Cai Lu, Wang Dengke, Gui Tianxiang, Wang Xiaoyu, Zhao Lingyu, Boron Walter F, Chen Li-Ming, Liu Ying
Key Laboratory of Molecular Biophysics of Ministry of Education, School of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei, China.
Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH, United States.
Front Physiol. 2023 Apr 4;14:1154694. doi: 10.3389/fphys.2023.1154694. eCollection 2023.
The kidney plays a central role in maintaining the fluid and electrolyte homeostasis in the body. Bicarbonate transporters NBCn1, NBCn2, and AE2 are expressed at the basolateral membrane of the medullary thick ascending limb (mTAL). In a previous study, NBCn1, NBCn2, and AE2 are proposed to play as a regulatory pathway to decrease NaCl reabsorption in the mTAL under high salt condition. When heterologously expressed, the activity of these transporters could be stimulated by the InsP3R binding protein released with inositol 1,4,5-trisphosphate (IRBIT), L-IRBIT (collectively the IRBITs), or protein phosphatase PP1. In the present study, we characterized by immunofluorescence the expression and localization of the IRBITs, and PP1 in rat kidney. Our data showed that the IRBITs were predominantly expressed from the mTAL through the distal renal tubules. PP1 was predominantly expressed in the TAL, but is also present in high abundance from the distal convoluted tubule through the medullary collecting duct. Western blotting analyses showed that the abundances of NBCn1, NBCn2, and AE2 as well as the IRBITs and PP1 were greatly upregulated in rat kidney by dietary sodium. Co-immunoprecipitation study provided the evidence for protein interaction between NBCn1 and L-IRBIT in rat kidney. Taken together, our data suggest that the IRBITs and PP1 play an important role in sodium handling in the kidney. We propose that the IRBITs and PP1 stimulates NBCn1, NBCn2, and AE2 in the basolateral mTAL to inhibit sodium reabsorption under high sodium condition. Our study provides important insights into understanding the molecular mechanism for the regulation of sodium homeostasis in the body.
肾脏在维持机体的液体和电解质平衡中起着核心作用。碳酸氢盐转运体NBCn1、NBCn2和AE2表达于髓袢升支粗段（mTAL）的基底外侧膜。在先前的一项研究中，有人提出NBCn1、NBCn2和AE2作为一条调节途径，在高盐条件下减少mTAL中NaCl的重吸收。当在异源系统中表达时，这些转运体的活性可被与肌醇1,4,5 -三磷酸（IP3）一起释放的IP3R结合蛋白、L - IRBIT（统称为IRBITs）或蛋白磷酸酶PP1所刺激。在本研究中，我们通过免疫荧光法对IRBITs和PP1在大鼠肾脏中的表达及定位进行了表征。我们的数据显示，IRBITs主要从mTAL到远端肾小管表达。PP1主要在TAL中表达，但在远端曲管到髓质集合管中也大量存在。蛋白质印迹分析表明，饮食中的钠可使大鼠肾脏中NBCn1、NBCn2和AE2以及IRBITs和PP1的丰度显著上调。免疫共沉淀研究为大鼠肾脏中NBCn1与L - IRBIT之间的蛋白质相互作用提供了证据。综上所述，我们的数据表明IRBITs和PP1在肾脏钠处理中起重要作用。我们提出，在高钠条件下，IRBITs和PP1刺激基底外侧mTAL中的NBCn1、NBCn2和AE2以抑制钠重吸收。我们的研究为理解机体钠平衡调节的分子机制提供了重要见解。
