title: Evans blue is a specific antagonist of the human epithelial Na+ channel delta-subunit.
abstract: The epithelial Na(+) channel (ENaC) regulates Na(+) homeostasis in cells and across epithelia. Four homologous ENaC subunits (alpha, beta, gamma, and delta) have been isolated in mammals. Combination of alpha-, beta-, and gamma-subunits or delta-, beta-, and gamma-subunits forms fully functional channels. Amiloride is a well known blocker of the ENaC family that inhibits both channel complexes. However, no specific antagonists are currently known that distinguish them. Here, we show that Evans blue, a diagnostic aid for the measurement of blood volume and vascular permeability, inhibits the activity of the delta-subunit expressed in Xenopus oocytes. The inward currents at a holding potential of -60 mV in human ENaCdeltabetagamma-expressing oocytes were inhibited by the application of Evans blue in a concentration-dependent manner with an IC(50) value of 143 muM. Evans blue markedly inhibited the delta-subunit current but did not block the alpha-subunit current. In conclusion, Evans blue is the first known delta-subunit-specific antagonist of ENaC. This finding provides us with a key compound for elucidating the physiological and pathological functions of ENaCdelta in humans and for drug development in the ENaC family.
authors.affiliation: Department of Molecular Morphology, Graduate School of Medical Sciences, Nagoya City University, Japan. yamamura@med.nagoya-cu.ac.jp
authors.forename: Hisao
authors.initials: H
authors.lastname: Yamamura
authors.forename: Shinya
authors.initials: S
authors.lastname: Ugawa
authors.forename: Takashi
authors.initials: T
authors.lastname: Ueda
authors.forename: Shoichi
authors.initials: S
authors.lastname: Shimada
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D053503:Epithelial Sodium Channels; D005070:Evans Blue / Q000494:pharmacology*; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D026941:Sodium Channel Blockers; D015222:Sodium Channels / Q000187:drug effects*; D014981:Xenopus
chemical_list: D053503:Epithelial Sodium Channels; C507051:SCNN1D protein, human; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D005070:Evans Blue