PRESSURE ADAPTATION OF Na+/K+-ATPase IN GILLS OF MARINE TELEOSTS

The effects of pressure and temperature on an integral membrane protein, Na+/K+-adenosine triphosphatase (Na+/K+-ATPase), were studied in fish gill membrane preparations from shallow- and deep-living marine teleosts. The inhibition by pressure of maximal velocity of the enzyme is nonlinear, increasing at higher pressures. Na+/K+-ATPases from deep-sea fish were less inhibited by pressure than those of shallow-living species. Habitat temperature also affected the pressure response of the enzyme. As a function of physiological pressure and temperature, the order of increasing pressure-sensitivity was cold, deep-sea < warm, deep-sea (hydrothermal vents) < polar = shallow and mid-depth, cold< shallow, warm. Activation volumes in all species were conserved at 30-60ml moP 1 at physiological pressures, which may reflect a similar membrane physical state at the actual pressure the animal experiences. Arrhenius plots [ln(Na+/K+-ATPase activity) vs l/T] were steeper for warm-water and shallow-living species than for deep-sea species. The depth at which adaptation was first observed was about 2000m («=200atm; latm = 101-3kPa). The data are consist-ent with a model of increased membrane fluidity resulting in reduced pressure-sensitivity of Na+/K+-ATPase from deep-sea species