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Uebner M, Carr RW, Messlinger K, De Col R. Activity-dependent sensory signal processing in mechanically responsive slowly conducting meningeal afferents. J Neurophysiol 2014; 112:3077-85. [DOI: 10.1152/jn.00243.2014] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Activity-dependent processes in slowly conducting afferents have been shown to modulate conduction and receptive properties, but it is not known how the frequency of action potential firing determines the responses of such fibers to mechanical stimulation. We examined the responses of slowly conducting meningeal afferents to mechanical stimuli and the influence of preceding action potential activity. In hemisected rat heads with adhering cranial dura mater, recordings were made from meningeal nerves. Dural receptive fields of mechanically sensitive afferent fibers were stimulated with a custom-made electromechanostimulator. Sinusoidal mechanical stimuli of different stimulus durations and amplitudes were applied to produce either high-frequency (phasic) or low-frequency (tonic) discharges. Most fibers showed slowing of their axonal conduction velocity on electrically evoked activity at ≥2 Hz. In this state, the peak firing frequency of phasic responses to a 250-ms mechanical stimulus was significantly reduced compared with control. In contrast, the frequency of tonic responses induced by mechanical stimuli of >500 ms did not change. In a rare subtype of afferents, which showed conduction velocity speeding during activity, an increase in the phasic responses to mechanical stimuli was observed. Depending on the axonal properties of the afferent fibers, encoding of phasic components of mechanical stimuli is altered according to the immediate firing history. Preceding activity in mechanoreceptors slowing their conduction velocity seems to provide a form of low-pass filtering of action potential discharges predominantly reducing the phasic component. This may improve discrimination between harmless and potentially harmful mechanical stimuli in normal tissue.
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Affiliation(s)
- Michael Uebner
- Institute of Physiology and Pathophysiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany; and
| | - Richard W. Carr
- Department of Anaesthesia and Intensive Care Medicine, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany
| | - Karl Messlinger
- Institute of Physiology and Pathophysiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany; and
| | - Roberto De Col
- Department of Anaesthesia and Intensive Care Medicine, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany
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2
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Marshall KL, Lumpkin EA. The molecular basis of mechanosensory transduction. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 739:142-55. [PMID: 22399400 PMCID: PMC4060607 DOI: 10.1007/978-1-4614-1704-0_9] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Multiple senses, including hearing, touch and osmotic regulation, require the ability to convert force into an electrical signal: A process called mechanotransduction. Mechanotransduction occurs through specialized proteins that open an ion channel pore in response to a mechanical stimulus. Many of these proteins remain unidentified in vertebrates, but known mechanotransduction channels in lower organisms provide clues into their identity and mechanism. Bacteria, fruit flies and nematodes have all been used to elucidate the molecules necessary for force transduction. This chapter discusses many different mechanical senses and takes an evolutionary approach to review the proteins responsible for mechanotransduction in various biological kingdoms.
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Affiliation(s)
- Kara L. Marshall
- Integrated Graduate Program in Cellular, Molecular, Structural and Genetic Studies, Columbia University College of Physicians & Surgeons, New York, NY 10032
| | - Ellen A. Lumpkin
- Departments of Dermatology and Physiology and Cellular Biophysics, Columbia University College of Physicians & Surgeons, New York, NY 10032
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3
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De Col R, Messlinger K, Carr RW. Repetitive activity slows axonal conduction velocity and concomitantly increases mechanical activation threshold in single axons of the rat cranial dura. J Physiol 2011; 590:725-36. [PMID: 22144575 DOI: 10.1113/jphysiol.2011.220624] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The passage of an action potential along a peripheral axon modulates the conduction velocity of subsequent action potentials. In C-neurones with unmyelinated axons repetitive activity progressively slows axonal conduction velocity and in microneurographic recordings from healthy human subjects the magnitude of this slowing can be used to predict the receptive properties of individual axons. Recently, a reduction in the number of available voltage-gated sodium channels (Na(V)) through inactivation has been implicated as the predominant factor responsible for the slowing of axonal conduction. Since Na(V)s are also responsible for the initiation of action potentials in sensory nerve terminals, changes in their availability may be expected to affect activation threshold for sensory stimuli. To examine this proposal, dynamic mechanical stimuli were used to make precise estimates of activation threshold in single unmyelinated axons innervating the rat cranial dura mater. Decreases in axonal conduction velocity induced by repetitive electrical stimulation were paralleled by an increase in mechanical activation threshold. Application of TTX (10-20 nM) also slowed axonal conduction velocity in all 11 fibres examined and in 9 of these this resulted in a parallel increase in mechanical activation threshold. We interpret this as indicating that a reduction in available Na(V) number contributes to both axonal conduction velocity slowing and the observed parallel increase in mechanical activation threshold. The slowing of axonal conduction velocity observed during repetitive activity thus represents a form of accommodation, i.e. self inhibition, which is likely to be decisive in limiting peripheral input to the spinal dorsal horn and thereby regulating processes that could otherwise lead to central sensitization.
