Electron microscopic analysis of lipid clusters and membrane proteins in plasma membrane.

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We examined transbilayer and lateral lipid distribution in plasma membrane using recently developed peptide/proteins that selectively bind specific lipids or lipid clusters. The liposome experiments demonstrated that the lipids were effectively detected by the probes even when the membrane concentration was as low as 1 mol%, and the probes bound similarly to the model membranes that mimic outer or inner leaflet lipid environment.Next, we examined the distribution of sphingomyelin and phosphatidylserine in resting and thrombin-stimulated platelets as well as platelet microparticles that are highly procoagulant. Our results indicate that the scrambled membranes are selectively released in the form of microparticles in thrombin-activated platelets and suggest the idea that the exposure of phosphatidylserine in inner leaflet to the outer triggers the vesiculation of platelets.