. These mouse models represent mild CAA, moderate CAA with disease progression to tau pathology and neuron loss, severe CAA and severe CAA with disease progression to tau pathology and neuron loss. We found that CAA and disease progression both resulted in distinct NVU astrocytic changes. CAA causes a loss of apparent glial fibrillary acidic protein (GFAP)-positive astrocytic end-feet and loss of water channels (aquaporin 4) localized to astrocytic end feet. The potassium channels Kir4.1, an inward rectifying potassium channel, and BK, a calcium-sensitive large-conductance potassium channel, were also lost. The anchoring protein, dystrophin 1, is common to these channels and was reduced in association with CAA. Disease progression was associated with a phenotypic switch in astrocytes indicated by a loss of GFAP-positive cells and a gain of S100 beta-positive cells. Aquaporin 4, Kir4.1 and dystrophin 1 were also reduced in autopsied brain tissue from individuals with AD that also display moderate and severe CAA. Together, these data suggest that damage to the neurovascular unit may be a factor in the pathogenesis of Alzheimer's disease.
Collapse
Affiliation(s)
- D M Wilcock
- Duke University Medical Center, Division of Neurology, Bryan Research Building, Box 2900, Research Drive, Durham, NC 27710, USA.
| | | | | |
Collapse
|
23
|
Rusznák Z, Szucs G. Spiral ganglion neurones: an overview of morphology, firing behaviour, ionic channels and function. Pflugers Arch 2008; 457:1303-25. [PMID: 18777041 DOI: 10.1007/s00424-008-0586-2] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2008] [Revised: 08/22/2008] [Accepted: 08/26/2008] [Indexed: 11/29/2022]
Abstract
The spiral ganglion cells provide the afferent innervation of the hair cells of the organ of Corti. Ninety-five percent of these cells (termed type I spiral ganglion neurones) are in synaptic contact with the inner hair cells, whereas about 5% of them are type II cells, which are responsible for the sensory innervation of the outer hair cells. To understand the function of the spiral ganglion neurones, it is important to explore their membrane properties, understand their activity patterns and describe the variety of ionic channels determining their behaviour. In this review, a brief description is given of the various experimental methods that allow the investigation of the spiral ganglion cells, followed by the discussion of their action potential firing patterns and ionic conductances. The presence, distribution and significance of the K(+) currents of the spiral ganglion cells are specifically addressed, along with the introduction of the putative subunit compositions of the relevant voltage-gated K(+) channels.
Collapse
Affiliation(s)
- Zoltán Rusznák
- Department of Physiology, Medical and Health Science Centre, University of Debrecen, Debrecen, P O Box 22, H-4012, Hungary.
| | | |
Collapse
|
24
|
Kim DS, Kim JE, Kwak SE, Won MH, Kang TC. Seizure activity affects neuroglial Kv1 channel immunoreactivities in the gerbil hippocampus. Brain Res 2007; 1151:172-87. [PMID: 17397809 DOI: 10.1016/j.brainres.2007.03.017] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2007] [Revised: 03/01/2007] [Accepted: 03/02/2007] [Indexed: 11/20/2022]
Abstract
In order to confirm the species-specific distribution of voltage-gated K(+) (Kv) channels and the definitive relationship between their immunoreactivities and seizure activity, we investigated Kv1 channel immunoreactivities in the hippocampus of seizure resistant (SR) and seizure sensitive (SS) gerbils. There was distinct difference of the Kv1 channel subtypes immunoreactivity in the hippocampi in both SR and SS gerbils. Kv1.1, Kv1.2, Kv1.3, Kv1.4, and Kv1.6 immunoreactivities in the SS gerbil hippocampus were lower than that in the SR gerbil hippocampus. However, Kv1 immunoreactivities were obviously presented in astrocyte within the stratum radiatum of the CA1 region of pre-seizure SS gerbil hippocampus. Following seizure-onset, Kv1 immunoreactivities (except Kv1.5) were markedly elevated, whereas their immunoreactivites in astrocytes were down-regulated. Therefore, the present study demonstrates that seizure activity may distinctly affect neuroglial Kv1 immunoreactivities in the gerbil hippocampus.