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Affiliation(s)
- Roberto De Col
- Institute for Physiology and Pathophysiology, Friedrich-Alexander-University, Erlangen, Germany
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Abstract
The nervous system detects and interprets a wide range of thermal and mechanical stimuli, as well as environmental and endogenous chemical irritants. When intense, these stimuli generate acute pain, and in the setting of persistent injury, both peripheral and central nervous system components of the pain transmission pathway exhibit tremendous plasticity, enhancing pain signals and producing hypersensitivity. When plasticity facilitates protective reflexes, it can be beneficial, but when the changes persist, a chronic pain condition may result. Genetic, electrophysiological, and pharmacological studies are elucidating the molecular mechanisms that underlie detection, coding, and modulation of noxious stimuli that generate pain.
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Affiliation(s)
- Allan I Basbaum
- Department of Anatomy, University of California, San Francisco, San Francisco, CA 94158, USA.
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5
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Tsunozaki M, Bautista DM. Mammalian somatosensory mechanotransduction. Curr Opin Neurobiol 2009; 19:362-9. [PMID: 19683913 PMCID: PMC4044613 DOI: 10.1016/j.conb.2009.07.008] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2009] [Revised: 07/10/2009] [Accepted: 07/13/2009] [Indexed: 11/22/2022]
Abstract
In the mammalian somatosensory system, mechanosensitive neurons mediate the senses of touch and pain. Among sensory modalities, mechanosensation has been the most elusive with regard to the identification of transduction molecules. One factor that has hindered the identification of transduction molecules is the diversity of neurons; physiological studies have revealed many subtypes of neurons, specialized to detect a variety of mechanical stimuli. Do different subtypes use the same transduction molecules that are modified by cellular context? Or, are there multiple mechanotransducers that specialize in sensing different mechanical stimuli? This review highlights recent progress in identifying and characterizing candidate molecular force transducers, as well as the development of new tools to characterize touch transduction at the molecular, cellular, and behavioral levels.
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Affiliation(s)
- Makoto Tsunozaki
- Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, CA 94720, USA
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6
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Radial stretch reveals distinct populations of mechanosensitive mammalian somatosensory neurons. Proc Natl Acad Sci U S A 2008; 105:20015-20. [PMID: 19060212 DOI: 10.1073/pnas.0810801105] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Primary afferent somatosensory neurons mediate our sense of touch in response to changes in ambient pressure. Molecules that detect and transduce thermal stimuli have been recently identified, but mechanisms underlying mechanosensation, particularly in vertebrate organisms, remain enigmatic. Traditionally, mechanically evoked responses in somatosensory neurons have been assessed one cell at a time by recording membrane currents in response to application of focal pressure, suction, or osmotic challenge. Here, we used radial stretch in combination with live-cell calcium imaging to gain a broad overview of mechanosensitive neuronal subpopulations. We found that different stretch intensities activate distinct subsets of sensory neurons as defined by size, molecular markers, or pharmacological attributes. In all subsets, stretch-evoked responses required extracellular calcium, indicating that mechanical force triggers calcium influx. This approach extends the repertoire of stimulus paradigms that can be used to examine mechanotransduction in mammalian sensory neurons, facilitating future physiological and pharmacological studies.
