Meeting Abstract

76.2  Friday, Jan. 7  Hormonal control and developmental changes in the salinity-dependent isoforms of the branchial sodium pump of Atlantic salmon. MCCORMICK, S.D.*; REGISH, A.M.; CHADWICK, J.G.; CHRISTENSEN, A.K.; USGS, Conte Anadromous Fish Research Center mccormick@umext.umass.edu

The sodium pump, Na+,K+-ATPase (NKA), in the gills of teleost fish is involved in ion regulation in both freshwater and seawater. Recent molecular evidence indicates that isoforms of the main catalytic alpha subunit may be differentially regulated by environmental salinity. We have developed and validated two antibodies specific for the NKA alpha1a (a1a) or NKA alpha1b (a1b) isoform of Atlantic salmon, and used western blots and immunocytochemisry to examine their abundance and localization. Gill NKA a1a decreases after Atlantic salmon are acclimated to seawater, whereas, whereas NKA a1b becomes more abundant. The abundance of NKA a1a is higher in parr than in the downstream migratory smolt, and decreases in parr and smolt from winter through spring. NKA a1b increases dramatically in smolts in spring coincident with their increased salinity tolerance. There is a further increase in NKA a1b abundance in smolts after seawater exposure. Gill NKA a1a and a1b abundance and chloride cell size were increased by treatment with exogenous cortisol. Growth hormone (GH) by itself did not affect the abundance of either isoform. However, when co-injected with cortisol, GH caused a decrease in NKA a1a and an increase in NKA a1b abundance, indicating that GH is acting as a switch to alter the effects of cortisol.