Quantitative fluorescence microscopy on single capillaries: alpha-lactalbumin transport

Area of Science:

• Physiology
• Microcirculation
• Transport Phenomena

Background:

• The existing microscope densitometric technique was extended to measure solute permeability.
• This method allows for the measurement of transcapillary flux for solutes larger than 10,000 mol wt.

Purpose of the Study:

• To measure solute permeability coefficients (Pa) of fluorescently labeled solutes in single perfused frog capillaries.
• To investigate the influence of capillary pressure on solute transport.

Main Methods:

• Utilized a microscope densitometric technique on single perfused frog capillaries.
• Employed fluorescently labeled solutes, including alpha-lactalbumin.
• Measured solute permeability coefficients (Pa) under controlled hydrostatic pressures.

Main Results:

• Solute permeability (Pa) for alpha-lactalbumin (14,176 mol wt) increased with capillary pressure, from 2.1 x 10(-6) cm/s at 3.0 cmH2O to over 4.0 x 10(-6) cm/s at 15 cmH2O.
• Calculated a hydraulic conductivity of 3.6 x 10(-7) cm x s-1 x cmH2O-1, indicating significant solvent drag.
• Data supports the hypothesis of restricted diffusion and solvent drag in the primary water pathway.

Conclusions:

• Alpha-lactalbumin transport across capillary walls is influenced by solvent drag.
• The primary water pathway in capillaries accounts for 90% of transcapillary water flow.
• The findings validate the use of microscope densitometry for measuring solute permeability in microcirculation.