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Shenton F, Bewick GS, Banks RW. A study of the expression of small conductance calcium-activated potassium channels (SK1-3) in sensory endings of muscle spindles and lanceolate endings of hair follicles in the rat. PLoS One 2014; 9:e107073. [PMID: 25191752 PMCID: PMC4156425 DOI: 10.1371/journal.pone.0107073] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2014] [Accepted: 08/08/2014] [Indexed: 11/21/2022] Open
Abstract
Processes underlying mechanotransduction and its regulation are poorly understood. Inhibitors of Ca2+-activated K+ channels cause a dramatic increase in afferent output from stretched muscle spindles. We used immunocytochemistry to test for the presence and location of small conductance Ca2+-activated K+ channels (SK1-3) in primary endings of muscle spindles and lanceolate endings of hair follicles in the rat. Tissue sections were double immunolabelled with antibodies to one of the SK channel isoforms and to either synaptophysin (SYN, as a marker of synaptic like vesicles (SLV), present in many mechanosensitive endings) or S100 (a Ca2+-binding protein present in glial cells). SK channel immunoreactivity was also compared to immunolabelling for the Na+ ion channel ASIC2, previously reported in both spindle primary and lanceolate endings. SK1 was not detected in sensory terminals of either muscle spindles or lanceolate endings. SK2 was found in the terminals of both muscle spindles and lanceolate endings, where it colocalised with the SLV marker SYN (spindles and lanceolates) and the satellite glial cell (SGC) marker S100 (lanceolates). SK3 was not detected in muscle spindles; by contrast it was present in hair follicle endings, expressed predominantly in SGCs but perhaps also in the SGC: terminal interface, as judged by colocalisation statistical analysis of SYN and S100 immunoreactivity. The possibility that all three isoforms might be expressed in pre-terminal axons, especially at heminodes, cannot be ruled out. Differential distribution of SK channels is likely to be important in their function of responding to changes in intracellular [Ca2+] thereby modulating mechanosensory transduction by regulating the excitability of the sensory terminals. In particular, the presence of SK2 throughout the sensory terminals of both kinds of mechanoreceptor indicates an important role for an outward Ca2+-activated K+ current in the formation of the receptor potential in both types of ending.
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Affiliation(s)
- Fiona Shenton
- School of Biological & Biomedical Sciences, Durham University, Durham, United Kingdom
| | - Guy S. Bewick
- School of Medical Sciences, University of Aberdeen, Aberdeen, United Kingdom
| | - Robert W. Banks
- School of Biological & Biomedical Sciences, Durham University, Durham, United Kingdom
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52
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Formation of cholinergic synapse-like specializations at developing murine muscle spindles. Dev Biol 2014; 393:227-235. [DOI: 10.1016/j.ydbio.2014.07.011] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2014] [Revised: 07/14/2014] [Accepted: 07/15/2014] [Indexed: 12/30/2022]
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53
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Mueller JK, Tyler WJ. A quantitative overview of biophysical forces impinging on neural function. Phys Biol 2014; 11:051001. [DOI: 10.1088/1478-3975/11/5/051001] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
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54
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Characterization of proton-induced currents in rat trigeminal mesencephalic nucleus neurons. Brain Res 2014; 1583:12-22. [PMID: 25128599 DOI: 10.1016/j.brainres.2014.08.009] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2014] [Revised: 08/05/2014] [Accepted: 08/06/2014] [Indexed: 01/15/2023]
Abstract
Acid-sensing ion channels (ASICs) are widely expressed in central as well as peripheral neurons. Here we have characterized the proton-induced currents in acutely isolated rat trigeminal mesencephalic nucleus (Vmes) neurons using a whole cell patch-clamp technique. In a voltage-clamp condition, the application of acid extracellular solution (≤ pH 6.5) induced the inward currents in a pH-dependent manner. The proton-induced currents disappeared in the Na(+)-free external solution, and were concentration-dependently blocked by amiloride, a general ASIC blocker. The reversal potential of proton-induced currents was similar to the theoretical Na(+) equilibrium potential, suggesting that the proton-induced currents are mainly mediated by the activation of ASICs, which are highly selective to Na(+). The modulation of proton-induced currents by divalent cations and the expression patterns of ASIC transcripts using by the multi-cell RT-PCR assay suggest that Vmes neurons express functional ASIC2a and ASIC1b subunits. In a current-clamp condition, acidic pH directly depolarized the membrane potential and generated a burst of action potentials at Vmes neurons, which innervate the masseter muscle spindles. Considering that cell bodies of Vmes neurons are located within the central nervous system, ASICs expressed on Vmes neurons, by sensing peripheral and/or central acidosis, might play pivotal roles in the transduction of proprioceptive information from the masseter muscles and periodontal ligaments.
