Biomedical subjects
Publications and source records attributed to R Kundra.
Meckel's diverticulum is known to present with myriad complications. However, its perforation followed by development of subphrenic abscess has not been reported in literature. We report this complication in an eleven-month-old child.
Lysosomes contain several integral membrane proteins (termed Lamps and Limps) that are extensively glycosylated with asparagine-linked oligosaccharides. It has been postulated that these glycans protect the underlying polypeptides from the proteolytic environment of the lysosome. Previous attempts to test this hypothesis have been inconclusive because they utilized approaches that prevent initial glycosylation and thereby impair protein folding. We have used endoglycosidase H to remove the Asn-linked glycans from fully folded lysosomal membrane proteins in living cells. Deglycosylation of Lamp-1 and Lamp-2 resulted in their rapid degradation, whereas Limp-2 was relatively stable in the lysosome in the absence of high mannose Asn-linked oligosaccharides. Depletion of Lamp-1 and Lamp-2 had no measurable effect on endosomal/lysosomal pH, osmotic stability, or density, and cell viability was maintained. Transport of endocytosed material to dense lysosomes was delayed in endoglycosidase H treated cells, but the rate of degradation of internalized bovine serum albumin was unchanged. These data provide direct evidence that Asn-linked oligosaccharides protect a subset of lysosomal membrane proteins from proteolytic digestion in intact cells.
The effect of wortmannin on the trafficking of the mannose 6-phosphate/insulin-like growth factor II receptor (Man-6-P/IGF-II receptor) and its ligand beta-glucuronidase has been determined in murine L cells and normal rat kidney cells. The drug induced a 90% decrease in the steady-state level of the Man-6-P/IGF-II receptor at the plasma membrane without affecting the rate of internalization, indicating that the return of receptor from endosomes to the plasma membrane is retarded. Wortmannin also slowed the movement of receptor from endosomes to the trans-Golgi network by about 60%. Such a kinetic block would dramatically reduce the number of Man-6-P/IGF-II receptors in the trans-Golgi network, which could account for the previously described hypersecretion of procathepsin D induced by wortmannin. In addition, the drug slowed delivery of endocytosed beta-glucuronidase from endosomes to dense lysosomes. These data, taken together with the published reports of others, indicate that wortmannin inhibits membrane trafficking out of multiple compartments of the endosomal system and suggest a role for phosphatidylinositol 3-kinase in regulating these processes.
Actin is cross-linked by actin-binding proteins in the cytoplasm to form either isotropic or highly oriented anisotropic structures. The inherent orientation among actin filaments could influence whether an isotropic or highly oriented anisotropic structure is formed. A highly oriented state can arise spontaneously through the formation of liquid crystals as predicted by polymer theory. In this study, the ability of filamentous actin to form liquid crystalline domains was detected using the anisotropic component of scattered light and by observation of birefringence. As liquid crystalline domains formed, the intensity of the anisotropic component of scattered light increased, and birefringent macroscopic oriented domains were directly observed. The formation of liquid crystalline domains was dependent on the concentration of actin filaments and on the average filament length controlled by varying the ratio of gelsolin to actin monomers. The concentration of actin filaments required to form liquid crystalline domains increased moderately as the average length was decreased. At a fixed actin concentration, orientation among the filaments attained a maximum value at a ratio of actin to gelsolin in the range from 1500 to 2000 and decreased as the ratio was increased or decreased from this range. The results are not well explained by theoretical treatments for liquid crystal formation by monodisperse, charged worm-like chains. Differences from the theoretical predictions for formation of liquid crystals are most likely due to the polydisperse filament length of actin. This phenomenon may have important effects on the structural and rheological properties of the cytoplasm in living cells.