title: Novel gating and sensitizing mechanism of capsaicin receptor (TRPV1): tonic inhibitory regulation of extracellular sodium through the external protonation sites on TRPV1.
abstract: Transient receptor potential V1 (TRPV1) is a nonselective cation channel expressed in nociceptors and activated by capsaicin. TRPV1 detects diverse stimuli, including acid, heat, and endogenous vanilloids, and functions as a molecular integrator of pain perception. Herein we demonstrate a novel regulatory role of extracellular Na(+) ([Na(+)](o)) on TRPV1 function. In human embryonic kidney 293 cells expressing porcine TRPV1, low [Na(+)](o) evoked increases of [Ca(2+)](i) that were suppressed by TRPV1 antagonists and facilitated responses to capsaicin, protons, heat, and an endovanilloid. [Na(+)](o) removal simultaneously elicited a [Ca(2+)](i) increase and outward-rectified current with a reversal potential similar to those of capsaicin. Neutralization of the two acidic residues which confer the proton sensitivity to TRPV1 resulted in a reduction of low [Na(+)](o)-induced responses. In primary culture of porcine sensory neurons, the removal of [Na(+)](o) produced a [Ca(2+)](i) increase and current responses only in the cells responding to capsaicin. Low [Na(+)](o) evoked a [Ca(2+)](i) increase in sensory neurons of wild type mice, but not TRPV1-null mice, and in human embryonic kidney 293 cells expressing human TRPV1. The present results suggest that [Na(+)](o) negatively regulates the gating and polymodal sensitization of the TRPV1 channel. [Na(+)](o) surrounding several proton-sensitive sites on the extracellular side of the pore-forming loop of the TRPV1 channel may play an important role as a brake to suppress the excessive activity of this channel under physiological conditions.
authors.affiliation: Laboratory of Pharmacology, Department of Biomedical Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan. tohta@vetmed.hokudai.ac.jp
authors.forename: Toshio
authors.initials: T
authors.lastname: Ohta
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Imagawa
authors.forename: Shigeo
authors.initials: S
authors.lastname: Ito
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002211:Capsaicin / Q000494:pharmacology; D002460:Cell Line; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D017136:Ion Transport / Q000187:drug effects / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D009619:Nociceptors / Q000378:metabolism*; D010146:Pain / Q000378:metabolism; D017433:Protein Structure, Secondary / Q000502:physiology; D011522:Protons; D018689:Sensory System Agents / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism*; D013552:Swine; D050916:TRPV Cation Channels / Q000235:genetics / Q000378:metabolism*
chemical_list: D011522:Protons; D018689:Sensory System Agents; D050916:TRPV Cation Channels; C494482:TRPV1 protein, human; C493921:TRPV1 protein, mouse; D012964:Sodium; D002211:Capsaicin; D002118:Calcium