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PubMed1988

Single capillary permeability to proteins having similar size but different charge.

We investigated the hypothesis that solute charge modulates transcapillary exchange in microvessels with continuous endothelium. Two globular proteins, alpha-lactalbumin and ribonuclease, having approximately the same size (mol wt 14,176 and 13,683, respectively) but different net charge (-10 and +4, respectively) were test solutes. Each solute was labeled with the fluorescent probe tetramethylrhodamine isothiocyanate. Labeling did not significantly change solute size, but increased negative charge on each solute by one valency unit. An in vivo fluorescent microscope technique [Huxley et. al., Am. J. Physiol. 252 (Heart Circ. Physiol. 21): H188-H197, 1987] was used to measure solute permeability coefficients (P) in single microvessels of frog mesentery at 14-16 degrees C. The mean P for alpha-lactalbumin, measured when capillary pressure was 10 cmH2O, was 2.1 X 10(-6) cm/s and the mean P for ribonuclease was 4.3 X 10(-6) cm/s. Our results conform to the hypothesis that the transcapillary pathways of frog mesenteric microvessels are negatively charged. With the use of a Donnan-type model for electrostatic partitioning, charge density in the pathway is estimated as 11.4 meq/l. Comparison of measured Ps with those for small solutes in frog mesenteric microvessels indicates that molecular size is a proportionally more significant determinant of solute permeability in continuous capillaries than is solute charge.

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PubMed1967

The ultrastructural basis of capillary permeability studied with peroxidase as a tracer.

The transendothelial passage of horseradish peroxidase, injected intravenously into mice, was studied at the ultrastructural level in capillaries of cardiac and skeletal muscle. Peroxidase appeared to permeate endothelial intercellular clefts and cell junctions. Abnormal peroxidase-induced vascular leakage was excluded. Neutral lanthanum tracer gave similar results. The endothelial cell junctions were considered to be maculae occludentes, with gaps of about 40 A in width between the maculae, rather than zonulae occludentes. Some observations in favor of concurrent vesicular transport of peroxidase were also made. It is concluded that the endothelial cell junctions are most likely to be the morphological equivalent of the small pore system proposed by physiologists for the passage of small, lipid-insoluble molecules across the endothelium.

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