The regulation of urea excretion in a batrachoidid fish

海湾蟾鱼Opsanus beta是一种不寻常的鱼，它以不同的脉冲排出尿素作为其主要的氮废物，通过周围水中尿素的突然增加来测量。已从蟾鱼鳃（tUT）中克隆出一种尿素转运蛋白，其氨基酸序列与哺乳动物尿素转运蛋白相似，据信尿素的脉冲是由于tUT的周期性激活，允许尿素从血液中移动，穿过鳃，进入水中。然而，tUT是如何被打开和关闭的还不太清楚，但是到目前为止的研究已经确定，压力激素、皮质醇和神经递质5-羟色胺（5-HT）都参与其中。高水平的皮质醇似乎阻止tUT激活，而5-HT刺激tUT功能。5-HT的作用似乎是由5-羟色胺受体亚型介导的，该受体亚型具有与哺乳动物5-羟色胺2A型（5-HT 2A）受体相似的药理学特征。本研究旨在通过研究皮质醇和5-HT如何控制tUT功能，并确定皮质醇和5-HT的作用是否相互影响，进一步研究tUT的调节。分子技术和体外组织制备将与整体动物研究平行使用，以检验tUT功能直接受5-HT控制和间接受皮质醇控制的假设。这些研究还将测试以下假设：鳃中的蟾鱼5-HT 2A受体参与tUT激活，并且当皮质醇水平高时，这些受体不能激活tUT。该项目的发现将扩大我们对鱼类和陆生生物体内氮废物代谢和排泄的理解。此外，这项研究的结果将提供深入了解5 HT和皮质醇之间的相互作用，这些信号是几种人类疾病的核心。迈阿密大学有一个多元化的学生团体，这个项目将为科学和工程专业代表性不足的学生提供研究经验。

The Gulf toadfish, Opsanus beta, is an unusual fish that excretes urea as its primary nitrogen waste product in distinct pulses, measured by a sudden increase in the appearance of urea in the surrounding water. A urea transporter has been cloned from toadfish gill (tUT) that is similar in amino acid sequence to mammalian urea transporters and the pulse of urea is believed to be due to the periodic activation of tUT, allowing for the movement of urea from the blood, across the gill, into the water. How tUT is turned on and off is not well understood, however, but research to this point has determined that the stress hormone, cortisol, and the neurotransmitter, serotonin (5-HT), are involved. High levels of cortisol appear to prevent tUT activation while 5-HT stimulates tUT function. The action of 5-HT appears to be mediated by a serotonin receptor subtype with pharmacological characteristics similar to mammalian serotonin type 2A (5-HT2A) receptors. This project aims to further examine the regulation of tUT by investigating how cortisol and 5-HT control tUT function and determine whether the actions of cortisol and 5-HT influence each other. Molecular techniques and in vitro tissue preparations will be used in parallel with whole animal studies to test the hypothesis that tUT function is controlled directly by 5-HT and indirectly by cortisol. These studies will also test the hypothesis that toadfish 5-HT2A receptors in the gill are involved in tUT activation and these receptors are not able to activate tUT when cortisol levels are high. The findings of this project will expand our understanding of nitrogen waste metabolism and excretion in fish and terrestrial organisms. In addition, results of this research will provide insight into the interactions between 5HT and cortisol, signals that are central to several human disorders. University of Miami has a diverse student body and this project will provide research experiences for students who are underrepresented in science and engineering.