Cytoplasmic filaments in intracerebral cortical vessels.

Actin filaments measuring 5 nm in diameter are present in the endothelium of systemic vessels and presumably have a contractile function that may be related to vascular permeability. Little attention has been directed to the presence of similar cytoplasmic filaments in the endothelium of cerebral vessels. This study was undertaken to determine whether filaments are present in the endothelial cells of intracerebral cortical vessels of rats and humans. Ultrastructural studies revealed two populations of endothelial cytoplasmic filaments 5 nm and 10 nm in diameter, respectively. The 5-nm filaments were abundant in the endothelium of penetrating cortical arterioles, being grouped near the cytoplasmic margins in proximity to cell junctions and along the abluminal side of the endothelial cells. The filaments were scant in capillaries and venules.