期刊
JOURNAL OF COMPARATIVE PHYSIOLOGY B-BIOCHEMICAL SYSTEMS AND ENVIRONMENTAL PHYSIOLOGY
卷 183, 期 2, 页码 203-213出版社
SPRINGER HEIDELBERG
DOI: 10.1007/s00360-012-0700-9
关键词
Gill; Ion homeostasis; Kidney; Epithelial permeability; Tight junction; Zebrafish
资金
- Natural Sciences and Engineering Research Council of Canada (NSERC)
Freshwater teleosts are challenged by diffusive ion loss across permeable epithelia including gills and skin. Although the mechanisms regulating ion loss are poorly understood, a significant component is thought to involve paracellular efflux through pathways formed via tight junction proteins. The mammalian orthologue (claudin-4) of zebrafish (Danio rerio) tight junction protein, claudin-b, has been proposed to form a cation-selective barrier regulating the paracellular loss of Na+. The present study investigated the cellular localization and regulation of claudin-b, as well as its potential contribution to Na+ homeostasis in adult zebrafish acclimated to ion-poor water. Using a green fluorescent protein-expressing line of transgenic zebrafish, we found that claudin-b was expressed along the lamellar epithelium as well as on the filament in the inter-lamellar regions. Co-localization of claudin-b and Na+/K+-ATPase was observed, suggesting its interaction with mitochondrion-rich cells. Claudin-b also appeared to be associated with other cell types, including the pavement cells. In the kidney, claudin-b was expressed predominantly in the collecting tubules. In addition, exposure to ion-poor water caused a significant increase in claudin-b abundance as well as a decrease in Na+ efflux, suggesting a possible role for claudin-b in regulating paracellular Na+ loss. Interestingly, the whole-body uptake of a paracellular permeability marker, polyethylene glycol-400, increased significantly after prolonged exposure to ion-poor water, indicating that an increase in epithelial permeability is not necessarily coupled with an increase in passive Na+ loss. Overall, our study suggests that in ion-poor conditions, claudin-b may contribute to a selective reduction in passive Na+ loss in zebrafish.
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