Volk K A, Sigmund R D, Snyder P M, McDonald F J, Welsh M J, Stokes J B
Department of Internal Medicine, University of Iowa College of Medicine, Iowa City 52242, USA.
J Clin Invest. 1995 Dec;96(6):2748-57. doi: 10.1172/JCI118344.
The terminal nephron segment, the inner medullary collecting duct (IMCD), absorbs Na+ by an electrogenic process that involves the entry through an apical (luminal) membrane Na+ channel. To understand the nature of this Na+ channel, we employed the patch clamp technique on the apical membrane of primary cultures of rat IMCD cells grown on permeable supports. We found that all ion channels detected in the cell-attached configuration were highly selective for Na+ (Li+) over K+. The open/closed transitions showed slow kinetics, had a slope conductance of 6-11 pS, and were sensitive to amiloride and benzamil. Nonselective cation channels with a higher conductance (25-30 pS), known to be present in IMCD cells, were not detected in the cell-attached configuration, but were readily detected in excised patches. The highly selective channels had properties similar to the recently described rat epithelial Na+ channel complex, rENaC. We therefore asked whether rENaC mRNA was present in the IMCD. We detected mRNA for all three rENaC subunits in rat renal papilla and also in primary cultures of the IMCD. Either glucocorticoid hormone or mineralocorticoid hormone increased the amount of alpha-rENaC subunit mRNA but had no effect on the mRNA level of the beta-rENaC or gamma-rENaC subunits. From these data, taken in the context of other studies on the characteristics of Na+ selective channels and the distribution of rENaC mRNA, we conclude that steroid stimulated Na+ absorption by the IMCD is mediated primarily by Na+ channels having properties of the rENaC subunit complex.
终末肾单位节段，即髓质内集合管（IMCD），通过一种电生过程吸收Na⁺，该过程涉及通过顶端（管腔）膜Na⁺通道进入。为了解这种Na⁺通道的性质，我们对生长在可渗透支持物上的大鼠IMCD细胞原代培养物的顶端膜采用了膜片钳技术。我们发现，在细胞贴附模式下检测到的所有离子通道对Na⁺（Li⁺）的选择性远高于K⁺。开放/关闭转换显示出缓慢的动力学，斜率电导为6 - 11 pS，并且对氨氯吡咪和苄甲咪敏感。已知存在于IMCD细胞中的具有较高电导（25 - 30 pS）的非选择性阳离子通道，在细胞贴附模式下未检测到，但在切除的膜片中很容易检测到。高度选择性的通道具有与最近描述的大鼠上皮Na⁺通道复合物rENaC相似的特性。因此，我们询问rENaC mRNA是否存在于IMCD中。我们在大鼠肾乳头以及IMCD原代培养物中检测到了所有三种rENaC亚基的mRNA。糖皮质激素或盐皮质激素均可增加α-rENaC亚基mRNA的量，但对β-rENaC或γ-rENaC亚基的mRNA水平没有影响。结合其他关于Na⁺选择性通道特性和rENaC mRNA分布的研究数据，我们得出结论，类固醇刺激的IMCD对Na⁺的吸收主要由具有rENaC亚基复合物特性的Na⁺通道介导。
