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Guley NH, Rogers JT, Del Mar NA, Deng Y, Islam RM, D'Surney L, Ferrell J, Deng B, Hines-Beard J, Bu W, Ren H, Elberger AJ, Marchetta JG, Rex TS, Honig MG, Reiner A. A Novel Closed-Head Model of Mild Traumatic Brain Injury Using Focal Primary Overpressure Blast to the Cranium in Mice. J Neurotrauma 2016; 33:403-22. [PMID: 26414413 PMCID: PMC4761824 DOI: 10.1089/neu.2015.3886] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Mild traumatic brain injury (TBI) from focal head impact is the most common form of TBI in humans. Animal models, however, typically use direct impact to the exposed dura or skull, or blast to the entire head. We present a detailed characterization of a novel overpressure blast system to create focal closed-head mild TBI in mice. A high-pressure air pulse limited to a 7.5 mm diameter area on the left side of the head overlying the forebrain is delivered to anesthetized mice. The mouse eyes and ears are shielded, and its head and body are cushioned to minimize movement. This approach creates mild TBI by a pressure wave that acts on the brain, with minimal accompanying head acceleration-deceleration. A single 20-psi blast yields no functional deficits or brain injury, while a single 25-40 psi blast yields only slight motor deficits and brain damage. By contrast, a single 50-60 psi blast produces significant visual, motor, and neuropsychiatric impairments and axonal damage and microglial activation in major fiber tracts, but no contusive brain injury. This model thus reproduces the widespread axonal injury and functional impairments characteristic of closed-head mild TBI, without the complications of systemic or ocular blast effects or head acceleration that typically occur in other blast or impact models of closed-skull mild TBI. Accordingly, our model provides a simple way to examine the biomechanics, pathophysiology, and functional deficits that result from TBI and can serve as a reliable platform for testing therapies that reduce brain pathology and deficits.
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Affiliation(s)
- Natalie H. Guley
- Department of Anatomy and Neurobiology, The University of Tennessee Health Science Center, Memphis, Tennessee
| | - Joshua T. Rogers
- Department of Anatomy and Neurobiology, The University of Tennessee Health Science Center, Memphis, Tennessee
| | - Nobel A. Del Mar
- Department of Anatomy and Neurobiology, The University of Tennessee Health Science Center, Memphis, Tennessee
| | - Yunping Deng
- Department of Anatomy and Neurobiology, The University of Tennessee Health Science Center, Memphis, Tennessee
| | - Rafiqul M. Islam
- Department of Anatomy and Neurobiology, The University of Tennessee Health Science Center, Memphis, Tennessee
- Department of Anatomy and Histology, Bangladesh Agricultural University, Mymensingh, Bangladesh
| | - Lauren D'Surney
- Department of Anatomy and Neurobiology, The University of Tennessee Health Science Center, Memphis, Tennessee
- Department of Ophthalmology, The University of Tennessee Health Science Center, Memphis, Tennessee
| | - Jessica Ferrell
- Department of Anatomy and Neurobiology, The University of Tennessee Health Science Center, Memphis, Tennessee
| | - Bowei Deng
- Department of Anatomy and Neurobiology, The University of Tennessee Health Science Center, Memphis, Tennessee
| | - Jessica Hines-Beard
- Department of Ophthalmology, The University of Tennessee Health Science Center, Memphis, Tennessee
- Department of Ophthalmology and Visual Sciences, Vanderbilt University, Nashville, Tennessee
| | - Wei Bu
- Department of Anatomy and Neurobiology, The University of Tennessee Health Science Center, Memphis, Tennessee
| | - Huiling Ren
- Department of Anatomy and Neurobiology, The University of Tennessee Health Science Center, Memphis, Tennessee
| | - Andrea J. Elberger
- Department of Anatomy and Neurobiology, The University of Tennessee Health Science Center, Memphis, Tennessee
| | | | - Tonia S. Rex
- Department of Ophthalmology, The University of Tennessee Health Science Center, Memphis, Tennessee
- Department of Ophthalmology and Visual Sciences, Vanderbilt University, Nashville, Tennessee
| | - Marcia G. Honig
- Department of Anatomy and Neurobiology, The University of Tennessee Health Science Center, Memphis, Tennessee
| | - Anton Reiner
- Department of Anatomy and Neurobiology, The University of Tennessee Health Science Center, Memphis, Tennessee
- Department of Ophthalmology, The University of Tennessee Health Science Center, Memphis, Tennessee
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2