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7
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Raoux M, Rodat-Despoix L, Azorin N, Giamarchi A, Hao J, Maingret F, Crest M, Coste B, Delmas P. Mechanosensor Channels in Mammalian Somatosensory Neurons. SENSORS 2007; 7:1667-1682. [PMID: 28903189 PMCID: PMC3841838 DOI: 10.3390/s7091667] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/10/2007] [Accepted: 08/31/2007] [Indexed: 12/11/2022]
Abstract
Mechanoreceptive sensory neurons innervating the skin, skeletal muscles and viscera signal both innocuous and noxious information necessary for proprioception, touch and pain. These neurons are responsible for the transduction of mechanical stimuli into action potentials that propagate to the central nervous system. The ability of these cells to detect mechanical stimuli impinging on them relies on the presence of mechanosensitive channels that transduce the external mechanical forces into electrical and chemical signals. Although a great deal of information regarding the molecular and biophysical properties of mechanosensitive channels in prokaryotes has been accumulated over the past two decades, less is known about the mechanosensitive channels necessary for proprioception and the senses of touch and pain. This review summarizes the most pertinent data on mechanosensitive channels of mammalian somatosensory neurons, focusing on their properties, pharmacology and putative identity.
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Affiliation(s)
- Matthieu Raoux
- Laboratoire de Neurophysiologie Cellulaire, Centre National de la Recherche Scientifique UMR 6150, Université de la Méditerranée, Marseille, France.
| | - Lise Rodat-Despoix
- Laboratoire de Neurophysiologie Cellulaire, Centre National de la Recherche Scientifique UMR 6150, Université de la Méditerranée, Marseille, France.
| | - Nathalie Azorin
- Laboratoire de Neurophysiologie Cellulaire, Centre National de la Recherche Scientifique UMR 6150, Université de la Méditerranée, Marseille, France.
| | - Aurélie Giamarchi
- Laboratoire de Neurophysiologie Cellulaire, Centre National de la Recherche Scientifique UMR 6150, Université de la Méditerranée, Marseille, France.
| | - Jizhe Hao
- Laboratoire de Neurophysiologie Cellulaire, Centre National de la Recherche Scientifique UMR 6150, Université de la Méditerranée, Marseille, France.
| | - François Maingret
- Laboratoire de Neurophysiologie Cellulaire, Centre National de la Recherche Scientifique UMR 6150, Université de la Méditerranée, Marseille, France.
| | - Marcel Crest
- Laboratoire de Neurophysiologie Cellulaire, Centre National de la Recherche Scientifique UMR 6150, Université de la Méditerranée, Marseille, France.
| | - Bertrand Coste
- Laboratoire de Neurophysiologie Cellulaire, Centre National de la Recherche Scientifique UMR 6150, Université de la Méditerranée, Marseille, France.
| | - Patrick Delmas
- Laboratoire de Neurophysiologie Cellulaire, Centre National de la Recherche Scientifique UMR 6150, Université de la Méditerranée, Marseille, France.
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Abstract
Light touch, a sense of muscle position, and the responses to tissue-damaging levels of pressure all involve mechanosensitive sensory neurons that originate in the dorsal root or trigeminal ganglia. A variety of mechanisms of mechanotransduction are proposed. These ranges from direct activation of mechanically activated channels at the tips of sensory neurons to indirect effects of intracellular mediators, or chemical signals released from distended tissues, or specialized mechanosensory end organs. This chapter describes the properties of mechanosensitive channels present in sensory neurons and the potential molecular candidates that may underlie. Mechanically regulated electrical activity by touch and tissue damaging levels of pressure in sensory neurons seems to involve a variety of direct and indirect mechanisms and ion channels, and the involvement of specialized end organs in mechanotransduction complicates matters even more. Imaging studies are providing useful information about the events in the central nervous system associated with touch pain and allodynia (a pathological state where touch becomes painful this type of activity).
