Characterization of gill Na/K-ATPase activity and ouabain binding in Antarctic and New Zealand nototheniid fishes

Abstract

The effects of thermal acclimation in two Nototheniid species, the stenothermal Antarctic Trematomous bernacchii and the eurythermal New Zealand Notothenia angustata, were investigated. Serum osmolality, gill Na/K-ATPase activity, sodium pump density and ouabain affinity were determined. Both fish were acclimated at their upper and lower viable thermal temperatures. Warm acclimation (+4 °C) of the T. bernacchii significantly decreased their serum osmolality from 550 to 450 mOsm/kg compared to cold-acclimation (−1.5 °C) and this was accompanied by a two-fold increase in gill Na/K-ATPase activity. Warm-acclimation (+14 °C) of N. angustata did not significantly change their serum osmolality from 330 mOsm/kg or gill Na/K-ATPase activity compared to the cold-acclimated (+4 °C) N. angustata. Using [ 3H]ouabain binding techniques, the B max and K d values of gill Na/K-ATPase enzymes were determined. No difference in the B max or K d of the warm-acclimated T. bernacchii accounted for the increase in Na/K-ATPase activity. We conclude that the change in gill Na/K-ATPase activity in the warm-acclimated T. bernacchii is not mediated by an increase in the number of enzyme sites and is not reflected in a change in ouabain affinity for Na/K-ATPase.