title: The quaternary lidocaine derivative, QX-314, exerts biphasic effects on transient receptor potential vanilloid subtype 1 channels in vitro.
abstract: BACKGROUND
  Transient receptor potential vanilloid subfamily member 1 (TRPV1) channels are important integrators of noxious stimuli with pronounced expression in nociceptive neurons. The experimental local anesthetic, QX-314, a quaternary (i.e., permanently charged) lidocaine derivative, recently has been shown to interact with and permeate these channels to produce nociceptive and sensory blockade in animals in vivo. However, little is known about the specific interactions between QX-314 and TRPV1 channels. Thus, the authors examined the mechanistic basis by which QX-314 acts on TRPV1 channels.
  
  
  METHODS
  The authors conducted an in vitro laboratory study in which they expressed TRPV1 and TRPV4 channels in Xenopus laevis oocytes and recorded cation currents with the two-electrode voltage clamp method. They used confocal microscopy for Ca²⁺ imaging in TRPV1 transient transfected tsA201 cells. Drugs were bath-applied by gravity perfusion. Statistical analyses were performed using Student t test, ANOVA, and post tests as appropriate (P < 0.05).
  
  
  RESULTS
  QX-314 activated TRPV1 channels at 10, 30, and 60 mM (0.4 ± 0.1%, 3.5 ± 1.3%, and 21.5 ± 6.9% of normalized peak activation, respectively; mean ± SEM; n = 12) but not TRPV4 channels (P < 0.001). Activation by QX-314 was blocked by the TRPV1 antagonist, capsazepine (100 μM). QX-314 (60 mM) activation and blockade by capsazepine was also demonstrated in Ca²⁺ imaging studies on TRPV1-expressing tsA201 cells. At subactivating concentrations (less than 1 mM), QX-314 potently inhibited capsaicin-evoked TRPV1 currents with an IC₅₀ of 8.0 ± 0.6 μM.
  
  
  CONCLUSIONS
  The results of this study show that the quaternary lidocaine derivative QX-314 exerts biphasic effects on TRPV1 channels, inhibiting capsaicin-evoked TRPV1 currents at lower (micromolar) concentrations and activating TRPV1 channels at higher (millimolar) concentrations. These findings provide novel insights into the interactions between QX-314 and TRPV1 and may provide an explanation for the irritant properties of intrathecal QX-314 in mice in vivo.
authors.affiliation: St. Paul's Hospital, and Department of Anesthesiology, Pharmacology & Therapeutics, The University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Ricardo E
authors.initials: RE
authors.lastname: Rivera-Acevedo
authors.forename: Stephan A
authors.initials: SA
authors.lastname: Pless
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Ahern
authors.forename: Stephan K W
authors.initials: SK
authors.lastname: Schwarz
mesh_terms: D000818:Animals; D005260:Female; D006801:Humans; D008012:Lidocaine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology; D050916:TRPV Cation Channels / Q000819:agonists / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D050051:Transient Receptor Potential Channels / Q000819:agonists / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D014982:Xenopus laevis
chemical_list: D050916:TRPV Cation Channels; C494482:TRPV1 protein, human; C416986:TRPV4 protein, human; D050051:Transient Receptor Potential Channels; C012647:QX-314; D008012:Lidocaine