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Kiyatkin ME, Feng B, Schwartz ES, Gebhart GF. Combined genetic and pharmacological inhibition of TRPV1 and P2X3 attenuates colorectal hypersensitivity and afferent sensitization. Am J Physiol Gastrointest Liver Physiol 2013; 305:G638-48. [PMID: 23989007 PMCID: PMC3840237 DOI: 10.1152/ajpgi.00180.2013] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The ligand-gated channels transient receptor potential vanilloid 1 (TRPV1) and P2X3 have been reported to facilitate colorectal afferent neuron sensitization, thus contributing to organ hypersensitivity and pain. In the present study, we hypothesized that TRPV1 and P2X3 cooperate to modulate colorectal nociception and afferent sensitivity. To test this hypothesis, we employed TRPV1-P2X3 double knockout (TPDKO) mice and channel-selective pharmacological antagonists and evaluated combined channel contributions to behavioral responses to colorectal distension (CRD) and afferent fiber responses to colorectal stretch. Baseline responses to CRD were unexpectedly greater in TPDKO compared with control mice, but zymosan-produced CRD hypersensitivity was absent in TPDKO mice. Relative to control mice, proportions of mechanosensitive and -insensitive pelvic nerve afferent classes were not different in TPDKO mice. Responses of mucosal and serosal class afferents to mechanical probing were unaffected, whereas responses of muscular (but not muscular/mucosal) afferents to stretch were significantly attenuated in TPDKO mice; sensitization of both muscular and muscular/mucosal afferents by inflammatory soup was also significantly attenuated. In pharmacological studies, the TRPV1 antagonist A889425 and P2X3 antagonist TNP-ATP, alone and in combination, applied onto stretch-sensitive afferent endings attenuated responses to stretch; combined antagonism produced greater attenuation. In the aggregate, these observations suggest that 1) genetic manipulation of TRPV1 and P2X3 leads to reduction in colorectal mechanosensation peripherally and compensatory changes and/or disinhibition of other channels centrally, 2) combined pharmacological antagonism produces more robust attenuation of mechanosensation peripherally than does antagonism of either channel alone, and 3) the relative importance of these channels appears to be enhanced in colorectal hypersensitivity.
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Affiliation(s)
- Michael E. Kiyatkin
- Center for Pain Research, Department of Anesthesiology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Bin Feng
- Center for Pain Research, Department of Anesthesiology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Erica S. Schwartz
- Center for Pain Research, Department of Anesthesiology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - G. F. Gebhart
- Center for Pain Research, Department of Anesthesiology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania
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3
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Nair A, Simonetti M, Birsa N, Ferrari MD, van den Maagdenberg AMJM, Giniatullin R, Nistri A, Fabbretti E. Familial hemiplegic migraine Ca(v)2.1 channel mutation R192Q enhances ATP-gated P2X3 receptor activity of mouse sensory ganglion neurons mediating trigeminal pain. Mol Pain 2010; 6:48. [PMID: 20735819 PMCID: PMC2940876 DOI: 10.1186/1744-8069-6-48] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2010] [Accepted: 08/24/2010] [Indexed: 02/01/2023] Open
Abstract
BACKGROUND The R192Q mutation of the CACNA1A gene, encoding for the α1 subunit of voltage-gated P/Q Ca2+ channels (Ca(v)2.1), is associated with familial hemiplegic migraine-1. We investigated whether this gain-of-function mutation changed the structure and function of trigeminal neuron P2X3 receptors that are thought to be important contributors to migraine pain. RESULTS Using in vitro trigeminal sensory neurons of a mouse genetic model knockin for the CACNA1A R192Q mutation, we performed patch clamp recording and intracellular Ca2+ imaging that showed how these knockin ganglion neurons generated P2X3 receptor-mediated responses significantly larger than wt neurons. These enhanced effects were reversed by the Ca(v)2.1 blocker ω-agatoxin. We, thus, explored intracellular signalling dependent on kinases and phosphatases to understand the molecular regulation of P2X3 receptors of knockin neurons. In such cells we observed strong activation of CaMKII reversed by ω-agatoxin treatment. The CaMKII inhibitor KN-93 blocked CaMKII phosphorylation and the hyperesponsive P2X3 phenotype. Although no significant difference in membrane expression of knockin receptors was found, serine phosphorylation of knockin P2X3 receptors was constitutively decreased and restored by KN-93. No change in threonine or tyrosine phosphorylation was detected. Finally, pharmacological inhibitors of the phosphatase calcineurin normalized the enhanced P2X3 receptor responses of knockin neurons and increased their serine phosphorylation. CONCLUSIONS The present results suggest that the CACNA1A mutation conferred a novel molecular phenotype to P2X3 receptors of trigeminal ganglion neurons via CaMKII-dependent activation of calcineurin that selectively impaired the serine phosphorylation state of such receptors, thus potentiating their effects in transducing trigeminal nociception.
