QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

First published online September 14, 2007
Journal of Experimental Biology 210, 3494-3504 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.007146

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Chang, J. C.-H. Articles by Hwang, P.-P. Search for Related Content PubMed PubMed Citation Articles by Chang, J. C.-H. Articles by Hwang, P.-P.

Regulation of glycogen metabolism in gills and liver of the euryhaline tilapia (Oreochromis mossambicus) during acclimation to seawater

Joshua Chia-Hsi Chang¹, Su-Mei Wu², Yung-Che Tseng³, Yi-Chun Lee², Otto Baba⁴ and Pung-Pung Hwang^1,*

¹ Institute of Cellular and Organismic Biology, Academia Sinica, Nankang, Taipei, Taiwan, Republic of China
² Department of Aquatic Biosciences, National Chiayi University, Chiayi, Taiwan, Republic of China
³ Institute of Zoology, National Taiwan University, Taipei, Taiwan, Republic of China
⁴ Department of Hard Tissue Engineering, Tokyo Medical and Dental University, Tokyo, Japan

^* Author for correspondence (e-mail: pphwang{at}gate.sinica.edu.tw)

Accepted 18 June 2007

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 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.

Key words: glycogen phosphorylase, glycogen synthase, Na⁺/K⁺-ATPase, osmoregulation, mitochondrion-rich cells, salinity