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Affiliation(s)
- Liam J Drew
- Molecular Nociception Group, Biology Department, University College London, London WC1E 6BT, United Kingdom
| | - Francois Rugiero
- Molecular Nociception Group, Biology Department, University College London, London WC1E 6BT, United Kingdom
| | - John N Wood
- Molecular Nociception Group, Biology Department, University College London, London WC1E 6BT, United Kingdom
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9
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Matsukawa K, Nakamoto T, Inomoto A. Gadolinium does not blunt the cardiovascular responses at the onset of voluntary static exercise in cats: a predominant role of central command. Am J Physiol Heart Circ Physiol 2006; 292:H121-9. [PMID: 16980340 DOI: 10.1152/ajpheart.00028.2006] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The cardiovascular adaptation at the onset of voluntary static exercise is controlled by the autonomic nervous system. Two neural mechanisms are responsible for the cardiovascular adaptation: one is central command descending from higher brain centers, and the other is a muscle mechanosensitive reflex from activation of mechanoreceptors in the contracting muscles. To examine which mechanism played a major role in producing the initial cardiovascular adaptation during static exercise, we studied the effect of intravenous administration of gadolinium (55 micromol/kg), a blocker of stretch-activated ion channels, on the increases in heart rate (HR) and mean arterial blood pressure (MAP) at the onset of voluntary static exercise (pressing a bar with a forelimb) in conscious cats. HR increased by 31 +/- 5 beats/min and MAP increased by 15 +/- 1 mmHg at the onset of voluntary static exercise. Gadolinium affected neither the baseline values nor the initial increases of HR and MAP at the onset of exercise, although the peak force applied to the bar tended to decrease to 65% of the control value before gadolinium. Furthermore, we examined the effect of gadolinium on the reflex responses in HR and MAP (18 +/- 7 beats/min and 30 +/- 6 mmHg, respectively) during passive mechanical stretch of a forelimb or hindlimb in anesthetized cats. Gadolinium significantly blunted the passive stretch-induced increases in HR and MAP, suggesting that gadolinium blocks the stretch-activated ion channels and thereby attenuates the reflex cardiovascular responses to passive mechanical stretch of a limb. We conclude that the initial cardiovascular adaptation at the onset of voluntary static exercise is predominantly induced by feedforward control of central command descending from higher brain centers but not by a muscle mechanoreflex.
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Affiliation(s)
- Kanji Matsukawa
- Dept. of Physiology, Graduate School of Health Sciences, Hiroshima Univ., Kasumi 1-2-3, Minami-ku, Hiroshima 734-8551, Japan.
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10
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McCarter GC, Levine JD. Ionic basis of a mechanotransduction current in adult rat dorsal root ganglion neurons. Mol Pain 2006; 2:28. [PMID: 16923187 PMCID: PMC1563451 DOI: 10.1186/1744-8069-2-28] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2006] [Accepted: 08/21/2006] [Indexed: 01/30/2023] Open
Abstract
Sensory mechanical transduction - necessary for hearing, proprioception, and the senses of touch and pain - remains poorly understood. In somatosensation, even the basic properties of the mechanically sensitive excitatory ionic currents that are assumed to mediate mechanical transduction are largely undescribed. We have recorded, from the soma of rat dorsal root ganglion (DRG) neurons in vitro, whole-cell ionic currents induced by the impact of a piezo-electrically driven glass probe. This transient mechanically activated current was observed in virtually all DRG neurons tested. In ion substitution experiments the current could be carried nonselectively by most cations, including divalent and organic cations, but not by chloride or sulfate ions. In addition, the mechanically activated current carried by monovalent cations was consistently blocked by millimolar concentrations of external calcium or magnesium. Based on these results, the transient mechanical transduction current observed in somatosensory neurons in vitro is mediated by large-pore mechanically gated channels nonselective for cations but impermeable to anions.