Collapse
Affiliation(s)
- Duk-Soo Kim
- Department of Anatomy, College of Medicine, Hallym University, Chunchon 200-702, Kangwon-Do, South Korea
| | | | | | | | | |
Collapse
|
25
|
Reyes-Haro D, Miledi R, García-Colunga J. Potassium currents in primary cultured astrocytes from the rat corpus callosum. ACTA ACUST UNITED AC 2006; 34:411-20. [PMID: 16902762 DOI: 10.1007/s11068-006-8727-z] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2004] [Revised: 02/23/2005] [Accepted: 04/08/2005] [Indexed: 11/25/2022]
Abstract
The corpus callosum (CC) is the main white matter tract in the brain and is involved in interhemispheric communication. Using the whole-cell voltage-clamp technique, a study was made of K(+)-currents in primary cultured astrocytes from the CC of newborn rats. These cells were positive to glial fibrillary acidic protein after culturing in Dulbecco's Modified Eagle Medium (> 95% of cells) or in serum-free neurobasal medium with G5 supplement (> 99% of cells). Astrocytes cultured in either medium displayed similar voltage-activated ion currents. In 81% of astrocytes, the current had a transient component and a sustained component, which were blocked by 4-aminopyridine and tetraethylammonium, respectively; and both had a reversal potential of -66 mV, indicating that they were carried by K(+) ions. Based on the Ba(2+)-sensitivity and activation kinetics of the K(+)-current, two groups of astrocytes were discerned. One group (55% of cells) displayed a strong Ba(2+) blockade of the K(+)-current whose activation kinetics, time course of decay, and the current-voltage relationship were modified by Ba(2+). This current was greatly blocked (52%) by Ba(2+) in a voltage-dependent way. Another group (45% of cells) presented weak Ba(2+)-blockade, which was only blocked 24% by Ba(2+). The activation kinetics and time course of decay of this current component were unaffected by Ba(2+). These results may help to understand better the roles of voltage-activated K(+)-currents in astrocytes from the rat CC in particular and glial cells in general.
Collapse
Affiliation(s)
- Daniel Reyes-Haro
- Instituto de Neurobiología, Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro, 76230, México
| | | | | |
Collapse
|
26
|
Feng JJ, Morest DK. Development of synapses and expression of a voltage-gated potassium channel in chick embryonic auditory nuclei. Hear Res 2006; 216-217:116-26. [PMID: 16530363 DOI: 10.1016/j.heares.2006.01.012] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/30/2005] [Revised: 01/12/2006] [Accepted: 01/12/2006] [Indexed: 11/30/2022]
Abstract
The potassium channel protein, Kv3.1, is abundantly expressed in the chick auditory pathway. Its b-isoform is found in nucleus magnocellularis, which receives the cochlear input, both before and after the establishment of synaptic connections. It is also present in cell cultures in the absence of any peripheral input. However, the expression of this isoform in the embryo has been shown to increase with development. Here, we address the question of the correlation between maturation of synapses in the auditory pathway and the pattern of expression of the b-isoform in a series of embryos prepared for immunohistochemistry at Hamburger-Hamilton stages equivalent to E10, E12, E14, and E17. We show here that this subunit translocates from the perinuclear cytoplasm to the cell membrane domain in nucleus magnocellularis at the time that cochlear nerve endings emerge as endbulbs of Held (E17). In nucleus laminaris, by this time, while abundant Kv3.1b occurs in the perinuclear cytoplasm, a translocation to the cell membrane domain has not yet occurred, and the mature peri-synaptic localization is delayed to a later stage. This difference suggests a hierarchy in the developmental expression of Kv3.1. An unexpected finding is the expression of the a-isoform of Kv3.1 in astrocytes, especially those which surround the developing nuclei and their connecting fibers. We also report here for the first time the presence of Kv3.1b in the initial segments of axons at the times when they begin to form. Our observations suggest that the Kv3.1 channel protein is regulated through mechanisms linked to the development of synaptic activity.
