血管壁の微細構造と物質輸送経路

Abstract

The pathways of material transport across the endothelium at the ultrastructural level were examined in different kinds of blood vessels by using tannic acid or horseradish peroxidase as a tracer. Freeze-fracture replicas from the endothelial cells of the aorta and basilar artery of the rat were also made and examined by electron microscopy.Tracer materials could be transported through the cytoplasm of the endothelial cells by means of vesicles linked with pinocytotic activity, transient transendothelial channels formed by serial fusion of vesicles, and fenestrae. The intercelluar gaps of the hepatic sinusoid endothelium could also be a pathway for tracer materials. In the aorta the intercellular junction between adjacent endothelial cells could be a passageway for both tannic acid and horseradish peroxidase, whereas in the basilar artery, these materials could not pass through that junction beyond the tight junction area. Freeze-fracture replicas showed that the strands of intramembrane particles at the tight junction constitute continuous complex networks in the basilar artery whereas those in the aorta were simple in organization, consisting of a few discontinuous strands accompanied with sporadic gap junctions. The observation in freeze-fracture replicas may well explain the fact that tannic acid and peroxidase cannot be transported through the intercellular clefts beyond the tight juction in the basilar artery.