Permeability characteristics of microvascular walls

Area of Science:

• Physiology
• Biochemistry
• Cell Biology

Background:

• Previous models of macromolecule transport across microvessels assumed numerous small and few large pores.
• These "black box" models could not identify specific transport pathways.
• Potential structures like intercellular junctions, vesicles, and fenestrae were observed but often considered static.

Purpose of the Study:

• To investigate the precise pathways and mechanisms of macromolecule transport across microvascular walls.
• To evaluate the role of molecular properties (size, charge, chemical constitution) in transport.
• To explore whether transport is a dynamic, biochemically stimulated process rather than passive diffusion.

Main Methods:

• Review of electron microscopy findings identifying potential transport structures.
• Analysis of differing transport properties across arterioles, capillaries, and venules.
• Consideration of identified transport barriers: endothelial surface layer, endothelial cells, and basement membrane.

Main Results:

• Electron microscopy revealed structures like intercellular junctions, vesicles, and fenestrae as potential transport routes.
• Transport is influenced by macromolecule size, charge, and crucially, chemical constitution.
• The simple vesicle "shuttling" model is insufficient; transport appears to be a dynamic, biochemically driven process.

Conclusions:

• Macromolecular transport across microvessels is a complex, dynamic process.
• The chemical nature of macromolecules significantly impacts their passage.
• Future research should focus on the biochemical regulation of these dynamic transport events.