title: The endocannabinoid anandamide inhibits voltage-gated sodium channels Nav1.2, Nav1.6, Nav1.7, and Nav1.8 in Xenopus oocytes.
abstract: BACKGROUND
  Anandamide is an endocannabinoid that regulates multiple physiological functions by pharmacological actions, in a manner similar to marijuana. Recently, much attention has been paid to the analgesic effect of endocannabinoids in terms of identifying new pharmacotherapies for refractory pain management, but the mechanisms of the analgesic effects of anandamide are still obscure. Voltage-gated sodium channels are believed to play important roles in inflammatory and neuropathic pain. We investigated the effects of anandamide on 4 neuronal sodium channel α subunits, Nav1.2, Nav1.6, Nav1.7, and Nav1.8, to explore the mechanisms underlying the antinociceptive effects of anandamide.
  
  
  METHODS
  We studied the effects of anandamide on Nav1.2, Nav1.6, Nav1.7, and Nav1.8 α subunits with β1 subunits by using whole-cell, 2-electrode, voltage-clamp techniques in Xenopus oocytes.
  
  
  RESULTS
  Anandamide inhibited sodium currents of all subunits at a holding potential causing half-maximal current (V1/2) in a concentration-dependent manner. The half-maximal inhibitory concentration values for Nav1.2, Nav1.6, Nav1.7, and Nav1.8 were 17, 12, 27, and 40 μmol/L, respectively, indicating an inhibitory effect on Nav1.6, which showed the highest potency. Anandamide raised the depolarizing shift of the activation curve as well as the hyperpolarizing shift of the inactivation curve in all α subunits, suggesting that sodium current inhibition was due to decreased activation and increased inactivation. Moreover, anandamide showed a use-dependent block in Nav1.2, Nav1.6, and Nav1.7 but not Nav1.8.
  
  
  CONCLUSIONS
  Anandamide inhibited the function of α subunits in neuronal sodium channels Nav1.2, Nav1.6, Nav1.7, and Nav1.8. These results help clarify the mechanisms of the analgesic effects of anandamide.
authors.affiliation: From the *Department of Anesthesiology, School of Medicine; †Department of Occupational Toxicology, Institute of Industrial Ecological Sciences, University of Occupational and Environmental Health, ‡Department of Pharmacology, School of Medicine, University of Occupational and Environmental Health, Fukuoka; §Department of Molecular Pathology & Metabolic Disease, Faculty of Pharmaceutical Sciences, Tokyo university of Science, Chiba; and ‖Cancer Pathophysiology Division, National Cancer Center Research Institute, Tokyo, Japan.
authors.forename: Dan
authors.initials: D
authors.lastname: Okura
authors.forename: Takafumi
authors.initials: T
authors.lastname: Horishita
authors.forename: Susumu
authors.initials: S
authors.lastname: Ueno
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Yanagihara
authors.forename: Yuka
authors.initials: Y
authors.lastname: Sudo
authors.forename: Yasuhito
authors.initials: Y
authors.lastname: Uezono
authors.forename: Takeyoshi
authors.initials: T
authors.lastname: Sata
mesh_terms: D000818:Animals; D001095:Arachidonic Acids / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D063388:Endocannabinoids / Q000494:pharmacology*; D005260:Female; D062551:NAV1.2 Voltage-Gated Sodium Channel / Q000378:metabolism*; D062557:NAV1.6 Voltage-Gated Sodium Channel / Q000378:metabolism*; D062556:NAV1.7 Voltage-Gated Sodium Channel / Q000378:metabolism*; D062559:NAV1.8 Voltage-Gated Sodium Channel / Q000378:metabolism*; D009865:Oocytes / Q000187:drug effects* / Q000378:metabolism; D053284:Polyunsaturated Alkamides / Q000494:pharmacology*; D026941:Sodium Channel Blockers / Q000494:pharmacology*; D061566:Voltage-Gated Sodium Channels; D014982:Xenopus laevis
chemical_list: D001095:Arachidonic Acids; D063388:Endocannabinoids; D062551:NAV1.2 Voltage-Gated Sodium Channel; D062557:NAV1.6 Voltage-Gated Sodium Channel; D062556:NAV1.7 Voltage-Gated Sodium Channel; D062559:NAV1.8 Voltage-Gated Sodium Channel; D053284:Polyunsaturated Alkamides; C568317:SCN10A protein, human; C100681:SCN8A protein, human; C486866:SCN9A protein, human; D026941:Sodium Channel Blockers; D061566:Voltage-Gated Sodium Channels; C078814:anandamide