Role of Glycogen Phosphorylase in Energy Supplying for Osmoregulation in Gills of Tilapia (Oreochromis mossambicus)
Date Issued
2004
Date
2004
Author(s)
Tseng, Yung-Che
DOI
en-US
Abstract
Upon external salinity challenges, euryhaline teleosts perform rapid modulations of functions of several ion transporters or channels in gills to maintain the internal homeostasis. Ion- and osmo-regulation are highly energy consuming, therefore there must be an efficient metabolism system, which supplies immediate and sufficient energy sources for the active ion transport in gills.
Glycogen is the main energy reserve in highly energy depletion tissues, such as brain, liver and muscle, and has been proposed to be an emergency fuel store during physiological stresses. In the processes of glycogen metabolism, glycogen phosphorylase (GP) catalyzes the initial glycogen degradation, i.e., the breakdown of glycogen to glucose-1-phosphate, which enters glycogenolysis or glycolysis to fulfill the energetic requirements of different cell types. The homodimeric enzyme exists as 3 isozymes named according to the tissues in which they predominate; LL (liver), MM (skeletal muscle) and BB (brain) forms in most mammalians.
Using subtraction PCR, a clone of tGP was found to express differentially in the gills between freshwater (FW)-and seawater (SW)-acclimated tilapia. In present study, we have cloned and sequenced the full length cDNA of the tGP from tilapia gill. Alignment analysis showed that the tGP may be a homologue of the liver form of the mammalian GP. qRT-PCR, western blot analysis, and enzyme activity assay indicated that the tGP expression in SW tilapia gills was higher than that in FW ones. In situ hybridization result indicated that the tGP mRNA is localized in the epithelial cells of tilapia gills. However, the double labeling with Na+-K+-ATPase protein images show that tGP was not colocalized with the protein of Na+-K+-ATPase, implying that tGP mRNA was predominantly expressed in un-identified cells, but not in MR cells. In addition, tGP and Na+-K+-ATPase activity simultaneously inhibited by the GP specific inhibitor-caffeine.
Taken together, the tGP gene expression is stimulated in tilapia gills upon salinity challenge, suggesting that the breakdown of glycogen may be directly providing energy for the osmoregulation mechanisms in gill highly energy consuming cells. And there are another types of cell corresponding to energy supplying.
Subjects
肝糖磷酸化酵素
鰓
滲透壓調節
osmoregulation
glycogen phosphorylase
gill
Type
other
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