Ultrastructural localization of the core protein of a basement membrane-specific chondroitin sulfate proteoglycan in adult rat skin

Basement membranes are complex extracellular matrices present at epithelial/mesenchymal interfaces of tissues. The dermal-epidermal junction has been shown to contain numerous components, some of the most well known being laminin, types IV and VII collagens, heparan sulfate proteoglycan, fibronectin, and entactin/nidogen. IN this paper we show, using core protein-specific antibodies, the presence of a newly described basement membrane-specific chondroitin sulfate proteoglycan at the epithelial/mesenchymal interface of adult rat skin. Ultrastructurally, this antigen was proven to reside primarily within the basal lamina, apparently concentrated in the lamina densa. In addition, some of the proteoglycan was also present beneath the lamina densa, associated with the reticular lamina collagen fibrils.

Lipids in gap junction assembly and function

Gap junctions (GJ) are important regulators of cellular function. They provide channels for the direct movement of small molecules between cells and thus control cell-to-cell transfer of metabolites and the transmission of various stimuli. Gap junctions have been shown to be involved in a multitude of cellular processes ranging from cell synchronization and neuronal function to cell differentiation and carcinogenesis. Much knowledge has been gained in recent years concerning the structure and molecular organization of GJ proteins; yet, the mechanisms that control and modulate gap junction assembly and function are still not well understood. Although it is quite apparent that the GJ proteins assemble in the lipid milieu of the plasma membrane, and that the cluster of proteins assembled in the junction do function in a lipid environment, there is a general paucity of information on the role of lipids in the gap junction assembly process and in the function of gap junctions. The present review is a comprehensive account of current knowledge on gap junction lipids. We also discuss what is known to date on the involvement of lipids in gap junction formation. Special emphasis is being placed on the potential role of membrane cholesterol in gap junction assembly and function.

Cardiac myocyte gap junctions: evidence for a major connexon protein with an apparent relative molecular mass of 70,000

It is widely accepted that there is a family of gap junction connexon proteins, their distribution appearing to vary with tissue type and species. In cardiac tissues the major junctional channel component identified is a 43K (K = 10(3) Mr) polypeptide. Using a gap junction isolation protocol in which low temperatures are maintained, and which is detergent-free, we have identified a second gap junction-related protein in cardiac tissues with an apparent relative molecular mass of 70,000. Antibodies raised to three synthetic peptides matching portions of the 43K gap junction protein cDNA sequence cross-react with the 70K protein, but biochemical studies indicate that these proteins are distinct from one another. The structures that contain the 70K protein are susceptible to fragmentation at warm temperatures, and by electron microscopy this can be correlated with loss of ‘minidomains’ within the junctional plaque. Using a gap junction enriched-fraction prepared from purified isolated adult myocytes we show that both the 43K and 70K gap junction proteins are present in ventricular cardiac myocytes. In such preparations, and those from whole heart, the 70K protein appears to be the major gap junction-related protein present.

Cardiac gap junctions in rat ventricle: localization using site-directed antibodies and laser scanning confocal microscopy

Antibodies were raised to three synthetic peptides, each constructed to match a different cytoplasmic region of the 43kD protein of the cardiac gap junction. These antibodies have all been used for immunohistochemical localization of gap junctions in the rat ventricle. Each is shown to have different staining characteristics which provide supporting evidence for the model proposed for the configuration of the gap junction protein within the membrane. Laser scanning confocal microscopy has confirmed that the localization of ventricular myocyte gap junctions is solely within intercalated disks. This technique is demonstrated to provide a greater overview of the three dimensional arrangement of the junctions than other microscopical techniques. Larger gap junctions occur typically at the periphery of the disk, with smaller junctions situated in the central zone. The analysis of the number and distribution of gap junctions over large volumes of myocardial tissue (three-dimensional tomography) is now feasible with this approach, and may be used to delineate conduction pathways.