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Affiliation(s)
- Asha Nair
- Neurobiology Sector, International School for Advanced Studies (SISSA), Via Bonomea 265, 34136 Trieste, Italy
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4
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Cross-inhibition between native and recombinant TRPV1 and P2X3 receptors. Pain 2009; 143:26-36. [DOI: 10.1016/j.pain.2009.01.006] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2008] [Revised: 12/16/2008] [Accepted: 01/05/2009] [Indexed: 11/19/2022]
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5
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Chung RS, Penkowa M, Dittmann J, King CE, Bartlett C, Asmussen JW, Hidalgo J, Carrasco J, Leung YKJ, Walker AK, Fung SJ, Dunlop SA, Fitzgerald M, Beazley LD, Chuah MI, Vickers JC, West AK. Redefining the role of metallothionein within the injured brain: extracellular metallothioneins play an important role in the astrocyte-neuron response to injury. J Biol Chem 2008; 283:15349-58. [PMID: 18334482 DOI: 10.1074/jbc.m708446200] [Citation(s) in RCA: 117] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A number of intracellular proteins that are protective after brain injury are classically thought to exert their effect within the expressing cell. The astrocytic metallothioneins (MT) are one example and are thought to act via intracellular free radical scavenging and heavy metal regulation, and in particular zinc. Indeed, we have previously established that astrocytic MTs are required for successful brain healing. Here we provide evidence for a fundamentally different mode of action relying upon intercellular transfer from astrocytes to neurons, which in turn leads to uptake-dependent axonal regeneration. First, we show that MT can be detected within the extracellular fluid of the injured brain, and that cultured astrocytes are capable of actively secreting MT in a regulatable manner. Second, we identify a receptor, megalin, that mediates MT transport into neurons. Third, we directly demonstrate for the first time the transfer of MT from astrocytes to neurons over a specific time course in vitro. Finally, we show that MT is rapidly internalized via the cell bodies of retinal ganglion cells in vivo and is a powerful promoter of axonal regeneration through the inhibitory environment of the completely severed mature optic nerve. Our work suggests that the protective functions of MT in the central nervous system should be widened from a purely astrocytic focus to include extracellular and intra-neuronal roles. This unsuspected action of MT represents a novel paradigm of astrocyte-neuronal interaction after injury and may have implications for the development of MT-based therapeutic agents.
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Affiliation(s)
- Roger S Chung
- NeuroRepair Group, Menzies Research Institute, University of Tasmania, Hobart, Tasmania 7001, Australia.
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6
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Fountain SJ, North RA. A C-terminal lysine that controls human P2X4 receptor desensitization. J Biol Chem 2006; 281:15044-9. [PMID: 16533808 DOI: 10.1074/jbc.m600442200] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Receptor desensitization can determine the time course of transmitter action and profoundly alter sensitivity to drugs. Among P2X receptors, ion currents through homomeric P2X4 receptors exhibit intermediate desensitization when compared with P2X1 and P2X3 (much faster) and P2X2 and P2X7 (slower). We recorded membrane currents in HEK293 cells transfected to express the human P2X4 receptor. The decline in current during a 4-s application of ATP (100 microm) was about 30%; this was not different during whole-cell or perforated patch recording. Alanine-scanning mutagenesis of the intracellular C terminus identified two positions with much accelerated desensitization kinetics (Lys373: 92% and Tyr374: 74%). At position 373, substitution of Arg or Cys also strongly accelerated desensitization: however, in the case of K373C the wild-type phenotype was fully restored by adding ethylammonium methanethiosulfonate. At position 374, phenylalanine could replace tyrosine. These results indicate that wild-type desensitization properties requires an aromatic moiety at position 374 and an amino rather than a guanidino group at position 373. These residues lie between previously identified motifs involved in membrane trafficking (YXXXK and YXXGL) and implicates the C-terminal also in rearrangements leading to channel closing during the presence of agonist.
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Affiliation(s)
- Samuel J Fountain
- Faculty of Life Sciences, Michael Smith Building, University of Manchester, Manchester, M13 9PT, United Kingdom.
