Cloning and characterization of sea bream Na+-K+-ATPase α and β subunit genes: In vitro effects of hormones on transcriptional and translational expression

The full length genes encoding the catalytic α and glycosylated β subunits of the sodium pump (Na+-K+-ATPase) were cloned and characterized from silver sea bream gill. Using in vitro preparations of gill tissue it was found that growth hormone (10 and 100 ng/ml) caused an increase in subunit transcription, translation, and Na+-K+-ATPase enzyme activity. Similarly, insulin-like growth factor 1 (10 and 100 ng/ml) also caused an increase in Na+-K+-ATPase subunit amounts and enzyme activity. Cortisol (10 and 100 ng/ml) increased α subunit transcript and protein but did not modulate β subunit expression or enzyme activity. Ovine prolactin did not cause any changes in Na+-K+-ATPase subunit transcription, translation or enzyme activity. This study is the first to describe how both Na+-K+-ATPase α and β subunits are modulated at transcriptional and translational levels in fish osmoregulatory tissue upon exposure to hormones.