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First published online June 11, 2007
Journal of Experimental Biology 210, 2113-2120 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.004101

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Effect of osmotic shrinkage and hormones on the expression of Na⁺/H⁺ exchanger-1, Na⁺/K⁺/2Cl^– cotransporter and Na⁺/K⁺-ATPase in gill pavement cells of freshwater adapted Japanese eel, Anguilla japonica

William K. F. Tse¹, Doris W. T. Au² and Chris K. C. Wong^1,*

¹ Department of Biology, Hong Kong Baptist University, Kowloon Tong, Hong Kong
² Departments of Biology and Chemistry, City University of Hong Kong, Hong Kong

^* Author for correspondence (e-mail: ckcwong{at}hkbu.edu.hk)

Accepted 4 April 2007

It is well-known that gill epithelial cells are important in fish osmoregulation. However, studies on the effect of osmotic stress on the direct cellular responses of the gill epithelial cells are limited. In this paper, we aimed to determine the effects of osmotic hypertonicity, hormones and cellular signaling molecules on the expression of ion transporters in the cultured primary freshwater pavement cells (PVCs), prepared from freshwater-adapted eels (Anguilla japonica). Our data demonstrated that the hypertonic (500 mOsmol l^–1) treatment of the isolated PVCs induced cell shrinkage, followed by regulatory volume increase (RVI). Application of blockers (i.e. ouabain, bumetanide and EIPA) demonstrated that Na⁺/K⁺-ATPase, Na⁺/K⁺/2Cl^– cotransporter (NKCC) and Na⁺/H⁺ exchanger-1 (NHE-1) were involved in RVI. Western blot analysis of the hypertonic-treated cells revealed a significant induction of NHE-1, NKCC and, and ß subunits of Na⁺/K⁺-ATPase. In nonshrunken cultured PVCs, we found that dexamethasone and dibutyryl cAMP treatments significantly stimulated the expression levels of the three ion transporters. Both prolactin and insulin-like growth factor-1, can only induce the expression of NKCC. The effect of thyroid hormone (T₃) and dibutyryl cGMP was negligible. In this study, the induction of ion transporter expression was found to be post-transcriptionally regulated as no significant change in mRNA levels was detected. This observation implies that the regulation is rapid and is probably induced via nongenomic actions.

Key words: dexamethasone, hypertonic stress, dibutyryl cAMP, regulatory volume increase

This article has been cited by other articles:

				W. K. F. Tse, S. C. Chow, and C. K. C. Wong The cloning of eel osmotic stress transcription factor and the regulation of its expression in primary gill cell culture J. Exp. Biol., June 15, 2008; 211(12): 1964 - 1968. [Abstract] [Full Text] [PDF]