STIMULATION OF THE ACTIVE-TRANSPORT OF SEROTONIN INTO MOUSE PLATELETS BY THE SULFHYDRYL OXIDIZING-AGENT DIAMIDE

The purpose of this study was to determine the effects of diamide, a reversible sulfhydryl oxidizing agent, on the transport of serotonin (5-HT) by mouse platelets. Diamide produced a concentration-dependent (10-200 muM) stimulation of 5-HT transport that was rapid and sustained over 0-10 minutes of incubation. When platelets were incubated with diamide (10-200 muM) in the presence of glucose, the content of reduced glutathione was significantly decreased only at a final concentration of 200 muM, while washed platelets incubated with diamide (10-200 muM), in the absence of glucose, had a significant concentration-dependent decrease in their content of reduced glutathione. Fluoxetine, an inhibitor of the platelet 5-HT transporter, blocked diamide-induced stimulation of 5-HT transport. The kinetics of 5-HT transport showed that diamide caused a marked increase in the maximal rate of transport (V(max) control = 28.4 +/- 1.4 vs. V(max) diamide = 60.9 +/- 4.1 pM/10(8) platelets/4 min) but did not significantly alter the K(m) values. Ouabain, an inhibitor of platelet Na+-K+ ATPase, blocked the stimulation by diamide in a concentration-dependent manner. Dithiothreitol, a disulfide reducing agent, was able to partially reverse the stimulation of platelet 5-HT transport caused by diamide. This study has shown that diamide can stimulate the active transport of 5-HT by mouse platelets and suggests a possible role for free sulfhydryl groups in the regulation of this process.