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7
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Chung RS, Staal JA, McCormack GH, Dickson TC, Cozens MA, Chuckowree JA, Quilty MC, Vickers JC. Mild Axonal Stretch Injury In Vitro Induces a Progressive Series of Neurofilament Alterations Ultimately Leading to Delayed Axotomy. J Neurotrauma 2005; 22:1081-91. [PMID: 16238485 DOI: 10.1089/neu.2005.22.1081] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
We report a new model of transient axonal stretch injury involving pressurized fluid deflection of bundles of axons, resulting in a transient 1-6% increase in original axon length to investigate the slow progression of axonal alterations that are characteristic of diffuse axonal injury (DAI). We found no discernable difference in axon bundle morphology or cytoskeletal neurofilament protein arrangement between unstretched and stretched axonal bundles at 24 h post-injury. However, by 48 h post-injury, there was a stereotypical response of stretched axons involving characteristic neurofilament alterations that bear similarities to in vivo neuronal responses associated with DAI that have been reported previously. For instance, neurofilament protein immunoreactivity (SMI-312) was increased in axons contained within 51% of all injured axon bundles at 48 h compared to surrounding unstretched axon bundles, suggestive of neurofilament compaction. Furthermore, axonal bundle derangement occurred in 25% of injured axon bundles, with individual fibres segregating from each other and becoming undulating and wavy. By 72 h post-stretch, 70% of injured axon bundles underwent secondary axotomy, becoming completely severed at the site of initial stretch injury. While these results suggest a temporal series of stereotypical responses of axons to injury, we were able to distinguish very clear differences between mildly (100-103% increase in original axonal length) injured and strongly injured (106%+) axons. For instance, mildly injured axons developed increased neurofilament immunoreactivtity (SMI-312) within 48 h, and the marked development of ring-like neurofilament immunoreactive structures within axonal bundles, which were rarely axotomized. Conversely, at more severe strain levels increased neurofilament immunoreactivity was less apparent, while axons often became distorted and disorganised within axonal bundles and eventually became completely disconnected. Almost no ring-like neurofilament structures were observed in these severely injured axonal bundles. This suggests that axons do not respond in a stereotypical manner to a transient stretch insult, and indeed that variable degrees of stretch injury activate different responses within axons, with dramatically different outcomes. Hence, it is possible that the cytoskeletal characteristics that we have used in this study may be useful parameters for discriminating between mildly and severely injured axons following TBI.
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Affiliation(s)
- Roger S Chung
- NeuroRepair Group, School of Medicine, University of Tasmania, Hobart, Tasmania, Australia.
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8
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Mohapatra DP, Nau C. Regulation of Ca2+-dependent desensitization in the vanilloid receptor TRPV1 by calcineurin and cAMP-dependent protein kinase. J Biol Chem 2005; 280:13424-32. [PMID: 15691846 DOI: 10.1074/jbc.m410917200] [Citation(s) in RCA: 223] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The vanilloid receptor TRPV1 is a polymodal nonselective cation channel of nociceptive sensory neurons involved in the perception of inflammatory pain. TRPV1 exhibits desensitization in a Ca2+-dependent manner upon repeated activation by capsaicin or protons. The cAMP-dependent protein kinase (PKA) decreases desensitization of TRPV1 by directly phosphorylating the channel presumably at sites Ser116 and Thr370. In the present study we investigated the influence of protein phosphatase 2B (calcineurin) on Ca2+-dependent desensitization of capsaicin- and proton-activated currents. By using site-directed mutagenesis, we generated point mutations at PKA and protein kinase C consensus sites and studied wild type (WT) and mutant channels transiently expressed in HEK293t or HeLa cells under whole cell voltage clamp. We found that intracellular application of the cyclosporin A.cyclophilin A complex (CsA.CyP), a specific inhibitor of calcineurin, significantly decreased desensitization of capsaicin- or proton-activated TRPV1-WT currents. This effect was similar to that obtained by extracellular application of forskolin (FSK), an indirect activator of PKA. Simultaneous applications of CsA.CyP and FSK in varying concentrations suggested that these substances acted independently from each other. In mutation T370A, application of CsA.CyP did not reduce desensitization of capsaicin-activated currents as compared with WT and to mutant channels S116A and T144A. In a double mutation at candidate protein kinase C phosphorylation sites, application of CsA.CyP or FSK decreased desensitization of capsaicin-activated currents similar to WT channels. We conclude that Ca2+-dependent desensitization of TRPV1 might be in part regulated through channel dephosphorylation by calcineurin and channel phosphorylation by PKA possibly involving Thr370 as a key amino acid residue.
