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Biomedical subjects

T Berg

Publications and source records attributed to T Berg.

At least 253 records · Page 14Linked to original sources
PubMed1986

Isolation of pronephros cells which endocytose chemically modified proteins in the rainbow trout.

Modified serum albumin is cleared from the blood by kidney cells in salmonid fishes. The present study deals with isolation of cells from pronephros which endocytose formaldehyde-treated human serum albumin (fHSA). Radioactively labelled fHSA or dinitrophenyl-conjugated albumin (DNP-HSA) were injected intravenously into rainbow trouts. Pronephros cells, containing the endocytosed protein, were isolated and further separated by centrifugal elutriation and density-gradient centrifugation. Most of the radioactive protein was elutriated together with small cells. After centrifuging the cells through a Percoll density gradient, radioactive protein was located in cells recovered in the upper part of the gradient. In mammals, fHSA and other modified proteins are mainly taken up by sinusoidal endothelial cells in the liver via a "scavenger receptor"0. Our results suggest that a comparable function in salmonids is located in a subpopulation of relatively small cells in kidney tissue, possibly sinusoidal lining cells. The separation techniques used seemed to be suitable for isolation of different populations of pronephros cells.

Animals↗
PubMed1986

Immunohistochemical localization of two angiotensin I-converting isoenzymes in the reproductive tract of the male rabbit.

The male reproductive tract contains two different isoenzymes of angiotensin I-converting enzyme (ACE), i.e., pulmonary and testicular ACE. The present study shows selectively the cellular distribution of the ACE isoenzymes in the reproductive tract of male rabbit, using indirect immunofluorescence or immunoperoxidase methods. Testicular ACE was found in the seminiferous tubules of the testes in spermatocytes containing mature spermatids, and in spermatids within the epididymal tubular lumen in sexually mature, but not in immature, rabbits. Epididymal tubular cells contained pulmonary ACE. In the young rabbit, epididymal tissue contained more ACE than that in adult rabbit, since ACE was observed in principal cells in addition to basal cells. In mature rabbit, ACE was observed in basal cells only. Strong staining for pulmonary ACE was observed in cells of the vas deferens in both young and adult rabbit. Therefore, synthesis of epididymal ACE, unlike the testicular isoenzyme, was not stimulated by sexual maturation. Enzymatically active ACE in seminal fluid corresponds to the pulmonary isoenzyme. The present study indicates that this seminal fluid ACE may originate from cells of the epididymal tubules, particularly those of the vas deferens. Endothelial cells of blood vessels lying in the interstitium of both testicular and epididymal tissue contained the pulmonary isoenzyme.

Animals↗
PubMed1985

Intracellular transport of endocytosed chylomicron [3H]retinyl ester in rat liver parenchymal cells. Evidence for translocation of a [3H]retinoid from endosomes to endoplasmic reticulum.

The intracellular transport of chylomicron remnants labeled with [3H]retinyl ester was studied in rat liver parenchymal cells by means of subcellular fractionation in Nycodenz and sucrose density gradients. The data presented indicate that endocytosed chylomicron remnant [3H]retinyl ester initially is located in low density endosomes. Radioactivity is subsequently transferred to a denser vesicle. Equilibrium as well as rate zonal centrifugation suggest that this denser [3H] retinoid-containing vesicle may represent endoplasmic reticulum. We have compared the intracellular transport of chylomicron remnant [3H]retinyl ester and 125I-asialofetuin. The receptor-mediated endocytosis of asialoglycoproteins in rat liver parenchymal cells is a thoroughly studied system. Our results suggest that the [3H] retinoid and 125I-asialofetuin follow the same path initially to the endosomes. After transit in endosomes, the intracellular transport differs. While asialofetuin is transported to the lysosomes, the retinoid is probably transferred to the endoplasmic reticulum.

Animals↗
PubMed1985

Hepatic retinol metabolism. Distribution of retinoids, enzymes, and binding proteins in isolated rat liver cells.

The main retinoids and some binding proteins and enzymes involved in retinol metabolism have been quantified in different types of rat liver cells. Hepatic perisinusoidal stellate cells contained 28-34 nmol of retinoids/10(6) cells, and parenchymal liver cells contained 0.5-0.8 nmol of retinoids/10(6) cells, suggesting that as much as 80% of more of total liver retinoids might be stored in stellate cells with the rest stored in parenchymal cells. Isolated endothelial cells and Kupffer cells contained very low levels of retinoids. More than 98% of the retinoids recovered in stellate cells were retinyl esters. Isolated parenchymal and stellate cell preparations both contained considerable retinyl palmitate hydrolase and acyl-CoA:retinol acyltransferase activities. Parenchymal cells accounted for about 75-80% of the total hepatic content of these two enzyme activities, with the rest located in stellate cells. On a cell protein basis, the concentrations of both of these activities were much greater in stellate cells than in parenchymal cells. In contrast, cholesteryl oleate and triolein hydrolase activities were fairly evenly distributed in all types of liver cells. Large amounts of cellular retinol binding proteins were also found in parenchymal and stellate cells. Although parenchymal cells accounted for more than 90% of hepatic cellular retinol binding protein, the concentration of the protein in stellate cells (per unit protein) was 22 X greater than that in parenchymal cells. Stellate cells were also enriched in cellular retinoic acid binding protein. Thus, both parenchymal and stellate cells contain substantial amounts of retinoids and of the enzymes and intracellular binding proteins involved in retinol metabolism. Stellate cells are particularly enriched in these several components.