Collapse
Affiliation(s)
- Jane J Feng
- Department of Biology, Southern Connecticut State University, New Haven, CT 06515, USA
| | | |
Collapse
|
27
|
Wang K, Xue T, Tsang SY, Van Huizen R, Wong CW, Lai KW, Ye Z, Cheng L, Au KW, Zhang J, Li GR, Lau CP, Tse HF, Li RA. Electrophysiological Properties of Pluripotent Human and Mouse Embryonic Stem Cells. Stem Cells 2005; 23:1526-34. [PMID: 16091557 DOI: 10.1634/stemcells.2004-0299] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Pluripotent embryonic stem cells (ESCs) possess promising potential for cell-based therapies, but their electrophysiological properties have not been characterized. Here we describe the presence of ionic currents in mouse (m) and human (h) ESCs and their physiological function. In mESCs, tetraethylammonium (TEA)-sensitive depolarization-activated delayed rectifier K+ currents (IK(DR)) (8.6 +/- 0.9 pA/pF at +40 mV; IC50 = 1.2 +/- 0.3 mM), which contained components sensitive to 4-aminopyridine (4-AP) (IC50 = 0.5 +/- 0.1 mM) and 100 nM Ca2+-activated K+ current (IK(Ca)) blocker iberiotoxin (IBTX),were detected in 52.3% of undifferentiated cells.IK(DR) was similarly present in hESCs (approximately 100%) but with an approximately sixfold higher current density (47.5 +/- 7.9 pA/pF at +40 mV). When assayed by bromodeoxyurindine incorporation, application of TEA, 4-AP, or IBTX significantly reduced the proliferation of mESCs and hESCs in a dose-dependent manner (p < .05). A hyperpolarization-activated inward current (I(h)) (-2.2 +/- 0.4 pA/pF at -120 mV) was detected in 23% of mESCs but not hESCs. Neither Na(v) nor Ca(v) currents were detected in mESCs and hESCs. Microarray and reverse transcription-polymerase chain reaction analyses identified several candidate genes for the ionic currents discovered. Collectively, our results indicate that pluripotent ESCs functionally express several specialized ion channels and further highlight similarities and differences between the two species. Practical considerations for the therapeutic use of ESCs are discussed.
Collapse
Affiliation(s)
- Kai Wang
- Department of Medicine, University of Hong Kong, Hong Kong, China
| | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
28
|
Shibukawa Y, Chilton EL, Maccannell KA, Clark RB, Giles WR. K+ currents activated by depolarization in cardiac fibroblasts. Biophys J 2005; 88:3924-35. [PMID: 15764658 PMCID: PMC1305624 DOI: 10.1529/biophysj.104.054429] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
K(+) currents expressed in freshly dispersed rat ventricular fibroblasts have been studied using whole-cell patch-clamp recordings. Depolarizing voltage steps from a holding potential of -90 mV activated time- and voltage-dependent outward currents at membrane potentials positive to approximately -30 mV. The relatively slow activation kinetics exhibited strong dependence on the membrane potential. Selected changes in extracellular K(+) concentration ([K(+)](o)) revealed that the reversal potentials of the tail currents changed as expected for a K(+) equilibrium potential. The activation and inactivation kinetics of this K(+) current, as well as its recovery from inactivation, were well-fitted by single exponential functions. The steady-state inactivation was well described by a Boltzmann function with a half-maximal inactivation potential (V(0.5)) of -24 mV. Increasing [K(+)](o) (from 5 to 100 mM) shifted this V(0.5) in the hyperpolarizing direction by -11 mV. Inactivation was slowed by increasing [K(+)](o) to 100 mM, and the rate of recovery from inactivation was decreased after increasing [K(+)](o). Block of this K(+) current by extracellular tetraethylammonium also slowed inactivation. These [K(+)](o)-induced changes and tetraethylammonium effects suggest an important role for a C-type inactivation mechanism. This K(+) current was sensitive to dendrotoxin-I (100 nM) and rTityustoxin Kalpha (50 nM).