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55
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Bewick GS, Banks RW. Mechanotransduction in the muscle spindle. Pflugers Arch 2014; 467:175-90. [PMID: 24888691 PMCID: PMC4281366 DOI: 10.1007/s00424-014-1536-9] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2014] [Revised: 04/09/2014] [Accepted: 05/12/2014] [Indexed: 12/26/2022]
Abstract
The focus of this review is on the principal sensory ending of the mammalian muscle spindle, known as the primary ending. The process of mechanosensory transduction in the primary ending is examined under five headings: (i) action potential responses to defined mechanical stimuli—representing the ending's input–output properties; (ii) the receptor potential—including the currents giving rise to it; (iii) sensory-terminal deformation—measurable changes in the shape of the primary-ending terminals correlated with intrafusal sarcomere length, and what may cause them; (iv) putative stretch-sensitive channels—pharmacological and immunocytochemical clues to their identity; and (v) synaptic-like vesicles—the physiology and pharmacology of an intrinsic glutamatergic system in the primary and other mechanosensory endings, with some thoughts on the possible role of the system. Thus, the review highlights spindle stretch-evoked output is the product of multi-ionic receptor currents plus complex and sophisticated regulatory gain controls, both positive and negative in nature, as befits its status as the most complex sensory organ after the special senses.
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Affiliation(s)
- Guy S Bewick
- School of Medical Sciences, Institute of Medical Sciences, University of Aberdeen, Aberdeen, AB25 2ZD, UK,
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56
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Shenton FC, Pyner S. Expression of transient receptor potential channels TRPC1 and TRPV4 in venoatrial endocardium of the rat heart. Neuroscience 2014; 267:195-204. [PMID: 24631674 DOI: 10.1016/j.neuroscience.2014.02.047] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2014] [Revised: 02/25/2014] [Accepted: 02/27/2014] [Indexed: 12/29/2022]
Abstract
The atrial volume receptor reflex arc serves to regulate plasma volume. Atrial volume receptors located in the endocardium of the atrial wall undergo mechanical deformation as blood is returned to the atria of the heart. The mechanosensitive channel(s) responsible for regulating plasma volume remain to be determined. Here we report that the TRP channel family members TRPC1 and TRPV4 were expressed in sensory nerve endings in the atrial endocardium. Furthermore, TRPC1 and TRPV4 were coincident with the nerve ending vesicle marker synaptophysin. Calcitonin gene-related peptide was exclusively confined to the myo- and epicardium of the atria. The small conductance Ca(2+)-activated K(+) channels (SK2 and SK4) were also present, however there was no relationship between SK and TRP channels. SK2 channels were expressed in nerves in the epicardium, while SK4 channels were in some regions of the endocardium but appeared to be present in epithelial cells rather than sensory endings. In conclusion, we have provided the first evidence for TRPC1 and TRPV4 channels as potential contributors to mechanosensation in the atrial volume receptors.
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Affiliation(s)
- F C Shenton
- School of Biological & Biomedical Sciences, Durham University, Durham DH1 3LE, UK
| | - S Pyner
- School of Biological & Biomedical Sciences, Durham University, Durham DH1 3LE, UK.
