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Cantero M, Gutierrez BC, Cantiello HF. Actin filaments modulate electrical activity of brain microtubule protein two‐dimensional sheets. Cytoskeleton (Hoboken) 2020; 77:167-177. [DOI: 10.1002/cm.21596] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2019] [Revised: 01/09/2020] [Accepted: 01/10/2020] [Indexed: 01/09/2023]
Affiliation(s)
- María Cantero
- Laboratorio de Canales IónicosInstituto Multidisciplinario de Salud, Tecnología y Desarrollo (IMSaTeD, UNSE‐CONICET) Santiago del Estero Argentina
| | - Brenda C. Gutierrez
- Laboratorio de Canales IónicosInstituto Multidisciplinario de Salud, Tecnología y Desarrollo (IMSaTeD, UNSE‐CONICET) Santiago del Estero Argentina
| | - Horacio F. Cantiello
- Laboratorio de Canales IónicosInstituto Multidisciplinario de Salud, Tecnología y Desarrollo (IMSaTeD, UNSE‐CONICET) Santiago del Estero Argentina
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2
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Drukarch B, Holland HA, Velichkov M, Geurts JJ, Voorn P, Glas G, de Regt HW. Thinking about the nerve impulse: A critical analysis of the electricity-centered conception of nerve excitability. Prog Neurobiol 2018; 169:172-185. [DOI: 10.1016/j.pneurobio.2018.06.009] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2018] [Revised: 06/22/2018] [Accepted: 06/30/2018] [Indexed: 12/16/2022]
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3
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Cocchi M, Minuto C, Tonello L, Gabrielli F, Bernroider G, Tuszynski JA, Cappello F, Rasenick M. Linoleic acid: Is this the key that unlocks the quantum brain? Insights linking broken symmetries in molecular biology, mood disorders and personalistic emergentism. BMC Neurosci 2017; 18:38. [PMID: 28420346 PMCID: PMC5395787 DOI: 10.1186/s12868-017-0356-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2017] [Accepted: 04/12/2017] [Indexed: 11/10/2022] Open
Abstract
In this paper we present a mechanistic model that integrates subneuronal structures, namely ion channels, membrane fatty acids, lipid rafts, G proteins and the cytoskeleton in a dynamic system that is finely tuned in a healthy brain. We also argue that subtle changes in the composition of the membrane's fatty acids may lead to down-stream effects causing dysregulation of the membrane, cytoskeleton and their interface. Such exquisite sensitivity to minor changes is known to occur in physical systems undergoing phase transitions, the simplest and most studied of them is the so-called Ising model, which exhibits a phase transition at a finite temperature between an ordered and disordered state in 2- or 3-dimensional space. We propose this model in the context of neuronal dynamics and further hypothesize that it may involve quantum degrees of freedom dependent upon variation in membrane domains associated with ion channels or microtubules. Finally, we provide a link between these physical characteristics of the dynamical mechanism to psychiatric disorders such as major depression and antidepressant action.
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Affiliation(s)
- Massimo Cocchi
- "Paolo Sotgiu" Institute for Research in Quantitative & Quantum Psychiatry & Cardiology, L.U.de.S. HEI, Malta, Switzerland. .,Department of Veterinary Medical Sciences, University of Bologna, Bologna, Italy.
