Stimulation of the active transport of serotonin into human platelets by hydrogen peroxide

The effect of H2O2 on the active transport of serotonin (5-HT) by human platelets was investigated. Platelets were exposed to either a single dose of H2O2 or to H2O2 generated by the glucose/glucose oxidase or xanthine/xanthine oxidase enzyme systems. H2O2 (12.5 to 100 microM) produced a rapid, concentration-dependent and time-dependent increase in 5-HT transport which was maximal after a 2-min incubation and decreased with continued incubation. Catalase (1000 units) completely prevented H2O2-induced stimulation, and fluoxetine (1 microM) totally blocked 5-HT uptake into stimulated platelets. The glucose/glucose oxidase (3.12 to 100 milliunits) and the xanthine/xanthine oxidase system, superoxide dismutase (250 units) failed to alter the stimulation, whereas catalase (1000 units) effectively prevented the response. The kinetics of 5-HT transport indicated that H2O2 treatment did not alter the Km of 5-HT transport (Km control = 1.0 +/- 0.2 x 10(-6) M vs Km H2O2 = 1.1 +/- 0.1 x 10(-6) M) but markedly increased the maximal rate of 5-HT transport (Vmax control = 131.4 +/- 4.6 pmol/10(8) platelets/4 min vs Vmax H2O2 = 206.7 +/- 9.1 pmol/10(8) platelets/4 min). These data demonstrated that exposure of human platelets to H2O2 resulted in a stimulation of the active transport of 5-HT and suggested that H2O2 may function to regulate this process.