title: Rapid modulation of gill Na+ + K+-dependent ATPase activity during acclimation of the killifish Fundulus heteroclitus to salinity change.
abstract: The enzymatic properties of membrane-bound Na+ + K+-ATPase from gills of killifish acclimated to fresh water, to 16% sea water, or to 30% sea water appear to be identical, indicating that the same enzyme may function to absorb Na+ in low salinities and excrete Na+ at the gills in high salinities. Ammonium ion is an effective substitute for K+: in the ATPase reaction itself, in blocking phosphorylation of the ATPase protein, and in inhibiting the binding of ouabain to the enzyme. The specific activities of the Na+ + K+-ATPase in the three different salinities are consistent with the expected Na+ pumping rates: higher in fresh water and 30% sea water than in 16% sea water. Within one-half hour after transfer of killifish from one salinity to another, gill Na+ + K+-ATPase activities reach equilibrium levels. The rapid increase in Na+ + K+-ATPase activity in gill microsomes of fish acclimating from fresh water to 30% sea water is accompanied by a slow decrease in the number of binding sites for ouabain, supporting the idea that acclimation to short-term salinity changes may involve modifications in the catalytic rate rather than the number of Na+ + K+-ATPase molecules.
mesh_terms: D000064:Acclimatization; D000251:Adenosine Triphosphatases / Q000302:isolation & purification / Q000378:metabolism*; D000818:Animals; D005399:Fishes / Q000378:metabolism*; D005618:Fresh Water; D005880:Gills / Q000201:enzymology*; D007695:Killifishes / Q000378:metabolism*; D008297:Male; D009994:Osmolar Concentration; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D012623:Seawater; D012964:Sodium / Q000378:metabolism
chemical_list: D010042:Ouabain; D012964:Sodium; D000251:Adenosine Triphosphatases; D011188:Potassium