Vesicular transport in capillary endothelium: does it occur?

Area of Science:

• Cell Biology
• Microcirculation Physiology
• Endothelial Cell Biology

Background:

• The structure and function of endothelial plasmalemmal vesicles have been debated.
• Vesicular transport is a proposed mechanism for substance exchange across capillary endothelium.

Purpose of the Study:

• To revise the understanding of endothelial plasmalemmal vesicle organization.
• To investigate the role of these structures in transport across capillary endothelia.

Main Methods:

• Three-dimensional reconstructions of capillary endothelial segments.
• Analysis of ultrathin serial sections from frog mesenteric and rat heart capillaries.

Main Results:

• Plasmalemmal vesicles are integral parts of the endothelial surface membrane, forming invaginations.
• No free cytoplasmic vesicles were observed in the analyzed endothelial cells.
• Previous studies on vesicular transport are reinterpreted as compatible with static membrane invaginations.

Conclusions:

• Endothelial plasmalemmal vesicles are not independent structures but part of a continuous surface membrane system.
• The absence of free vesicles challenges the concept of vesicular transport as a primary mechanism in capillary exchange.
• This revised model of endothelial cell organization likely applies broadly to capillary endothelia.