title: Α- and β-subunit composition of voltage-gated sodium channels investigated with μ-conotoxins and the recently discovered μO§-conotoxin GVIIJ.
abstract: We investigated the identities of the isoforms of the α (NaV1)- and β (NaVβ)-subunits of voltage-gated sodium channels, including those responsible for action potentials in rodent sciatic nerves. To examine α-subunits, we used seven μ-conotoxins, which target site 1 of the channel. With the use of exogenously expressed channels, we show that two of the μ-conotoxins, μ-BuIIIB and μ-SxIIIA, are 50-fold more potent in blocking NaV1.6 from mouse than that from rat. Furthermore, we observed that μ-BuIIIB and μ-SxIIIA are potent blockers of large, myelinated A-fiber compound action potentials (A-CAPs) [but not small, unmyelinated C-fiber CAPs (C-CAPs)] in the sciatic nerve of the mouse (unlike A-CAPs of the rat, previously shown to be insensitive to these toxins). To investigate β-subunits, we used two synthetic derivatives of the recently discovered μO§-conotoxin GVIIJ that define site 8 of the channel, as previously characterized with cloned rat NaV1- and NaVβ-subunits expressed in Xenopus laevis oocytes, where it was shown that μO§-GVIIJ is a potent inhibitor of several NaV1-isoforms and that coexpression of NaVβ2 or -β4 (but not NaVβ1 or -β3) totally protects against block by μO§-GVIIJ. We report here the effects of μO§-GVIIJ on 1) sodium currents of mouse NaV1.6 coexpressed with various combinations of NaVβ-subunits in oocytes; 2) A- and C-CAPs of mouse and rat sciatic nerves; and 3) sodium currents of small and large neurons dissociated from rat dorsal root ganglia. Our overall results lead us to conclude that action potentials in A-fibers of the rodent sciatic nerve are mediated primarily by NaV1.6 associated with NaVβ2 or NaVβ4.
authors: Department of Biology, University of Utah, Salt Lake City, Utah; and.
authors: Michael J
authors: MJ
authors: Wilson
authors: Department of Biology, University of Utah, Salt Lake City, Utah; and.
authors: Min-Min
authors: MM
authors: Zhang
authors: Department of Biology, University of Utah, Salt Lake City, Utah; and.
authors: Joanna
authors: J
authors: Gajewiak
authors: Department of Biology, University of Utah, Salt Lake City, Utah; and.
authors: Layla
authors: L
authors: Azam
authors: The Clayton Foundation Laboratories for Peptide Biology, The Salk Institute, La Jolla, California.
authors: Jean E
authors: JE
authors: Rivier
authors: Department of Biology, University of Utah, Salt Lake City, Utah; and.
authors: Baldomero M
authors: BM
authors: Olivera
authors: Department of Biology, University of Utah, Salt Lake City, Utah; and yoshikami@bioscience.utah.edu.
authors: Doju
authors: D
authors: Yoshikami
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D002478:Cells, Cultured; D020916:Conotoxins / Q000008:administration & dosage* / Q000737:chemistry; D004305:Dose-Response Relationship, Drug; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D009865:Oocytes; D021122:Protein Subunits; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000378:metabolism; D013329:Structure-Activity Relationship; D061567:Voltage-Gated Sodium Channel Blockers; D061566:Voltage-Gated Sodium Channels / Q000737:chemistry / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: D020916:Conotoxins; D021122:Protein Subunits; D061567:Voltage-Gated Sodium Channel Blockers; D061566:Voltage-Gated Sodium Channels; D012964:Sodium
keywords: Nav1.6; Navβ-subunit; conotoxin; dorsal root ganglion neuron; sciatic nerve action potential
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