| | | | - Lucio Tonello
- "Paolo Sotgiu" Institute for Research in Quantitative & Quantum Psychiatry & Cardiology, L.U.de.S. HEI, Malta, Switzerland
| | - Fabio Gabrielli
- "Paolo Sotgiu" Institute for Research in Quantitative & Quantum Psychiatry & Cardiology, L.U.de.S. HEI, Malta, Switzerland
| | - Gustav Bernroider
- Neurosignaling Unit, Department of Organismic Biology, University of Salzburg, Salzburg, Austria
| | - Jack A Tuszynski
- Department of Oncology, University of Alberta, Edmonton, Canada.,Department of Physics, University of Alberta, Edmonton, Canada
| | - Francesco Cappello
- Department of Biomedicine and Neuroscience, University of Palermo, Palermo, Italy.,Euro-Mediterranean Institute of Science and Technology, Palermo, Italy
| | - Mark Rasenick
- Department of Physiology & Biophysics and Psychiatry, University of Illinois College of Medicine, Chicago, IL, USA.,Jesse Brown VAMC, Chicago, IL, USA
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4
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Gardiner J, Overall R, Marc J. The microtubule cytoskeleton acts as a key downstream effector of neurotransmitter signaling. Synapse 2011; 65:249-56. [PMID: 20687109 DOI: 10.1002/syn.20841] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Microtubules are well known to play a key role in the trafficking of neurotransmitters to the synapse. However, less attention has been paid to their role as downstream effectors of neurotransmitter signaling in the target neuron. Here, we show that neurotransmitter-based signaling to the microtubule cytoskeleton regulates downstream microtubule function through several mechanisms. These include tubulin posttranslational modification, binding of microtubule-associated proteins, release of microtubule-interacting second messenger molecules, and regulation of tubulin expression levels. We review the evidence for neurotransmitter regulation of the microtubule cytoskeleton, focusing on the neurotransmitters serotonin, melatonin, dopamine, glutamate, glycine, and acetylcholine. Some evidence suggests that microtubules may even play a more direct role in propagating action potentials through conductance of electric current. In turn, there is evidence for the regulation of neurotransmission by the microtubule cytoskeleton.
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Affiliation(s)
- John Gardiner
- The School of Biological Sciences, The University of Sydney 2006, New South Wales, Australia.
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5
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Shcherbatko A, Ono F, Mandel G, Brehm P. Voltage-dependent sodium channel function is regulated through membrane mechanics. Biophys J 1999; 77:1945-59. [PMID: 10512815 PMCID: PMC1300476 DOI: 10.1016/s0006-3495(99)77036-0] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Cut-open recordings from Xenopus oocytes expressing either nerve (PN1) or skeletal muscle (SkM1) Na(+) channel alpha subunits revealed slow inactivation onset and recovery kinetics of inward current. In contrast, recordings using the macropatch configuration resulted in an immediate negative shift in the voltage-dependence of inactivation and activation, as well as time-dependent shifts in kinetics when compared to cut-open recordings. Specifically, a slow transition from predominantly slow onset and recovery to exclusively fast onset and fast recovery from inactivation occurred. The shift to fast inactivation was accelerated by patch excision and by agents that disrupted microtubule formation. Application of positive pressure to cell-attached macropatch electrodes prevented the shift in kinetics, while negative pressure led to an abrupt shift to fast inactivation. Simultaneous electrophysiological recording and video imaging of the cell-attached patch membrane revealed that the pressure-induced shift to fast inactivation coincided with rupture of sites of membrane attachment to cytoskeleton. These findings raise the possibility that the negative shift in voltage-dependence and the fast kinetics observed normally for endogenous Na(+) channels involve mechanical destabilization. Our observation that the beta1 subunit causes similar changes in function of the Na(+) channel alpha subunit suggests that beta1 may act through interaction with cytoskeleton.
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Affiliation(s)
- A Shcherbatko
- Department of Neurobiology and Behavior, State University of New York at Stony Brook, Stony Brook, New York 11794 USA.
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6
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Johnson BD. The company they keep: ion channels and their intracellular regulatory partners. ADVANCES IN SECOND MESSENGER AND PHOSPHOPROTEIN RESEARCH 1999; 33:203-28. [PMID: 10218120 DOI: 10.1016/s1040-7952(99)80011-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- B D Johnson
- Department of Physiology and Neurobiology, University of Connecticut, Storrs 06269, USA
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7
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Johnson BD, Byerly L. Ca2+ channel Ca(2+)-dependent inactivation in a mammalian central neuron involves the cytoskeleton. Pflugers Arch 1994; 429:14-21. [PMID: 7708473 DOI: 10.1007/bf02584025] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Ca2+ channel inactivation was investigated in acutely isolated hippocampal pyramidal neurons from adult rats and found to have a component dependent on intracellular Ca2+. Ca(2+)-dependent inactivation was indentified as the additional inactivation of channel current observed when Ca2+ replaced Ba2+ as the current carrying ion, and was found to be an independent process from that of Ba2+ current inactivation based on three lines of evidence: (1) no correlation between Ca(2+)-dependent inactivation and Ba2+ current inactivation was found, (2) only Ca(2+)-dependent inactivation was reduced by intracellular application of Ca2+ chelators, and (3) only Ca(2+)-dependent inactivation was sensitive to compounds which alter the cytoskeleton. Drugs which stabilize (taxol and phalloidin) and destabilize (colchicine and cytochalasin B) the cytoskeleton altered the development and recovery from Ca(2+)-dependent inactivation, indicating that the neuronal cytoskeleton may mediate Ca2+ channel sensitivity to intracellular Ca2+. Ca(2+)-dependent inactivation was not associated with a particular subset of Ca2+ channels, suggesting that all Ca2+ channels in these neurons are inactivated by intracellular Ca2+.