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57
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Affiliation(s)
- Susan Pyner
- School of Biological and Biomedical Sciences; Durham University; Durham UK
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58
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de Carlos F, Cobo J, Macías E, Feito J, Cobo T, Calavia M, García-Suárez O, Vega J. The Sensory Innervation of the Human Pharynx: Searching for Mechanoreceptors. Anat Rec (Hoboken) 2013; 296:1735-46. [DOI: 10.1002/ar.22792] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2013] [Accepted: 07/16/2013] [Indexed: 12/30/2022]
Affiliation(s)
- F. de Carlos
- Departamento de Cirugía y Especialidades Médicos-Quirúrgicas; Universidad de Oviedo; Oviedo Spain
- Instituto Asturiano de Odontología; Oviedo Spain
| | - J. Cobo
- Departamento de Cirugía y Especialidades Médicos-Quirúrgicas; Universidad de Oviedo; Oviedo Spain
- Instituto Asturiano de Odontología; Oviedo Spain
| | - E. Macías
- Instituto Asturiano de Odontología; Oviedo Spain
| | - J. Feito
- Departamento de Morfología y Biología Celular; Universidad de Oviedo; Oviedo Spain
- Servicio de Anatomía Patológica; Hospital Universitario Central de Asturias; Oviedo Spain
| | - T. Cobo
- Instituto Asturiano de Odontología; Oviedo Spain
| | - M.G. Calavia
- Departamento de Morfología y Biología Celular; Universidad de Oviedo; Oviedo Spain
| | - O. García-Suárez
- Departamento de Morfología y Biología Celular; Universidad de Oviedo; Oviedo Spain
| | - J.A. Vega
- Departamento de Morfología y Biología Celular; Universidad de Oviedo; Oviedo Spain
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59
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Chen CC, Wong CW. Neurosensory mechanotransduction through acid-sensing ion channels. J Cell Mol Med 2013; 17:337-49. [PMID: 23490035 PMCID: PMC3823015 DOI: 10.1111/jcmm.12025] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2012] [Accepted: 12/28/2012] [Indexed: 02/06/2023] Open
Abstract
Acid-sensing ion channels (ASICs) are voltage-insensitive cation channels responding to extracellular acidification. ASIC proteins have two transmembrane domains and a large extracellular domain. The molecular topology of ASICs is similar to that of the mechanosensory abnormality 4- or 10-proteins expressed in touch receptor neurons and involved in neurosensory mechanotransduction in nematodes. The ASIC proteins are involved in neurosensory mechanotransduction in mammals. The ASIC isoforms are expressed in Merkel cell-neurite complexes, periodontal Ruffini endings and specialized nerve terminals of skin and muscle spindles, so they might participate in mechanosensation. In knockout mouse models, lacking an ASIC isoform produces defects in neurosensory mechanotransduction of tissue such as skin, stomach, colon, aortic arch, venoatrial junction and cochlea. The ASICs are thus implicated in touch, pain, digestive function, baroreception, blood volume control and hearing. However, the role of ASICs in mechanotransduction is still controversial, because we lack evidence that the channels are mechanically sensitive when expressed in heterologous cells. Thus, ASIC channels alone are not sufficient to reconstruct the path of transducing molecules of mechanically activated channels. The mechanotransducers associated with ASICs need further elucidation. In this review, we discuss the expression of ASICs in sensory afferents of mechanoreceptors, findings of knockout studies, technical issues concerning studies of neurosensory mechanotransduction and possible missing links. Also we propose a molecular model and a new approach to disclose the molecular mechanism underlying the neurosensory mechanotransduction.
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Affiliation(s)
- Chih-Cheng Chen
- Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan.
