Ultrastructural expression of P-selectin on surface activated platelets

Area of Science:

• Hematology
• Cell Biology
• Biochemistry

Background:

• P-selectin is a glycoprotein found in platelet alpha granules.
• Its surface expression upon activation is crucial for platelet function.
• The exact mechanism of P-selectin surface expression remains unclear.

Purpose of the Study:

• To investigate the mechanism of P-selectin surface expression in activated platelets.
• To determine if P-selectin is transported from granule membranes or released by surface-activation.
• To elucidate the spatial and temporal distribution of P-selectin during platelet spreading.

Main Methods:

• Washed platelets were allowed to interact with grids for varying durations (5-20 min).
• Platelets were fixed and exposed to a monoclonal antibody against P-selectin.
• Immunogold labeling with anti-mouse IgG coupled to 10 nm gold particles was used.
• Electron microscopy was employed to examine the distribution of gold probes.

Main Results:

• Discoid platelets showed no P-selectin expression.
• Early dendritic platelets exhibited P-selectin near the central zone.
• Late dendritic and fully spread platelets displayed P-selectin distribution, concentrated peripherally.
• P-selectin probes were evenly distributed on fully spread platelets, with higher concentration at the margin.

Conclusions:

• P-selectin is released from activated platelets (SfA P1).
• Initial central zone expression suggests transport via the open canalicular system.
• The centrifugal movement of P-selectin contrasts with receptor-ligand complex translocation.