Vol. 47 No. 6, 2008

Expression of the Na-K-2Cl Cotransporter in Branchial MitochondrionRich Cells of Mozambique Tilapia (Oreochromis mossambicus) Subjected to Varying Chloride Conditions

Jiun-Lin Horng¹ and Li-Yih Lin^2,*

¹Institute of Cellular and Organismic Biology, Academia Sinica, Taipei 115, Taiwan
²Department of Life Science, National Taiwan Normal University, Taipei 106, Taiwan

Jiun-Lin Horng and Li-Yih Lin (2008) The Na/K/2Cl cotransporter (NKCC) plays a critical role of active Cl^- transport through the basolateral membranes of mitochondrion-rich (MR) cells in seawater teleosts.  Recently, the NKCC was also found in apical membranes of MR cells of freshwater (FW)-acclimated tilapia (Oreochromis mossambicus).  In this study, immunocytochemistry and immunoblotting were used to analyze the expression levels of the NKCC in FW-acclimated tilapia in response to different ambient chloride levels.  The amount of branchial NKCC from lowCl^-- (0.002-0.006 mM)-acclimated tilapia was about 3- and 5.5-fold higher than that from normal- (0.49-0.51 mM) and high-Cl^- (9.8-10.2 mM)-acclimated tilapia.  With confocal microscopy, the NKCC was localized mainly in the apical membranes of MR cells with Cl^--dependent abundances.  The staining intensity of the NKCC in individual MR cells was significantly higher in the low-Cl- group than in the normal and high-Cl^- groups.  Results suggest that the apically localized NKCC is induced by a Cl^- deficiency and is probably also involved in the Cl^- uptake mechanism of MR cells.

Key words: Mitochondrion-rich cells, Tilapia (Oreochromis mossambicus), Osmoregulation.

*Correspondence: Tel: 886-2-29326234 ext. 316.  Fax: 886-2-29312904.   E-mail:linly@ntnu.edu.tw