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60
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The genetic architecture of degenerin/epithelial sodium channels in Drosophila. G3-GENES GENOMES GENETICS 2013; 3:441-50. [PMID: 23449991 PMCID: PMC3583452 DOI: 10.1534/g3.112.005272] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/22/2012] [Accepted: 12/28/2012] [Indexed: 12/14/2022]
Abstract
Degenerin/epithelial sodium channels (DEG/ENaC) represent a large family of animal-specific membrane proteins. Although the physiological functions of most family members are not known, some have been shown to act as nonvoltage gated, amiloride-sensitive sodium channels. The DEG/ENaC family is exceptionally large in genomes of Drosophila species relative to vertebrates and other insects. To elucidate the evolutionary history of the DEG/ENaC family in Drosophila, we took advantage of the genomic and genetic information available for 12 Drosophila species that represent all the major species groups in the Drosophila clade. We have identified 31 family members (termed pickpocket genes) in Drosophila melanogaster, which can be divided into six subfamilies, which are represented in all 12 species. Structure prediction analyses suggested that some subunits evolved unique structural features in the large extracellular domain, possibly supporting mechanosensory functions. This finding is further supported by experimental data that show that both ppk1 and ppk26 are expressed in multidendritic neurons, which can sense mechanical nociceptive stimuli in larvae. We also identified representative genes from five of the six DEG/ENaC subfamilies in a mosquito genome, suggesting that the core DEG/ENaC subfamilies were already present early in the dipteran radiation. Spatial and temporal analyses of expression patterns of the various pickpocket genes indicated that paralogous genes often show very different expression patterns, possibly indicating that gene duplication events have led to new physiological or cellular functions rather than redundancy. In summary, our analyses support a rapid early diversification of the DEG/ENaC family in Diptera followed by physiological and/or cellular specialization. Some members of the family may have diversified to support the physiological functions of a yet unknown class of ligands.
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61
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Banks RW, Cahusac PMB, Graca A, Kain N, Shenton F, Singh P, Njå A, Simon A, Watson S, Slater CR, Bewick GS. Glutamatergic modulation of synaptic-like vesicle recycling in mechanosensory lanceolate nerve terminals of mammalian hair follicles. J Physiol 2013; 591:2523-40. [PMID: 23440964 PMCID: PMC3678041 DOI: 10.1113/jphysiol.2012.243659] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Our aim in the present study was to determine whether a glutamatergic modulatory system involving synaptic-like vesicles (SLVs) is present in the lanceolate ending of the mouse and rat hair follicle and, if so, to assess its similarity to that of the rat muscle spindle annulospiral ending we have described previously. Both types of endings are formed by the peripheral sensory terminals of primary mechanosensory dorsal root ganglion cells, so the presence of such a system in the lanceolate ending would provide support for our hypothesis that it is a general property of fundamental importance to the regulation of the responsiveness of the broad class of primary mechanosensory endings. We show not only that an SLV-based system is present in lanceolate endings, but also that there are clear parallels between its operation in the two types of mechanosensory endings. In particular, we demonstrate that, as in the muscle spindle: (i) FM1-43 labels the sensory terminals of the lanceolate ending, rather than the closely associated accessory (glial) cells; (ii) the dye enters and leaves the terminals primarily by SLV recycling; (iii) the dye does not block the electrical response to mechanical stimulation, in contrast to its effect on the hair cell and dorsal root ganglion cells in culture; (iv) SLV recycling is Ca2+ sensitive; and (v) the sensory terminals are enriched in glutamate. Thus, in the lanceolate sensory ending SLV recycling is itself regulated, at least in part, by glutamate acting through a phospholipase D-coupled metabotropic glutamate receptor.
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Affiliation(s)
- Robert W Banks
- University of Aberdeen, School of Medical Sciences, School of Medical Sciences, Institute of Medical Sciences, Foresterhill, Aberdeen AB25 2ZD, UK.
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62
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Sonner PM, Ladle DR. Early postnatal development of GABAergic presynaptic inhibition of Ia proprioceptive afferent connections in mouse spinal cord. J Neurophysiol 2013; 109:2118-28. [PMID: 23343895 DOI: 10.1152/jn.00783.2012] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Sensory feedback is critical for normal locomotion and adaptation to external perturbations during movement. Feedback provided by group Ia afferents influences motor output both directly through monosynaptic connections and indirectly through spinal interneuronal circuits. For example, the circuit responsible for reciprocal inhibition, which acts to prevent co-contraction of antagonist flexor and extensor muscles, is driven by Ia afferent feedback. Additionally, circuits mediating presynaptic inhibition can limit Ia afferent synaptic transmission onto central neuronal targets in a task-specific manner. These circuits can also be activated by stimulation of proprioceptive afferents. Rodent locomotion rapidly matures during postnatal development; therefore, we assayed the functional status of reciprocal and presynaptic inhibitory circuits of mice at birth and compared responses with observations made after 1 wk of postnatal development. Using extracellular physiological techniques from isolated and hemisected spinal cord preparations, we demonstrate that Ia afferent-evoked reciprocal inhibition is as effective at blocking antagonist motor neuron activation at birth as at 1 wk postnatally. In contrast, at birth conditioning stimulation of muscle nerve afferents failed to evoke presynaptic inhibition sufficient to block functional transmission at synapses between Ia afferents and motor neurons, even though dorsal root potentials could be evoked by stimulating the neighboring dorsal root. Presynaptic inhibition at this synapse was readily observed, however, at the end of the first postnatal week. These results indicate Ia afferent feedback from the periphery to central spinal circuits is only weakly gated at birth, which may provide enhanced sensitivity to peripheral feedback during early postnatal experiences.
