Effect of 5-hydroxytryptamine on sodium- and potassium-dependent adenosine triphosphatase and its reactivity toward ouabain.
Activity of vertebrate Na+,K+-ATPase was inhibited by 5-hydroxytryptamine. Inhibition was reversible, and activity could be restored by dilution of 5-hydroxytryptamine (5HT). The ability of indole derivatives to inhibit depended on the presence of a net charge on the third atom of the indole C-3 side chain. Indoles with a net positive charge, such as 5HT, were stronger inhibitors than those with a net negative charge. Derivatives with a net charge of zero were not inhibitors. The ability of indole derivatives to inhibit Na+, K+-ATPase activity decreased in the order 5HT > tryptamine > tryptophanamide > tryptophol > N-acetyl-5-methoxytryptamine > indole-3-acetic acid. Trp did not inhibit either ATPase or pNPPase activity. Charged indole derivatives also inhibited the pNPPase activity of Na+,K+-ATPase. 5HT and tryptophanamide were stronger inhibitors of pNPPase activity than indole-3-acetic acid. Binding of [3H]ouabain was inhibited by 5HT and tryptophanamide. Trp did not inhibit [3H]ouabain binding. The near equilibrium level of [3H]-ouabain binding in the presence of ATP, Mg2+, and Na+ was decreased by 5HT in the manner characteristic of a competitive inhibitor. Enzyme-bound [3H]ouabain could be displaced by 5HT. 5HT was a complex mixed inhibitor of K+ with interactions at two sites, Tris was a competitive inhibitor with interactions at three sites, and ouabain was a simple noncompetitive inhibitor. The data are explained through a model indole binding site containing oppositely charged residues.
Stepp
L R
LR
Department of Physiology, New York College of Osteopathic Medicine, Old Westbury 11568, USA.
Novakoski
M A
MA
D000818:Animals; D001665:Binding Sites; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006168:Guinea Pigs; D007211:Indoles / Q000737:chemistry / Q000494:pharmacology; D007668:Kidney / Q000201:enzymology; D007700:Kinetics; D010042:Ouabain / Q000494:pharmacology*; D011189:Potassium Chloride / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D012701:Serotonin / Q000494:pharmacology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013329:Structure-Activity Relationship
D004791:Enzyme Inhibitors; D007211:Indoles; D012701:Serotonin; D010042:Ouabain; D011189:Potassium Chloride; D000254:Sodium-Potassium-Exchanging ATPase