Postembedment staining of complex carbohydrates: Influence of fixation and embedding procedures

Characterization of glycoproteins in the epithelial cells of human and other mammalian gallbladder. A review

The mammalian gallbladder mucosa is lined by a simple columnar epithelium. Typical surface epithelial cells (principal cells) contain short microvilli, secretory granules, dense bodies, mitochondria and Golgi apparatus. Dense bodies are thought to be lysosomes. Secretory granules contain mucous glycoproteins which are released to the lumen by exocytosis. Oligosaccharide side chains of mucous glycoproteins may provide a favorable environment for nucleation of cholesterol in gallstone formation; therefore they have been studied during the past decades. Histochemical techniques allow the in situ identification of carbohydrates at both the cellular and subcellular levels. The oligosaccharide chains of principal cell mucous glycoproteins have been studied by classical histochemical techniques (PAS, alcian blue, HID, etc). These techniques indicate that mammalian gallbladder mucous glycoproteins are heavily sulphated, whereas sialic acid residues are scarce. Neutral mucins have not been described in the mammalian gallbladder. Electron microscopic studies have located the oligosaccharide chains in secretory granules and Golgi apparatus. More recently, lectins (molecules which specifically recognize and bind with different saccharides or saccharide sequences) have been applied for the intracellular localization of carbohydrate residues. Lectin histochemistry has detected fucose, galactose, N-acetylglucosamine, N-acetylgalactosamine and N-acetylneuraminic acid residues in mucous granules, Golgi apparatus and apical membrane of human principal cells. Mannose residues were observed only in dense bodies. The combined use of deglycosylation procedures and lectin histochemistry has revealed a variety of terminal sequences in oligosaccharide chains of gallbladder mucous glycoproteins: Neu5Ac(alpha 2-3)Gal(beta 1-3)GalNAc, Neu5Ac(alpha 2-3)Gal(beta 1-4)GlcNAc and Gal(beta 1-4)GlcNAc. This technology also suggested the occurrence of N-linked oligosaccharides in the dense bodies of principal cells. Mucous granules mainly contained mucin-type O-linked oligosaccharides although some N-linked chains have also been detected. Gallstone formation is probably a complex process depending on multiple factors. Mucous glycoproteins are one of the factors involved in this process. Histochemical methods offer an excellent research tool for the characterization of glycoproteins in the epithelial cells of the gallbladder, thus contributing to the elucidation of the pathophysiology of gallstone formation.

Alterations of inner ear morphology in experimental hypercholesterolemia

Previous clinical and experimental studies have indicated that auditory function may be compromised by hypercholesterolemia. In this investigation, inner ear tissue from chinchillas maintained on a cholesterol-supplemented diet for 3 months was examined for morphological alterations which might underlie the physiological changes observed with this condition in earlier studies. Ultrastructural analysis of cochleas from 16 hypercholesterolemic chinchillas revealed alterations in both the stria vascularis and outer hair cells. Strial marginal cells throughout the cochlea and outer hair cells of the apical turn, contained electron-lucent patches of an amorphous material. These patches had the morphological characteristics and histochemical properties of glycogen. Mild extracellular edema and increased numbers of lysosomes were also noted in the stria vascularis of experimental animals. These alterations suggest that chronic hypercholesterolemia metabolically stresses inner ear tissue. It is hypothesized that such changes could increase susceptibility of the cochlea to ototraumatic agents.

Ultrastructural localization and semiquantitative analysis of glycoconjugates in the tectorial membrane

The tectorial membrane of the gerbil cochlea was analyzed with lectin-gold cytochemical methods for demonstrating and characterizing glycoconjugates (GCs) in situ. Binding of lectins from Limax flavus (LFA), Lens culinaris (LCA), Datura stramonium (DSA), Ricinus communis (RCA I), Ulex europeus (UEA I) and Phaseolus vulgaris (PHA L) was assayed semiquantitatively on ultrathin sections. Binding occurred throughout the tectorial membrane with all lectins except UEA I but the labelling density with a given lectin differed among substructures. The cover net disclosed the highest level of GC with four lectins whereas the fibrous layer revealed the lowest level. DSA, LCA and PHA L demonstrated considerable similarity between the cover net and the marginal band in content of GC with N-linked oligosaccharide. The cover net differed from the marginal band, however, in containing more RCA I reactive GC with terminal lactosamine. Hensen's stripe, with which inner hair cell stereocilia are thought to interact, differed from other substructures in containing the highest level of PHA L-reactive traintennate N-linked chains and except for the basal layer the lowest concentration of GC with terminal lactosamine. Fucosylated GC detectable with UEA I-gold was present at low levels in all substructures except the cover net and marginal band. Distribution of GCs in the fibrous layer and less consistently in the cover net differed between limbal and middle zones. The differences observed here in the carbohydrate composition among substructures in the tectorial membrane support and extend previous cytochemical observations and imply a role for different classes of GCs in determining the biophysical and physiological properties of the tectorial membrane.

