Endothelial plasmalemmal vesicles have a characteristic striped bipolar surface structure.

Area of Science:

• Cell Biology
• Microscopy
• Endothelial Cell Biology

Background:

• Capillary endothelial cells contain numerous small vesicles (65-80 nm diameter).
• A significant portion of these vesicles are associated with the plasmalemma on both luminal and abluminal sides.

Purpose of the Study:

• To investigate the fine structure and distribution of plasmalemmal vesicles.
• To characterize these vesicles in cultured endothelial cells from bovine adrenal cortical capillaries.

Main Methods:

• High-resolution scanning electron microscopy (SEM) was employed.
• Cultured endothelial cells were prepared using polylysine-coated silicon chips, high potassium buffer splitting, aldehyde fixation, and OsO4/thiocarbohydrazide treatment.
• Specimens were critical point dried and coated with a thin chromium film.

Main Results:

• Plasmalemmal vesicles appeared as uniform protrusions (70-90 nm diameter) on the cytoplasmic aspect of plasmalemmal fragments.
• Vesicles were concentrated in distinct fields, often as single units.
• Individual vesicles displayed a unique striped surface structure with meridional ridges, distinct from coated pits.
• A fibrillar infrastructure on the plasmalemma, distinct from vesicles, served as an anchoring point via fine filaments.

Conclusions:

• High-resolution SEM revealed detailed morphology of plasmalemmal vesicles.
• The observed striped surface structure and anchoring mechanism provide new insights into vesicle function.
• These findings contribute to understanding transport processes in capillary endothelial cells.