Formation of basement membrane-like structure terminates the cellular encapsulation of microfilariae in the haemocoel of Anopheles quadrimaculatus

The encapsulation of microfilariae in the haemocoels of mosquitoes combines both humoral and cellular reactions: the microfilariae are first encased in an acellular layer of melanin, followed by a cellular encapsulation by plasmatocytes. In this study, we demonstrated that cellular encapsulation of Brugia pahangi microfilariae in the haemocoel of the mosquito Anopheles quadrimaculatus was terminated by the formation of a basement membrane-like structure on the outermost surface of the cellular capsule. This structure occurred in the early stage of cellular encapsulation and was evident on the exterior surface of the plasmatocyte, when the active haemocytes were attaching to the already melanized microfilariae. The termination structure appears to be laid down by releasing the vesicle inclusions of haemocytes and has similarities in ultrastructure and cationic colloidal gold staining properties with that of mosquito basement membranes.

Distribution of glycosaminoglycans in rat renal tubular epithelium.

Polyanionic constituents of the glomerular capillary wall have been previously shown to have a primary role in the control of glomerular filtration. In the study presented here, the distribution and biochemical nature of polyanionic constituents in proximal (PT) and distal (DT) tubules have been investigated as possible determinants of tubulointerstitial function. For histochemical localization of sialic acid, paraffin sections were treated with Arachis hypogaea lectin (PNA) before and after neuraminidase treatment. Electron microscopic characterization of glycosaminoglycans (GAG) was performed on thin LR-white sections, using cationic colloidal gold (CCG) as an histochemical probe, and GAG-degrading enzymes. Without neuraminidase, PNA binded to collecting ducts but not to PT or DT. Neuraminidase pretreatment resulted in intense PNA binding to the tubulointerstitial blood vessels but only in mild apical tubular binding, which implies a lack of sialoglycoconjugates in the tubular basolateral membranes. In contrast, all PT and DT showed intense CCG binding to basolateral, but not to apical, membranes. All basement membranes showed CCG labeling, with considerable variations in labeling densities between PT (124 +/- 8.8/micron 2) and DT (52 +/- 1.8/micron 2), as well as between tubules and Bowman's capsule (P < 0.0001). Heparinase III treatment induced an almost complete loss of CCG binding in all basement and basolateral membranes, whereas chondroitinase ABC treatment led to a lesser but significant loss (P < 0.0001). The results indicate that rat tubulointerstitium expresses polyanionic constituents, consisting mainly of heparan and chondroitin sulfate. The role of these anionic sites in tubular function has yet to be clarified.

Visualization of the anionic sites in the cell wall of apple fruit using a cationic colloidal gold probe

The ripening of fleshy fruits involves a softening process that consists of biochemical changes in the cell wall and leads to cell separation. Calcium is an important constituent of the cell wall and plays roles in maintaining the firmness of fruit and in reducing postharvest decay. The modification of cell wall strength is believed to be influenced by calcium that interacts with acidic pectic polymers to form crossbridges. This study examined how the frequency and distribution of anionic binding sites in the cell walls of apple fruit were influenced by calcium infiltration.Mature “Golden Delicious” apple fruits were pressure infiltrated with either H2O or a 4% solution of CaCl2 and the pericarp was sampled and processed according to standard procedures. Cationic poly-Llysine colloidal gold complex was used in a one-step procedure to visualize anionic sites in muro. Observations were performed with light microscopy, following silver intensification, and with transmission electron microscopy.