In vitro stimulation of Na+-K+-ATPase activity and ouabain binding by cortisol in coho salmon gill.

To investigate the hormonal control of gill Na+-K+-adenosinetriphosphatase (ATPase) (the sodium pump) in coho salmon, a technique for the culture of primary gill filaments for up to 4 days was developed. Trypan blue exclusion was greater than 99.9%, histological appearance of the cells was normal, and total [Na+], [K+], and protein content of gill filaments cultured for 2-4 days was unchanged from initial levels (measured immediately after isolation). In fish with initially low gill Na+-K+-ATPase activity (presmolts), cortisol (0.1, 1.0, and 10.0 micrograms/ml) caused a significant dose-dependent increase in gill Na+-K+-ATPase activity over initial (41%) and control levels (45%) after 4 days in culture. In fish with initially high gill Na+-K+-ATPase activity (postsmolts), cortisol partially prevented the decline in activity that occurred during 4 days of culture. The relative ability of steroids to increase gill Na+-K+-ATPase activity was dexamethasone greater than cortisol = 11-deoxycortisol greater than cortisone. Insulin (0.1, 1.0, and 10.0 micrograms/ml), alone or in combination with cortisol, had no significant effect on gill Na+-K+-ATPase activity. Cortisol treatment significantly increased maximum binding capacity of [3H]ouabain in gill tissue (from 2.92 to 5.22 pmol/mg dry wt) but had no significant effect on the dissociation constant. These results demonstrate that cortisol has direct effects on the osmoregulatory physiology of the teleost gill.