Electron dense

MTOCs with a ring-like, spherical structure consisting of amorphous electron-dense material. 

It is possible to observe effects of organotin(lV) compounds exposure such as inhibition of cleavage of fertilized eggs, interference with the formation of the mitotic spindle, damages affecting chromosome structure, and electron-dense precipitate formation in organelles. 

Figure 4.10 An electron micrograph of a terminal varicosity containing a large dense-core vesicle (LDCV), indicated by the arrow and many small synaptic vesicles (SSVs), some of which contain an electron dense core. Calibration mark 250 nM. (Figure kindly supplied by M. Fillenz)...

The presence of inorganic polyphosphate in electron-dense particulate structures of M. luteus has been demonstrated by n.m.r., confirming an earlier observation based on chemical techniques. ... 

The microvillar surface is coated with a layer of electron-dense amorphous material (glycocalyx). In H. contortus, helical filaments composed of contortin are associated with this layer and fill the spaces between the microvilli. There can be up to ten strands of contortin in each microvillus ... 

Roffman, E., Spiegel, Y., and Wilchek, M. (1980) Ferritin hydrazide, a novel conalent electron dense reagent for the ultrastructural localization of glycoconjugates. Biochem. Biophys. Res. Comm. 97, 1192-1198. 

Olofsson-Martensson, M., U. Haussermann, J. Tomkinson, and D. Noreus, Stabilization of electron-dense palladium-hydrido complexes in solid-state hydrides, /. Am. Chem. Soc., 122, 6960,2000. 

The pathological hallmark of the disease is the presence in the brain of Lafora bodies round, basophilic, PAS-positive intracellular inclusions varying in size from small, dust-like bodies less than 3 nm in diameter to large bodies up to 30 nm in diameter. Lafora bodies are typically seen in neuronal perikarya and processes, not in glial cells, and are more abundant in cerebral cortex, substantia nigra, thalamus, globus pallidus and dentate nucleus. Ultrastructural studies have shown that Lafora bodies consist of two components amorphous electron-dense... 

Conventional electron microscopy (Devine et al 1972) and freeze-etch (Somlyo Franzini-Armstrong 1985) of VSMCs reveals that the jSR is separated from overlying PL by a 12—15nm cytosolic space that is traversed by electron-dense structures. These structures appear similar to the foot processes of cardiac and skeletal muscle (Franzini-Armstrong et al 1998). Indeed, there is striking structural similarity between these PL—jSR regions in VSMC and the diads and triads of cardiac and skeletal muscle (Franzini-Armstrong et al 1998). Moreover,... 

Some SR compartments (jSR) lie just beneath special microdomains of PM, and are joined to this PL by electron-dense processes (observed with electron microscopy). Na+ pumps with high-ouabain-affinity a. subunits (a2/a3 subunits), NCX and SOCs, appear to be confined to these PL microdomains. These PL microdomains, the subjacent jSR, and the intervening tiny cytosolic volume, form functionally specialized units we call PLasmERosomes. Through the operation of these units (which are apparently present in many types of cells), modulation of Na+ pump activity may have a profound influence on Ca2+ signalling in smooth muscles and many other types of cells. 

It is commonly known that lipids, carbohydrates, and glycolipids are present in the Golgi apparatus (27). The determination of the components that react with the ZIO mixture was carried out by removing each component from tissues before incubation in the ZIO mixture. After lipid extraction by acetone (14), chloroform-methanol (15), or propylene oxide (27), no osmium-zinc precipitates could be detected in structures that normally reacted with ZIO. Blumcke et al. (15) summarized the nature of the lipids that react with the ZIO mixture as follows lipids and lipoproteins of cell membranes, neutral fat droplets (41), and lipid globules of type II pneumocytes and alveolar macrophages were, however, not as electron dense as the normally reactive lamellae containing highly unsaturated fatty acids. 

Fig. 1. Diagram of an EM immunogold assay localizing a protein on plastic sections. The primary antibody binds to an exposed surface epitope of the embedded cells. The antibody is then visualized by binding a second antibody coupled to a colloidal gold particle. The electron-dense gold particle visibly marks the position of the bound antibodies when visualized with the electron microscope. 

At the EM level, detection usually involves using a probe (oligonucleotide) in which a hapten has been incorporated. Incorporation of the hapten does not interfere with the hybridization of the complementary sequences. The next step is the binding of a reporter (may be an antibody) to the hapten. The reporter is then subjected to a binding molecule (may be a secondary antibody) that is coupled with an electron-dense material such as colloidal gold for visualization. Nonetheless, the many affinity-detection and immunodetection systems developed for immuno-cytochemistry may now with ingenuity be applied to molecular biology at the EM level. 

When the light microscope (LM) alone is not sufficient to study a system, the binding of an electron-dense ligand to an antibody facilitates the use of an EM. There are times when, in addition to EM study, immunoelectron microscopic analysis is necessary. Observed anatomical changes often lead to inquiries on the molecular events. This proved true in the case of the report by Inada et al. (22) in which they described a three-dimensional analysis of the senescence program in rice (Oryza sativa L.) coleoptiles. Immunoelectron microscopy was used to determine the behavior of cellular DNA during senescence. The procedure employed by the investigators is detailed below. 

In mouse glioma cells, many kinds of changes in cell organelles after exposure to 5 x 10 5 M mercuric chloride in vitro could be found [ 144]. Nuclei showed pyknotic and irregular shapes mitochondria lost their normal cristae and abnormal electron-dense areas were present within the matrix polyribosomes were dispersed. Numerous electron-dense granules and vacuolations were seen in the cytoplasm, especially around the Golgi region,... 

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