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Affiliation(s)
- Gordon C McCarter
- Department of Oral and Maxillofacial Surgery, Division of Neurosciences, University of California at San Francisco, San Francisco, CA 94143-0440, USA
- College of Pharmacy, Touro University – California, 1310 Johnson Lane, Mare Island, Vallejo, CA 94592-1118, USA
| | - Jon D Levine
- Department of Oral and Maxillofacial Surgery, Division of Neurosciences, University of California at San Francisco, San Francisco, CA 94143-0440, USA
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11
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Cho H, Koo JY, Kim S, Park SP, Yang Y, Oh U. A novel mechanosensitive channel identified in sensory neurons. Eur J Neurosci 2006; 23:2543-50. [PMID: 16817857 DOI: 10.1111/j.1460-9568.2006.04802.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Mechanosensitive (MS) channels are ion channels gated by different types of mechanical stimuli. MS channels in sensory neurons are thought to be molecular transducers for somatic sensations such as touch, pressure, proprioception and pain. Previously, we reported that two types of MS channels are present in sensory neurons. These channels are termed low threshold (LT) and high threshold (HT) MS channels based on their pressure threshold for activation. Here, we report another type of MS channel present in sensory neurons. The channel is activated by low pressure applied to a patch (threshold approximately 20 mmHg, similar to that in the LT channel). However, because this channel has a smaller single-channel conductance than that of the LT channel, the newly classified MS channel is now called a low threshold small conductance (LTSC) channel. Unlike the LT channel, which has outwardly rectifying currents, the current-voltage relationship of the LTSC is linear. The LTSC was permeable to monovalent cations and Ca2+, and reversibly blocked by gadolinium, a blocker of MS channels. Unlike the LT channel, the LTSC was sensitized by prostaglandin E2, an inflammatory mediator that is known to sensitize nociceptors to mechanical stimuli. LTSC channels were found mostly in small cultured sensory neurons. Thus, these results suggest that the LTSC is a distinct type of MS channel that is different from the LT and HT channels in sensory neurons, and that LTSCs might play a role in mediating somatosensations, including pain.
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Affiliation(s)
- Hawon Cho
- The Sensory Research Centre, Creative Research Initiatives, Seoul National University, College of Pharmacy, Kwanak, Shinlim 9-dong, Seoul 151-742, Korea
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12
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Piao L, Lee H, Li HY, Park CK, Cho IH, Piao ZG, Jung SJ, Choi SY, Lee SJ, Park K, Kim JS, Oh SB. Mechanosensitivity of voltage-gated K+currents in rat trigeminal ganglion neurons. J Neurosci Res 2006; 83:1373-80. [PMID: 16493687 DOI: 10.1002/jnr.20810] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
We investigated the mechanosensitivity of voltage-gated K+ channel (VGPC) currents by using whole-cell patch clamp recording in rat trigeminal ganglion (TG) neurons. On the basis of biophysical and pharmacological properties, two types of VGPC currents were isolated. One was transient (I(K,A)), the other sustained (I(K,V)). Hypotonic stimulation (200 mOsm) markedly increased both I(K,A) and I(K,V) without affecting their activation and inactivation kinetics. Gadolinium, a well-known blocker of mechanosensitive channels, failed to block the enhancement of I(K,A) and I(K,V) induced by hypotonic stimulation. During hypotonic stimulation, cytochalasin D, an actin-based cytoskeletal disruptor, further increased I(K,A) and I(K,V), whereas phalloidin, an actin-based cytoskeletal stabilizer, reduced I(K,A) and I(K,V). Confocal imaging with Texas red-phalloidin showed that actin-based cytoskeleton was disrupted by hypotonic stimulation, which was similar to the effect of cytochalasin D. Our results suggest that both I(K,A) and I(K,V) are mechanosensitive and that actin-based cytoskeleton is likely to regulate the mechanosensitivity of VGPC currents in TG neurons.
