Molecular characterization and expression of Na+/K+-ATPase α1 isoforms in the European sea bass Dicentrarchus labrax osmoregulatory tissues following salinity transfer

The Na+/K+-ATPase (NKA) is considered as the main pump involved in active ion transport. In the European sea bass, Dicentrarchus labrax, we found two genes encoding for the alpha 1 subunit isoforms (NKA alpha 1a and NKA alpha 1b). NKA alpha 1a and NKA alpha 1b isoform amino acid (aa) sequences were compared through phylogeny and regarding key functional motifs between salmonids and other acanthomorph species. Analysis of aa sequences of both isoforms revealed a high degree of conservation across teleosts. The expression pattern of both nka alpha 1a and nka alpha 1b was measured in the gill, kidney and posterior intestine of fish in seawater (SW) and transferred to fresh water (FW) at different exposure times. Nka alpha 1a was more expressed than nka alpha 1b whatever the condition and the tissue analyzed. After long-term salinity acclimation (2.5 years) either in FW or SW, transcript levels of nka alpha 1a were higher in the kidney followed by the posterior intestine and the gill. Compared to SW conditions, expression of nka alpha 1a in FW was significantly increased or decreased, respectively, in gill and posterior intestine. In contrast, branchial nka alpha 1b was significantly decreased in FW-acclimated fish. Short-term FW acclimation seems to rapidly increase nka alpha 1a transcript levels in the kidney unlike in gill tissues where different gene expression levels are detected only after long-term acclimation.