A facilitative urea transporter is localized in the renal collecting tubule of the dogfish Triakis scyllia
A facilitative urea transporter is localized in the renal collecting tubule of the dogfish Triakis scyllia
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DOI：
10.1242/jeb.00773
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发表时间：
2004-01-01
影响因子：
2.8
通讯作者：
Takei, Y
中科院分区：
文献类型：
--
作者：
Hyodo, S;Katoh, F;Takei, Y
过滤后的尿素被肾小管重吸收对于保持海洋弹簧鱼体液中高水平的尿素是必不可少的。为了阐明尿素再吸收的机制，我们研究了促尿素转运蛋白(UT)在角鱼肾脏中的分布。我们分离到了一个编码UT的基因，该基因与从另一种角鱼中克隆的促进UT同源。Triakis UT在肾脏中大量表达，而在脑和肝脏中表达水平较低。在角鱼肾脏，每个肾单位旋转四圈，在束区和窦区之间反复穿行。在束状区中，得到的五个管段以逆流回路的方式排列。免疫组织化学显示，在肾单位节段中，UT仅在束带的最后一段即Triakis肾的集合管中表达。与UT有限的定位相反，转运酶Na+/K+-ATPase分布于许多肾小管段的基底膜上，包括窦区和束区。但在集合管中未检测到Na+/K+-ATPase免疫反应。本研究表明，集合管是海洋弹簧鱼肾脏对尿素重吸收的主要原因。其他逆流部分可能有助于产生促进尿素通过UT扩散的驱动力。
Reabsorption of filtered urea by the kidney tubule is essential for retaining high levels of urea in body fluids of marine elasmobranchs. To elucidate the mechanisms of urea reabsorption, we examined the distribution of a facilitative urea transporter (UT) in the kidney of the dogfish Triakis scyllia. We isolated a cDNA encoding a UT that is homologous to the facilitative UT cloned from another dogfish species, Squalus acanthias. The Triakis UT mRNA is abundantly expressed in the kidney, while low levels of expression were detected in the brain and liver. In the dogfish kidney, each nephron makes four turns and traverses repeatedly between bundle zone and sinus zone. In the bundle zone, the resulting five tubular segments are arranged in a countercurrent loop fashion. Inummohistochemistry using specific antibodies raised against the cloned UT revealed that, among the nephron segments, the UT is expressed exclusively in the final segment of the bundle zone, i.e. in the collecting tubule of the Triakis kidney. In contrast to the limited localization of UT, the transport enzyme Na+/K+-ATPase is distributed in the basolateral membrane of numerous tubular segments both in the sinus zone and the bundle zone. However, in the collecting tubule, Na+/K+-ATPase immunoreactivity was not detected. The present study suggests that the collecting tubule is responsible for the reabsorption of urea in the marine elasmobranch kidney. Other countercurrent segments may contribute to production of a driving force for facilitative diffusion of urea through the UT.