We previously proposed a two-pathway model for solute and water transport across vascular endothelium (Fu, B. M., R. Tsay, F. E. Curry, and S. Weinbaum. J. Biomech. Eng. 116: 502-513, 1994) that hypothesized the existence of a continuous slit 2 nm wide along tight junction strands within the interendothelial cleft in parallel with 20 X 150-nm breaks in tight junctions. We tested this model by measuring capillary permeability coefficients (P) to a small solute (sodium fluorescein, radius 0.45 nm), assumed to permeate primarily the 2-nm small pore, and an intermediate-sized solute (FITC-α-lactalbumin, radius 2.01 nm) excluded from the small pore. Mean values of the paired diffusive permeability coefficients, Psodium fluorescein and PFITC-α-lactalbumin, were 34.4 and 2.9 X 10-6 cm/s, respectively, after corrections for solvent drag and free dye (n = 26). These permeabilities were accounted for by transport through the large-break pathway without the additional capacity of the hypothetical 2-nm pathway. As a further test we examined the relative reductions of Psodium fluorescein and PFITC-α-lactalbumin produced by elevated intracellular cAMP. Within 20 min after the introduction of rolipram and forskolin, Psodium fluorescein and PFITC-α-lactalbumin decreased to 0.67 and 0.64 times their respective baseline values. These similar responses to permeability decrease were evidence that the two solutes were carried by a common pathway. Combined results in both control and reduced permeability states did not support the hypothesis that a separate pathway across tight junctions is available for solutes with a radius as large as 0.75 nm. If such a pathway is present, then its size must be smaller than that of sodium fluorescein.
|Original language||English (US)|
|Journal||American Journal of Physiology - Heart and Circulatory Physiology|
|State||Published - Jun 1998|
- Paired measurements on single capillaries
- Quantitative fluorescence microscope photometry
- Three-dimensional junction-pore matrix model for interendothelial cleft
ASJC Scopus subject areas