Garty H, Palmer L G
Department of Membrane Research and Biophysics, Weizmann Institute of Science, Rehovot, Israel.
Physiol Rev. 1997 Apr;77(2):359-96. doi: 10.1152/physrev.1997.77.2.359.
The apical (outward-facing) membranes of high-resistance epithelia contain Na+ channels, traditionally identified by their sensitivity to block by the K(+)-sparing diuretic amiloride. Such channels have been characterized in amphibian skin and urinary bladder, renal collecting duct, distal colon, sweat and salivary glands, lung, and taste buds. They mediate the first step of active Na+ reabsorption and play a major role in the maintenance of electrolyte and water homeostasis in all vertebrates. In the past, these channels were classified according to their biophysical and pharmacological properties. The recent cloning of the three homologous channel subunits denoted alpha-, beta-, and gamma-epithelial Na+ channels (ENaC) has provided a molecular definition of at least one class of amiloride-blockable channels. Subsequent studies have established that ENaC is a major Na(+)-conducting pathway in both absorbing and secretory epithelia and is related to one type of channel involved in mechanosensation. This review summarizes the biophysical characteristics, molecular properties, and regulatory mechanisms of epithelial amiloride-blockable Na+ channels. Special emphasis is given to recent studies utilizing cloned ENaC subunits and purified amiloride-binding proteins.
高电阻上皮细胞的顶端（朝外）膜含有钠离子通道，传统上通过它们对保钾利尿剂氨氯吡咪阻断的敏感性来识别。此类通道已在两栖动物的皮肤和膀胱、肾集合管、远端结肠、汗腺和唾液腺、肺以及味蕾中得到表征。它们介导主动钠离子重吸收的第一步，并在所有脊椎动物的电解质和水平衡维持中发挥主要作用。过去，这些通道根据其生物物理和药理特性进行分类。最近克隆出的三种同源通道亚基，即α-、β-和γ-上皮钠离子通道（ENaC），为至少一类可被氨氯吡咪阻断的通道提供了分子定义。随后的研究证实，ENaC是吸收性和分泌性上皮细胞中主要的钠离子传导途径，并且与一种参与机械感觉的通道类型有关。本综述总结了上皮性可被氨氯吡咪阻断的钠离子通道的生物物理特性、分子特性和调节机制。特别强调了利用克隆的ENaC亚基和纯化的氨氯吡咪结合蛋白进行的最新研究。
