Na+/K+-ATPase response to salinity change and its correlation with FXYD11 expression in Anguilla marmorata

The Na+/K+-ATPase (NKA) is a primary electrogenic protein that promotes ion transport in teleosts. FXYD11 is a putative regulatory subunit of the NKA pump. The regulation of Na (+)/K (+) -ATPase and FXYD11 is of critical importance for osmotic homeostasis. To investigate the changes of the two genes under different salinity environments, we first identified NKA (AmNKA alpha 1) and FXYD11 (AmFXYD11) in Anguilla marmorata, and then evaluated the mRNA levels of NKA and FXYD11 as well as the activity of NKA in the gill and kidney at different timepoints (0, 1, 3, 6, 12, 24, 48, 72, 96, and 360 h) under three salinity conditions-0aEuro degrees (fresh water: FW), 10aEuro degrees (brackish water: BW), and 25aEuro degrees (seawater: SW). In the gill, the mRNA levels of AmNKA alpha 1 and AmFXYD11 and the enzyme activity of AmNKA alpha 1 were higher in BW and SW than in FW; the protein abundance was positively correlated with the specific activity of NKA in BW/SW. However, in the kidney, the mRNA level of AmNKA alpha 1 in the BW group was higher than that in the FW group. In addition, AmFXYD mRNA levels in both BW and SW groups were significantly lower than that in the FW control group. These results suggested that AmFXYD11 was tissue specific in response to different salinity environment. Our results clearly demonstrated the important roles of AmNKA alpha 1 and AmFXYD11 in osmotic homeostasis of juvenile A. marmorata under saline environment.