title: The three-dimensional organization of plasmalemmal vesicular profiles in the endothelium of rat heart capillaries.
abstract: The organization of plasmalemmal vesicular profiles in the endothelium of rat heart capillaries has been reinvestigated. Judged from random thin sections approximately 50% of the vesicles appeared free in the cytoplasm, the rest opening to the surfaces of the endothelial cells--a distribution which corroborates previous studies. However, three-dimensional reconstructions based on ultrathin serial sections (thickness congruent to 12 nm) gave a very different picture. All plasmalemmal vesicular profiles (921 from 5 capillaries) were parts of the surface membrane either as caveolae or as more complex racemose invaginations. This organization has previously been observed in frog mesenteric capillaries ((M. Bundgaard, J. Frøkjaer-Jensen, and C. Crone, 1979, Proc. Nat. Acad. Sci. USA 76, 6439-6442) and (J. Frøkjaer-Jensen, 1980, J. Ultrastruct. Res. 73, 9-20)). It is therefore proposed that absence or extreme rarity of free plasmalemmal vesicles is a general feature of capillary endothelia. Consequently, we suggest that the term "endothelial, plasmalemmal vesicles" be replaced by "endothelial plasmalemmal invaginations." The results imply that trans-endothelial vesicular transport is unlikely to occur and that this membrane system performs other--as yet unknown--functions.
mesh_terms: D000818:Animals; D002196:Capillaries / Q000648:ultrastructure*; D002462:Cell Membrane / Q000648:ultrastructure*; D004727:Endothelium / Q000648:ultrastructure*; D006329:Heart Conduction System / Q000648:ultrastructure*; D008297:Male; D008854:Microscopy, Electron; D051381:Rats; D011919:Rats, Inbred Strains