Derst C, Hirsch J R, Preisig-Müller R, Wischmeyer E, Karschin A, Döring F, Thomzig A, Veh R W, Schlatter E, Kummer W, Daut J
Institut für Normale und Pathologische Physiologie, Philipps-Universität, Marburg, Germany.
Kidney Int. 2001 Jun;59(6):2197-205. doi: 10.1046/j.1523-1755.2001.00735.x.
K(+) channels have important functions in the kidney, such as maintenance of the membrane potential, volume regulation, recirculation, and secretion of potassium ions. The aim of this study was to obtain more information on the localization and possible functional role of the inwardly rectifying K(+) channel, Kir7.1.
Kir7.1 cDNA (1114 bp) was isolated from guinea pig kidney (gpKir7.1), and its tissue distribution was analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR). In addition, a genomic DNA fragment (6153 bp) was isolated from a genomic library. cRNA was expressed in Xenopus laevis oocytes for functional studies. Immunohistochemistry and RT-PCR were used to localize Kir7.1 in guinea pig and human kidney.
The expression of gpKir7.1 in Xenopus laevis oocytes revealed inwardly rectifying K(+) currents. The reversal potential was strongly dependent on the extracellular K(+) concentration, shifting from -14 mV at 96 mmol/L K(+) to -90 mV at 1 mmol/L K(+). gpKir7.1 showed a low affinity for Ba(2+). Significant expression of gpKir7.1 was found in brain, kidney, and lung, but not in heart, skeletal muscle, liver, or spleen. Immunocytochemical detection in guinea pig identified the gpKir7.1 protein in the basolateral membrane of epithelial cells of the proximal tubule. RT-PCR analysis identified strong gpKir7.1 expression in the proximal tubule and weak expression in glomeruli and thick ascending limb. In isolated human tubule fragments, RT-PCR showed expression in proximal tubule and thick ascending limb.
Our results suggest that Kir7.1 may contribute to basolateral K(+) recycling in the proximal tubule and in the thick ascending limb.
钾通道在肾脏中具有重要功能，如维持膜电位、调节容积、再循环以及钾离子的分泌。本研究的目的是获取更多关于内向整流钾通道Kir7.1的定位及可能的功能作用的信息。
从豚鼠肾脏中分离出Kir7.1 cDNA（1114 bp）（gpKir7.1），并通过逆转录聚合酶链反应（RT-PCR）分析其组织分布。此外，从基因组文库中分离出一个基因组DNA片段（6153 bp）。将cRNA在非洲爪蟾卵母细胞中表达以进行功能研究。采用免疫组织化学和RT-PCR对豚鼠和人肾脏中的Kir7.1进行定位。
gpKir7.1在非洲爪蟾卵母细胞中的表达显示出内向整流钾电流。反转电位强烈依赖于细胞外钾离子浓度，从96 mmol/L钾时的 -14 mV转变为1 mmol/L钾时的 -90 mV。gpKir7.1对钡离子（Ba(2+)）具有低亲和力。在脑、肾脏和肺中发现gpKir7.1有显著表达，但在心脏、骨骼肌、肝脏或脾脏中未发现。在豚鼠中的免疫细胞化学检测确定了gpKir7.1蛋白存在于近端小管上皮细胞的基底外侧膜中。RT-PCR分析确定在近端小管中有强烈的gpKir7.1表达，而在肾小球和髓袢升支粗段中表达较弱。在分离的人肾小管片段中，RT-PCR显示在近端小管和髓袢升支粗段中有表达。
我们的结果表明，Kir7.1可能有助于近端小管和髓袢升支粗段中基底外侧钾离子的再循环。
