Esophageal expression of Na+/H+ exchanger 2 and -3 (nhe2 and -3) gene transcripts in Atlantic salmon during smoltification and seawater acclimation

Atlantic salmon ( Salmo salar) undergo smoltification, a springtime transformation associated with the development of physiological, morphological, and behavioral traits that enable individuals to thrive in pelagic marine habitats. In particular, the capacity for salmon to maintain hydromineral balance in seawater is attained through the coordinated development of ion- and water-transporting processes in key organs such as the gill, kidney, and gastrointestinal tract. To combat dehydration, Atlantic salmon drink ambient seawater that is initially desalinated in the esophagus to enable subsequent solute-linked water absorption by the intestine. The molecular processes underlying esophageal desalination of imbibed seawater and their regulation during smoltification and following seawater exposure remain largely unresolved. The current study explored whether Na + /H + exchangers in the esophagus may contribute to the removal of Na + from luminal seawater. We first determined that both nhe2 and -3 were robustly expressed in the esophagus of smolts; nhe2 was also highly expressed in gill and stomach. Next, we sampled salmon undergoing smoltification and observed springtime elevations in branchial Na + /K + -ATPase activity, Na + /K + /2Cl - cotransporter 1 and cystic fibrosis transmembrane regulator 1 transcription that coincided with increased seawater tolerance. There were no parallel springtime changes in esophageal nhe2 or -3 expression; but nhe3 expression was enhanced in smolts after 2 days of seawater exposure. In a subsequent experiment, we observed elevated nhe2 and -3 expression in smolts that were long-term acclimated (2 weeks) to seawater versus freshwater. Collectively, our results indicate that Na + /H + exchangers contribute to the desalination processes in the esophagus. The next challenge will be to determine whether essential “seawater-adapting hormones,” such as growth hormone and cortisol, regulate the expression of Na + /H + exchangers in support of seawater acclimation. Supported by the National Science Foundation (IOS-1755131 to J.P.B.). National Science Foundation [IOS-1755131] This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.