Yamamura Hisao, Ugawa Shinya, Ueda Takashi, Shimada Shoichi
Department of Molecular Morphology, Graduate School of Medical Sciences, Nagoya City University, Japan.
J Pharmacol Exp Ther. 2005 Nov;315(2):965-9. doi: 10.1124/jpet.105.092775. Epub 2005 Aug 17.
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.
上皮钠离子通道（ENaC）调节细胞内以及跨上皮的钠稳态。在哺乳动物中已分离出四种同源的ENaC亚基（α、β、γ和δ）。α、β和γ亚基的组合或δ、β和γ亚基的组合形成功能完整的通道。氨氯地平是一种著名的ENaC家族阻滞剂，可抑制这两种通道复合物。然而，目前尚无已知的能区分它们的特异性拮抗剂。在此，我们表明伊文思蓝（一种用于测量血容量和血管通透性的诊断辅助剂）可抑制非洲爪蟾卵母细胞中表达的δ亚基的活性。在表达人ENaCδβγ的卵母细胞中，在-60 mV的钳制电位下，内向电流会被伊文思蓝以浓度依赖性方式抑制，IC50值为143 μM。伊文思蓝显著抑制δ亚基电流，但不阻断α亚基电流。总之，伊文思蓝是首个已知的ENaCδ亚基特异性拮抗剂。这一发现为我们提供了一种关键化合物，用于阐明人类ENaCδ的生理和病理功能以及用于ENaC家族的药物开发。