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Affiliation(s)
- Durga Prasanna Mohapatra
- Department of Anesthesiology, Friedrich-Alexander-University Erlangen-Nuremberg, 91054 Erlangen, Germany
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9
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Wildman SS, Brown SG, Rahman M, Noel CA, Churchill L, Burnstock G, Unwin RJ, King BF. Sensitization by extracellular Ca(2+) of rat P2X(5) receptor and its pharmacological properties compared with rat P2X(1). Mol Pharmacol 2002; 62:957-66. [PMID: 12237343 DOI: 10.1124/mol.62.4.957] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The recombinant rat P2X(5) (rP2X(5)) receptor, a poorly understood ATP-gated ion channel, was studied under voltage-clamp conditions and compared with the better understood homomeric rP2X(1) receptor with which it may coexist in vivo. Expressed in defolliculated Xenopus laevis oocytes, rP2X(5) responded to ATP with slowly desensitizing inward currents that, for successive responses, ran down in the presence of extracellular Ca(2+) (1.8 mM). Replacement of Ca(2+) with either Ba(2+) or Mg(2+) prevented rundown, although agonist responses were very small, whereas reintroduction of Ca(2+) for short periods of time (<300 s) before and during agonist application yielded consistently larger responses. Using this Ca(2+)-pulse conditioning, rP2X(5) responded to ATP and other nucleotides (ATP, 2-methylthio-ATP, adenosine-5'-O-(thiotriphosphate), 2'-&-3'-O-(4-benzoylbenzoyl)-ATP, alpha,beta-methylene-ATP, P(1)-P((4))-diadenosine-5'-phosphate, and more) with pEC(50) values within 1 log unit of respective determinations for rP2X(1). Only GTP was selective for rP2X(5), although 60-fold less potent than ATP. At rP2X(5), lowering extracellular pH reduced the potency and efficacy of ATP, whereas extracellular Zn(2+) ions (0.1-1000 microM) potentiated then inhibited ATP responses in a concentration-dependent manner. However, these modulators affected rP2X(1) receptors in subtly different ways-with increasing H(+) and Zn(2+) ion concentrations reducing agonist potency. For P2 receptor antagonists, the potency order at rP2X(5) was pyridoxal-5-phosphate-6-azophenyl-2',4'-disulfonic acid (PPADS) > 2',3'-O-(2,4,6-trinitrophenyl)ATP (TNP-ATP) > suramin > reactive blue 2 (RB-2) > diinosine pentaphosphate (Ip(5)I). In contrast, the potency order at rP2X(1) was TNP-ATP = Ip(5)I > PPADS > suramin = RB-2. Thus, the Ca(2+)-sensitized homomeric rP2X(5) receptor is similar in agonist profile to homomeric rP2X(1)-although it can be distinguished from the latter by GTP agonism, antagonist profile, and the modulatory effects of H(+) and Zn(2+) ions.
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Affiliation(s)
- Scott S Wildman
- Department of Physiology (Centre for Nephrology), Royal Free and University College Medical School, London, United Kingdom
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10
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Abstract
ATP, besides an intracellular energy source, is an agonist when applied to a variety of different cells including cardiomyocytes. Sources of ATP in the extracellular milieu are multiple. Extracellular ATP is rapidly degraded by ectonucleotidases. Today ionotropic P2X(1--7) receptors and metabotropic P2Y(1,2,4,6,11) receptors have been cloned and their mRNA found in cardiomyocytes. On a single cardiomyocyte, micromolar ATP induces nonspecific cationic and Cl(-) currents that depolarize the cells. ATP both increases directly via a G(s) protein and decreases Ca(2+) current. ATP activates the inward-rectifying currents (ACh- and ATP-activated K(+) currents) and outward K(+) currents. P2-purinergic stimulation increases cAMP by activating adenylyl cyclase isoform V. It also involves tyrosine kinases to activate phospholipase C-gamma to produce inositol 1,4,5-trisphosphate and Cl(-)/HCO(3)(-) exchange to induce a large transient acidosis. No clear correlation is presently possible between an effect and the activation of a given P2-receptor subtype in cardiomyocytes. ATP itself is generally a positive inotropic agent. Upon rapid application to cells, ATP induces various forms of arrhythmia. At the tissue level, arrhythmia could be due to slowing of electrical spread after both Na(+) current decrease and cell-to-cell uncoupling as well as cell depolarization and Ca(2+) current increase. In as much as the information is available, this review also reports analog effects of UTP and diadenosine polyphosphates.
