The ultrastructure of capillaries and arterioles of the hamster dental pulp This investigation was supported by U.S.P.H.S. research grant D-1620 from the National Institute of Dental Research, National Institutes of Health.

Abstract

The ultrastructure of capillaries and arterioles of the hamster dental pulp has been studied. Pieces of the incisor pulp were fixed in 1% OsO 4 buffered with 0.14 M veronal acetate, embedded in epoxy resin and studied in an electron microscope. The basic cytoplasmic organization of endothelial cells confirmed observations on blood vessels of other organs made by previous investigators. A large number of intracytoplasmic fibrils were found in many endothelial cells, and their presence was discussed in relation to earlier reports on the contractility of endothelial cells. Previous observations on the structural details of the intercellular region of the endothelium were confirmed and elaborated upon. The manner in which the cytoplasmic flaps of adjoining cells were oriented indicated that, if the integrity of the capillary wall was maintained, only cells with capacity for ameboid movement could creep through the region. Thus they were thought to play a role as an effective barrier against the passage of red blood cells. Numerous micropinocytosis and pinocytosis vesicles were found in association with plasma membranes. The significance of their structure in the transport of materials across the capillary wall is discussed. The fine structure of the pericyte resembled that of the fibroblast. Portions of plasma membranes of adjacent smooth muscle cells in the media of arterioles were brought together closely and resembled attachment zones.