A Journal of Integrative Biology Relative Changes in the Abundance of Branchial Na1/K1-ATPase a-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 Na1/K1-ATPase (NKA) activity with different Na1 and K1 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., a1, a2, and a3) 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 a1- and a3-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 a1-like and a3-like proteins decreased significantly after 96 and 12hr, respectively, and no significant difference was found in NKA a2-like protein. Furthermore, when fish were transferred from SW to FW, the amounts of NKA a1- and a3-like proteins was significantly decreased after 96hr. Taken together, acute and chronic changes in the abundance of branchial NKA a1- and a3-like proteins may fulfill the requirements of altering NKA activity with different Na1 or K1 affinity for euryhaline milkfish acclimated to environments o