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Affiliation(s)
- Patrick M Sonner
- Department of Neuroscience, Cell Biology, and Physiology, Wright State University, Dayton, Ohio, USA
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63
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Ji HL, Zhao RZ, Chen ZX, Shetty S, Idell S, Matalon S. δ ENaC: a novel divergent amiloride-inhibitable sodium channel. Am J Physiol Lung Cell Mol Physiol 2012; 303:L1013-26. [PMID: 22983350 DOI: 10.1152/ajplung.00206.2012] [Citation(s) in RCA: 78] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The fourth subunit of the epithelial sodium channel, termed delta subunit (δ ENaC), was cloned in human and monkey. Increasing evidence shows that this unique subunit and its splice variants exhibit biophysical and pharmacological properties that are divergent from those of α ENaC channels. The widespread distribution of epithelial sodium channels in both epithelial and nonepithelial tissues implies a range of physiological functions. The altered expression of SCNN1D is associated with numerous pathological conditions. Genetic studies link SCNN1D deficiency with rare genetic diseases with developmental and functional disorders in the brain, heart, and respiratory systems. Here, we review the progress of research on δ ENaC in genomics, biophysics, proteomics, physiology, pharmacology, and clinical medicine.
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Affiliation(s)
- Hong-Long Ji
- Department of Cellular and Molecular Biology, University of Texas Health Science Center at Tyler, Tyler, Texas, USA.
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64
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Cabo R, Gálvez MA, San José I, Laurà R, López-Muñiz A, García-Suárez O, Cobo T, Insausti R, Vega JA. Immunohistochemical localization of acid-sensing ion channel 2 (ASIC2) in cutaneous Meissner and Pacinian corpuscles of Macaca fascicularis. Neurosci Lett 2012; 516:197-201. [PMID: 22708125 DOI: 10.1016/j.neulet.2012.03.081] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Abstract
Acid-sensing ion channel 2 (ASIC2) is a member of the degenerin/epithelial sodium channel superfamily, presumably involved mechanosensation. Expression of ASIC2 has been detected in mechanosensory neurons as well as in both axons and Schwann-like cells of cutaneous mechanoreceptors. In these studies we analysed expression of ASIC2 in the cutaneous sensory corpuscles of Macaca fascicularis using immunohistochemistry and laser confocal-scanner microscopy. ASIC2 immunoreactivity was detected in both Meissner and Pacinian corpuscles. It was found to co-localize with neuron-specific enolase and RT-97, but not with S100 protein, demonstrating that ASIC2 expression is restricted to axons supplying mechanoreceptors. These results demonstrate for the first time the presence of the protein ASIC2 in cutaneous rapidly adapting low-threshold mechanoreceptors of monkey, suggesting a role of this ion channel in touch sense.
