Localization of the tetrodotoxin-resistant sodium channel NaN in nociceptors

Fjell, Jenny; Hjelmström, Peter; Hormuzdiar, W. N.; Milenković, Milan; Aglieco, Fabio; Tyrrell, Lynda; Dib‐Hajj, Sulayman D.; Waxman, Stephen G.; Black, Joel A.

doi:10.1097/00001756-200001170-00039

Cited by 116 publications

(92 citation statements)

References 10 publications

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“…The influence of TTX-R sodium current in shaping the action potential probably is not limited to the cell body, because there is evidence that TTX-R current contributes to the generation of action potentials in nerve endings of nociceptors (Brock et al, 1998;Strassman and Raymond, 1999) as well as the propagation of action potentials in unmyelinated C-fibers under some conditions (Jeftinija, 1994;Quasthoff et al, 1995). In addition, immunocytochemistry suggests that Na V 1.8 and 1.9 channels are expressed widely in unmyelinated DRG neurons, with labeling in peripheral endings, axons, somata, and nerve terminals (Amaya et al, 2000;Coward et al, 2000;Fjell et al, 2000;Fang et al, 2002).…”

Section: Discussionmentioning

confidence: 99%

Roles of Tetrodotoxin (TTX)-Sensitive Na⁺Current, TTX-Resistant Na⁺Current, and Ca²⁺Current in the Action Potentials of Nociceptive Sensory Neurons

2002

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Nociceptive sensory neurons are unusual in expressing voltage-gated inward currents carried by sodium channels resistant to block by tetrodotoxin (TTX) as well as currents carried by conventional TTX-sensitive sodium channels and voltagedependent calcium channels. To examine how currents carried by each of these helps to shape the action potential in smalldiameter dorsal root ganglion cell bodies, we voltage clamped cells by using the action potential recorded from each cell as the command voltage. Using intracellular solutions of physiological ionic composition, we isolated individual components of current flowing during the action potential with the use of channel blockers (TTX for TTX-sensitive sodium currents and a mixture of calcium channel blockers for calcium currents) and ionic substitution (TTX-resistant current measured by the replacement of extracellular sodium by N-methyl-D-glucamine in the presence of TTX, with correction for altered driving force). TTX-resistant sodium channels activated quickly enough to carry the largest inward charge during the upstroke of the nociceptor action potential (ϳ58%), with TTX-sensitive sodium channels also contributing significantly (ϳ40%), especially near threshold, and high voltage-activated calcium currents much less (ϳ2%). Action potentials had a prominent shoulder during the falling phase, characteristic of nociceptive neurons. TTXresistant sodium channels did not inactivate completely during the action potential and carried the majority (58%) of inward current flowing during the shoulder, with high voltage-activated calcium current also contributing significantly (39%). Unlike calcium current, TTX-resistant sodium current is not accompanied by opposing calcium-activated potassium current and may provide an effective mechanism by which the duration of action potentials (and consequently calcium entry) can be regulated.

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Section: Discussionmentioning

confidence: 99%

Roles of Tetrodotoxin (TTX)-Sensitive Na⁺Current, TTX-Resistant Na⁺Current, and Ca²⁺Current in the Action Potentials of Nociceptive Sensory Neurons

2002

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“…Both Na v 1.1 and Na v 1.2 have been observed at the nodes of Ranvier in young mice and are gradually replaced with Na v 1.6 during development (23,24). Na v 1.6 is the VGSC isoform found at most adult nodes in the peripheral nervous system and the central nervous system (25); however, Na v 1.2, -1.8, and -1.9 have also been detected at adult nodes (24,26,27). A similar diversity is observed at the IS where Na v 1.2, -1.6, and -1.8 have been localized (11,26).…”

Section: Discussionmentioning

confidence: 99%

Identification of a Conserved Ankyrin-binding Motif in the Family of Sodium Channel α Subunits

