Effect of thio reagents on platelet transport processes and responses to stimuli

N-ethylmaleimide at submillimolar concentrations inhibited platelet aggregation and shape-change induced by ADP, collagen-induced aggregation, and the active transport of adenosine (but not of adenine or serotonin). p-Chloromercuribenzene sulphonate had broadly similar activity but was much less potent, lodoacetate, which at 0.3 mM caused leakage of ³H from the cytoplasm of platelets prelabelled with ³'H]adenine, had no inhibitory effects at lower concentrations, and 5'5'-dithio-bisnitrobenzoic acid was inactive up to 3 mM. Dithiothreitol. which slightly inhibited aggregation at 0.5 mM, induced aggregation directly at concentrations above 1 mM. and 2-amino(4-isothioureylmethyl-ene)-thiazol di HCl was a potent and selective inhibitor of serotonin transport, and also inhibited collagen-induced aggregation. Ecto-SH groups are apparently not involved in regulating platelet active transport processes or responses to stimuli, but intracellular thio groups are important in platelet secretion, aggregation, and shape-change, and also in the transport of serotonin and adenosine, but not of adenine.