Acyltransferases↗
PubMed1985

Hepatic uptake of [3H]retinol bound to the serum retinol binding protein involves both parenchymal and perisinusoidal stellate cells.

We have studied the hepatic uptake of retinol bound to the circulating retinol binding protein-transthyretin complex. Labeled complex was obtained from the plasma of donor rats that were fed radioactive retinol. When labeled retinol-retinol binding protein-transthyretin complex was injected intravenously into control rats, about 45% of the administered dose was recovered in liver after 56 h. Parenchymal liver cells were responsible for an initial rapid uptake. Perisinusoidal stellate cells initially accumulated radioactivity more slowly than did the parenchymal cells, but after 16 h, these cells contained more radioactivity than the parenchymal cells. After 56 h, about 70% of the radioactivity recovered in liver was present in stellate cells. For the first 2 h after injection, most of the radioactivity in parenchymal cells was recovered as unesterified retinol. The radioactivity in the retinyl ester fraction increased after a lag period of about 2 h, and after 5 h more than 60% of the radioactivity was recovered as retinyl esters. In stellate cells, radioactivity was mostly present as retinyl esters at all time points examined. Uptake of retinol in both parenchymal cells and stellate cells was reduced considerably in vitamin A-deficient rats. Less than 5% of the injected dose of radioactivity was found in liver after 5-6 h (as compared to 25% in control rats), and the radioactivity recovered in liver from these animals was mostly in the unesterified retinol fraction. Studies with separated cells in vitro suggested that both parenchymal and stellate cells isolated from control rats were able to take up retinol from the retinol-retinol binding protein-transthyretin complex. This uptake was temperature dependent.

Animals↗
PubMed1985

Retinol esterification in cultured rat liver cells.

Retinol esterification was examined in cultured hepatocytes and stellate cells from the rat. Esterification of [3H]retinol was linear for 2 h in both cell types. By increasing the concentration of retinol in the medium, there was a marked increase in retinol esterification in both cell types. The capacity for esterification of retinol was in the same order of magnitude in the two cell types at 3.5 microM-retinol in the medium. This represents a rate of retinol esterification which far exceeds that required to esterify the amount of retinol absorbed in the intestine. It was demonstrated in particulate homogenates from cultured hepatocytes that the esterification of retinol was dependent on acyl-CoA. Addition of 25-hydroxycholesterol or mevalonolactone promoted an increase in cholesterol esterification, whereas retinol esterification was unaffected, suggesting that cholesterol and retinol are esterified by two different enzymes. Some 80% of vitamin A in cultured hepatocytes is retinyl esters, mostly retinyl palmitate. By adding 87 microM-retinol in the medium the cells accumulated 100-fold free retinol and 2.5-3.0-fold retinyl esters within 1 h. When retinol-loaded cells were incubated without retinol, there was a marked decrease especially in free but also in esterified retinol. In the presence of 1 mM-oleic acid in the medium the amount of retinyl oleate was twice that in control cells.

Acyltransferases↗
PubMed1985

The influence of cellular ATP levels on receptor-mediated endocytosis and degradation of asialo-glycoproteins in suspended hepatocytes.

Receptor-mediated endocytosis in suspended hepatocytes was studied in conjunction with ATP levels of the cells, which were decreased by the use of metabolic inhibitors. The receptor system studied was the asialo-glycoprotein receptor, and multiple aspects of the endocytic pathway were examined: binding of ligand, internalization, intracellular transport and proteolysis. Moderate concentrations of the inhibitors (e.g. 30 microM rotenone or 200 microM iodoacetamide) produced only a transient decline in the ATP levels of the cells. Two to four times higher concentrations reduced the ATP levels to about 1/10 of control cells. At low levels of ATP (less than 30% of controls) the uptake ceased completely after 10-20 min. Moderate reductions brought about by rotenone reduced the uptake roughly in proportion to the ATP levels; iodoacetamide and sodium fluoride had little influence on the energy production by the cells, but the rate of asialo-glycoprotein uptake was reduced to a small fraction of controls. The effect of rotenone on the rate of uptake was mainly due to a lower rate of internalization of occupied receptors; the half-time for internalization of surface-bound ligand was increased from 2.9 to 6.2 min in the presence of 42 microM rotenone. The binding capacity of the cell surface was also somewhat lower. There was no degradation of the asialo-glycoproteins which were taken up by cells treated with high concentrations of rotenone or iodoacetamide. This was shown to be due to a low rate of transport of the endocytosed protein into those endosomes (at density 1.15 g/ml in a sucrose gradient) which were delivering their contents to the lysosomes; coincidentally, there was an accumulation of ligand in light endosomes (density 1.11 g/ml), in which the ligand appears immediately after endocytosis.

