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 (AmNKAα1) 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-0‰ (fresh water: FW), 10‰ (brackish water: BW), and 25‰ (seawater: SW). In the gill, the mRNA levels of AmNKAα1 and AmFXYD11 and the enzyme activity of AmNKAα1 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 AmNKAα1 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 AmNKAα1 and AmFXYD11 in osmotic homeostasis of juvenile A. marmorata under saline environment.