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MESH Headings
- Actin Cytoskeleton/drug effects
- Actin Cytoskeleton/metabolism
- Animals
- Animals, Newborn
- Cells, Cultured
- Cytochalasin D/pharmacology
- Hypotonic Solutions/pharmacology
- Mechanoreceptors/metabolism
- Mechanotransduction, Cellular/drug effects
- Mechanotransduction, Cellular/physiology
- Membrane Potentials/drug effects
- Membrane Potentials/physiology
- Microscopy, Confocal
- Neurons, Afferent/cytology
- Neurons, Afferent/drug effects
- Neurons, Afferent/metabolism
- Nucleic Acid Synthesis Inhibitors/pharmacology
- Patch-Clamp Techniques
- Phalloidine/pharmacology
- Potassium Channel Blockers/pharmacology
- Potassium Channels, Voltage-Gated/drug effects
- Potassium Channels, Voltage-Gated/metabolism
- Rats
- Rats, Sprague-Dawley
- Trigeminal Ganglion/cytology
- Trigeminal Ganglion/drug effects
- Trigeminal Ganglion/metabolism
- Xanthenes
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Affiliation(s)
- Lin Piao
- Department of Physiology and Molecular and Cellular Neuroscience Program, College of Dentistry and Dental Research Institute, Seoul National University, Chongno-Ku, Seoul, Korea
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13
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Lumpkin EA, Bautista DM. Feeling the pressure in mammalian somatosensation. Curr Opin Neurobiol 2005; 15:382-8. [PMID: 16023849 PMCID: PMC4354856 DOI: 10.1016/j.conb.2005.06.005] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2005] [Accepted: 06/30/2005] [Indexed: 11/17/2022]
Abstract
Mechanoreceptor cells of the somatosensory system initiate the perception of touch and pain. Molecules required for mechanosensation have been identified from invertebrate neurons, and recent functional studies indicate that ion channels of the transient receptor potential and degenerin/epithelial Na+ channel families are likely to be transduction channels. The expression of related channels in mammalian somatosensory neurons has fueled the notion that these channels mediate mechanotransduction in vertebrates; however, genetic disruption and heterologous expression have not yet revealed a direct role for any of these candidates in somatosensory mechanotransduction. Thus, new systems are needed to define the function of these ion channels in somatosensation and to pinpoint molecules or signaling pathways that underlie mechanotransduction in vertebrates.
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Affiliation(s)
- Ellen A Lumpkin
- Department of Physiology, University of California, 600 16th Street, San Francisco, CA 94143-2280, USA.
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14
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Kalapesi FB, Tan JCH, Coroneo MT. Stretch-activated channels: a mini-review. Are stretch-activated channels an ocular barometer? Clin Exp Ophthalmol 2005; 33:210-7. [PMID: 15807835 DOI: 10.1111/j.1442-9071.2005.00981.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
All cells are subject to physical forces by virtue of their position in a dynamically changing environment. This review outlines the various putative 'mechanosensors', or sensors of pressure cells possess, and discusses in particular the role stretch-activated membrane channels play in pressure recognition and transduction. The widespread occurrence of these channels is discussed and these 'mechanosensors' are related to pressure-related diseases, in particular, glaucoma.
