Effect of high ionic strength and inhibitors of H,K-ATPase on the ouabain-sensitive K-p-nitrophenylphosphatase activity in the sea anemone Stichodactyla helianthus.
The ouabain-sensitive, K-stimulated p-nitrophenyl phosphatase (K-pNPPase) activity, an associated activity of the Na,K-ATPase, was assayed in tentacles of the sea anemone Stichodactyla helianthus to investigate the possibility that the sea anemone Na,K-ATPase activity is an associated activity of an H,K-ATPase. Activity was maximal at pH 6.5-7.0, decreasing only slightly in acidic medium but falling abruptly in alkaline medium to 60% of maximum at pH 7.4. The pH of maximum activity was not remarkably altered in high ionic strength medium (560 mM choline chloride), but ouabain-sensitive K-pNPPase activity of both rat and sea anemone was strongly inhibited. Inhibitors of the gastric H,K-ATPase, 100 microM omeprazole and 10 microM SCH 28080, did not inhibit the ouabain-sensitive K-pNPPase activity. Activity of the sea anemone enzyme was inhibited by 10 microM ammonium vanadate, an inhibitor of P-type ATPase, and not by 2.5 mM sodium azide, an inhibitor of both F-type and V-type ATPase. Because the sea anemone K-pNPPase activity was previously found to be more sensitive to ouabain than the Na,K-ATPase activity, K(+)-ouabain antagonism was investigated and found to be relatively muted, whereas K(+)-Na+ competition was stronger than in the rat kidney.
Specht
S C
SC
Department of Pharmacology, University of Puerto Rico Medical Sciences Campus, San Juan, PR, 00901.
Rodriguez
C
C
Quiñones
L
L
Velazquez
S
S
D009597:4-Nitrophenylphosphatase / Q000378:metabolism*; D000818:Animals; D002794:Choline; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles / Q000494:pharmacology; D009853:Omeprazole / Q000494:pharmacology; D009994:Osmolar Concentration; D010042:Ouabain / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology*; D011189:Potassium Chloride / Q000494:pharmacology; D054328:Proton Pump Inhibitors; D051381:Rats; D012615:Sea Anemones / Q000201:enzymology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism; D014638:Vanadates / Q000494:pharmacology
D004791:Enzyme Inhibitors; D007093:Imidazoles; D054328:Proton Pump Inhibitors; C035235:Sch 28080; D014638:Vanadates; D010042:Ouabain; D011189:Potassium Chloride; D009597:4-Nitrophenylphosphatase; D000254:Sodium-Potassium-Exchanging ATPase; D009853:Omeprazole; D002794:Choline; D011188:Potassium