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Affiliation(s)
- B D Johnson
- Department of Biological Sciences, University of Southern California, Los Angeles 90089-2520
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Johnson BD, Byerly L. A cytoskeletal mechanism for Ca2+ channel metabolic dependence and inactivation by intracellular Ca2+. Neuron 1993; 10:797-804. [PMID: 8098608 DOI: 10.1016/0896-6273(93)90196-x] [Citation(s) in RCA: 183] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Many different types of voltage-dependent Ca2+ channels inactivate when intracellular ATP declines or intracellular Ca2+ rises. An inside-out, patch-clamp technique was applied to the Ca2+ channels of Lymnaea neurons to determine the mechanism(s) underlying these two phenomena. Although no evidence was found for a phosphorylation mechanism, agents that act on the cytoskeleton were found to alter Ca2+ channel activity. The cytoskeletal disrupters colchicine and cytochalasin B were found to speed Ca2+ channel decline in ATP, whereas the cytoskeletal stabilizers taxol and phalloidin were found to prolong Ca2+ channel activity without ATP. In addition, cytoskeletal stabilizers reduced Ca(2+)-dependent channel inactivation, suggesting that both channel metabolic dependence and Ca(2+)-dependent inactivation result from a cytoskeletal interaction.
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Affiliation(s)
- B D Johnson
- Department of Biological Sciences, University of Southern California, Los Angeles 90089-2520
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9
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Waxman SG, Black JA, Stys PK, Ransom BR. Ultrastructural concomitants of anoxic injury and early post-anoxic recovery in rat optic nerve. Brain Res 1992; 574:105-19. [PMID: 1638387 DOI: 10.1016/0006-8993(92)90806-k] [Citation(s) in RCA: 104] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
To study the effects of anoxia on CNS white matter, we examined the ultrastructure of axons and glial cells in a white matter tract, the rat optic nerve, that was subjected to a standardized anoxic insult in vitro. Previous electrophysiological studies showed that in this model, action potential conduction is rapidly abolished by anoxia, and conduction is restored after reoxygenation in about 30% of axons following a 60-min anoxic period. The present study examined the ultrastructural correlates of anoxic injury and early post-anoxic recovery in this model. Optic nerves examined immediately following 60 min of anoxia displayed numerous large, apparently empty zones located within myelin sheaths adjacent to the axon. The myelin remained compact and retained its periodicity. In some regions, the extracellular space was enlarged. There was mitochondrial swelling with loss of normal cristae. There was also loss of microtubules and, to a smaller degree, of neurofilaments in large-diameter axons. Some nodes of Ranvier in anoxic optic nerves displayed detachment of terminal oligodendroglial loops or retraction of the myelin from the node; the presence of tongue-like processes, extending from nearby cells under the detached myelin loops, suggested a possible role of cell-mediated damage to the paranodal myelin. Bundles of dense astrocyte processes were present, and there was vesicular degeneration of perinodal astrocyte processes. In optic nerves that had been permitted to recover for 60 min in oxygenated Ringers following the anoxic period, empty zones were only rarely observed within myelin sheaths and, when present, were smaller than in optic nerves immediately following 60 min of anoxia. The axoplasm of large fibers continued to show loss of microtubules and neurofilaments, as well as mitochondrial swelling. Myelin appeared normal, and only rare paranodal oligodendroglial processes remained unattached from the axon membrane. These results provide support for the idea that, during anoxia, myelinated axons are damaged with significant injury to cytoskeletal elements, probably due to an influx of calcium. The ultrastructural results, together with our earlier observations on the physiological correlates of anoxia and re-oxygenation, suggest that the development of intramyelinic spaces or damage to paranodes lead to conduction block in the anoxic optic nerve. These results also suggest that repair of these structural abnormalities may provide a morphological basis for the early recovery of conduction that occurs after re-oxygenation.
