Department of Biological Sciences, University of Manitoba, Winnipeg, MB R3T 0A8, Canada.
Laboratory of Physiology, Atmosphere and Ocean Research Institute, University of Tokyo, Kashiwa, Chiba, Japan.
Comp Biochem Physiol A Mol Integr Physiol. 2023 Jun;280:111418. doi: 10.1016/j.cbpa.2023.111418. Epub 2023 Mar 23.
As part of their osmoregulatory strategy, marine elasmobranchs retain large quantities of urea to balance the osmotic pressure of the marine environment. The main source of nitrogen used to synthesize urea comes from the digestion and absorption of food across the gastrointestinal tract. In this study we investigated possible mechanisms of nitrogen movement across the spiral valve of the cloudy catshark (Scyliorhinus torazame) through the molecular identification of two Rhesus glycoprotein ammonia transporters (Rhp2 and Rhbg) and a urea transporter (UT). We used immunohistochemistry to determine the cellular localizations of Rhp2 and UT. Within the spiral valve, Rhp2 was expressed along the apical brush border membrane, and UT was expressed along the basolateral membrane and the blood vessels. The mRNA abundance of Rhp2 was significantly higher in all regions of the spiral valve of fasted catsharks compared to fed catsharks. The mRNA abundance of UT was significantly higher in the anterior spiral valve of fasted catsharks compared to fed. The mRNA transcript of four ornithine urea cycle (OUC) enzymes were detected along the length of the spiral valve and in the renal tissue, indicating the synthesis of urea via the OUC occurs in these tissues. The presence of Rhp2, Rhbg, and UT along the length of the spiral valve highlights the importance of ammonia and urea movement across the intestinal tissues, and increases our understanding of the mechanisms involved in maintaining whole-body nitrogen homeostasis in the cloudy catshark.
作为其渗透调节策略的一部分，海洋软骨鱼类保留大量的尿素以平衡海洋环境的渗透压。用于合成尿素的氮的主要来源来自于通过胃肠道的消化和吸收。在这项研究中，我们通过分子鉴定两种恒河猴糖蛋白氨转运体（Rhp2 和 Rhbg）和尿素转运体（UT），研究了氮在皱唇鲨（Scyliorhinus torazame）的螺旋瓣中移动的可能机制。我们使用免疫组织化学来确定 Rhp2 和 UT 的细胞定位。在螺旋瓣中，Rhp2 表达于顶膜刷状缘，而 UT 表达于基底外侧膜和血管。与摄食的鲨鱼相比，禁食鲨鱼的螺旋瓣各区域 Rhp2 的 mRNA 丰度显著升高。与摄食的鲨鱼相比，禁食鲨鱼的前螺旋瓣 UT 的 mRNA 丰度显著升高。在螺旋瓣和肾脏组织中检测到四个鸟氨酸尿素循环（OUC）酶的 mRNA 转录本，表明这些组织中通过 OUC 合成尿素。Rhp2、Rhb 和 UT 沿着螺旋瓣的长度存在，突出了氨和尿素在肠组织中的移动的重要性，并增加了我们对维持皱唇鲨全身氮稳态的机制的理解。
