DIFFERENCES IN STRUCTURE BETWEEN ENDOCARDIAL AND VASCULAR ENDOTHELIUM

Knowledge of the functional structure of endocardial endothelium (EE) is required to understand the mechanisms underlying the recently described modulation of myocardial performance by EE. Current morphological information about EE is scattered and it is unclear whether the EE differs from or shares the same characteristics with vascular endothelia. The organization of the EE in the left ventricle of the rat and cat was further characterized with transmission electron microscopy and light microscopy. The EE contained a variable number of Weibel-Palade bodies, dispersed throughout the cytoplasm, while other structures were restricted to the nuclear compartment of the EE cell. Gap junctions were prominent in areas with extensive membrane overlapping and interdigitations. Fibroblastic cells had close contacts with the EE, but gap junctions were not observed. These ultrastructural data show that EE has a different morphology than vascular endothelial cells.