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Affiliation(s)
- S G Waxman
- Department of Neurology, Yale University School of Medicine, New Haven, CT 06510
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Ichikawa M, Urayama M, Matsumoto G. Anticalmodulin drugs block the sodium gating current of squid giant axons. J Membr Biol 1991; 120:211-22. [PMID: 1675687 DOI: 10.1007/bf01868532] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The effects of calmodulin (CaM) antagonists (W-7, W-5, trifluoperazine, chlorpromazine, quinacrine, diazepam, propericyazine and carmidazolium) on the sodium and potassium channels were studied on the intracellularly perfused and voltage-clamped giant axon of the squid. It was found that the drugs are more potent blockers of the sodium current than of the potassium current. The drugs also reduce the sodium gating current. The blockage of the sodium and gating current can be explained by assuming that the drugs interact with the sodium gating subunit in one of its closed states. The site of action is probably the intracellular surface of the axolemma where presumably a Ca(2+)-calmodulin complex can be formed.
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Affiliation(s)
- M Ichikawa
- Electrotechnical Laboratory, Molecular and Cellular Neuroscience Section, Ibaraki, Japan
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Abstract
The change in birefringence during depolarizing voltage-clamp pulses of internally perfused squid giant axons are biphasic. There is a rapid decrease in birefringence with a 220-microsec half time at 8 degrees C followed by a slow decrease over the next several milliseconds. After the pulse there is a rapid recovery which is smaller than the initial rapid decrease followed by a slow recovery phase. The rate of change of the slow phase during the pulse is more rapid for larger depolarizations. After the pulse the rate of change is more rapid for more negative potentials. 3.6 mM chloramine-T, applied externally until the sodium currents were prolonged and inactivation was removed, removed the slow phase of the birefringence response both during and after the pulse and made the fast 'off' response as large as the fast 'on' response. Two anesthetics reduced the birefringence response by about 20%. A rocking helix model is presented which relates the birefringence findings and earlier gating current experiments.
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Affiliation(s)
- D Landowne
- Department of Physiology and Biophysics, University of Miami School of Medicine, Florida 33101
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12
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Arai T, Matsumoto G. Axolinin localization in the nervous tissue of squid revealed by monoclonal antibodies specific for axolinin: cellular and subcellular localization of axolinin in the squid neuron. J Neurochem 1989; 52:93-100. [PMID: 2908895 DOI: 10.1111/j.1471-4159.1989.tb10902.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Cellular and subcellular distributions of axolinin, the 260-kilodalton (kD) microtubule-associated glycoprotein originally purified from squid axons, in various squid tissues such as optical lobes, bundles of small nerve fibers (fin nerves), giant stellate ganglia, skin, muscle, liver, and gill, were immunologically studied using monoclonal antibodies specifically recognizing the polypeptide chain of axolinin. The following results were obtained: (1) Axolinin is confined to squid neurons and skin; (2) axolinin is localized in the axon whereas another 260-kD microtubule-associated protein, MAP B, is localized in the cell bodies; and (3) axolinin is localized mainly in the peripheral part of the axoplasm of the squid giant axon. The last result has confirmed our previous conclusion obtained using polyclonal antisera against axolinin, which contain antibodies recognizing not only axolinin-specific epitopes but also nonspecific epitopes. The physiological importance of the localization of axolinin in axons and the skin is discussed based on its possible relationship to excitability function.
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Affiliation(s)
- T Arai
- Institute of Basic Medical Sciences, University of Tsukuba, Ibaraki, Japan
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Arai T, Matsumoto G. Axolinin localization in the nervous tissue of squid revealed by monoclonal antibodies specific for axolinin: characterization of monoclonal antibodies against axolinin. Hybridoma (Larchmt) 1988; 7:583-93. [PMID: 2466762 DOI: 10.1089/hyb.1988.7.583] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Monoclonal antibodies against squid axolinin (the 260-kD glycoprotein in squid axoplasm) have been produced using spleen cells immunized with purified axolinin in vivo and in vitro. The produced antibodies can be categorized into two groups according to the nature of their antigenic site. The monoclonal antibodies belonging to group I recognize the protein backbone of axolinin, while those belonging to group II bind to the sugar chains of axolinin. Group II was further divided into two subgroups IIA and IIB; the subgroup IIA antibodies recognize sugar chains to which concanavalin A binds, while the IIB antibodies bind to sugar chains lacking the lectin-binding sites. Only the group I antibodies can be used as specific probes for axolinin since the sugar chains recognized by the group II antibodies are present on other squid glycoproteins in addition to axolinin. It follows from our results that polyclonal antisera against axolinin cannot generally be expected to be specific for this protein.
