Abstract
The epithelial Na+ channel (ENaC) regulates Na+ homeostasis in cells and across epithelia. Four homologous ENaC subunits (α, β, γ, and δ) have been isolated in mammals. Combination of α-, β-, and γ-subunits or δ-, β-, and γ-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 δ-subunit expressed in Xenopus oocytes. The inward currents at a holding potential of -60 mV in human ENaCδβγ-expressing oocytes were inhibited by the application of Evans blue in a concentration-dependent manner with an IC50 value of 143 μM. Evans blue markedly inhibited the δ-subunit current but did not block the α-subunit current. In conclusion, Evans blue is the first known δ-subunit-specific antagonist of ENaC. This finding provides us with a key compound for elucidating the physiological and pathological functions of ENaCδ in humans and for drug development in the ENaC family.
Footnotes
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This work was supported by a grant-in-aid for scientific research from the Japan Society for the Promotion of Sciences (to H.Y. and S.S.).
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.105.092775.
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ABBREVIATIONS: ENaC, epithelial Na+ channel; hENaC, human epithelial Na+ channel.
- Received July 17, 2005.
- Accepted August 15, 2005.
- The American Society for Pharmacology and Experimental Therapeutics
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