Intracellular Membrane Transport in Vascular Endothelial Cells

Figures

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  Figure 1. Structure of different types of endothelial cell from rats and mice. (A,B) Scanning electron microscopic images of the luminal surface of ECs from the high endothelial venule in lymphatic node. (C) SEM of the luminal surface of the endothelium with open contact in rat spleen. White arrows show erythrocytes. (D) Scanning electron microscopic image of the luminal surface of rat aorta after perfusion fixation. Cytoplasmic outgrowth (white arrows) are visible along the EC contacts. (E) Scanning electron microscopic image of the surface of EGs of the lymphatic thoracic duct. White arrows show near-contact protrusions. (F) Scanning electron microscopic image of the luminal surface of vena cava inferior. Black arrow shows rare outgrowths along intercellular contacts. Protrusions/elevation of nuclei of EC are shown with red arrows. Outgrowths along cell contacts are almost invisible. (G) Cross section of the brain blood capillary. ECs contain low number of caveolae. (H) The virtual EM tomo-slice of cross section of central zone of EC from lymphatic capillary of small intestine villus after starvation. The PM of ECs have only a few caveolae. (I) The ECs of lymphatic vessels are divided…

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  Figure 2. Structure of transcytosis compartments of rat endothelial cells. (A) Tangential freeze-fracture of the endothelium of blood capillary in frozen intestinal villus. White asterisks indicate the fields of fenestrae. White arrows demonstrate the thick zone of endothelial cytoplasm between the fields of fenestrae. (B) Scanning electron microscopy (SEM) of the surface of the thin endothelium with small pores in the glomerular blood capillary. Red arrows indicate the intercellular contact. (C,D) Thin fenestrated endothelium. Transmission electron microscopic (TEM) sections across the blood capillary of intestinal villus. White arrows demonstrate fenestrae. Red arrows show cross section of caveolae. (E) The tangential TEM section of the thin fenestrated EC. White arrows indicate fenestrae. Red arrows show cross sections of caveolae. (F) Scanning electron microscopic image of the lumina surface of the sinusoid in rat red bone marrow. White arrows indicate large pores. Red arrow shows lymphocyte. (G) SEM of the luminal surface of blood sinusoid in liver. White arrow shows large pore. Red arrow demonstrates the field of small pores. (H) Tangential fracture of frozen liver blood sinusoid.…

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  Figure 3. Structure of endothelial cells in different types vessels in rats and mice. (A,B) The cross-freeze-fractures of ECs in the capillary of the heart. Platinum replicas obtained after freeze-fracture and evaporation of platinum of closed multicaveolar endothelium. White arrows show fractures of caveolae on the perpendicular fracture of the capillary. Red arrow in (B) demonstrates the presumable fracture of clathrin-coated bud. (C) Tangential fracture of the frozen thin multi-caveolar endothelium with closed contact from the heart blood capillary. Evaporation with platinum during rotation of the sample. White arrows indicate fracture of caveolae. (D) White arrow shows the rare caveolae in cross section of EC in brain blood capillary. (D–F) Serial virtual EM tomo–slices of the caveolae (D, white arrow) and caveosome (E,F, black arrows) which appears like a bunch of grapes. (G) The tomography section of EC of lymphatic thoracic duct. No caveolae are visible. Basement membrane is shown with the white arrow. The ER is shown with the red arrow. (H) Cross section of EC from brain blood capillary. Caveolae are not visible. Arrow shows near-contact protrusions. (I) Mouse brain. Virtual EM…

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  Figure 5. Structure of the EC contacts and junctions in rats and mice. (A) ECs of blood capillary in derma. Platinum replicas obtained after tangential freeze-fracture of the EC near the inter-endothelial contact. Green arrow indicates the fracture of tight junction. Red arrow demonstrates the fracture of caveolae. (B) The freeze-fracture of the typical TJ between ECs of blood brain capillary. Green arrows indicate the locking fibril of TJ. (C,D) Serial virtual tomography electron microscopic slices. White arrows show the locking fibrils of TJ which appears as a white dot connecting two membranes of opposite ECs. (E) Scheme of TJ. On the freeze-fracture, of the contact zone of ECs, locking fibrils consisting of intramembrane particles appear as widely anastomosing and fence-like elevations (ridges; black arrow)) or depressions (grooves; magenta arrow). (F) The tile-like contact between ECs. It is supplemented with TJ (white arrow). The green arrow indicates the near-contact cytoplasmic protrusions between ECs of blood capillary in brain. Red arrow shows clathrin-coated pit on APM of EC. On the surface of APM the glycocalyx is visible. (G) Interdigitating contact between ECs of lymphatic…