Collapse
Affiliation(s)
- Yoshiyuki Shibukawa
- Department of Physiology and Biophysics, Faculty of Medicine, University of Calgary, Alberta, Canada
| | | | | | | | | |
Collapse
|
29
|
Abstract
The adult CNS has the capacity to remyelinate following metabolic, toxic and autoimmune demyelinating insults. In cuprizone-induced demyelination, spontaneous remyelination occurs after the cessation of cuprizone diet. We used the cuprizone model to investigate the role of glial K(+) channels in oligodendroglial (OLG) regeneration and remyelination in vivo. We found that treatment with 4-aminopyridine (4-AP), a broad-spectrum K(+) channel antagonist, results in: (1) decreased number of oligodendroglial progenitors (OP) and OLGs; (2) diminished astrogliosis; and (3) decreased remyelination in the corpus callosum based on the immunoreactivity to myelin basic protein (MBP), Rip monoclonal antibody, and by electron microscopy. Our findings support the concept that glial K(+) channels play an important role during OLG regeneration and remyelination, a crucial factor to be considered during the development of therapeutic strategies to facilitate recovery in demyelinating diseases and spinal cord injury.
Collapse
Affiliation(s)
- Andrzej Bacia
- Department of Neurology and Committee on Neurobiology, Brain Research Institute, University of Chicago, Chicago, Illinois 60637, USA
| | | | | |
Collapse
|
30
|
Abstract
Depolarization-activated outward currents of bushy neurones of 6-14-day-old Wistar rats have been investigated in a brain slice preparation. Under current-clamp, the cells produced a single action potential at the beginning of suprathreshold depolarizing current steps. On voltage-clamp depolarizations, the cells produced a mixed outward K+ current that included a component with rapid activation and rapid inactivation, little TEA+ sensitivity, a half-inactivation voltage of -77 +/- 2 mV (T = 25 degrees C; n = 7; Mean +/- S.E.M.) and single-exponential recovery from inactivation (taurecovery= 12 +/- 1 ms at -100 mV; n=3). This transient component was identified as an A-type K+ current. Bushy cells developed a high-threshold TEA-sensitive K+ current that exhibited less prominent inactivation. These characteristics suggested that this current was associated with the activation of delayed rectifier K+ channels. Bushy neurones also possessed a low-threshold outward K+ current that showed partial inactivation and high 4-aminopyridine sensitivity. Part of this current component was blocked by 200 nmol/l dendrotoxin-I. Application of 100 micromol/l 4-aminopyridine changed the firing behaviour of the bushy neurones from the primary-like pattern to a much less rapidly adapting one, suggesting that the low-threshold current might have important roles in maintaining the physiological function of the cells.
Collapse
Affiliation(s)
- B Pál
- Department of Physiology, Medical and Health Science Centre, University of Debrecen, Debrecen, Hungary
| | | | | | | |
Collapse
|
31
|
Guihard G, Bellocq C, Grelet E, Escande D. Human Kv1.6 current displays a C-type-like inactivation when re-expressed in cos-7 cells. Biochem Biophys Res Commun 2003; 311:83-9. [PMID: 14575698 DOI: 10.1016/j.bbrc.2003.09.167] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The human Kv1.6K(+) channel was functionally re-expressed in COS-7 cells at different levels. Voltage-activated K(+) currents are recorded upon cell membrane depolarization independently of the level of Kv1.6 expression. The current acquires a fast inactivation when Kv1.6 expression is increased. Inactivation was not affected by divalent cations or by extracellular tetraethylammonium. We have characterized the inactivation properties in biophysical terms. The fraction of inactivated current and the kinetics of inactivation are increased as the cell becomes more depolarized. Inactivated current can be reactivated according to a bi-exponential function of time. Additional experiments indicate that Kv1.6 inactivation properties are close to those of a conventional C-type inactivation. This work suggests that the concentration of Kv1.6 channel in the cell membrane strongly modulates the kinetic properties of Kv1.6-induced K(+) current. The physiological implications of these modifications are discussed.
