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

Abstract

The effect of H 2O 2 on the active transport of serotonin (5-HT) by human platelets was investigated. Platelets were exposed to either a single dose of H 2O 2 or to H 2O 2 generated by the glucose/glucose oxidase or xanthine/xanthine oxidase enzyme systems. H 2O 2 (12.5 to 100 μM) produced a rapid, concentration-dependent and time-dependent increase in 5-HT transport which was maximal after a 2min incubation and decreased with continued incubation. Catalase (1000 units) completely prevented H 2O 2-induced stimulation, and fluoxetine (1 μM) totally blocked 5-HT uptake into stimulated platelets. The glucose/glucose oxidase (3.12 to 100 milliunits) and the xanthine/xanthine oxidase generating systems produced a similar response to that of H 2O 2. In 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 H 2O 2 treatment did not alter the K m of 5-HT transport ( K m control = 1.0 ± 0.2 × 10 −6 M vs K m H 2O 2 = 1.1 ± 0.1 × 10 −6 M) but markedly increased the maximal rate of 5-HT transport ( V max control = 131.4 ± 4.6 pmol/10 8 platelets/4 min vs V max H 2O 2 = 206.7 ± 9.1 pmol/10 8 platelets/4 min). These data demonstrated that exposure of human platelets to H 2O 2 resulted in a stimulation of the active transport of 5-HT and suggested that H 2O 2 may function to regulate this process.