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Affiliation(s)
- R Cabo
- Departamento de Morfología y Biología Celular, Universidad de Oviedo, Spain
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65
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Wilkinson KA, Kloefkorn HE, Hochman S. Characterization of muscle spindle afferents in the adult mouse using an in vitro muscle-nerve preparation. PLoS One 2012; 7:e39140. [PMID: 22745708 PMCID: PMC3380032 DOI: 10.1371/journal.pone.0039140] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2012] [Accepted: 05/18/2012] [Indexed: 11/18/2022] Open
Abstract
We utilized an in vitro adult mouse extensor digitorum longus (EDL) nerve-attached preparation to characterize the responses of muscle spindle afferents to ramp-and-hold stretch and sinusoidal vibratory stimuli. Responses were measured at both room (24°C) and muscle body temperature (34°C). Muscle spindle afferent static firing frequencies increased linearly in response to increasing stretch lengths to accurately encode the magnitude of muscle stretch (tested at 2.5%, 5% and 7.5% of resting length [Lo]). Peak firing frequency increased with ramp speeds (20% Lo/sec, 40% Lo/sec, and 60% Lo/sec). As a population, muscle spindle afferents could entrain 1:1 to sinusoidal vibrations throughout the frequency (10-100 Hz) and amplitude ranges tested (5-100 µm). Most units preferentially entrained to vibration frequencies close to their baseline steady-state firing frequencies. Cooling the muscle to 24°C decreased baseline firing frequency and units correspondingly entrained to slower frequency vibrations. The ramp component of stretch generated dynamic firing responses. These responses and related measures of dynamic sensitivity were not able to categorize units as primary (group Ia) or secondary (group II) even when tested with more extreme length changes (10% Lo). We conclude that the population of spindle afferents combines to encode stretch in a smoothly graded manner over the physiological range of lengths and speeds tested. Overall, spindle afferent response properties were comparable to those seen in other species, supporting subsequent use of the mouse genetic model system for studies on spindle function and dysfunction in an isolated muscle-nerve preparation.
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Affiliation(s)
- Katherine A Wilkinson
- Department of Physiology, Emory University School of Medicine, Atlanta, Georgia, United States of America.
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66
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Raouf R, Rugiero F, Kiesewetter H, Hatch R, Hummler E, Nassar MA, Wang F, Wood JN. Sodium channels and mammalian sensory mechanotransduction. Mol Pain 2012; 8:21. [PMID: 22449024 PMCID: PMC3378430 DOI: 10.1186/1744-8069-8-21] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2011] [Accepted: 03/26/2012] [Indexed: 12/27/2022] Open
Abstract
BACKGROUND Members of the degenerin/epithelial (DEG/ENaC) sodium channel family are mechanosensors in C elegans, and Nav1.7 and Nav1.8 voltage-gated sodium channel knockout mice have major deficits in mechanosensation. β and γENaC sodium channel subunits are present with acid sensing ion channels (ASICs) in mammalian sensory neurons of the dorsal root ganglia (DRG). The extent to which epithelial or voltage-gated sodium channels are involved in transduction of mechanical stimuli is unclear. RESULTS Here we show that deleting β and γENaC sodium channels in sensory neurons does not result in mechanosensory behavioural deficits. We had shown previously that Nav1.7/Nav1.8 double knockout mice have major deficits in behavioural responses to noxious mechanical pressure. However, all classes of mechanically activated currents in DRG neurons are unaffected by deletion of the two sodium channels. In contrast, the ability of Nav1.7/Nav1.8 knockout DRG neurons to generate action potentials is compromised with 50% of the small diameter sensory neurons unable to respond to electrical stimulation in vitro. CONCLUSION Behavioural deficits in Nav1.7/Nav1.8 knockout mice reflects a failure of action potential propagation in a mechanosensitive set of sensory neurons rather than a loss of primary transduction currents. DEG/ENaC sodium channels are not mechanosensors in mouse sensory neurons.
