title: Stimulation of platelet serotonin transport by substituted 1,4-naphthoquinone-induced oxidant stress.
abstract: The effect of oxidant stress produced by redox cycling of substituted 1,4-naphthoquinones on the activity of platelet (Na(+)-K+)ATPase and the active transport of serotonin (5-HT) was studied. 2-Methyl-1,4-naphthoquinone (menadione) produced a concentration-dependent (0-100 microM) and time-dependent (2-20 min) stimulation of platelet 5-HT transport. Exogenous superoxide dismutase (250 units) and/or catalase (500 units) failed to block the stimulation. Fluoxetine, an inhibitor of the platelet 5-HT transporter, blocked menadione-induced stimulation of 5-HT uptake as did ouabain, an inhibitor of platelet (Na(+)-K+)ATPase. The structure-activity relationship of select 1,4-naphthoquinones suggested that stimulation was due to redox cycling and not arylation. The kinetics of 5-HT transport revealed that menadione markedly increased the maximal rate of 5-HT transport (Vmax control = 20.6 +/- 2.0 pmol/10(8) platelets/4 min vs Vmax menadione = 46.4 +/- 3.9 pmol/10(8) platelets/4 min) but did not significantly alter the Km values. The activity of (Na(+)-K+)ATPase was determined by measuring the uptake of 86Rb+ into intact platelets. Menadione produced a concentration-dependent and time-dependent stimulation of platelet 86Rb+ uptake. These changes in platelet (Na(+)-K+)ATPase activity paralleled the changes observed in 5-HT transport and were inhibited in a concentration-dependent manner by ouabain. The data have shown that the redox cycling of 1,4-naphthoquinones caused an increase in (Na(+)-K+)ATPase activity that resulted in the stimulation of the rate of platelet 5-HT transport.
authors.affiliation: Pharmacology Section, Indiana University School of Medicine, Bloomington 47405.
authors.forename: T R
authors.initials: TR
authors.lastname: Bosin
authors.forename: S L
authors.initials: SL
authors.lastname: Schaltenbrand
mesh_terms: D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D002478:Cells, Cultured; D008297:Male; D051379:Mice; D009285:Naphthoquinones / Q000494:pharmacology*; D010042:Ouabain / Q000494:pharmacology; D010084:Oxidation-Reduction; D012701:Serotonin / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013329:Structure-Activity Relationship; D015219:Substrate Cycling; D014812:Vitamin K / Q000494:pharmacology
chemical_list: D009285:Naphthoquinones; D014812:Vitamin K; D012701:Serotonin; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase; C035342:1,4-naphthoquinone