Regulation of Epithelia Solute Transport in Elasmobranch Fish

在板鳃鱼中，尿素的渗透性保留已经有125年的历史了，但我们对这种古老鱼类中溶质在上皮中的运输知之甚少。人们试图通过鳃和肾组织来了解尿素运输机制，然而，这些研究受到所用组织复杂性的阻碍。肠道组织具有相对平坦的表面和均匀的上皮，因此可以很好地用于运输生理学研究。最近在建立一种可行的弹性支膜制剂方面取得了进展，数据一致表明，喂养导致从肠道管腔对尿素的净吸收与浓度梯度相反，饥饿导致尿素在肠道管腔的净损失。这些研究表明肠上皮转运蛋白在食物的作用下发生了重大的重新定位和/或肠上皮细胞形态的重塑。无论哪种方式，这种生理反应都需要通过胃肠胰腺（GEP）激素的作用进行实质性的协调，其中许多激素已经在板鳃鱼的肠道中被发现。虽然许多研究已经研究了这些激素在血液流动和平滑肌收缩中的调节作用，但研究它们在调节板鳃鱼肠道溶质运输中的作用的研究并不存在。利用分离的肠道制剂，本研究将建立这种组织作为理解弹性分支中溶质运输机制的主要资源。使用经典的使用室设置选择性筛选特异性抑制剂和激动剂将确定参与尿素和其他溶质通过肠上皮运动的关键转运蛋白。分子技术将量化这些蛋白质在喂食和饥饿鱼中的mRNA表达。这些研究结合免疫组织化学技术，将基于来自相对均匀上皮的直接经验证据，开发出弹性支的尿素和溶质运输模型。光，扫描和透射显微镜将被用来识别肠道上皮在喂养反应中的形态学变化。usingchamber制备将用于筛选候选GEP激素以控制尿素和溶质运输。一旦确定，将检查抑制激素和刺激激素的受体表达。类似地，胰腺

The retention of urea for osmotic purposes in elasmobranch fish has been known for over 125 years yet we know little about solute transport across epithelia in this ancient group of fishes. Attempts have been made to understand urea transport mechanisms using gill and renal tissue, however, these studies are hampered by the complexity of the tissue used. Intestinal tissue lends itself well to transport physiology studies as it has a relatively flat surface and uniform epithelia. Recent advances have been made in establishing a viable preparation in elasmobranchs and data have consistently shown that feeding results in a net uptake of urea from the lumen of the intestine against a concentration gradient, and starvation leads to a net loss of urea to the intestinal lumen. These studies suggest significant repositioning of transport proteins in intestinal epithelia and/or remodeling of intestinal epithelia cell morphology in response to the presence of food. Either way such physiological responses would require substantial coordination through the actions of gastro-entero-pancreatic (GEP) hormones, many of which have been identified in the intestine of elasmobranch fish. While a number of studies have examined regulatory roles for these hormones in blood flow and smooth muscle contraction research investigating their role in the regulation of intestinal solute transport in elasmobranch fish is non-existent. Using isolated intestinal preparations, the proposed research will establish this tissue as a primary resource for understanding the mechanisms of solute transport in elasmobranchs. Using a classic Ussing chamber setup selective screening of specific inhibitors and agonists will identify key transport proteins involved in the movement of urea and other solutes across the intestinal epithelia. Molecular techniques will quantify mRNA expression of these proteins in fed and starved fish. These studies combined with immunohistochemical techniques will result in the development of a urea and solute transport model for elasmobranchs based on direct empirical evidence from a relatively homogeneous epithelia. Light, scanning and transmission microscopy will be used to identify morphological changes in the intestinal epithelia in response to feeding. The Ussing chamber preparation will be used to screen candidate GEP hormones for the control of urea and solute transport. Once identified, receptor expression for inhibitory and stimulatory hormones will be examined. Similarly a pancreatic