Studies on intra-arterial cushions

The basement membrane of Bowman's capsule (BCBM) of the rat was studied by means of a modified tissue-preservation technique for transmission electron microscopy, which avoids the usual thorough fixation in OsO4 and applies tannic acid and uranyl acetate for staining (Sakai et al. 1986). At most sites the BCBM is multilayered, consisting of one to seven dense layers separated by electron-lucent layers. The latter, which can be termed laminae rarae, contain fine filaments which connect the dense layers to each other and the innermost dense layer to the basal cell membrane of the parietal epithelium. The laminae densae are basically composed of fine filaments arranged in an anastomosing pattern. Individual filaments ranging from 5 to 15 nm in diameter, combine to form filament bundles up to 100 nm in thickness and 1 to 2 micron in length. Within a dense layer, filaments and filamentous bundles are oriented mainly in the same direction. Often the inner dense layers do not form a continuous sheet, and the filamentous bundles are arranged in anastomosing or spiral patterns to form a ribbon-like structure that we call a "microligament". These microligaments are often embedded in basal furrows of the parietal epithelium and are best developed around the vascular pole. Intracellular actin bundles of the parietal cells are regularly associated with these extracellular ribbon-like structures of the basement membrane. In conclusion, the BCBM has an unusual structure: the laminae densae are characterized by their filamentous nature and are arranged in different patterns, i.e. as a multilayered mat and as microligaments.

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The ultrastructural organization of the basement membrane of Bowman's capsule in the rat renal corpuscle

Mbassa

Elger

Kriz

1988

Cell Tissue Res.

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Cell membrane features of rabbit arterial smooth muscle

Litwin¹

1980

Cell Tissue Res.

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The cell membrane of smooth muscle cells from four large arteries of rabbits was investigated by freeze-fracture. On the surface of the smooth muscle smooth zones could be distinguished arranged in an alternate manner with zones characterised by numerous openings of surface vesicles. Vesiculate zones formed bands of variable width, generally parallel to the long axis of the cell, or irregular patches of different size. The density of vesicles within bands and patches varied from a very loose packing to a dense, quasi-hexagonal array. Comparative morphometric studies of the cell membrane replicas showed differences in the ratio vesiculate area: smooth area and also different surface vesicle frequencies expressed either as mean values or as values for vesiculate zones, in the arteries investigated. Communicating junctions (nexuses, gap junctions) characterized by a random arrangement of particles on the P-face and a more ordered, rhomboidal array of pits on the E-face were the only type of intercellular junctions found between arterial smooth muscle cells.

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The fine structure of human digital arterio-venous anastomoses (Hoyer-Grosser's organs)

et al. 1977

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Hoyer-Grosser's organs were studied in human digital biopsies. The fine structure of both the supplying arteries and collecting veins was found to be inconspicuous. Endothelial cells in the AV canals form a continuous layer. They are characterized by their rich content of specific organelles (Weibel-Palade bodies), especially in the venous segments. The epitheloid zone is composed of a variety of ramified smooth muscle cells (RSM). These appear either dense, when well provided with bundles of myofilaments, or clear, when including only a few myofilaments. The nuclei of dense RSM show condensed chromatin, while those of clear RSM are larger with loose chromatin texture. In addition, all transitional forms occur. Cell organelles are rarely seen within all types of RSM. The cytoplasmic processes reach other as well as endothelial cells. The preservation of our material did not allow observation of specialized membrane contacts in these zones. All RSM are invested with a regular basal lamina and well provided with surface vesicles. Profiles of free basal lamina material and faint collagen (argyrophil) fibers are seen in the wide intercellular spaces. RSM poor in myofilaments are interpreted to represent "epitheloid cells" of light microscopy. Their number constantly decreases from the arterial segment of the AV canal to the venous segment. Here the cytoplasmic processes of RSM become less pronounced and the wall of the anastomotic segment continuously changes to that of the collecting vein. Dense RSM rich in myofilaments are compared with pacemaker cells found inthe ureter. Both internal and external elastic membranes are absent in AV canals. A dense network of unmyelinated nerve fibers is found in the adventitial layer of the AV canal, especially in its arterial segment. The axons branch out from small dermal nerves which also contain two or three myelinated axons. The myelin sheaths terminate where the axons reach the adventitia of the AV canals. Axon varicosities filled with mitochondria are thought to be terminals of myelinated axons and are interpreted as receptory. Axon varicosities with synaptic-type vesicles are assumed to be terminals of sympathetic and para sympathetic fibers. All axon profiles are confined to the adventitial layer of the anastomotic segment.

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Studies on intra-arterial cushions

Cited by 7 publications

References 7 publications

The ultrastructural organization of the basement membrane of Bowman's capsule in the rat renal corpuscle

The ultrastructural organization of the basement membrane of Bowman's capsule in the rat renal corpuscle

Cell membrane features of rabbit arterial smooth muscle

The fine structure of human digital arterio-venous anastomoses (Hoyer-Grosser's organs)

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