Effects of environmental calcium concentration on calcium absorption in fish
Date Issued
2006
Date
2006
Author(s)
Deng, Ang-Ni
DOI
zh-TW
Abstract
Freshwater fish absorb Ca2+ mainly from environment, and over 95% of Ca2+ is actively absorbed via gill mitochondria-rich cells (MRCs). In the current model for Ca2+ in fish gill MRCs, Ca2+ is passively diffused into the cytosol through the apical unidentified voltage-independent Ca2+ channels, and then is transported out of the cells via the basolateral plasma Ca2+-ATPase (PMCA) and Na+/Ca2+ exchanger (NCX). However, so far there is only very few convincing molecular and cellular evidence to support this model. In the present study, we aimed: (1) to provide molecular evidence for the current model for Ca2+ uptake in fish gill MR cells; (2) to examine how environmental Ca2+ concentration regulates gene expressions of Ca2+ transporters in fish gills.
Experiments of in situ hybridization and immunocytochemistry showed that Na+/K+-ATPase (a marker for MRCs) and the tilapia epithelial Ca2+ channel (ECaC) mRNA were colocalized in tilapia (Oreochromis mossambicus) gills, and only part of MRCs express the tECaC, the expression patterns of the tPMCA2 and tNCX1b were similar to the pattern of tECaC. The zECaC, zPMCA2 and zNCX1b were also found specifically expressed in zebrafish (Danio rerio) gills. These indicate that a subtype of MRCs is specifically responsible for Ca2+ uptake.
Quantitative-PCR（qRT-PCR） results showed that mRNA expression of the tECaC and NCX1b in gills was higher in tilapia acclimated to low-Ca2+ freshwater (FW) than that acclimated to high-Ca2+ FW. However, tPMCA2 mRNA expression did not show any significant change between the 2 groups. In the experiments on the model animal, zebrafish, the expression patterns of the zECaC was similar to that in tilapia, but zPMCA2 and zNCX1b mRNA expression did not show any significant change between the 2 groups. In another experiments, the expression level of tECaC was higher in SW acclimated tilapia gill than that in FW group. The expression of tPMCA2 was higher in FW gill than that in SW ones. However, tNCX1b mRNA did not show any significant changes in all the conditions.
For conclusions, ECaC, PMCA and NCX1b, co-expressed in a subtype of MRCs, may be the major players in Ca2+ uptake function of fish gills, and ECaC is probably the main regulatory transporter in this mechanism.
Subjects
鈣離子
富含粒腺體細胞
離子調控
calcium
MR cells
ion regulation
Type
other