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

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 alpha-subunit (i.e., the catalytic subunit), it is, thus, intriguing to compare the patterns of protein abundance of three major NKA alpha-isoform-like proteins (i.e., alpha 1, alpha 2, and alpha 3) in the gills of euryhaline milkfish following salinity challenge. The protein abundance of three NKA alpha-isoform-like proteins in gills of milkfish reared in seawater (SW), fresh water (FW), as well as hypersaline water (HSW, 60 parts per thousand) were analyzed by immunoblotting. In the acclimation experiments, the SW group revealed significantly higher levels of NKA alpha 1- and alpha 3-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 alpha 1-like and alpha 3-like proteins decreased significantly after 96 and 12 hr, respectively, and no significant difference was found in NKA alpha 2-like protein. Furthermore, when fish were transferred from SW to FW, the amounts of NKA alpha 1- and alpha 3-like proteins was significantly decreased after 96 hr. Taken together, acute and chronic changes in the abundance of branchial NKA alpha 1- and alpha 3-like proteins may fulfill the requirements of altering NKA activity with different Na+ or K+ affinity for euryhaline milkfish acclimated to environments or various salinities. J. Exp. Zool. 311A:521-529, 2009. (c) 2009 Wiley-Liss, Inc.