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Affiliation(s)
- Freny B Kalapesi
- Department of Ophthalmology, Prince of Wales Hospital, University of New South Wales, Sydney, New South Wales, Australia
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15
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Chaban VV, Li J, Ennes HS, Nie J, Mayer EA, McRoberts JA. N-methyl-D-aspartate receptors enhance mechanical responses and voltage-dependent Ca2+ channels in rat dorsal root ganglia neurons through protein kinase C. Neuroscience 2004; 128:347-57. [PMID: 15350646 DOI: 10.1016/j.neuroscience.2004.06.051] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/24/2004] [Indexed: 11/28/2022]
Abstract
N-methyl-D-aspartate (NMDA)receptors (NMDARs) located on peripheral terminals of primary afferents are involved in the transduction of noxious mechanical stimuli. Exploiting the fact that both NMDARs and stretch-activated channels are retained in short-term culture and expressed on the soma of dorsal root ganglia (DRG) neurons, we examined the effect of NMDA on mechanically mediated changes in intracellular calcium concentration ([Ca2+]i). Our aims were to determine whether NMDARs modulate the mechanosensitivity of DRG neurons. Primary cultures of adult rat lumbosacral DRG cells were cultured for 1-3 days. [Ca2+]i responses were determined by Fura-2 ratio fluorescence. Somas were mechanically stimulated with fire-polished glass pipettes that depressed the cell membrane for 0.5 s. Voltage-activated inward Ca2+ currents were measured by the whole cell patch clamp. Stimulation of neurons with 100 microM NMDA in the presence, but not the absence, of co-agonist (10 microM D-serine) caused transient [Ca2+]i responses (101+/-9 nM) and potentiated [Ca2+]i peak responses to subsequent mechanical stimulation more than two-fold (P < 0.001). NMDA-mediated potentiation of mechanically induced [Ca2+]i responses was inhibited by the selective protein kinase C (PKC) inhibitor GF109203X (GFX; 10 microM), which had no independent effects on NMDA- or mechanically induced responses. Short-term treatment with the PKC activator phorbol dibutyrate (1 microM PDBu for 1-2 min) also potentiated mechanically induced [Ca2+]i responses nearly two-fold (P < 0.001), while longer exposure (>10 min) inhibited the [Ca2+]i transients by 44% (P < 0.001). Both effects of PDBu were prevented by prior treatment with GFX. Inhibition of voltage-dependent Ca2+ channels with 25 microM La3+ had no effect on mechanically induced [Ca2+]i transients prior to NMDA, but prevented enhancement of the transients by NMDA and PDBu. NMDA pretreatment transiently enhanced nifedipine-sensitive, voltage-activated Ca2+ currents by a process that was sensitive to GFX. In conclusion, activation of NMDARs on cultured DRG neurons sensitize voltage-dependent L-type Ca2+ channels which contribute to mechanically induced [Ca2+]i transients through a PKC-mediated process.
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Affiliation(s)
- V V Chaban
- Center for Neurovisceral Sciences and Women's Health, Department of Medicine, University of California, Warren Hall, Room 14-103, 900 Veterans Avenue, Los Angeles 90095, USA
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17
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Abstract
Mechanosensitive (MS) ion channels are present in a variety of cells. However, very little is known about the ion channels that account for mechanical sensitivity in sensory neurons. We identified the two most frequently encountered but distinct types of MS channels in 1390 of 2962 membrane patches tested in cultured dorsal root ganglion neurons. The two MS channels exhibited different thresholds, thus named as low-threshold (LT) and high-threshold (HT) MS channels, and sensitivity to pressure. The two channels retained different single-channel conductances and current-voltage relationships: LT and HT channels elicited large- and small-channel conductance with outwardly rectifying and linear I-V relationships, respectively. Both LT and HT MS channels were permeable to monovalent cations and Ca2+ and were blocked by gadolinium, a blocker of MS channels. Colchicine and cytochalasin D markedly reduced the activities of the two MS channels, indicating that cytoskeletal elements support the mechanosensitivity. Both types of MS channels were found primarily in small sensory neurons with diameters of <30 microm. Furthermore, HT MS channels were sensitized by a well known inducer of mechanical hyperalgesia, prostaglandin E2, via the protein kinase A pathway. We identified two distinct types of MS channels in sensory neurons that probably give rise to the observed MS whole-cell currents and transduce mechanical stimuli to neural signals involved in somatosensation, including pain.
