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This Article Full Text Full Text (PDF) All Versions of this Article: 293/1/R482    most recent 00681.2006v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Web of Science (2) Citing Articles via Google Scholar Google Scholar Articles by Tseng, Y.-C. Articles by Hwang, P.-P. Search for Related Content PubMed PubMed Citation Articles by Tseng, Y.-C. Articles by Hwang, P.-P.

COMPARATIVE AND EVOLUTIONARY PHYSIOLOGY

Glycogen phosphorylase in glycogen-rich cells is involved in the energy supply for ion regulation in fish gill epithelia

¹Institute of Cellular and Organismic Biology, Academia Sinica, Nankang, Taipei; ²Institute of Zoology, National Taiwan University, Taipei; ³Institute of Biological Chemistry, Academia Sinica, Nankang; ⁴Department of Hard Tissue Engineering, Tokyo Medical and Dental University, Tokyo, Japan; and ⁵Department of Life Sciences, National Yang Ming University, Taipei, Taiwan, Republic of China

Submitted 26 September 2006 ; accepted in final form 8 March 2007

The molecular and cellular mechanisms behind glycogen metabolism and the energy metabolite translocation between mammal neurons and astrocytes have been well studied. A similar mechanism is proposed for rapid mobilization of local energy stores to support energy-dependent transepithelial ion transport in gills of the Mozambique tilapia (Oreochromis mossambicus). A novel gill glycogen phosphorylase isoform (tGPGG), which catalyzes the initial degradation of glycogen, was identified in branchial epithelial cells of O. mossambicus. Double in situ hybridization and immunocytochemistry demonstrated that tGPGG mRNA and glycogen were colocalized in glycogen-rich cells (GRCs), which surround ionocytes (labeled with a Na⁺-K⁺-ATPase antiserum) in gill epithelia. Concanavalin-A (a marker for the apical membrane) labeling indicated that GRCs and mitochondria-rich cells share the same apical opening. Quantitative real-time PCR analyses showed that tGPGG mRNA expression levels specifically responded to environmental salinity changes. Indeed, the glycogen content, glycogen phosphorylase (GP) protein level and total activity, and the density of tGPGG-expressing cells (i.e., GRCs) in fish acclimated to seawater (SW) were significantly higher than those in freshwater controls. Short-term acclimation to SW caused an evident depletion in the glycogen content of GRCs. Taken altogether, tGPGG expression in GRCs is stimulated by hyperosmotic challenge, and this may catalyze initial glycogen degradation to provide the adjacent ionocytes with energy to carry out iono- and osmoregulatory functions.

osmoregulation; Na⁺-K⁺-ATPase; salinity; ionocytes