Chang Joshua Chia-Hsi, Wu Su-Mei, Tseng Yung-Che, Lee Yi-Chun, Baba Otto, Hwang Pung-Pung
Institute of Cellular and Organismic Biology, Academia Sinica, Nankang, Taipei, Taiwan, Republic of China.
J Exp Biol. 2007 Oct;210(Pt 19):3494-504. doi: 10.1242/jeb.007146.
Glucose, which plays a central role in providing energy for metabolism, is primarily stored as glycogen. The synthesis and degradation of glycogen are mainly initialized by glycogen synthase (GS) and glycogen phosphorylase (GP), respectively. The present study aimed to examine the glycogen metabolism in fish liver and gills during acute exposure to seawater. In tilapia (Oreochromis mossambicus) gill, GP, GS and glycogen were immunocytochemically colocalized in a specific group of glycogen-rich (GR) cells, which are adjacent to the gill's main ionocytes, mitochondrion-rich (MR) cells. Na+/K+-ATPase activity in the gills, protein expression and/or activity of GP and GS and the glycogen content of the gills and liver were examined in tilapia after their acute transfer from freshwater (FW) to 25 per thousand seawater (SW). Gill Na+/K+-ATPase activity rapidly increased immediately after SW transfer. Glycogen content in both the gills and liver were significantly depleted after SW transfer, but the depletion occurred earlier in gills than in the liver. Gill GP activity and protein expression were upregulated 1-3 h post-transfer and eventually recovered to the normal level as determined in the control group. At the same time, GS protein expression was downregulated. Similar changes in liver GP and GS protein expression were also observed but they occurred later at 6-12 h post-transfer. In conclusion, GR cells are initially stimulated to provide prompt energy for neighboring MR cells that trigger ion-secretion mechanisms. Several hours later, the liver begins to degrade its glycogen stores for the subsequent energy supply.
葡萄糖在为新陈代谢提供能量方面起着核心作用，主要以糖原的形式储存。糖原的合成和降解分别主要由糖原合酶（GS）和糖原磷酸化酶（GP）启动。本研究旨在检测罗非鱼在急性暴露于海水中时肝脏和鳃中的糖原代谢情况。在罗非鱼（莫桑比克罗非鱼）的鳃中，GP、GS和糖原通过免疫细胞化学方法共定位在一组特定的富含糖原（GR）的细胞中，这些细胞与鳃的主要离子细胞、富含线粒体（MR）的细胞相邻。在罗非鱼从淡水（FW）急性转移到25‰海水（SW）后，检测了鳃中的Na+/K+-ATP酶活性、GP和GS的蛋白表达和/或活性以及鳃和肝脏的糖原含量。转移到SW后，鳃中的Na+/K+-ATP酶活性立即迅速增加。转移到SW后，鳃和肝脏中的糖原含量均显著减少，但鳃中的减少比肝脏中更早发生。转移后1-3小时，鳃中GP的活性和蛋白表达上调，最终恢复到对照组测定的正常水平。与此同时，GS蛋白表达下调。在肝脏中也观察到GP和GS蛋白表达的类似变化，但它们在转移后6-12小时出现得较晚。总之，GR细胞最初受到刺激，为触发离子分泌机制相邻的MR细胞提供即时能量。几小时后，肝脏开始分解其糖原储备以提供后续的能量供应。
