Effects of salinity changes or ammonia exposure on three ion transporters (nkcc, cftr & nka) in the gills of two mudskippers

Project Number
RI 4/12 CSF

Project Duration
April 2013 - March 2016

Status
Completed

Abstract
This project is the extension of a previous grant (NIE AcRF RI 9/08 CSF) entitled "Functional roles of Na+/K+-ATPase and inorganic osmolytes in the giant mudskipper exposed to seawater or seawater plus ammonium chloride". Results from that project revealed that the giant mudskipper, Periophthalmodon schlosseri, tightly regulated its plasma osmolality and concentrations of Na+ and Cl−, and did not depend on free amino acids for cell volume regulation. Instead, it expressed mRNA of two Na+/K+-ATPase (nka) á isoforms in its gills. The mRNA of nka á1 was upregulated after the fish was acclimated to high salinity (salinity 30) and ammonium chloride (75 mmol l-1). By contrast, nka á3 was upregulated only by ammonia exposure. Different from other euryhaline fishes, P. schlosseri can survive an abrupt transfer from water of low salinity to water of high salinity. Thus, understanding how the gill epithelia of P. schlosseri could pump out the excess Na+ and Cl- during an abrupt transfer from salinity 3 to salinity 30 could provide valuable information to the water purification industry especially concerning the possibility of constructing artificial membrane based on the principle of membrane transporters rather than restricted pore size to purify water. In addition, P. schlosseri has the unique ability of tolerating 100 mmol l-1 NH4Cl by actively excreting NH4+ through its gills. Studying how the gill epithelia of this fish excrete NH4+ could provide information on the possibility of constructing artificial membranes for ammonia removal, which may have application in the food industry, aquaculture, and blood dialysis in patients with acute liver failure. Thus, it is proposed to perform a molecular study on the gene and gene/protein expression of three ion transporters, Na+:K+:2Cl- cotransporter (nkcc), cystic fibrosis transmembrane conductance regulator (cftr) and nka á-subunit in the gills of the giant mudskipper, with the objective of understanding the mechanism which allow this fish to survive abrupt changes in salinity and exposure to extremely high concentrations of NH4Cl. In addition, it would be interesting to make a comparison of these mechanisms utilized by P. schlosseri with those utilized by Boleophthalmus boddarti, another mudskipper which can survive an abrupt change of salinity but has a much lower tolerance for NH4Cl and is not known to actively excrete NH4+. ich allow this fish to survive abrupt changes in salinity and exposure to extremely high concentrations of NH4Cl. In addition, it would be interesting to make a comparison of these mechanisms utilized by P. schlosseri with those utilized by Boleophthalmus boddarti, another mudskipper which can survive an abrupt change of salinity but has a much lower tolerance for NH4Cl and is not known to actively excrete NH4+.

Funding Source
NIE

Related Projects