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Affiliation(s)
- T Arai
- Institute of Basic Medical Sciences, University of Tsukuba, Ibaraki, Japan
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14
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Gordon R, Brodland GW. The cytoskeletal mechanics of brain morphogenesis. Cell state splitters cause primary neural induction. CELL BIOPHYSICS 1987; 11:177-238. [PMID: 2450659 DOI: 10.1007/bf02797122] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
There is a functional device in embryonic ectodermal cells that we propose causes them to differentiate into either neuroepithelial or epidermal tissue during the process called primary neural induction. We call this apparatus the "cell state splitter." Its main components are the apical microfilament ring and the coplanar apical mat of microtubules, which exert forces in opposite radial directions. We analyze the mechanical interaction between these cytoskeletal components and show that they are in an unstable mechanical equilibrium. The role of the cell state splitter is thus to create a mechanical instability corresponding to the embryonic state of "competence" in an otherwise mechanically stable cell. When the equilibrium of the cell state splitter is disturbed so as to produce a slight contraction of the apical end, apical contraction continues and the distinctive columnar neuroepithelial cells are produced. A slight expansion from the equilibrium state, on the other hand, results in flattened epidermal cells. The calculated forces are consistent with the known constitutive and force-generating properties and morphology of microfilaments and microtubules, and with free tubulin concentrations. There are no free parameters in the analysis. The first cells to assume the neuroepithelial state lie over the notochord. Propagation of the neuroepithelial state (homoiogenetic induction) then proceeds via stretch-induced constriction of the apical microfilament rings, until a hemisphere is covered, at which point the high rate of change of the meridional stress component necessary for further propagation vanishes. The remaining cells are stretched somewhat by this process and become epidermis. A sharp boundary between the tissues is thus formed (explaining "compartmentalization" and the binary nature of differentiation in general). Normal induction apparently involves setup of the cell state splitters in all of the ectoderm cells, perhaps synchronously timed by global embryo tension. The initial transition of cells from the ectodermal to the neuroepithelial state begins at the notoplate, where cell attachments to the notochord may both cause basal actin deposition and significantly reduce the stress induced in the ectoderm by the global tension, biasing the notoplate cell state splitters toward the neuroepithelial state. Introduction of an organizer or other solid substrate (artificial inducer) elsewhere, to which ectodermal cells can adhere, may likewise have both of these effects. Differentiation to either epidermis or neuroepithelium is thus a mechanical event followed by the synthesis of specific proteins.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- R Gordon
- Department of Botany, University of Manitoba, Winnipeg, Canada
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Sherwin T, Schneider A, Sasse R, Seebeck T, Gull K. Distinct localization and cell cycle dependence of COOH terminally tyrosinolated alpha-tubulin in the microtubules of Trypanosoma brucei brucei. J Biophys Biochem Cytol 1987; 104:439-46. [PMID: 3546334 PMCID: PMC2114556 DOI: 10.1083/jcb.104.3.439] [Citation(s) in RCA: 147] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
alpha-Tubulin can be posttranslationally modified in that its COOH-terminal amino acid residue, tyrosine, can be selectively removed and replaced again. This reaction cycle involves two enzymes, tubulin carboxypeptidase and tubulin tyrosine ligase. The functional significance of this unusual modification is unclear. The present study demonstrates that posttranslational tyrosinolation of alpha-tubulin does occur in the parasitic hemoflagellate Trypanosoma brucei brucei and that posttranslational tyrosinolation can be detected in both alpha-tubulin isoforms found in this organism. Trypanosomes contain a number of microtubular structures: the flagellar axoneme; the subpellicular layer of singlet microtubules which are closely associated with the cell membrane; the basal bodies; and a cytoplasmic pool of soluble tubulin. Tyrosinolated alpha-tubulin is present in all these populations. However, immunofluorescence studies demonstrate a distinct localization of tyrosinolated alpha-tubulin within individual microtubules and organelles. This localization is subject to a temporal modulation that correlates strongly with progress of a cell through the cell cycle. Our results indicate that the presence of tyrosinolated alpha-tubulin is a marker for newly formed microtubules.
