Oxidant stress stimulates active transport of serotonin by platelets.
The effect of oxidant stress on the active transport of serotonin (5-HT) into mouse platelets was examined. Oxidant stress was produced using either H2O2 or the xanthine-xanthine oxidase generating system that yields both superoxide anion and H2O2. H2O2 (6.25-100 microM) caused a rapid (2-4 min) stimulation of platelet 5-HT transport that returned to control levels after 15 min of incubation. Catalase (1500 U/ml) completely prevented the stimulation, and the hydroxyl radical trapping agents mannitol (1 nM) and thiourea (1 mM) failed to alter the stimulation. Fluoxetine (1 microM) totally blocked all 5-HT uptake into stimulated platelets. The xanthine-xanthine oxidase (3.12-25 mU/ml) generating system produced a response similar to that of H2O2. In this system, superoxide dismutase (250 U/ml) did not alter the stimulatory response, whereas catalase (1500 U/ml) totally prevented the stimulation. The kinetics of 5-HT transport showed that oxidant stress did not alter the Km of 5-HT transport (Km control = 8.0 +/- 1.0 x 10(-7) M versus Km H2O2 = 9.5 +/- 1.1 x 10(-7) M) but markedly increased the maximal rate of transport (Vmax control = 36.1 +/- 4.8 pmol/10(8) platelets/4 min versus Vmax H2O2 = 79.9 +/- 9.1 pmol/10(8) platelets/4 min). Washed platelets failed to be stimulated by H2O2; however, the addition of small amounts of plasma to the buffer medium fully restored the stimulating response to H2O2. These data suggest that a plasma factor regulates the active transport of 5-HT by platelets that are oxidatively stressed.
Bosin
T R
TR
Pharmacology Section, Indiana University School of Medicine, Bloomington.
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D051379:Mice; D012701:Serotonin / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors; D014969:Xanthine Oxidase / Q000494:pharmacology
D012701:Serotonin; D006861:Hydrogen Peroxide; D014969:Xanthine Oxidase; D000254:Sodium-Potassium-Exchanging ATPase