EXPRESSION OF NA-K+-ATPASE IN THE BROWN TROUT, SALMO-TRUTTA - IN-VIVOMODULATION BY HORMONES AND SEAWATER()

Expression of the Na+-K+-ATPase alpha-subunit was investigated in the gill and trunk kidney of Salmo trutta. Groups of freshwater (FW) fish were treated with various hormones [cortisol: 3 x 4.0 mu g/g; recombin ant salmon growth hormone (rsGH): 3 x 0.25 mu g/g; salmon prolactin (s PRL): 3 x 0.25 mu g/g; recombinant bovine insulin-like growth factor-I (rbIGF-I): 2 x 0.01 mu g/g or 2 x 0.1 mu g/g] or transferred to 25 pa rts per thousand seawater (SW) and sampled after 1, 2, 3, and 50 days. Total RNA was analyzed by Northern blotting using Xenopus laevis Na+- K+-ATPase alpha-subunit cDNA as probe. The probe detected a 3.8-kb tra nscript. Relative to untreated FW control fish, the abundance of alpha -subunit Na+-K+-ATPase mRNA in gill tissue increased 1.7-to 2.5-fold a fter treatment with cortisol, rsGH, and rbIGF-I and after transfer to SW. Na+-K+-ATPase enzyme activity was also significantly stimulated in these groups, except at 0.01 mu g/g rbIGF-I. sPRL was without effect. In the kidney, alpha-subunit mRNA level and Na+-K+-ATPase activity we re unaffected by hormone treatment and SW transfer. The results indica te that an increased abundance of alpha-subunit mRNA is part of the mo lecular mechanism behind the increased gill Na+-K+-ATPase activity ind uced by SW transfer, cortisol, GH, and IGF-I.