Lemaillet

Walker

Lambert

2003

Journal of Biological Chemistry

226

231

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Interactions with ankyrin G are crucial to the localization of voltage-gated sodium channels (VGSCs) at the axon initial segment and for neurons to initiate action potentials. However, the molecular nature of these interactions remains unclear. Here we report that VGSC-␣, but not -␤, subunits bind to ankyrin G using pull-down assays. Further dissection of this activity identifies a conserved 9-amino acid motif ((V/A)P(I/L)AXXE(S/D)D) required for ankyrin G binding. This motif is also required for the localization of chimeric neurofascin/sodium channel molecules to the initial segment of cultured hippocampal neurons. The conserved nature of this motif suggests that it functions to localize sodium channels to a variety of "excitable" membrane domains both inside and outside of the nervous system.The concentration of voltage-gated sodium channels (VGSCs) 1 into excitable membrane domains is crucial to information processing and transmission in the nervous system and to excitation/contraction coupling in muscle. Localized concentrations of VGSCs at the initial segment (IS) and the nodes of Ranvier are necessary for the initiation and propagation of action potentials through myelinated axons. However, mechanisms underlying the localization of VGSCs to these excitable membrane domains remain relatively unknown. In neurons, VGSCs exist as heterotrimers composed of a large pore-forming ␣ subunit associated with two smaller accessory ␤ subunits (reviewed in Ref. 1). At least 10 genes encoding putative ␣ subunits have been identified in mammals (reviewed in Ref.2) along with three ␤ subunit genes. ␤ subunits not only modulate the activity of ␣ subunits (3, 4) but also exhibit characteristics of cell adhesion molecules (CAMs) binding to extracellular matrix molecules such as tenascin-C and -R (5) and other CAMs such as neurofascin (6).Polarized localization of VGSCs in the axonal membrane requires interactions with members of the ankyrin family of peripheral membrane proteins (reviewed in Ref. 7). Ankyrins function as membrane-cytoskeleton adaptors that immobilize integral membrane proteins to the spectrin-based membrane skeleton. Ankyrins co-purify with and directly bind to purified VGSCs (8), and specific isoforms of the ankyrin G gene are concentrated with VGSCs at the IS (9), the nodes of Ranvier (9), and the neuromuscular junction (10). The functional importance of the interaction between ankyrin G and VGSCs is demonstrated in knockouts of ankyrin G in the mouse cerebellum. Purkinje cells from knockout animals are deficient in localized VGSC concentrations at the IS (11) and are unable to initiate action potentials (12).In addition to VGSCs, ankyrins also interact with a variety of other integral membrane proteins present at the node including the CAMs neurofascin and NrCAM (13,14). Interactions of ankyrins with VGSCs (15) and other integral membrane proteins are mediated through the N-terminal 90-kDa repeat or membrane-binding (MB) domain. The interaction between the ankyrin MB domain and neurofascin/NrCAM is depende...

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“…Na v 1.8 is expressed almost exclusively in small and medium sized DRG neurons, most of which are nociceptors (33,34), and is up-regulated in inflammatory pain states (35,36). The role of Na v 1.8 in pain was confirmed by studies of Na v 1.8 null mutant mice, which exhibited a decreased response to noxious mechanical stimuli and reduced inflammatory-induced hyperalgesia (3).…”

Section: Discussionmentioning

confidence: 99%

Structures of μO-conotoxins from Conus marmoreus

Daly

Ekberg

Thomas

et al. 2004

Journal of Biological Chemistry

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The O-conotoxins are an intriguing class of conotoxins targeting various voltage-dependent sodium channels and molluscan calcium channels. In the current study, we have shown MrVIA and MrVIB to be the first known peptidic inhibitors of the transient tetrodotoxinresistant (TTX-R) Na ؉ current in rat dorsal root ganglion neurons, in addition to inhibiting tetrodotoxinsensitive Na ؉ currents. Human TTX-R sodium channels are a therapeutic target for indications such as pain, highlighting the importance of the O-conotoxins as potential leads for drug development. Furthermore, we have used NMR spectroscopy to provide the first structural information on this class of conotoxins. MrVIA and MrVIB are hydrophobic peptides that aggregate in aqueous solution but were solubilized in 50% acetonitrile/water. The three-dimensional structure of MrVIB consists of a small ␤-sheet and a cystine knot arrangement of the three-disulfide bonds. It contains four backbone "loops" between successive cysteine residues that are exposed to the solvent to varying degrees. The largest of these, loop 2, is the most disordered part of the molecule, most likely due to flexibility in solution. This disorder is the most striking difference between the structures of MrVIB and the known ␦-and -conotoxins, which along with the O-conotoxins are members of the O superfamily. Loop 2 of -conotoxins has previously been shown to contain residues critical for binding to voltage-gated calcium channels, and it is interesting to speculate that the flexibility observed in MrVIB may accommodate binding to both sodium and molluscan calcium channels.

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Localization of the tetrodotoxin-resistant sodium channel NaN in nociceptors

Cited by 116 publications

References 10 publications

Roles of Tetrodotoxin (TTX)-Sensitive Na⁺Current, TTX-Resistant Na⁺Current, and Ca²⁺Current in the Action Potentials of Nociceptive Sensory Neurons

Roles of Tetrodotoxin (TTX)-Sensitive Na⁺Current, TTX-Resistant Na⁺Current, and Ca²⁺Current in the Action Potentials of Nociceptive Sensory Neurons

Identification of a Conserved Ankyrin-binding Motif in the Family of Sodium Channel α Subunits

Structures of μO-conotoxins from Conus marmoreus

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Localization of the tetrodotoxin-resistant sodium channel NaN in nociceptors

Cited by 116 publications

References 10 publications

Roles of Tetrodotoxin (TTX)-Sensitive Na+Current, TTX-Resistant Na+Current, and Ca2+Current in the Action Potentials of Nociceptive Sensory Neurons

Roles of Tetrodotoxin (TTX)-Sensitive Na+Current, TTX-Resistant Na+Current, and Ca2+Current in the Action Potentials of Nociceptive Sensory Neurons

Identification of a Conserved Ankyrin-binding Motif in the Family of Sodium Channel α Subunits

Structures of μO-conotoxins from Conus marmoreus

Contact Info

Product

Resources

About

Roles of Tetrodotoxin (TTX)-Sensitive Na⁺Current, TTX-Resistant Na⁺Current, and Ca²⁺Current in the Action Potentials of Nociceptive Sensory Neurons

Roles of Tetrodotoxin (TTX)-Sensitive Na⁺Current, TTX-Resistant Na⁺Current, and Ca²⁺Current in the Action Potentials of Nociceptive Sensory Neurons