Na+, K+ ATPase, quabain binding and quabain-sensitive oxygen consumption in gills fromPlatichthys flesus adapted to seawater and freshwater

Summary The levels of Na⁺, K⁺ ATPase were measured in gills fromPlatichthys flesus adapted to seawater and freshwater using a variety of experimental techniques. Na⁺, K⁺ ATPase was assayed directly in crude gill homogenates,³H-ouabain binding was determined in isolated, perfused gills and ouabainsensitive oxygen consumption measured in sliced gill filaments. These experimental approaches all failed to show any difference in Na⁺, K⁺ ATPase activity or in enzyme turnover rate in gills from seawateradapted and freshwater-adaptedPlatichthys. The results are discussed in terms of the marine origin of the flounder and the energetic demands of ion regulation in euryhaline fish.