Electron microscopic observation of pseudopodia from choriocapillary endothelium.

The choriocapillary endothelial cells project pseudopodia-like processes (pseudopodia) through defects in the basement membrane in eyes without any insult or new vessel formation. The ultrastructure of these pseudopodia was observed by transmission and scanning electron microscopy. The pseudopodia contained microfilaments, ribosome-like organella, and/or endoplasmic reticulum-like organella; about half of the pseudopodia contained bundles of microfilaments, and 10% of these contained cytoplasmic organella. The frequency of pseudopodia was not correlated with age, sex, racial difference, location in ocular fundus, or age-related changes in Bruch's membrane. The results of this study did not reveal a relationship between pseudopodia and subretinal new vessel formation. Pseudopodia oriented toward the retinal pigment epithelium (RPE) were significantly more frequent than those oriented toward the choroid or projecting from the lateral side of the choriocapillaris, which suggests a close relationship between the pseudopodia and the function of the RPE.