| Summary: | It is increasingly clear, that alterations in Na + ,K + -ATPase kinetics to fit the demands in specialized cell types is vital for the enzyme to execute its different physiological roles in diverse tissues. In addition to tissue dependent expression of isoforms of the conventional subunits, and a and ß auxiliary FXYD proteins appear to be essential regulatory components. We identified genes belonging to this family in Atlantic salmon by analysis of expressed sequence tags. Based on the conserved domain of these small membrane proteins, we identified eight expressed FXYD isoforms. Using QPCR, we analyzed the tissue dependent expression of the different isoforms in gill, kidney, intestine, heart, muscle, brain and liver. When inspecting the relative expression levels we found, that while two isoforms were detected at comparable levels in several of the examined tissues, 6 isoforms were expressed in a more discrete manner. In excitatory tissues, two isoforms were highly expressed in brain and one in skeletal muscle. In osmoregulatory tissues, one isoform was expressed predominantly in gill, one in kidney and one equally in kidney and intestine. We observed that expression of several FXYD genes in kidney and gill differed between fresh water and seawater salmon. The present study identified novel FXYD isoforms and demonstrated the tissue dependence in their expression. Modulation of FXYD proteins in osmoregulatory organs in response to salinity substantiate the importance of these genes in ion transport processes and suggests a significance of their specific regulation during development of osmoregulatory capacity.
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