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Affiliation(s)
- G Vassort
- Institut National de la Santé et de la Recherche Médicale U. 390, Centre Hospitalier Universitaire Arnaud de Villeneuve, Montpellier, France.
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11
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Dickson TC, Adlard PA, Vickers JC. Sequence of cellular changes following localized axotomy to cortical neurons in glia-free culture. J Neurotrauma 2000; 17:1095-103. [PMID: 11101211 DOI: 10.1089/neu.2000.17.1095] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
This study utilizes an in vitro model of localized physical injury to axons to examine the specific responses of neocortical neurons to trauma in isolation from glia cell types. The neuronal response to axotomy was closely linked with nerve cell maturity. Cultures grown for 14 days in vitro showed no accumulation of either neurofilaments or, the axonal sprouting marker, GAP43, within injured axons following injury. In older cultures (21 days in vitro), however, temporally distinct axonal changes were evident following transection of axonal bundles. At 12 h postinjury, these included extensive accumulation of neurofilaments into ring-like structures within the cut stumps and an increase in punctate GAP43 labelling throughout the damaged area. At 24 h postinjury, bulb-like accumulations of neurofilaments were also present within the transected axons. Finally at 3 days postinjury, distinct GAP43 and neurofilament immunolabeled axons, and GAP43 immunopositive growth cones, emanated from the cut stump. These results indicate that injured axons of mature neurons undergo a defined series of reactive changes, ultimately culminating in a sprouting response, which occur independently of the presence or effects of glial cell populations.
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Affiliation(s)
- T C Dickson
- Department of Pathology, Clinical School, University of Tasmania, Hobart, Australia
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12
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Dunn PM, Liu M, Zhong Y, King BF, Burnstock G. Diinosine pentaphosphate: an antagonist which discriminates between recombinant P2X(3) and P2X(2/3) receptors and between two P2X receptors in rat sensory neurones. Br J Pharmacol 2000; 130:1378-84. [PMID: 10903979 PMCID: PMC1572177 DOI: 10.1038/sj.bjp.0703404] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
1. We have compared the antagonist activity of trinitrophenyl-ATP (TNP-ATP) and diinosine pentaphosphate (Ip(5)I) on recombinant P2X receptors expressed in Xenopus oocytes with their actions at native P2X receptors in sensory neurones from dorsal root and nodose ganglia. 2. Slowly-desensitizing responses to alpha,beta-methylene ATP (alpha,beta-meATP) recorded from oocytes expressing P2X(2/3) receptors were inhibited by TNP-ATP at sub-micromolar concentrations. However, Ip(5)I at concentrations up to 30 microM was without effect. 3. Nodose ganglion neurones responded to alpha,beta-meATP with slowly-desensitizing inward currents. These were inhibited by TNP-ATP (IC(50), 20 nM), but not by Ip(5)I at concentrations up to 30 microM. 4. In DRG neurones that responded to ATP with a rapidly-desensitizing inward current, the response was inhibited by TNP-ATP with an IC(50) of 0.8 nM. These responses were also inhibited by Ip(5)I with an IC(50) of 0.1 microM. Both antagonists are known to inhibit homomeric P2X(3) receptors. 5. Some DRG neurones responded to alpha,beta-meATP with a biphasic inward current, consisting of transient and sustained components. While the transient current was abolished by 1 microM Ip(5)I, the sustained component remained unaffected. 6. In conclusion, Ip(5)I is a potent antagonist at homomeric P2X(3) receptors but not at heteromeric P2X(2/3) receptors, and therefore should be a useful tool for elucidating the subunit composition of native P2X receptors.
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MESH Headings
- Adenosine Triphosphate/analogs & derivatives
- Adenosine Triphosphate/pharmacology
- Animals
- Animals, Newborn
- DNA, Complementary/administration & dosage
- DNA, Complementary/genetics
- DNA, Recombinant/administration & dosage
- DNA, Recombinant/genetics
- Dinucleoside Phosphates/pharmacology
- Dose-Response Relationship, Drug
- Female
- Ganglia, Spinal/cytology
- Ganglia, Spinal/drug effects
- Ganglia, Spinal/physiology
- Membrane Potentials/drug effects
- Neurons, Afferent/cytology
- Neurons, Afferent/drug effects
- Neurons, Afferent/physiology
- Nodose Ganglion/cytology
- Nodose Ganglion/drug effects
- Nodose Ganglion/physiology
- Oocytes
- Rats
- Receptors, Purinergic P2/genetics
- Receptors, Purinergic P2/physiology
- Receptors, Purinergic P2X2
- Receptors, Purinergic P2X3
- Xenopus
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Affiliation(s)
- P M Dunn
- Autonomic Neuroscience Institute, Royal Free and University College Medical School, London.