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Landowne D. Molecular motion underlying activation and inactivation of sodium channels in squid giant axons. J Membr Biol 1985; 88:173-85. [PMID: 2419567 DOI: 10.1007/bf01868431] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Measurements of the changes in birefringence associated with changes in membrane potential were made with internally perfused squid giant axons in low sodium solutions at 0-8 degrees C. The time course of the birefringence changes share many properties of the 'gating' (polarization) currents previously studied in this nerve. Both can be demonstrated as an asymmetry in the response to voltage pulses symmetrical about the resting potential which is not present about a hyperpolarized holding potential. Both have a rapid relaxation, which precedes the sodium permeability change. Both exhibit an initial delay or rising phase. Both are reversibly blocked by perfusion with 30 mM or 300 nM tetrodotoxin. The birefringence response has a decrease in the amplitude of the rapid relaxation associated with the appearance of a slow relaxation. This is similar to the immobilization of fast gating charges which parallels sodium current inactivation. The amplitude of the birefringence and the gating current responses is consistent with a change in the alignment of several hundred peptide bonds per sodium channel.
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Malbouisson AM, Ghabriel MN, Allt G. Axonal degeneration in large and small nerve fibres. An electron-microscopic and morphometric study. J Neurol Sci 1985; 67:307-18. [PMID: 3989574 DOI: 10.1016/0022-510x(85)90155-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Using computer-aided morphometric methods, axonal degeneration following nerve crush was analysed to reassess whether small fibres degenerate before large fibres or vice versa, or simultaneously. Axonal microtubule density was used as the criterion for determining the extent of fibre degeneration. Axonal areas and axonal microtubule numbers were recorded from a large sample of myelinated fibres in the right unoperated rat sural nerve and distal to crush in the left sural nerve. Both samples were divided into small and large fibre groups, according to axonal areas. Statistical analysis of the data confirmed a significant loss of microtubules from the left crushed nerve fibres but no significant difference in the relative loss of microtubules from small and large fibres. It is concluded, therefore, that in Wallerian degeneration, axonal breakdown, as assessed by microtubule loss, occurs simultaneously in small and large fibres. The findings are related to the electrophysiological changes which occur in Wallerian degeneration.
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Matsumoto G, Urayama M, Ichikawa M. Modified Hodgkin-Huxley gating kinetics of sodium activation in giant axons of squid (Doryteuthis bleekeri). J Theor Biol 1985; 112:695-705. [PMID: 2582207 DOI: 10.1016/s0022-5193(85)80054-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The probabilities m of the sodium activation gate being open are shown to fit experimentally-determined running integrals Qg of recordings of the colchicine-sensitive fraction of the asymmetry current, within the Hodgkin-Huxley framework that the gate could have only two conformations, open and closed. Using the Hodgkin-Huxley framework, we are obliged to assume that the transition velocities, alpha m and beta m, between the open and closed gates depend not only on membrane potentials V but also on the time after a potential step was externally applied. We introduce the following functions of alpha m and beta m. (sequence in text) where VH, td and tau p stand for holding potential, constant delay time of 10 microseconds, and transit time of the transition velocity of alpha m (or beta m) from its initial value alpha om (or beta om) to its final steady value alpha infinity m (or beta infinity m), respectively. The transit time tau p was found to be potential-dependent; typically it was 30 microseconds at -20 mV, and 100 microseconds at 20-40 mV. The values of alpha infinity m, alpha om, beta infinity m and beta om were found to be in reasonable agreement with those obtained by others, under the Hodgkin-Huxley assumption that the gate followed first-order kinetics. The requirement of new parameters, tau p and td, in the transition velocities was discussed in a relation to a membrane model where a voltage-receptor and a sodium channel macromolecule are spatially separated but functionally connected through underlying cytoskeletons (Matsumoto, 1984).