Collapse
Affiliation(s)
- G Guihard
- INSERM U533, Hotel-Dieu, 44035 Nantes Cedex, France.
| | | | | | | |
Collapse
|
32
|
Soliven B, Ma L, Bae H, Attali B, Sobko A, Iwase T. PDGF upregulates delayed rectifier via Src family kinases and sphingosine kinase in oligodendroglial progenitors. Am J Physiol Cell Physiol 2003; 284:C85-93. [PMID: 12475761 DOI: 10.1152/ajpcell.00145.2002] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
An increase in the expression of the delayed rectifier current (I(K)) has been shown to correlate with mitogenesis in many cell types. However, pathways involved in the upregulation of I(K) by growth factors in oligodendroglial progenitors (OPs) have not been well-elucidated. In this study, we found that treatment with platelet-derived growth factor (PDGF) and basic fibroblast growth factor but not ciliary neurotrophic factor resulted in increased I(K) density and upregulation of Kv1.5 and Kv1.6 mRNA transcripts. The effect of PDGF on I(K) was blocked by mimosine, a cell cycle inhibitor, and by genistein, a tyrosine kinase inhibitor. Using inhibitors of PDGF-activated pathways, we found that PDGF-induced upregulation of Kv1.5 and I(K) density involves Src family tyrosine kinases, sphingosine kinase, and intracellular Ca(2+) but not ERK1/2 or phosphatidylinositol 3-kinase pathways. Furthermore, agents that were effective inhibitors of PDGF-induced I(K) upregulation also attenuated OP proliferation, supporting the concept that I(K) is an important link between PDGF-activated signaling cascades and cell cycle progression.
Collapse
Affiliation(s)
- Betty Soliven
- Department of Neurology and Committee on Neurobiology, The Brain Research Institute, University of Chicago, 5841 S. Maryland, Chicago, IL 60637, USA.
| | | | | | | | | | | |
Collapse
|
33
|
Edwards L, Nashmi R, Jones O, Backx P, Ackerley C, Becker L, Fehlings MG. Upregulation of Kv 1.4 protein and gene expression after chronic spinal cord injury. J Comp Neurol 2002; 443:154-67. [PMID: 11793353 DOI: 10.1002/cne.10115] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
After spinal cord injury (SCI), white matter tracts are characterized by demyelination and increased sensitivity to the K(+) channel blocker 4-aminopyridine (4-AP). These effects appear to contribute to neurological impairment after SCI, although the molecular changes in K(+) channel subunit expression remain poorly understood. We examined changes in gene expression of the 4-AP-sensitive voltage-gated K(+) channel Kv 1.4 after chronic SCI in the rat. Quantitative immunoblotting showed that Kv 1.4 protein was significantly increased at 6 weeks, but not at 1 week, after SCI in spinal cord white matter. Kv 1.4 was localized to astrocytes, oligodendrocytes, and oligodendrocyte progenitor cells but not to axons in both the normal and the injured spinal cord white matter. Because glial cells proliferate after SCI, we used immunogold electron microscopy to quantify Kv 1.4 protein in individual glial cells and found a sixfold increase of Kv 1.4 in cells of the oligodendrocyte lineage after chronic injury. Finally, quantitative in situ hybridization showed that Kv 1.4 mRNA was significantly upregulated in spinal cord white matter, but not gray matter, after SCI. In summary, we show that Kv 1.4 is expressed in glial cells and not in axons in the rat spinal cord white matter and that its expression is markedly increased in cells of the oligodendrocyte lineage after chronic SCI. Given that K(+) channels play a role in glial cell proliferation, cells exhibiting changes in Kv 1.4 expression may represent proliferating oligodendroglia in the chronically injured spinal cord.