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13
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Piper AS, Docherty RJ. One-way cross-desensitization between P2X purinoceptors and vanilloid receptors in adult rat dorsal root ganglion neurones. J Physiol 2000; 523 Pt 3:685-96. [PMID: 10718747 PMCID: PMC2269837 DOI: 10.1111/j.1469-7793.2000.t01-1-00685.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
1. Capsaicin and ATP can activate ligand-gated cation channels in nociceptive rat dorsal root ganglion (DRG) neurones. We have studied cross-desensitization between these two agents in rat isolated DRG neurones using the whole-cell voltage-clamp technique. 2. ATP (10 microM) activated an inward current in DRG neurones at a holding potential of -60 mV. ATP evoked 'fast' responses that underwent rapid activation and desensitization, 'slow' responses that activated and desensitized more slowly, or responses that displayed a mixture of these two characteristics. The time course of the response to ATP was not related obviously to capsaicin sensitivity. 3. Prior application of capsaicin (0.5 microM) increased the proportion of cells displaying only fast responses to ATP (10 microM) suggesting that cross-desensitization had occurred between capsaicin and the slow component of the ATP response. Prior desensitization to ATP had no apparent effect on the inward current response to capsaicin (0.5 microM). 4. Cross-desensitization between capsaicin and ATP was Ca2+ dependent. 5. Changing the membrane holding potential (Vh) to +40 mV for brief period before applying ATP at -60 mV had a similar effect to capsaicin, i.e. the proportion of cells displaying only fast responses to ATP was increased significantly. This effect of depolarization was not Ca2+ dependent. 6. The heterogenity of responses to ATP is probably due to co-expression of homomeric P2X3 receptors and heteromeric receptors comprising P2X3 subunits with other P2X subunits. We propose that the change in time course of the ATP response produced by prior desensitization to capsaicin is due to selective cross-desensitization with the heteromeric P2X receptors.
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Affiliation(s)
- A S Piper
- Centre for Neuroscience and Department of Pharmacology, GKT School of Biomedical Sciences, King's College London, St Thomas' Hospital Campus, Lambeth Palace Road, London SE1 7EH, UK
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Herzig S, Neumann J. Effects of serine/threonine protein phosphatases on ion channels in excitable membranes. Physiol Rev 2000; 80:173-210. [PMID: 10617768 DOI: 10.1152/physrev.2000.80.1.173] [Citation(s) in RCA: 202] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
This review deals with the influence of serine/threonine-specific protein phosphatases on the function of ion channels in the plasma membrane of excitable tissues. Particular focus is given to developments of the past decade. Most of the electrophysiological experiments have been performed with protein phosphatase inhibitors. Therefore, a synopsis is required incorporating issues from biochemistry, pharmacology, and electrophysiology. First, we summarize the structural and biochemical properties of protein phosphatase (types 1, 2A, 2B, 2C, and 3-7) catalytic subunits and their regulatory subunits. Then the available pharmacological tools (protein inhibitors, nonprotein inhibitors, and activators) are introduced. The use of these inhibitors is discussed based on their biochemical selectivity and a number of methodological caveats. The next section reviews the effects of these tools on various classes of ion channels (i.e., voltage-gated Ca(2+) and Na(+) channels, various K(+) channels, ligand-gated channels, and anion channels). We delineate in which cases a direct interaction between a protein phosphatase and a given channel has been proven and where a more complex regulation is likely involved. Finally, we present ideas for future research and possible pathophysiological implications.
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Affiliation(s)
- S Herzig
- Institut für Pharmakologie, Universität Köln, Köln, Germany.
