Permeability of single capillaries to intermediate-sized colored solutes

Area of Science:

• Physiology
• Biophysics
• Microcirculation Research

Background:

• Capillary permeability is crucial for substance exchange between blood and tissues.
• The fiber matrix theory proposes that fibers within intercellular junctions regulate this permeability.
• Quantifying the impact of these fibers on solute transport is essential for understanding microvascular function.

Purpose of the Study:

• To evaluate the fiber matrix theory of capillary permeability.
• To measure permeability coefficients for various colored solutes in frog mesenteric capillaries.
• To determine the contribution of fiber density to solute restriction in intercellular junctions.

Main Methods:

• In vivo measurement of permeability coefficients using colored solutes with defined Stokes radii (0.5–1.76 nm).
• Calibration of a microscope photometer for accurate optical density measurements.
• Individual perfusion of frog mesenteric capillaries to assess solute transport.

Main Results:

• Permeability coefficients varied significantly with solute size, with larger solutes showing restricted diffusion.
• Azure C (0.5 nm radius) had a permeability coefficient of 11.0 x 10^-5 cm/s, while FITC-dextran 3 (1.76 nm radius) was 0.48 x 10^-5 cm/s.
• Estimated fiber density (8.5% of junctional volume) adequately explains the observed 22-fold range in permeability and suggests a role for negative charges in solute exclusion.

Conclusions:

• The fiber matrix theory provides a valid framework for understanding capillary permeability.
• Fiber density and potential charge interactions within intercellular junctions significantly restrict the diffusion of larger solutes.
• These findings enhance our understanding of microvascular transport mechanisms and the factors governing substance exchange.