Ookata Kayoko, Tojo Akihiro, Suzuki Yoshiro, Nakamura Nobuhiro, Kimura Kenjiro, Wilcox Christopher S, Hirose Shigehisa
Division of Nephrology and Endocrinology, University of Tokyo, Tokyo, Japan.
Department of Biological Sciences, Tokyo Institute of Technology, Yokohama, Japan.
J Am Soc Nephrol. 2000 Nov;11(11):1987-1994. doi: 10.1681/ASN.V11111987.
Inward rectifier potassium channels (Kir) play an important role in the K(+) secretion from the kidney. Recently, a new subfamily of Kir, Kir7.1, has been cloned and shown to be present in the kidney as well as in the brain, choroid plexus, thyroid, and intestine. Its cellular and subcellular localization was examined along the renal tubule. Western blot from the kidney cortex showed a single band for Kir7.1 at 52 kD, which was also observed in microdissected segments from the thick ascending limb of Henle, distal convoluted tubule (DCT), connecting tubule, and cortical and medullary collecting ducts. Kir7.1 immunoreactivity was detected predominantly in the DCT, connecting tubule, and cortical collecting duct, with lesser expression in the thick ascending limb of Henle and in the medullary collecting duct. Kir7.1 was detected by electron microscopic immunocytochemistry on the basolateral membrane of the DCT and the principal cells of cortical collecting duct, but neither type A nor type B intercalated cells were stained. The message levels and immunoreactivity were decreased under low-K diet and reversed by low-K diet supplemented with 4% KCl. By the double-labeling immunogold method, both Kir7.1 and Na(+), K(+)-ATPase were independently located on the basolateral membrane. In conclusion, the novel Kir7.1 potassium channel is located predominantly in the basolateral membrane of the distal nephron and collecting duct where it could function together with Na(+), K(+)-ATPase and contribute to cell ion homeostasis and tubular K(+) secretion.
内向整流钾通道（Kir）在肾脏钾分泌中起重要作用。最近，Kir的一个新亚家族Kir7.1已被克隆，并显示存在于肾脏以及大脑、脉络丛、甲状腺和肠道中。研究了其在肾小管中的细胞和亚细胞定位。肾脏皮质的蛋白质免疫印迹显示，Kir7.1在52 kD处有一条单带，在亨氏袢厚升支、远曲小管（DCT）、连接小管以及皮质和髓质集合管的显微切割节段中也观察到了该条带。Kir7.1免疫反应主要在DCT、连接小管和皮质集合管中检测到，在亨氏袢厚升支和髓质集合管中的表达较少。通过电子显微镜免疫细胞化学在DCT的基底外侧膜和皮质集合管的主细胞上检测到了Kir7.1，但A型和B型闰细胞均未染色。低钾饮食时，其信使水平和免疫反应性降低，补充4%氯化钾的低钾饮食可使其恢复。通过双标记免疫金法，Kir7.1和钠钾ATP酶均独立位于基底外侧膜上。总之，新型Kir7.1钾通道主要位于远端肾单位和集合管的基底外侧膜，在那里它可以与钠钾ATP酶共同发挥作用，有助于细胞离子稳态和肾小管钾分泌。