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Naemsch LN, Weidema AF, Sims SM, Underhill TM, Dixon SJ. P2X(4) purinoceptors mediate an ATP-activated, non-selective cation current in rabbit osteoclasts. J Cell Sci 1999; 112 ( Pt 23):4425-35. [PMID: 10564660 DOI: 10.1242/jcs.112.23.4425] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Extracellular nucleotides act as signaling molecules in numerous tissues. In bone, nucleotides stimulate osteoclast formation and activity; however, the receptors and signaling mechanisms underlying these effects have yet to be identified. To identify specific P2X purinoceptor subtypes in osteoclasts, degenerate oligonucleotide primers were used to PCR-amplify DNA fragments from a rabbit osteoclast cDNA library. A 372-base-pair fragment was obtained that encoded an amino acid sequence with 88% identity to the rat P2X(4) purinoceptor. The presence of P2X(4) mRNA in purified osteoclasts was confirmed by reverse transcription-PCR. Endogenous purinoceptors were functionally characterized in isolated rabbit osteoclasts by patch-clamp recording in whole-cell configuration. At negative membrane potentials, application of ATP or ADP rapidly activated an inward current followed by an outward current. In contrast, UTP or ADPbetaS elicited only an outward current, due to activation of a Ca(2+)-dependent K(+) conductance. The initial inward current was non-selective for cations and inactivated during agonist application. Furthermore, the inward current was insensitive to suramin and Cibacron blue, and was potentiated by Zn(2+). These characteristics are consistent with properties of P2X(4) purinoceptors. Activation of P2X(4) purinoceptors leads to cation influx and depolarization. Nucleotides, released at sites of trauma or inflammation, may act through these receptors on osteoclasts to stimulate bone resorption.
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Affiliation(s)
- L N Naemsch
- Department of Physiology, Division of Oral Biology, Faculty of Medicine and Dentistry, The University of Western Ontario, London, Ontario, Canada, N6A 5C1
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Abstract
ATP has been identified as an excitatory neurotransmitter in both the CNS and peripheral nervous system; however, little is known about the functional properties of ATP-gated channels in central neurons. Here we used a culture preparation of the postnatal rat retina to test the responsiveness of identified retinal ganglion cells (RGCs) and putative amacrines to exogenous ATP and other purinoceptor agonists. Rapidly activating ATP-induced currents (IATP) were exclusively generated in a subpopulation (approximately 65%) of RGCs. The latter were identified by Thy1.1 immunostaining, repetitive firing patterns, and activation of glutamatergic autaptic currents. None of the putative amacrine cells was ATP-sensitive. IATP could be induced with ATP, ADP, and alpha,beta-mATP but not with adenosine. It was antagonized by suramin. The current-voltage relationship of IATP showed marked inward rectification. Dose-response analysis yielded an EC50 of 14.5 microM, with a Hill coefficient of 0.9. Noise analysis of IATP suggested a mean single channel conductance of 2.3 pS. Retinal P2X purinoceptor channels exhibited a high permeability for Ca2+. PCa/PCs obtained from reversal potentials of IATP under bi-ionic conditions amounted to 2. 2 +/- 0.7. In the majority of cells, the decay of IATP was biphasic. The degree of current inactivation during the first 2 sec of agonist application was highly variable. Heterogeneity was also found with respect to the sensitivity to ADP and alpha,beta-mATP and the blocking action of suramin, suggesting expression of multiple P2X receptor subtypes. Our results indicate that activation of P2X receptor channels represents an important pathway for Ca2+ influx in postnatal RGCs.
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Edwards FA, Robertson SJ, Gibb AJ. Properties of ATP receptor-mediated synaptic transmission in the rat medial habenula. Neuropharmacology 1997; 36:1253-68. [PMID: 9364480 DOI: 10.1016/s0028-3908(97)00127-5] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The properties of central ATP-mediated synaptic currents were studied using whole-cell patch-clamp recording in rat medial habenula slices. Release was shown to be calcium dependent with a Hill coefficient of approximately 2. The voltage dependence of synaptic current amplitudes was approximately linear. Some reduction of the synaptic current amplitudes was observed at 10 mM extracellular calcium, suggesting calcium block/permeability of the channels. This was confirmed by observation of current-voltage reversal potentials in different calcium concentrations. We estimate that the channels underlying half the synapses showed a negligible calcium permeability. In the other four out of eight synapses the results suggest a very high calcium permeability with an estimated PCa/PCs of > 10. Thus, at -70 mV, in 1 mM calcium, more than 15% of the ATP-mediated synaptic current is estimated to be carried by calcium, but only at synapses with calcium-permeable channels. Net current through these synaptic channels is also controlled by the voltage dependence of synaptic current decay time constants (increasing e-fold for 158 mV depolarization) and by a strong dependence of transmitter release on the frequency of stimulation of the presynaptic neurone, with failure rates increasing 3-fold as stimulation rates were increased from 1 to 10 Hz.
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Affiliation(s)
- F A Edwards
- Department of Physiology, University College London, U.K.
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