Adenosine Triphosphate↗
PubMed1985

The effects of monensin on secretion of very-low-density lipoprotein and metabolism of asialofetuin by cultured rat hepatocytes.

Primary cultures of rat hepatocytes were used to study secretion of very-low-density lipoproteins and metabolism of asialofetuin. The ionophore monensin inhibited both secretion of very-low-density lipoproteins and binding and degradation of asialofetuin in a concentration-dependent manner. Secretion as well as receptor binding were markedly decreased after 15 min treatment with monensin. The inhibitory effect of the ionophore was fully reversible, and no effect on protein synthesis was observed at concentrations up to 50 microM. The secretion of apoproteins (B-small, B-large and E) and that of albumin were inhibited to the same extent as was triacylglycerol secretion. Secretion of very-low-density lipoproteins was more sensitive to low concentrations of monensin than was the metabolism of asialofetuin. Maximum inhibition of very-low-density-lipoprotein secretion was obtained at 5-10 microM-monensin, whereas 25 microM was required to obtain maximum inhibition of binding and degradation of asialofetuin. The number of surface receptors for asialofetuin decreased to about half when the cells were exposed to 25 microM-monensin. It is possible that monensin inhibits endo- and exo-cytosis via a similar mechanism, e.g. by disturbing proton gradients. Since secretion of very-low-density lipoproteins was more sensitive to low concentrations of monensin, it is likely that monensin independently inhibits endocytic and secretory functions in cultured hepatocytes.

Animals↗
PubMed1985

Intracellular transport of asialoglycoproteins in rat hepatocytes. Evidence for two subpopulations of lysosomes.

The intracellular transport and degradation of asialoorosomucoid (AOM) in isolated rat hepatocytes was studied by means of subcellular fractionation in Nycodenz gradients. The asialoglycoprotein was labelled by covalent attachment of a radioiodinated tyramine-cellobiose adduct ( [125I]TC) which leads to labelled degradation products being trapped intracellularly and thus serving as markers for the degradative organelles. The ligand was initially (1 min) in a slowly sedimenting (small) vesicle and subsequently in larger endosomes. Acid-soluble, radioactive degradation products were first found in a relatively light lysosome whose distribution coincided in the gradient with that of the larger endosome. Later (30 min) degradation products were found in denser lysosomes which banded in the same region of the gradient as the lysosomal enzyme, beta-acetylglucosaminidase. Colchicine, monensin and leupeptin all inhibited degradation of [125I]tyramine-cellobiose asialoorosomucoid ( [125I]TC-AOM) and reduced the formation of degradation products in both the light and the dense lysosomes. In presence of monensin and colchicine no undegraded ligand was seen in the dense lysosome, suggesting that uptake in these vesicles was inhibited. Leupeptin allowed accumulation of undegraded ligand in the dense lysosome. Therefore, transfer from light to dense lysosomes is not dependent on degradation as such. In the presence of monensin two peaks of undegraded ligand were found in the gradients. It seems possible that in the monensin-sensitive endosomes, dissociation of the ligand-receptor complex is inhibited, allowing ligand to recycle with the receptors in small vesicles.

Animals↗
PubMed1985

Intracellular degradation of asialoglycoproteins in hepatocytes starts in a subgroup of lysosomes.

Isolated rat hepatocytes take up and degrade [125I]tyramine-cellobiose-labelled asialofetuin [( 125I]TC-AF). The labelled degradation products are trapped at the site of degradation. The intracellular transport of [125I]TC-AF was studied by means of cell fractionation in Nycodenz gradients. The labelled ligand was kept in a small, slowly sedimenting vesicle during the first minutes after uptake in the cells, and was then transferred to a larger endosome. Labelled degradation products first appeared in an organelle with the same density distribution as the larger endosome and then in a denser organelle. These observations suggest that two types of lysosome, 'light' lysosomes and 'dense', are sequentially involved in the degradation of the asialoglycoprotein. The bulk of the lysosomal enzymes is associated with the dense lysosome.

Acetylglucosaminidase↗
PubMed1985

Uptake and degradation of bovine testes beta-galactosidase by parenchymal and nonparenchymal rat liver cells.

