THE ULTRASTRUCTURAL BASIS OF CAPILLARY PERMEABILITY STUDIED WITH PEROXIDASE AS A TRACER

TLDR

Endothelial cell junctions were traditionally viewed as maculae occludentes with ~40 Å gaps, rather than zonulae occludentes. The study examined the transendothelial movement of intravenously injected horseradish peroxidase in mouse cardiac and skeletal muscle capillaries at the ultrastructural level. Peroxidase traversed endothelial intercellular clefts and junctions without inducing abnormal leakage, with neutral lanthanum tracer showing similar behavior, and observations suggesting concurrent vesicular transport led the authors to conclude that these junctions represent the small‑pore system for lipid‑insoluble molecules.

Abstract

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.