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Affiliation(s)
- Ramin Raouf
- Molecular Nociception Group, Wolfson Institute for Biomedical Research, University College London, London WC1E 6BT, UK
- Pfizer KCL Pain Lab, Wolfson Centre for Age-Related Diseases, King's College London, London, UK
| | - Francois Rugiero
- Molecular Nociception Group, Wolfson Institute for Biomedical Research, University College London, London WC1E 6BT, UK
| | - Hannes Kiesewetter
- Molecular Nociception Group, Wolfson Institute for Biomedical Research, University College London, London WC1E 6BT, UK
| | - Rachel Hatch
- Molecular Nociception Group, Wolfson Institute for Biomedical Research, University College London, London WC1E 6BT, UK
| | - Edith Hummler
- Department of Pharmacology and Toxicology, University of Lausanne, Lausanne 1005, Switzerland
| | - Mohammed A Nassar
- Molecular Nociception Group, Wolfson Institute for Biomedical Research, University College London, London WC1E 6BT, UK
- Biomedical Science University of Sheffield, Sheffield S10 2TN, UK
| | - Fan Wang
- Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710, USA
| | - John N Wood
- Molecular Nociception Group, Wolfson Institute for Biomedical Research, University College London, London WC1E 6BT, UK
- DMMBPS, Seoul National University, Seoul 151-742, Korea
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67
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Abstract
The epithelial Na(+) channel (ENaC) and acid-sensitive ion channel (ASIC) branches of the ENaC/degenerin superfamily of cation channels have drawn increasing attention as potential therapeutic targets in a variety of diseases and conditions. Originally thought to be solely expressed in fluid absorptive epithelia and in neurons, it has become apparent that members of this family exhibit nearly ubiquitous expression. Therapeutic opportunities range from hypertension, due to the role of ENaC in maintaining whole body salt and water homeostasis, to anxiety disorders and pain associated with ASIC activity. As a physiologist intrigued by the fundamental mechanics of salt and water transport, it was natural that Dale Benos, to whom this series of reviews is dedicated, should have been at the forefront of research into the amiloride-sensitive sodium channel. The cloning of ENaC and subsequently the ASIC channels has revealed a far wider role for this channel family than was previously imagined. In this review, we will discuss the known and potential roles of ENaC and ASIC subunits in the wide variety of pathologies in which these channels have been implicated. Some of these, such as the role of ENaC in Liddle's syndrome are well established, others less so; however, all are related in that the fundamental defect is due to inappropriate channel activity.
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Affiliation(s)
- Yawar J Qadri
- Department of Physiology and Biophysics, University of Alabama at Birmingham, AL 35294, USA
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68
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Schaffhauser DF, Andrini O, Ghezzi C, Forster IC, Franco-Obregón A, Egli M, Dittrich PS. Microfluidic platform for electrophysiological studies on Xenopus laevis oocytes under varying gravity levels. LAB ON A CHIP 2011; 11:3471-3478. [PMID: 21870012 DOI: 10.1039/c0lc00729c] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Voltage clamp measurements reveal important insights into the activity of membrane ion channels. While conventional voltage clamp systems are available for laboratory studies, these instruments are generally unsuitable for more rugged operating environments. In this study, we present a non-invasive microfluidic voltage clamp system developed for the use under varying gravity levels. The core component is a multilayer microfluidic device that provides an immobilisation site for Xenopus laevis oocytes on an intermediate layer, and fluid and electrical connections from either side of the cell. The configuration that we term the asymmetrical transoocyte voltage clamp (ATOVC) also permits electrical access to the cytosol of the oocyte without physical introduction of electrodes by permeabilisation of a large region of the oocyte membrane so that a defined membrane patch can be voltage clamped. The constant low level air pressure applied to the oocyte ensures stable immobilisation, which is essential for keeping the leak resistance constant even under varying gravitational forces. The ease of oocyte mounting and immobilisation combined with the robustness and complete enclosure of the fluidics system allow the use of the ATOVC under extreme environmental conditions, without the need for intervention by a human operator. Results for oocytes over-expressing the epithelial sodium channel (ENaC) obtained under laboratory conditions as well as under conditions of micro- and hypergravity demonstrate the high reproducibility and stability of the ATOVC system under distinct mechanical scenarios.