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  Figure 4. Structure of rat endothelial cells. (A–D) Serial virtual tomography slices show clathrin-independent invaginations (red arrow in (A)) and clathrin-dependent invaginations (green arrows in B) of the EC APM. In (B) these seemingly isolated vacuoles are connected with the plasma membrane. The Golgi complex (asterisk in (A)) is composed of short cisternae. (C) EC from rat aorta from the zone of regenerating endothelium. EC is in the G2 phase. Red arrow shows the post-Golgi carrier filled with collagen. (D,E) ECs of aorta. Red arrows show mesh-like BM. White arrow indicates accumulation of the BM material which is more evident in the ECs from the zone of turbulent flow. Images (A,B) are taken from Supplementary Figures presented by Sesorova et al. [18]. Images (C,D) are taken from Figure 5 presented by Sesorova et al. [16]. The image (E) is taken from Figure 3C presented by Mironov et al. [6] in agreement with the CC By license. Scale bars: 85 nm (A,B); 200 nm (C); 500 nm (C); 305 nm (D,E).

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  Figure 6. Different types of endothelium. (A) The continuous thin oligocaveolar endothelium with close contacts (in brain capillaries and in lymphatic vessels). (B) The continuous thin multicaveolar endothelium with close contacts (in blood capillaries of the heart, striated muscles, uterus, and skin). (C) The thin endothelium with fenestrae (in renal peritubular capillaries, intestines, and endocrine organs). (D) The thin endothelium with small pores (in renal glomeruli). (E) Thin endothelium with large pores (in liver sinusoids and red bone marrow). (F) Endothelium with open contacts (in spleen). Arrow shows a red blood cell (colored in red) moving through an open contact. (G) The cuboidal (high) endothelium (in high endothelial venules of lymph nodes). (H) Scheme of the continuous thin endothelium of rat aorta. ECs contain mesh-like BM (below ECs and above IEM). Green dots indicate tight junctions (TJ). Abbreviations: Cav, caveola; CF, collagen fibrils; EC, endothelial cell; GJ, gap junction; IEM, internal elastic membrane; L, lymphocytes; N, nucleus; SMC, smooth muscle cell; TJ, tight junction. Image (H) is taken from Figure 2A by Mironov et al. (2020) [6] in agreement with the CC By…

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  Figure 7. (I) Scheme shows principles of the classification of vascular endothelium. (I: A) ECs without any BM are in some lymphatic capillaries, in capillaries supported cancer and during embryonic development. (I: B) ECs with the fragmented BM is observed in liver sinusoids. (I: C) ECs with a porous mesh-like BM are present in large arteries. (I: D) ECs with a continuous BM are observed in most other vessels. (I: E) ECs with open contacts are found in the spleen sinusoids. (I: F) ECs with semi-open contacts are found in lymphatic capillaries. (I: G) ECs with closed contacts are found in other locations with the exception of those mentioned in (I: E) and (I: F). (I: H) Thin ECs are found in most locations with the exception of those indicated in (I: I). (I: I) Thick ECs are observed in high endothelium venules of lymphatic nodes. (I: J) Continuous ECs can be oligocaveolar (I: L) in blood capillaries of the brain, in lymphatic vessels) and multicaveolar (I: M) in arteries, in blood capillaries of the heart, striated muscles, between smooth muscle cells of the uterus). ECs in veins are of intermediate type. (I: K) Porous ECs can be with fenestra (I: N), with small (I: O) or large pores (I:…

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  Figure 8. Mechanisms of transcytosis through ECs. (A,B) The endosome-like structure (black arrow) filled with gold particles. Accumulation of gold particles in the endosomal structure of EC after perfusion of brain with solution containing nanogold particles. Black arrows indicate the endosome. White arrows demonstrate empty caveolae. (C) ECs from the lymphatic capillary of small intestinal villus after starvation. Low number of caveolae. (D) EC from the same location after feeding with lipids. Accumulation of caveolae (arrow). Images (A,B) are taken from Figure 4h and Supplementary Figure 3 (the upper right one) (correspondingly) presented by Sanavio et al. [173]. The image (C) is taken from Figure 6A presented by Sesorova et al. [18]. The images (E,F) are taken from Figure 3A presented by Mironov et al. [6] in agreement with the CC By license. The additional images of ECs of blood capillaries within the smooth muscle cell tissue can be found here: (http://histologyguide.com/EM-view/EM-213-capillary/09-photo-1.html accessed on 30 December 2022. The image of pores in the peripheral zone of the EC within the glomerular capillary of the kidney can be found in the following websites:…