博士 / 國立臺灣大學 / 動物學研究所 / 96 / The purposes of the present study were to elucidate the molecular and cellular mechanisms of glycogen metabolism, the subsequent metabolites’ transport in fish gill/skin epithelial cells, and their roles in the iono- and osmoregulatory functions.
A novel gill glycogen phosphorylase (GP) isoform (tGPGG) was identified in tilapia (Oreochromis mossambicus) gill epithelia, and was colocalized in glycogen-rich cells (GR cells) which surround ionocytes. The tGPGG mRNA and protein levels and total activity, the glycogen content, and the density of GR cells in fish acclimated to seawater (SW) were significantly higher than those in the freshwater (FW) controls. Na+-K+-ATPase (NKA) activities in cultured gills were inhibited by caffeine (a GP inhibitor), and the addition of D-glucose rescued the inhibited NKA activity. In summary, tGPGG expression in GR cells is stimulated by environmental hyperosmotic challenges, and this may catalyze initial glycogen degradation to provide adjacent ionocytes with energy to carry out their iono- and osmoregulatory functions.
GP, glycogen synthase (GS), and glycogen were all immunocytochemically colocalized in GR cells. Glycogen contents in the gills and liver were significantly depleted after transfer to SW, but the depletion occurred earlier in gills than in the liver. Gill and brain NKA activities rapidly increased immediately after transfer to SW. Gill and brain GP protein expressions were subsequently upregulated 1~6 h post-transfer, while GS protein levels were simultaneously downregulated. Similar changes in liver GP and GS protein expressions were also observed, but they occurred later at 6~12 h post-transfer. In conclusion, glycogen storage cells were initially stimulated to provide prompt energy so that adjacent cells could initiate their ion regulation mechanisms, and then several hours later, the liver began to degrade its glycogen stores for an additional energy supply.
In subsequent experiments, 18 members of glucose transporters (GLUTs, SLC2A) were cloned from zebrafish (Danio rerio). Based on the experiments of foxi3a/3b knockdown and triple in situ hybridization/immunocytochemistry, 3 GLUT isoforms, zglut1a, -6, and -13a, and a monocarboxylate transporter, zmct4, were specifically localized in zebrafish skin/gill ionocytes and GR cells. Furthermore, zGLUT13a was demonstrated to absorb glucose to provide energy so that H+-ATPase-rich (HR) cells could take up Na+, while zGLUT6 was responsible for transporting glucose into GR cells, but was not directly related to ion regulation. Taken together, zGLUT13a and -6, specific transporters in HR cells and GR cells, absorb glucose into the respective cells with different affinities, but appear to fulfill different physiological demands in different types of epithelial cells.
| Identifer | oai:union.ndltd.org:TW/096NTU05312005 |
| Date | January 2008 |
| Creators | Yung-Che Tseng, 曾庸哲 |
| Contributors | Shyh-Jye Lee, 李士傑 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | en_US |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 167 |
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