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18
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Chaban VV, McRoberts JA, Ennes HS, Mayer EA. Nitric oxide synthase inhibitors enhance mechanosensitive Ca(2+) influx in cultured dorsal root ganglion neurons. Brain Res 2001; 903:74-85. [PMID: 11382390 DOI: 10.1016/s0006-8993(01)02407-6] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Nitric oxide (NO) can have opposite effects on peripheral sensory neuron sensitivity depending on the concentration and source of NO, and the experimental setting. The aim of this study was to determine the role of endogenous NO production in the regulation of mechanosensitive Ca(2+) influx of dorsal root ganglion (DRG) neurons. Adult mouse DRG neurons were grown in primary culture for 2-5 days, loaded with Fura-2, and tested for mechanically mediated changes in [Ca(2+)](i) by fluorescent ratio imaging. In the presence of the NOS inhibitors L-NAME, TRIM, or 7-NI, but not the inactive analogue D-NAME, peak [Ca(2+)](i) transients to mechanical stimulation were increased more than 2-fold. Neither La(3+) (25 microM), an inhibitor of voltage activated Ca(2+) channels, or tetrodotoxin (TTX, 1 microM), a selective inhibitor of voltage-gated Na(+) channels, had an effect on mechanically activated [Ca(2+)](i) transients under control conditions. However, in the presence of L-NAME, both La(3+) and TTX partially blocked the [Ca(2+)](i) response. Addition of Gd(3+), a blocker of mechanosensitive cation channels and L-type Ca(2+) channels, at a concentration (100 microM) that markedly inhibited the mechanical response under control conditions, only partially inhibited the response in the presence of L-NAME. The combination of either La(3+) or TTX with Gd(3+) caused near complete inhibition of mechanically stimulated [Ca(2+)](i) transients in the presence of L-NAME. We conclude that focal mechanical stimulation of DRG neurons causes Ca(2+) influx occurs primarily through mechanosensitive cation channels under control conditions. In the presence of NOS inhibitors, additional Ca(2+) influx occurs through voltage-sensitive Ca(2+) channels. These results suggest that endogenously produced NO in cultured DRG neurons decreases mechanosensitivity by inhibiting voltage-gated Na(+) and Ca(2+) channels.
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Affiliation(s)
- V V Chaban
- UCLA/CURE Neuroenteric Disease Program, Division of Digestive Diseases, Department of Medicine, University of California, VAGLAHS, West Los Angeles, Room 223, Building 115, 11301 Wilshire Boulevard, , Los Angeles, CA 90073, USA
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Abstract
The simplest cell-like structure, the lipid bilayer vesicle, can respond to mechanical deformation by elastic membrane dilation/thinning and curvature changes. When a protein is inserted in the lipid bilayer, an energetic cost may arise because of hydrophobic mismatch between the protein and bilayer. Localized changes in bilayer thickness and curvature may compensate for this mismatch. The peptides alamethicin and gramicidin and the bacterial membrane protein MscL form mechanically gated (MG) channels when inserted in lipid bilayers. Their mechanosensitivity may arise because channel opening is associated with a change in the protein's membrane-occupied area, its hydrophobic mismatch with the bilayer, excluded water volume, or a combination of these effects. As a consequence, bilayer dilation/thinning or changes in local membrane curvature may shift the equilibrium between channel conformations. Recent evidence indicates that MG channels in specific animal cell types (e.g., Xenopus oocytes) are also gated directly by bilayer tension. However, animal cells lack the rigid cell wall that protects bacteria and plants cells from excessive expansion of their bilayer. Instead, a cortical cytoskeleton (CSK) provides a structural framework that allows the animal cell to maintain a stable excess membrane area (i.e., for its volume occupied by a sphere) in the form of membrane folds, ruffles, and microvilli. This excess membrane provides an immediate membrane reserve that may protect the bilayer from sudden changes in bilayer tension. Contractile elements within the CSK may locally slacken or tighten bilayer tension to regulate mechanosensitivity, whereas membrane blebbing and tight seal patch formation, by using up membrane reserves, may increase membrane mechanosensitivity. In specific cases, extracellular and/or CSK proteins (i.e., tethers) may transmit mechanical forces to the process (e.g., hair cell MG channels, MS intracellular Ca(2+) release, and transmitter release) without increasing tension in the lipid bilayer.
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Affiliation(s)
- O P Hamill
- Physiology and Biophysics, University Of Texas Medical Branch, Galveston, Texas 77555, USA.
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