Biomedical subjects
Publications and source records attributed to E Reale.
The glomerular epithelial cells of the Atlantic hagfish (Myxine glutinosa) lack a slit diaphragm which is replaced by filaments. The epithelial cells show numerous occluding junctions (maculae and fasciae occludentes), septate desmosome-like junctions and desmosomes. The present findings are compared with available data on developing and mature glomerular epithelial cells of mammals.
The brush cells of the gallbladder epithelium of the mouse have microvilli not only at their luminal border but also on their lateral surface, from the level of the nucleus to the junctional complex. The lateral microvilli radiate from the brush cell in all directions, contain a core of filaments, and penetrate up to 3 mum into the adjacent cells. The microvilli in these locations display small desmosomes at their base.
Human amniotic epithelium was examined in cases of pregnancy complicated with hydramnios; the light- and electronmicroscopical results were compared with those of epithelium in normal pregnancy. The cells of the hydramniotic epithelium show an increased number of microvilli in apical and lateral cell surfaces. There are also a greater number of desmosomes and enlarged intercellular spaces. In a single case where hydramnios was correlated with maternal diabetes mellitus the amniotic epithelium is characterized by local foci showing cellular dystrophy.
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The mucous membrane of the first and second compartments (ventral regions) as well as of the third compartment of Lama guanacoe and Lama lamae stomach shows tubular glands opening into pits. Below the surface epithelium blood capillaries of the fenestrated type form a regular network, each mesh of which surrounds a gastric pit. From a morphological point of view (thin section and freeze-fracture replicas) the columnar cells of the surface epithelium and those of the pits closest to the capillaries are largely similar to the epithelial cells of the rabbit gallbladder. This similarity suggests that at the level of the columnar cells sodium-dependent water reabsorption occurs. This reabsorption has already been demonstrated in the abovementioned compartments by physiological methods. The surface and foveolae epithelial cells as well as some cells of the tubular glands have a secretory function. Their secretory granules contain mucosubstances, as indicated by light-(PAS- and Alcian blue reactions) and electron microscopic (PA-TCH-Ag-reaction) histochemistry. The secretory granules originate from the Golgi complex which shows a positive histochemical reaction in its innermost sacculi at the electron microscope level. Endocrine cells (s. second part of this investigation) are rare. The mucosal membrane of each muscular lip separating the glandular sacs in the first compartment shows a stratified, not keratinized, squamous epithelium.
Addition of Alcian Blue to the fixative reveals structural elements bearing negatively charged sites within the glomerular capillary wall of the rat kidney. According to previous research (review by Brenner et al., 1977), these charges represent one of the most important functional components of the glomerular filtration barrier. Alcian Blue also demonstrates negatively charged microfibrils (probably glycoproteins) of the mesangial matrix. Preliminary observations of glomeruli of lower vertebrates suggest that there is always a close correlation between the presence of microfibrils and mesangial cells.
Using the freeze-fracture technique communicating junctions could be identified between the cells of the adult human sensory retina. Communicating junctions with particles arranged in linear or circular rows as well as in small aggregates were found between adjacent photoreceptor endings. Communicating junctions with particles forming plaques were localized in the inner plexiform layer. They were isolated between unidentified cell processes or lay close to active sites of chemical synapses, thus suggesting the occurrence of "mixed" (chemical and electrical) synapses in this layer. Furthermore, communicating junctions were detected between portions of Müller's cells.
The reaction of Thiéry (periodic acid-thiocarbohydrazide-silver proteinate) has been applied for histochemical analysis of the structures composing the halo of the most peripheral human retinal vessels. It is suggested that glycoproteins lie in the ground substance of the halo as well as well as in the basement membranes of endothelial cells, pericytes, and Müller cells. Glycogen particles were found in endothelial cells, in pericytes and especially in Müller cells.
