title: Imiquimod enhances excitability of dorsal root ganglion neurons by inhibiting background (K(2P)) and voltage-gated (K(v)1.1 and K(v)1.2) potassium channels.
abstract: BACKGROUND
  Imiquimod (IQ) is known as an agonist of Toll-like receptor 7 (TLR7) and is widely used to treat various infectious skin diseases. However, it causes severe itching sensation as its side effect. The precise mechanism of how IQ causes itching sensation is unknown. A recent report suggested a molecular target of IQ as TLR7 expressed in dorsal root ganglion (DRG) neurons. However, we recently proposed a TLR7-independent mechanism, in which the activation of TLR7 is not required for the action of IQ in DRG neurons. To resolve this controversy regarding the involvement of TLR7 and to address the exact molecular identity of itching sensation by IQ, we investigated the possible molecular target of IQ in DRG neurons.
  
  
  RESULTS
  When IQ was applied to DRG neurons, we observed an increase in action potential (AP) duration and membrane resistance both in wild type and TLR7-deficient mice. Based on these results, we tested whether the treatment of IQ has an effect on the activity of K(+) channels, K(v)1.1 and K(v)1.2 (voltage-gated K(+) channels) and TREK1 and TRAAK (K(2P) channels). IQ effectively reduced the currents mediated by both K(+) channels in a dose-dependent manner, acting as an antagonist at TREK1 and TRAAK and as a partial antagonist at K(v)1.1 and K(v)1.2.
  
  
  CONCLUSIONS
  Our results demonstrate that IQ blocks the voltage-gated K(+) channels to increase AP duration and K(2P) channels to increase membrane resistance, which are critical for the membrane excitability of DRG neurons. Therefore, we propose that IQ enhances the excitability of DRG neurons by blocking multiple potassium channels and causing pruritus.
authors.affiliation: WCI Center for Functional Connectomics, Korea Institute of Science and Technology, Seoul, 136-791, Republic of Korea.
authors.forename: Jaekwang
authors.initials: J
authors.lastname: Lee
authors.forename: Taekeun
authors.initials: T
authors.lastname: Kim
authors.forename: Jinpyo
authors.initials: J
authors.lastname: Hong
authors.forename: Junsung
authors.initials: J
authors.lastname: Woo
authors.forename: Hyunjung
authors.initials: H
authors.lastname: Min
authors.forename: Eunmi
authors.initials: E
authors.lastname: Hwang
authors.forename: Sung Joong
authors.initials: SJ
authors.lastname: Lee
authors.forename: C Justin
authors.initials: CJ
authors.lastname: Lee
mesh_terms: D000200:Action Potentials / Q000187:drug effects*; D000634:Aminoquinolines / Q000494:pharmacology*; D000818:Animals; D019556:COS Cells; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D002522:Chlorocebus aethiops; D005727:Ganglia, Spinal / Q000166:cytology*; D000077271:Imiquimod; D015640:Ion Channel Gating / Q000187:drug effects; D051662:Kv1.1 Potassium Channel / Q000037:antagonists & inhibitors* / Q000378:metabolism; D051663:Kv1.2 Potassium Channel / Q000037:antagonists & inhibitors* / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000172:deficiency / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D024683:Potassium Channels, Tandem Pore Domain / Q000037:antagonists & inhibitors* / Q000378:metabolism; D051381:Rats; D051199:Toll-Like Receptor 7 / Q000172:deficiency / Q000378:metabolism
chemical_list: D000634:Aminoquinolines; D051663:Kv1.2 Potassium Channel; D008562:Membrane Glycoproteins; D024683:Potassium Channels, Tandem Pore Domain; C477038:Tlr7 protein, mouse; D051199:Toll-Like Receptor 7; D051662:Kv1.1 Potassium Channel; D000077271:Imiquimod