Biomedical subjects

R S Keresztes

Publications and source records attributed to R S Keresztes.

4 recordsLinked to original sources

PubMed1992

Lipopolysaccharides decrease angiotensin converting enzyme activity expressed by cultured human endothelial cells.

Angiotensin converting enzyme (ACE) is present on endothelial cells and plays a role in regulating blood pressure in vivo by converting angiotensin I to angiotensin II and metabolizing bradykinin. Since ACE activity is decreased in vivo in sepsis, the ability of lipopolysaccharide (LPS) to suppress endothelial cell ACE activity was tested by culturing human umbilical vein endothelial cells (HUVEC) for 0-72 hr with or without LPS and then measuring ACE activity. ACE activity in intact HUVEC monolayers incubated with LPS (10 micrograms/ml) decreased markedly with time and was inhibited by 33%, 71%, and 76% after 24 hr, 48 hr, and 72 hr, respectively, when compared with control, untreated cells. The inhibitory effect of LPS was partially reversible upon removal of the LPS and further incubation in the absence of LPS. The LPS-induced decrease in ACE activity was dependent on the concentrations of LPS (IC50 = 15 ng/ml at 24 hr) and was detectable at LPS concentrations as low as 1 ng/ml. That LPS decreased the Vmax of ACE in the absence of cytotoxicity and without a change in Km suggests that LPS decreased the amount of ACE present on the HUVEC cell membrane. While some LPS serotypes (Escherichia coli 0111:B4 and 055:B5, S. minnesota) were more potent inhibitors of ACE activity than others (E. coli 026:B6 and S. marcescens), all LPS serotypes tested were inhibitory. These finding suggest that LPS decreases endothelial ACE activity in septic patients; in turn, this decrease in ACE activity may decrease angiotensin II production and bradykinin catabolism and thus play a role in the pathogenesis of septic shock.

Bacterial Toxins↗

PubMed1984

Protein-lipid interactions in antipodal plasma membranes of rat colonocytes.

The isolation of apical membranes from rat proximal colonic epithelial cells is described. Differential centrifugation yielded a 'crude' membrane fraction which was further purified using sucrose density centrifugation. The final membrane fraction was enriched 20-28-fold over homogenate in alkaline phosphatase and cysteine-sensitive alkaline phosphatase specific activities. Lipid-protein interactions and lipid dynamics examined in apical and basolateral membranes prepared from colonocytes demonstrated: (1) apical membrane, as assessed by steady-state fluorescence polarization studies have a low lipid fluidity; (2) colonic basolateral membranes possess a greater lipid fluidity than apical membranes; (3) compositional differences in these antipodal membranes appear to explain these differences in lipid fluidity; (4) fluorescence polarization studies using diphenylhexatriene detect a thermotropic transition at 21-23 degrees C in apical membranes and liposomes prepared from lipid extracts of these membranes; (5) alkaline phosphatase and L-cysteine-sensitive alkaline phosphatase activities appear to be functionally dependent on the physical state of the apical membrane's lipid.

Adenosine Triphosphatases↗

PubMed1983

Isolation and partial characterization of basolateral membranes from rat proximal colonic epithelial cells.

The isolation of basolateral membranes from rat proximal colonic epithelial cells is described. Cells were harvested using a technique combining chelation of divalent cations with mechanical dissociation. After homogenization, differential centrifugation yielded a 'crude' membrane fraction which was further purified using sucrose density centrifugation. The final membrane fraction was enriched 10-14-fold over homogenate in ouabain-sensitive sodium-potassium dependent adenosine triphosphatase and ouabain-sensitive potassium-dependent phosphatase specific activities. SDS-polyacrylamide gel electrophoresis of this membrane revealed at least 18 protein bands with molecular weights of 14600-200000. Phosphatidylcholine, phosphatidylethanolamine, sphingomyelin, free cholesterol and fatty acids were the major lipid components of this membrane. The predominant fatty acids were palmitic (16:0), oleic (18:1), stearic (18:0) and linoleic (18:2) acid. Membranes and their liposomes were studied, using the lipid soluble fluorophore 1,6-diphenyl-1,3,5-hexatriene (DPH), by steady-state fluorescence polarization. The fluorescence anisotropy was greater in the intact membranes compared to their liposomes, indicating greater fluidity in the liposomes. Compositional studies suggested that the high fluidity of this membrane was due to its low ratios of protein/lipid (w/w), cholesterol/phospholipid (mol/mol), and sphingomyelin/phosphatidylcholine (mol/mol).

Animals↗

PubMed1983

Glycoprotein metabolism in rat colonic epithelial cell populations with different proliferative activities.

Epithelial cells with different proliferative activities were isolated from rat proximal and distal colon. The distribution of fucose, hexose, hexosamine, and sialic acid as well as the activities of three glycosyltransferases, eight glycosidases, and a nucleotide sugar pyrophosphatase, enzymes involved in glycoprotein metabolism, were then examined in these cells. The results of the present study demonstrate that: (1) all proximal cell populations appear to possess a higher content of hexose, fucose, and sialic acid than their distal counterparts; (2) in general, the proximal colonic populations have higher glycosyltransferase but similar glycosidase activities than their distal counterparts; (3) proliferative cells in both colonic regions have greater glycosyltransferase and glycosidase activities than non-proliferative cells, although their carbohydrate content is similar. These findings suggest that alterations in glycoprotein metabolism exist during differentiation along the length of the rat colon. Furthermore, these data indicate that certain enzymes involved in glycoprotein metabolism may serve as markers for cellular differentiation in this organ.

Animals↗