Spin-labelled human platelets

Human platelets were labelled with a variety of lipophilic and thiol reagent spin probes. Aggregation was not affected by the lipid probes but was blocked by the covalent protein-directed probes. ESR spectra before and after thrombin treatment indicated that lipid structure of the platelet membrane was not affected to any measurable extent by the thrombin interaction, although there was a change in the partition coefficient of the probe between solution and the membrane. From the fact that four different probes for different parts of the membrane lipid showed the same result, we conclude that thrombin interaction and resultant changes in the platelet membrane do not involve any substantial change in lipid organization.