title: Switching of Na+, K+-ATPase isoforms by salinity and prolactin in the gill of a cichlid fish.
abstract: We identified and investigated the changes in expression of two gill Na(+), K(+)-ATPase α-subunit isoforms (α-1a and α-1b) in relationship with salinity acclimation in a cichlid fish, Mozambique tilapia. Transfer of freshwater (FW)-acclimated fish to seawater (SW) resulted in a marked reduction in α-1a expression within 24 h and a significant increase in α-1b expression with maximum levels attained 7 days after the transfer. In contrast, transfer of SW-acclimated fish to FW induced a marked increase in α-1a expression within 2 days, while α-1b expression decreased significantly after 14 days. Hypophysectomy resulted in a virtual shutdown of α-1a mRNA expression in both FW- and SW-acclimated fish, whereas no significant effect was observed in α-1b expression. Replacement therapy by ovine prolactin (oPrl) fully restored α-1a expression in FW-acclimated fish, while cortisol had a modest, but significant, stimulatory effect on α-1a expression. In hypophysectomized fish in SW, replacement therapy with oPrl alone or in combination with cortisol resulted in a marked increase in α-1a mRNA to levels far exceeding those observed in sham-operated fish. Expression of α-1b mRNA was unaffected by hormone treatment either in FW-acclimated fish or in SW-acclimated fish. The mRNA expression of fxyd-11, a regulatory Na(+), K(+)-ATPase subunit, was transiently enhanced during both FW and SW acclimation. In hypophysectomized fish in FW, oPrl and cortisol stimulated fxyd-11 expression in a synergistic manner. The clear Prl dependence of gill α-1a expression may partially explain the importance of this hormone to hyperosmoregulation in this species.
authors.affiliation: Hawaii Institute of Marine Biology, University of Hawaii, Kaneohe, Hawaii 96744, USA.
authors.forename: C K
authors.initials: CK
authors.lastname: Tipsmark
authors.forename: J P
authors.initials: JP
authors.lastname: Breves
authors.forename: A P
authors.initials: AP
authors.lastname: Seale
authors.forename: D T
authors.initials: DT
authors.lastname: Lerner
authors.forename: T
authors.initials: T
authors.lastname: Hirano
authors.forename: E G
authors.initials: EG
authors.lastname: Grau
mesh_terms: D000064:Acclimatization; D000818:Animals; D029941:Fish Proteins / Q000378:metabolism; D005880:Gills / Q000201:enzymology*; D007016:Hypophysectomy; D007527:Isoenzymes / Q000378:metabolism; D008297:Male; D011388:Prolactin / Q000378:metabolism*; D054712:Salinity; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D017210:Tilapia / Q000378:metabolism*
chemical_list: D029941:Fish Proteins; D007527:Isoenzymes; D011388:Prolactin; D000254:Sodium-Potassium-Exchanging ATPase