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Lysosomes were studied by both cytochemical and quantitative methods in normal and degenerating neuroblasts of the chick embryo spinal ganglia. In normal neuroblasts (primitive and intermediate neuroblasts) both primary lysosomes and autophagic vacuoles were found; these organelles were usually located in the region containing the Golgi complex. In degenerating neuroblasts lysosomes appeared sharply decreased in number with respect to normal neuroblasts. Moreover, lysosomes were always evident as intact organelles surrounded by a membrane and the acid phosphatase activity appeared localized exclusively within these bodies. A diffuse distribution of acid phosphatase activity was only found in a limited number of cases during the terminal stage of the process. Possibly in these cases the enzymatic activity depended on the cells which enveloped the degenerated neuroblast remnants. The present results indicate that lysosomes do not play a primary role in the degenerative process studied.
Zonulae occludentes, gap junctions and desmosomes have been demonstrated in replicas of freeze-fractured follicular cells of normal human and rabbit thyroid glands. The zonulae occludentes between the human follicular cells are composed of two to eight strands, which completely separate the intercellular space from the follicular lumen. Four to twelve or more strands are visible between the follicular cells of the rabbit thyroid gland. In the meshes of the zonulae occludentes as well as below them, gap junctions are present. They are numerous on the fracture faces of the human follicular cell membranes, but infrequent in those of the rabbit. Aggregates of particles related to desomosomes are found in the deeper meshes of the zonulae occludentes or close to them.
The internal portion of the capsule of the spinal ganglia of rabbit is composed of continuous superimposed layers of flattended cells (perineurium). In replicas, extensive meshworks of strands, presumably forming zonulae occludentes, are found between the perineurial cells of the same layer. Adjacent layers are joint by maculae occludentes located on the lateral processes of the perineurial cells. Occasionally small gap junctions lie within the meshes of the zonulae occludentes.
The fine structure of the kidney (glomerulus and archinephric duct) of the hagfish. Myxine glutinosa (L.) was studied in thin sections and by freeze-fracture technique. The glomerular filtration barrier is similar to that of mammalian kidneys. However, endothelial fenestrations are relatively scanty and the basement membranes of endothelial cells and podocytes always appear separated by a layer of collagen fibrils and microfibrils often surrounding numerous and extended mesangial cells. Between podocytes and their processes maculae occludentes and peculiar junctions of another type occur. The zonulae occludentes between epithelial cells of the archinephric duct are composed of five or more strands, occasionally of only one or two.
Glomeruli isolated from rat and human kidneys were studied using the freeze-fracture technique. Discontinuous zonulae occludentes and gap junctions were found in the replicas of the split plasma membrane of the endothelial cells. A diaphragm across the endothelial pores was not demonstrated. The central layer of the basement membrane, corresponding to the lamina densa described in thin sections, revealed a coarse substructure. A slit membrane between the pedicles of the podocytes was not detectable; however, its position was indicated by the different texture of the replica, which abruptly changed at the transition of the basement membrane to the primary urinary space. Furthermore, at the level of the slit membrane arrays of particles were present within the cleaved membrane of the pedicles, probably representing the attachment points of the slit membrane. Isolated strands of a zonula occludens as well as gap junctions were seen on the split plasma membrane of the podocytes. The mesangial cells could be identified by their contiguity to the endothelial cells and by their numerous gap junctions.
Intercellular junctions between human kidney tubular cells were studied by the freeze-fracture technique. The number of strands of the zonulae occludentes increased gradually from the proximal segment to the collecting tubule. Only one strand was visible in the proximal segment (in contrast to 2-4 strands of the neighbouring Bowman's capsule). In the thin segment 2-4 strands were revealed. In the distal segment 1-5 strands were present in the pars recta, 4-6 in the pars convoluta. The most extensive and complex zonulae occludentes were found in the collecting tubule. Gap junctions were seen only between proximal tubular cells. The extent of the zonulae occludentes along the tubules in human kidneys is very similar to that observed in the kidney tubules of other mammals. The findings accord well with electrophysiological measurements and with the results of tracer studies on experimental animals.