The fine structure of endothelial cells of white-blooded fish Chaenocephalus aceratus

The fine structure of the arterial endothelial cells from an eye moving muscle--musculus obliquus inferior in an antarctic teleostean fish, Chaenocephalus aceratus, is described. Thin filaments of 4.6 nm in diameter occur in form of compact bundles situated just beneath the cell membranes, whereas the 9 nm thick filaments appeared in central part of the cell extensions. Both types of filaments, as well as the numerous microtubules (25 nm) are oriented along the axis of the artery. A large number of rounded, tubular bodies (0.26 micron-0.33 micron)--Weibel-Palade bodies (WPB), is localized mostly in cell protrusions close in the cell membrane. The role of the substances produced by WPB and well developed filaments system in the regulation of blood pressure in vessels of antarctic fish is discussed.