Relative changes in the abundance of branchial Na+/K+-ATPase α-isoform-like proteins in marine euryhaline milkfish (Chanos chanos) acclimated to environments of different salinities

Abstract

Previous studies revealed that upon salinity challenge, milkfish (Chanos chanos), the euryhaline teleost, exhibited adaptive changes in branchial Na+/K+-ATPase (NKA) activity with different Na+ and K+ affinities. Since alteration of activity and ion-affinity may be influenced by changes in different isoforms of NKA a-subunit (i.e., the catalytic subunit), it is, thus, intriguing to compare the patterns of protein abundance of three major NKA a-isoform-like proteins (i.e., α1, α2, and α3) in the gills of euryhaline milkfish following salinity challenge. The protein abundance of three NKA a-isoform-like proteins in gills of milkfish reared in seawater (SW), fresh water (FW), as well as hypersaline water (HSW, 60‰) were analyzed by immunoblotting. In the acclimation experiments, the SW group revealed significantly higher levels of NKA α1- and α3-like proteins than the FW or HSW group. Time-course experiments on milkfish that were transferred from SW to HSW revealed the abundance of branchial NKA α1-like and α3-like proteins decreased significantly after 96 and 12hr, respectively, and no significant difference was found in NKA α2-like protein. Furthermore, when fish were transferred from SW to FW, the amounts of NKA α1- and α3-like proteins was significantly decreased after 96hr. Taken together, acute and chronic changes in the abundance of branchial NKA α1- and α3-like proteins may fulfill the requirements of altering NKA activity with different Na+ or K+ affinity for euryhaline milkfish acclimated to environments of various salinities. © 2009 Wiley-Liss, Inc.