Regulation of Epithelia Solute Transport in Elasmobranch Fish

尿素在板鳃类鱼类中用于渗透目的的保留已经被知道超过125年了，但是我们对这一古老鱼类群体中溶质穿过上皮的转运知之甚少。人们曾试图利用鳃和肾组织来了解尿素的转运机制，然而，这些研究受到所用组织复杂性的阻碍。肠组织适合于运输生理学研究，因为它具有相对平坦的表面和均匀的上皮细胞。最近的进展已经在建立一个可行的准备在板鳃类和数据一致表明，喂养的结果在一个净摄取尿素从肠腔的浓度梯度，饥饿导致尿素的净损失到肠腔。这些研究表明，肠道上皮细胞中的转运蛋白的显著重新定位和/或肠道上皮细胞形态的重塑响应于食物的存在。无论哪种方式，这种生理反应都需要通过胃肠胰（GEP）激素的作用进行大量协调，其中许多激素已在板鳃鱼的肠道中被确定。虽然一些研究已经检查了这些激素在血液流动和平滑肌收缩中的调节作用，但调查它们在板鳃鱼类肠道溶质转运调节中的作用的研究是不存在的。使用分离的肠道准备，拟议的研究将建立这种组织作为了解板鳃类溶质运输机制的主要资源。使用经典的Ussing室设置，特异性抑制剂和激动剂的选择性筛选将鉴定参与尿素和其他溶质穿过肠上皮的运动的关键转运蛋白。分子技术将量化这些蛋白质的mRNA表达在喂养和饥饿的鱼。这些研究结合免疫组织化学技术将导致发展的尿素和溶质运输模型板鳃类的基础上，从一个相对均匀的上皮细胞的直接经验证据。将使用光学显微镜、扫描显微镜和透射显微镜来鉴定肠上皮细胞对摄食的响应的形态学变化。Ussing室制备将用于筛选用于控制尿素和溶质转运的候选GEP激素。一旦确定，将检查抑制性和刺激性激素的受体表达。类似地，

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