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Abstract
The excitability of the squid giant axon was studied as a function of transmembrane hydrostatic pressure differences, the latter being altered by the technique of intracellular perfusion. When a KF solution was used as the internal medium, a pressure difference of about 15 cm water had very little effect on either the membrane potential or excitability. However, within a few minutes after introducing either a KCl-containing, a KBr-containing, or a colchicine-containing solution as the internal medium, with the same pressure difference across the membrane, the axon excitability was suppressed. In these cases, removal of the pressure difference restored the excitability, indicating that the structure of membrane was not irreversibly damaged. Electron-microscopic observations of these axons revealed that the perfusion with a KF solution or colchicine-containing solution preserves the submembranous cytoskeletal layer, whereas perfusion with a KCl or KBr solution dissolves it. These results suggest that the submembranous cytoskeletons including microtubules provide an important mechanical support to the excitable membrane but are not essential elements in channel activities.
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20
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Matsumoto G, Ichikawa M. Kinetics of sodium activation in giant axons of squid (Doryteuthis bleekeri). Neuroscience 1985; 14:327-34. [PMID: 2579353 DOI: 10.1016/0306-4522(85)90182-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The variation with time of the rising phase of the sodium conductance in squid giant axons was fitted to the Xth power of running integrals of the colchicine-sensitive components of the asymmetry currents, where the running integrals were experimentally obtained. We found that excellent fitting was obtained for all of the potentials examined from -60 to +60 mV, when we put the value of X equal to 3 at potentials above 10 mV and equal to 5 below -20 mV, and it varied continuously from 3 to 5 when pulse potentials changed from 10 to -25 mV. Further, it was found that the voltage dependence of the peak sodium currents was fitted to the third power of charges carried by the colchicine-sensitive component of the asymmetry current by the moment when the sodium current attained its peak. These results agree well with the expectation by Hodgkin and Huxley [(1952) J. Physiol., Lond. 117, 500-544] although the gating kinetics differ from the Hodgkin-Huxley prediction [Matsumoto, Ichikawa and Tasaki (1983) J. Membr. Biol. 77, 93-99].
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Abstract
An experimental review to show that axonal undercoat and cytoskeletal structures underneath the axolemma of squid giant axons play an important role in generating sodium currents is presented. Correspondingly, two alternative membrane models are proposed; one is that the undercoat and cytoskeletal structures support the functioning of sodium channels and the other is that they are directly incorporated with the molecular mechanism of generating sodium currents. This latter model is probable in squid giant axons. The model of direct participation of the underlying cytoskeleton in the sodium activation mechanism modifies the sodium activation gating kinetics in the Hodgkin-Huxley scheme; that is, the transition velocities between the open and closed states of the activation gate depend not only on membrane potentials but also on the time after the onset of application of a potential step.
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Matsumoto G, Ichikawa M, Tasaki A, Murofushi H, Sakai H. Axonal microtubules necessary for generation of sodium current in squid giant axons: I. Pharmacological study on sodium current and restoration of sodium current by microtubule proteins and 260K protein. J Membr Biol 1983; 77:77-91. [PMID: 6142960 DOI: 10.1007/bf01925858] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Effects of the reagents suppressing or supporting axoplasmic microtubule assembly were studied on the Na ionic current of squid giant axons by perfusing the axon internally with the solution containing the reagent. Among the reagents suppressing the assembly, colchicine, vinblastine, podophyllotoxin, sulfhydryl reagents such as DTNB and NEM, and chaotropic anions such as iodide and bromide, were examined. These reagents reduced maximum Na conductance and shifted the voltage dependence of steady-state Na activation in a depolarizing direction along the voltage axis. They also made the voltage dependence less steep, but did not affect sodium inactivation appreciably. Effects on Na ionic current of reagents which support microtubule assembly (Taxol, DMSO, D2O and temperature) were opposite the effects of those agents suppressing assembly. At the same time, we demonstrated that after Na currents were partially reduced, they could be restored by internally perfusing the axon with a solution containing microtubule proteins, 260K proteins and cAMP under conditions favorable for microtubule assembly. For full restoration, it was found that the following conditions were necessary: (1) The microenvironment within the axon is suitable for microtubule assembly. (2) Tubulins incorporated into microtubules are fully tyrosinated at their C-termini. (3) A peripheral protein having a molecular weight of 260,000 daltons (260K protein) is indispensable. These results suggest that axoplasmic microtubules and 260K proteins in the structure underlying the axolemma play a role in generating Na currents in squid giant axons.
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