Summary
The effects of the SH-inhibitors monoiodoacetate (MIA) and N-ethylmaleimide (NEM)
on washed human blood platelets and on reactions of the platelets with immune complexes
and antiplatelet antisera were studied. The following results were obtained:
1. In the concentration range from 0.01 to 1 mM, only MIA in the highest concentration
had a direct effect on platelets, discernible by a small but significant release of
adenine nucleotides.
2. The reaction of human platelets with heterologous anti-platelet antisera, heat
aggregated human gammaglobulin, and gammaglobulin-coated latex particles was inhibited
by MIA in concentrations of 0.1 mM and by NEM in concentrations of 1 mM, and higher.
3. The SH-inhibitors tested exerted their influence on the platelet and not on the
immune agents.
4. L-cysteine was unable to reverse the effect of the SH-inhibitors on platelets.
If added at room temperature in equimolar amounts to MIA and NEM 10 min prior to their
contact with platelets, it abolished the effect of NEM, but not of MIA.
5. The inhibition by MIA and NEM of platelet reactions with a variety of immune agents
is comparable to the impairment of thrombin-induced viscous metamorphosis by SH-blockers.
The obtained results do not support the assumption that immune agents and thrombin
react with different, SH-group-containing substrates on the platelet surface.
