Peritoneal Defense Mechanisms—the Effects of New Peritoneal Dialysis Solutions

It remains to be determined whether the peritoneal dialysis procedure induces abnormalities in the normal host defenses of the abdominal cavity and whether these perturbations are important in the pathogenesis of peritonitis. The peritoneum is a smooth membrane that lines the abdominal cavity and participates in the diffusion of water and solutes during peritoneal dialysis. The diaphragmatic lymphatic uptake and the opsonization of micro-organisms, with phagocytosis and killing by peritoneal macrophages, mesothelial cells, lymphocytes, polymorphonuclear leukocytes, and newly defined proteins such as defensins, play a combined role in the peritoneal host defense. Because the composition of earlier peritoneal dialysis fluids is clearly non-physiologic, continuous exposure of peritoneal cells to these solutions may result in an impairment of the local peritoneal host defense mechanisms. However, with the newer solutions, it has been shown that peritoneal defense mechanisms may improve.

Degradation of aggrecan precursors within a specialized subcompartment of the chicken chondrocyte endoplasmic reticulum

Chicken chondrocytes in culture synthesize aggrecan proteoglycan as a 370 kDa precursor that is glycosylated and secreted into the medium with a half-life of 30 min. In metabolic studies the 370 kDa precursor was shown to render a degradation intermediate of 190 kDa, which appeared with no measurable lag phase; it was dependent on temperature (> 20 °C) and inhibited by certain serine and serine/cysteine protease inhibitors such as leupeptin and PMSF. By contrast, degradation was unaffected by treatment of the cells with brefeldin A or with lysosomotropic agents. Aggrecan precursors were detected by immunofluorescence analysis within a subcompartment of the endoplasmic reticulum (ER), previously characterized as a smooth-membrane-bound subregion [Vertel, Velasco, LaFrance, Walters and Kaczman-Daniel (1989) J. Cell Biol. 109, 1827–1836]. Analysis of the subcellular fractions derived from chondrocytes indicated that the degradation intermediate was concentrated in the ER subcompartment. Degradation was dependent on the Ca2+ concentration and the redox state in the ER. Treatment of the cells with agents or conditions that alter the degradation rate of aggrecan precursors, such as protease inhibitors, decreased temperature or dithiothreitol, also modified the retention of these molecules in the ER subcompartment, as seen by immunofluorescence. These results indicate that a fraction of the 370 kDa aggrecan precursor is targeted to a smooth ER subcompartment where it undergoes degradation.

Vitreous Changes and Retinal Detachment in Highly Myopic Eyes

This report on 496 highly myopic eyes that underwent transcleral or vitreoretinal surgery for retinal detachment (RD) focuses particularly on how changes in the vitreous gel and the resulting modifications of the vitreoretinal interface produce typical characteristics and complications. According to the pattern of vitreous modifications the 496 eyes were divided into five groups: 1) eyes with uniform PVD (108 eyes) 2) eyes with PVD spreading towards the upper quadrants (231 eyes) 3) eyes with extensive vitreous liquefaction (EVL) and condensations of the vitreous base (51 eyes) 4) eyes with posterior vitreous lacuna (PVL, 87 eyes) 5) eyes with very limited PVD (19 eyes). Age, degree of myopia, surgical procedures and final results are reported for each group. A strong correlation was observed between vitreous changes and clinical picture of RD especially in the group of PVL and EVL. In the PVL group a higher degree of myopia was found and more pronounced posterior staphyloma. Frequently the posterior hyaloid, in the form of a thin, extremely smooth membrane, was hard to separate from the inner posterior retina during surgery. Posterior retinal breaks, including macular holes, were found in 56% of eyes. The presence of EVL with condensation of the vitreous base was correlated with giant retinal tear (GRT) in 70% of cases (36 of 51 eyes). Sixteen GRT were also found in the group of uniform PVD, but these were less extensive and located more posteriorly than in the EVL group. In the former group there were better surgical results because of a lower incidence of PVR. In 46% of the eyes of our series (group 2), PVD extended mostly in the upper quadrants with no vitreous detachment inferiorly. In these cases there was a clinical appearance of inferior vitreous collapse. These eyes had 92% of peripheral superior retinal breaks. Relapses of RD in this group almost invariably occurred in the inferior quadrants.

Ultrastructural immunogold localization of osteopontin in human gallbladder epithelial cells.

We used a post-embedding ultrastructural immunogold method to localize osteopontin in human gallbladder epithelial cells. This glycoprotein, originally described in bone but recently found to have a much wider distribution in many epithelia and in some mesenchymal cells, was present in the filamentous glycocalyx, small apical cytoplasmic smooth membrane-bound vesicles, large membrane-bound cytoplasmic granules, and in portions of the Golgi complex in gallbladder columnar epithelial cells. These findings suggest that newly synthesized osteopontin is packaged in Golgi-derived granules that release their contents by classical exocytosis from the cell surface. At least a portion of secreted osteopontin remains on the cell surface, where it becomes integrated into the filamentous glycocalyx coating the luminal surface of gallbladder epithelial cells.

Induction of membrane proliferation in mouse CNS by gold sodium thiomalate with reference to increased virulence of the avirulent Semliki Forest virus

Separation of smooth membrane vesicles from whole mouse brain by isopycnic centrifugation in discontinuous sucrose density gradients show an increased membrane proliferation in gold sodium thiomalate (GSTM) treated mice. Induction of membrane proliferation by GSTM seems to be an important factor in converting the avirulent Semliki Forest virus infection into a lethal one.

Endocytosis of simian virus 40 into the endoplasmic reticulum.

The endocytosis of SV-40 into CV-1 cells we studied using biochemical and ultrastructural techniques. The half-time of binding of [35S]methionine-radiolabeled SV-40 to CV-1 cells was 25 min. Most of the incoming virus particles remained undegraded for several hours. Electron microscopy showed that some virus entered the endosomal/lysosomal pathway via coated vesicles, while the majority were endocytosed via small uncoated vesicles. After infection at high multiplicity, one third of total cell-associated virus was observed to enter the ER, starting 1-2 h after virus application. The viruses were present in large, tubular, smooth membrane networks generated as extentions of the ER. The results describe a novel and unique membrane transport pathway that allows endocytosed viral particles to be targeted from the plasma membrane to the ER.

Site of addition of N-acetyl-galactosamine to the E1 glycoprotein of mouse hepatitis virus-A59.

By pulse-chase labeling with [35S]methionine and long-term labeling with 3H-sugars, the E1 glycoprotein of coronavirus MHV-A59 has been shown to acquire O-linked oligosaccharides in a two-step process. About 10 min after synthesis of the E1 protein, N-acetyl-galactosamine was added. This was followed approximately 10 min later by the addition of both galactose and sialic acid to give the mature oligosaccharides. This sequence of additions was confirmed by analyzing the 3H-labeled oligosaccharides bound to each of the E1 forms using gel filtration on P4 columns. The intracellular location of the first step was determined by exploiting the temperature sensitivity of virus release. The virus normally buds first into a smooth membrane compartment lying between the rough endoplasmic reticulum and the cis side of the Golgi stack (Tooze et al., 1984). At 31 degrees C the virus is assembled but does not appear to enter the Golgi stacks. The addition of N-acetyl-galactosamine is unaffected although the addition of galactose and sialic acid is inhibited. These results strongly suggest that addition of N-acetyl-galactosamine occurs in this budding compartment, the morphology of which is similar to that of transitional elements and vesicles.