Collapse
Affiliation(s)
- Lori Edwards
- Division of Neurosurgery, The Toronto Western Research Institute, University Health Network, University of Toronto, Toronto, Ontario, Canada M5T 2S8
| | | | | | | | | | | | | |
Collapse
|
34
|
Modulation of Kv1.5 currents by Src tyrosine phosphorylation: potential role in the differentiation of astrocytes. J Neurosci 2000. [PMID: 10884308 DOI: 10.1523/jneurosci.20-14-05245.2000] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Using biophysical techniques, we previously have implicated outwardly rectifying potassium currents in the proliferation of cultured spinal cord astrocytes and have demonstrated that delayed rectifier potassium currents (I(Kd)), in particular, are upregulated on entry into the cell cycle and downregulated with cell cycle exit and differentiation. In the present study, using specific antibodies and antisense oligodeoxynucleotides, we show that this proliferation-dependent potassium current is mediated by the Shaker potassium channel Kv1.5. Downregulation of Kv1.5 protein by antisense oligodeoxynucleotides reduces astrocyte proliferation by approximately 50%, although no observed changes occur in Kv1.5 protein expression during spontaneous differentiation in culture. Tyrosine phosphorylation of Kv1.5, however, is downregulated markedly in differentiated cells but unaltered on cell cycle arrest. Using immunoprecipitation, we show that Kv1.5 is associated with Src family protein tyrosine kinases and that this association does not change with cell differentiation. Inhibition of kinase activity with the Src-specific inhibitor PP2 decreases Kv1.5 phosphorylation, reduces I(Kd), and inhibits astrocyte proliferation, specifically in the G(0)/G(1) phase of cell cycle. Conversely, I(Kd) are potentiated when active Src is present in the pipette. Transfection of quiescent astrocytes with constitutively active Src (Src Y529F) causes marked upregulation of astrocyte proliferation. These data suggest that Kv1. 5 is phosphorylated constitutively by Src kinases during growth and that downregulation of Src activity may underlie both astrocyte differentiation and the accompanying changes in delayed rectifier potassium channel activity.
Collapse
|
35
|
Abstract
Functional and molecular analysis of glial voltage- and ligand-gated ion channels underwent tremendous boost over the last 15 years. The traditional image of the glial cell as a passive, structural element of the nervous system was transformed into the concept of a plastic cell, capable of expressing a large variety of ion channels and neurotransmitter receptors. These molecules might enable glial cells to sense neuronal activity and to integrate it within glial networks, e.g., by means of spreading calcium waves. In this review we shall give a comprehensive summary of the main functional properties of ion channels and ionotropic receptors expressed by macroglial cells, i.e., by astrocytes, oligodendrocytes and Schwann cells. In particular we will discuss in detail glial sodium, potassium and anion channels, as well as glutamate, GABA and ATP activated ionotropic receptors. A majority of available data was obtained from primary cell culture, these results have been compared with corresponding studies that used acute tissue slices or freshly isolated cells. In view of these data, an active glial participation in information processing seems increasingly likely and a physiological role for some of the glial channels and receptors is gradually emerging.
Collapse
Affiliation(s)
- A Verkhratsky
- School of Biological Sciences, The University of Manchester, Oxford Road, Manchester, UK.
| | | |
Collapse
|
36
|
|
37
|
Expression of Kv1.1, a Shaker-like potassium channel, is temporally regulated in embryonic neurons and glia. J Neurosci 1998. [PMID: 9671659 DOI: 10.1523/jneurosci.18-15-05682.1998] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Kv1.1, a Shaker-like voltage-gated potassium channel, is strongly expressed in a variety of neurons in adult rodents, in which it appears to be involved in regulating neuronal excitability. Here we show that Kv1.1 is also expressed during embryonic development in the mouse, exhibiting two transient peaks of expression around embryonic day 9.5 (E9.5) and E14.5. Using both in situ hybridization and immunocytochemistry, we have identified several cell types and tissues that express Kv1.1 RNA and protein. At E9.5, Kv1.1 RNA and protein are detected transiently in non-neuronal cells in several regions of the early CNS, including rhombomeres 3 and 5 and ventricular zones in the mesencephalon and diencephalon. At E14.5, several cell types in both the CNS and peripheral nervous system express Kv1.1, including neuronal cells (sensory ganglia and outer aspect of cerebral hemispheres) and glial cells (radial glia, satellite cells, and Schwann cell precursors). These data show that Kv1.1 is expressed transiently in a variety of neuronal and non-neuronal cells during restricted periods of embryonic development. Although the functional roles of Kv1.1 in development are not understood, the cell-specific localization and timing of expression suggest this channel may play a role in several developmental processes, including proliferation, migration, or cell-cell adhesion.
Collapse
|