Alterations in the myocardial capillary vasculature accompany tachycardia-induced cardiomyopathy

Changes in capillary structure and distribution within the left ventricle (LV) occur with pressure and volume overload hypertrophy. These changes may cause an impairment in myocardial blood flow (MBF) and oxygen delivery resulting in myocyte injury and LV dysfunction. However, it is unknown whether changes in the capillary vasculature accompany the development of LV dysfunction in dilated cardiomyopathies. Accordingly, this study examined the relation between LV function, MBF and capillary architecture after the development of dilated cardiomyopathy in pigs produced by chronic supraventricular tachycardia (SVT). LV function was examined by echo-catheterization, and capillary morphometrics were computed using lectin histochemistry in two groups of pigs: sham controls (n = 8); and after 3 weeks of pacing-induced SVT (n = 8). Chronic SVT resulted in significantly increased LV end-diastolic dimension and pressure with a 50% reduction in LV fractional shortening compared to CON (p less than 0.05). Although no significant change in capillary density (2180 +/- 164 vs 2402 +/- 147/mm2, p = 0.25) occurred in the SVT group compared to CON, a significant reduction in the volume fraction of capillaries (12.2 +/- 0.5 vs 9.9 +/- 0.7%, p less than 0.05) and increased capillary diffusion distance (8.4 +/- 0.5 vs 7.5 +/- 0.3 microns, p less than 0.05) was observed. Frequency distribution analysis revealed a higher percentage of smaller diameter capillaries with chronic SVT vs CON (p less than 0.05). Ultrastructural examination revealed an increased capillary-myocyte distance with chronic SVT (0.95 +/- 0.08 vs 1.95 +/- 0.12 microns, p less than 0.05). These changes were accompanied by ultrastructural evidence of significant subendocardial injury (p less than 0.05). MBF was measured using microspheres in five additional conscious pigs in each group. MBF was significantly reduced and coronary vascular resistance increased in the SVT group compared to CON (p less than 0.05). Chronic SVT caused significant remodeling of the capillary vasculature; these changes were associated with reduced MBF, myocyte injury, and LV dysfunction.

Neuronal imaging with colloidal gold

Colloidal gold is easily prepared, and readily adsorbs to a number of immunoreagents and other proteins for a wide variety of uses for neuronal visualization. Gold probes serve a role as immunolabels for both light and electron microscopy. As an ultrastructural immunocytochemical marker for detection of proteins, peptides or amino acids, gold can be used for immunostaining thick or thin sections prior to embedding, or for immunostaining ultrathin sections after embedding tissue in conventional or unusual embedding matrices. By virtue of its particulate nature, gold as an immunolabel facilitates a semi-quantitative analysis of relative antigen densities on ultrathin sections. Various combinations of different size gold particles or dual immunolabelling with enzymatic immunolabels together with colloidal gold or silver-intensified gold serve well for ultrastructural immunocytochemical localization of two antigens in the same tissue section. Colloidal gold can be detected with light microscopy, transmission and scanning electron microscopy, and with confocal laser microscopy. Silver intensification allows detection of gold at both the light and electron microscope level, and increases the sensitivity of immunogold procedures. Colloidal gold is useful as a tracer for physiological studies of transport and internalization in neurons in vivo and in vitro; computer-assisted video imaging techniques allow detection and tracking of single gold particles in living cells.

Improved chondrocyte morphology and glycogen retention in the secondary center of ossification following osmium-potassium ferrocyanide fixation

The use of osmium-potassium ferrocyanide as the secondary fixative greatly improved chondrocyte preservation and stabilized the cartilage matrix proteoglycan. The proteoglycan was similar in appearance to that seen following fixation in the presence of cationic dyes. Extensive glycogen preservation was noted in these cells, occupying the area prior to and during the formation of the secondary center of ossification. The volume and organization of the glycogen within the cell cytoplasm were greater than that following buffered osmium fixation, and the cellular vacuoles within were greatly reduced. The cells forming the secondary center prior to the onset of mineralization were of greatest interest, because other studies compared them with the primary growth plate and described them as showing signs of hypertrophy as early as 5 days postnatally, as is found in the primary growth plate. Our observations indicate that glycogen is present in these cells, and cellular enlargement was not present. The cells do not resemble the hypertrophic chondrocytes of the primary growth plate, as far as cytoplasmic content is concerned, and we suggest that they may contribute to the development of the secondary center in a different fashion.

In situ visualization of glycosphingolipids on thin-layer chromatograms using lectin-peroxidase conjugates

A technique is described for direct detection by lectins conjugated to horseradish peroxidase of the oligosaccharides of glycosphingolipids on thin-layer chromatograms. Final visualization is accomplished using a substrate medium consisting of hydrogen peroxide and 3,3'-diaminobenzidine. The procedure is rapid, specific, sensitive and highly reproducible, and staining patterns are stable for years. In addition to providing preliminary structural information, this technique can be employed in combination with other methods, such as autoradiographic detection of tritium-labeled glycosphingolipids in the same chromatogram.

Lead-dependent deposits in diverse synaptic vesicles: suggestive evidence for the presence of anionic binding sites

We have observed electron dense deposits dependent on incubation of aldehyde-fixed tissues with lead ions within synaptic vesicles of several types of neurons that differ in the neurotransmitters utilized and in the secretory granules of the adrenal medulla. Evidently, vesicle components that can interact with lead ions are widespread. A plausible explanation for the occurrence of the deposits is the presence of anionic binding sites within the vesicles. This would agree well with other biochemical, cytochemical, and immunocytochemical evidence, such as that indicating the presence of sulfated macromolecules in certain synaptic vesicles. Anionic binding sites could play significant roles by participating in processes such as Ca2+ storage, stabilization of pH gradients, or the control of osmotic phenomena.