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Nishikawa S. Fluorescent AM1-43 and FM1-43 probes for dental sensory nerves and cells: Their labeling mechanisms and applications. JAPANESE DENTAL SCIENCE REVIEW 2011. [DOI: 10.1016/j.jdsr.2010.12.003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
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Bullinger KL, Nardelli P, Wang Q, Rich MM, Cope TC. Oxaliplatin neurotoxicity of sensory transduction in rat proprioceptors. J Neurophysiol 2011; 106:704-9. [PMID: 21593386 DOI: 10.1152/jn.00083.2011] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Neurotoxic effects of oxaliplatin chemotherapy, including proprioceptive impairments, are debilitating and dose limiting. Here, we sought to determine whether oxaliplatin interrupts normal proprioceptive feedback by impairing sensory transduction of muscle length and force by neurons that are not damaged by dying-back neuropathy. Oxaliplatin was administered over 4 wk to rats in doses that produced systemic changes, e.g., decreased platelets and stunted weight gain, but no significant abnormality in the terminal ends of primary muscle spindle sensory neurons. The absence of neuropathy enabled the determination of whether oxaliplatin caused functional deficits in sensory encoding without the confounding issue of axon death. Rats were anesthetized, and action potentials encoding muscle stretch and contraction were recorded intra-axonally from dorsal roots. In striking contrast with normal proprioceptors, those from oxaliplatin-treated rats typically failed to sustain firing during static muscle stretch. The ability of spindle afferents to sustain and centrally conduct trains of action potentials in response to rapidly repeated transient stimuli, i.e., vibration, demonstrated functional competence of the parent axons. These data provide the first evidence that oxaliplatin causes persistent and selective deficits in sensory transduction that are not due to axon degeneration. Our findings raise the possibility that even those axons that do not degenerate after oxaliplatin treatment may have functional deficits that worsen outcome.
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Affiliation(s)
- Katie L Bullinger
- Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton, OH 45435, USA
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Suslak TJ, Armstrong JD, Jarman AP. A general mathematical model of transduction events in mechano-sensory stretch receptors. NETWORK (BRISTOL, ENGLAND) 2011; 22:133-142. [PMID: 22149673 DOI: 10.3109/0954898x.2011.638967] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Crayfish (Astacus astacus) muscle stretch receptors show strong homology to mammalian muscle spindles and bipolar neurons in D. melanogaster. All are typical, non-ciliated, stretch-sensitive, afferent neurons. Such receptors are observed in many species and perform an important sensory role. However, they are poorly characterised. A previous study reported a bio-mechanical and behavioural model of A. astacus stretch receptors, which used the principles of elasticity and tension in a spring to describe the adaptation of a mechano-sensory ending. This model described the changing mechano-sensory currents in the receptor when subjected to a stretch protocol. Here, we re-implement and extend this model. Notably, we introduce additional descriptions of voltage-gated channels that are suggested to contribute to stretch receptor mechano-transduction. Our model presents a more complete picture of the initiation of the mechano-receptor potential in response to a stretching stimulus. The inclusion of voltage-dependent sodium and potassium currents in addition to the initial mechano-sensitive sodium current allowed the model to account for most of the initial stretch response of the receptor. This preliminary model has potential for extension to describe fully the behaviour of non-ciliated mechano-sensors across species and predict the molecular mediators of mechano-transduction.
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Affiliation(s)
- T J Suslak
- Doctoral Training Centre in Neuroinformatics and Neural Computation, University of Edinburgh, 10 Crichton St., Edinburgh, UK.
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Abstract
All animals use a sophisticated array of receptor proteins to sense their external and internal environments. Major advances have been made in recent years in understanding the molecular and genetic bases for sensory transduction in diverse modalities, indicating that both metabotropic and ionotropic pathways are important in sensory functions. Here, I review the historical background and recent advances in understanding the roles of a relatively newly discovered family of receptors, the degenerin/epithelial sodium channels (DEG/ENaC). These animal-specific cation channels show a remarkable sequence and functional diversity in different species and seem to exert their functions in diverse sensory modalities. Functions for DEG/ENaC channels have been implicated in mechanosensation as well as chemosensory transduction pathways. In spite of overall sequence diversity, all family members share a unique protein topology that includes just two transmembrane domains and an unusually large and highly structured extracellular domain, that seem to be essential for both their mechanical and chemical sensory functions. This review will discuss many of the recent discoveries and controversies associated with sensory function of DEG/ENaC channels in both vertebrate and invertebrate model systems, covering the role of family members in taste, mechanosensation, and pain.
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Affiliation(s)
- Owen P Hamill
- Department of Neuroscience and Cell Biology, University of Texas Medical Branch, 301 University Blvd, Galveston, TX 77555, USA.
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