The plasma half-life of beta-galactosidase in rat was about 1.5 min. Ten minutes after in vivo injection, 45% of the enzyme was recovered in liver, with hepatocytes and endothelial cells as the predominant cell types responsible for uptake. In vitro uptake of beta-galactosidase in hepatocytes and nonparenchymal liver cells was saturable, Ca2+-dependent and it could be partly inhibited by mannose or alpha-methyl-mannoside.

Animals↗
PubMed1985

In vitro degradation of endocytosed protein in pronephros cells of the char (Salmo alpinus L.). The effects of temperature and inhibitors.

In vitro degradation of 125I-formaldehyde treated human serum albumin (fHSA) in char (Salmo alpinus L.) pronephros cells was studied. The labelled protein was injected intravenously and after various intervals of time pronephros cells were isolated and degradation of internalized protein was measured. No degradation could be observed in cells isolated 30 min after injection. The degradation was very effective in cells isolated at later time points (60-90 min); as much as 65% of the initial cell associated labelled protein was degraded during 90 min incubation at 15 degrees C. The effect of temperature on degradation showed a linear course in the temperature range 0-20 degrees C when plotted in an Arrhenius plot. Monensin and ammonium ions inhibited degradation while colchicine had no effect when pronephros cells were isolated 75 min after the injection.

Ammonia↗
PubMed1985

Endocytosis of galactose-terminated glycoproteins by isolated liver cells of the rainbow trout (Salmo gairdneri).

Intravenously injected 125I-labeled galactose-terminated glycoproteins were mainly recovered in the liver of the rainbow trout. After injection of [14C]sucrose-labeled asialofetuin, the liver cells were isolated and separated by differential centrifugation. The radioactivity was located in the parenchymal cells. Uptake of asialoglycoproteins in liver cells was inhibited by EGTA, lactose and excess unlabeled ligand. Degradation was inhibited by ammonium chloride, suggesting a lysosomal process. Internalization of 125I-asialoglycoproteins was demonstrated by removing receptor-bound ligand with EGTA at different time points during the incubation. The cellular uptake occurred even at 0 degree C.

Ammonia↗
PubMed1985

Insulin potentiates cholecystokinin (CCK)-induced secretion of pancreatic kallikrein.

The effects of insulin on pancreatic kallikrein secretion were studied in streptozotocin diabetic rats and after acute administration of insulin to normal rats. Studies on total protein and amylase secretion were included for comparison. In diabetic rats, the concentration of amylase in pancreatic tissue as well as basal and CCK-stimulated amylase exocrine secretion were significantly reduced. Insulin treatment restored pancreatic tissue concentration and exocrine release of amylase to normal. Insulin deficiency did not induce any change in the concentration of kallikrein or trypsin-like activity in pancreatic tissue. However, basal kallikrein secretion was higher in diabetic rats than in controls. Insulin treatment of diabetics rats did not alter basal kallikrein secretion but potentiated CCK-stimulation of kallikrein release. In normal rats, CCK induced an increase of pancreatic protein, amylase, and kallikrein secretion but not pancreatic juice flow. Additional administration of insulin potentiated the CCK-induced secretory rate of pancreatic juice, protein, and kallikrein but not amylase. A 1.6 times higher concentration of kallikrein was found in the portal vein than in arterial blood, indicating an endocrine release of pancreatic kallikrein. No difference in the concentration of circulating kallikrein was observed between the control and the insulin-treated group.

Amylases↗
PubMed1985

Enzymatic activity of rat submandibular gland kallikrein released into blood.

Enzymatic activity of submandibular gland (SG) kallikrein released into saliva and blood was studied at rest and after autonomic nerve stimulation. Kallikrein was measured by an immunometric assay that allows measurement of immunoreactive kallikrein in complex with inhibitors as well as simultaneous determination of kallikrein enzymatic activity. Measurements using the chromogenic substrate S2266 gave identical results to the natural substrate kininogen. Endogenous SG kallikrein secretory rate was, at rest, 0.9 +/- 0.1 ng/min. Kallikrein secretion into blood in response to autonomic nerve stimulation paralleled that into saliva, and secretion was greatly enhanced by alpha-adrenergic stimulation. In plasma, kallikrein was bound to several inhibitors that completely or partially blocked the enzyme activity. In arterial and SG venous control plasma, 93 +/- 3 and 72 +/- 10% inhibition of kallikrein enzyme activity was observed, respectively. Sympathetic stimulation after administration of a beta-adrenergic blocker increased kallikrein enzyme activity 62 and 11 times in arterial and SG venous plasma, respectively, with a corresponding 78 +/- 8 and 70 +/- 8% inhibition of kallikrein enzyme activity. A fraction containing kallikrein resembling "free kallikrein" was always present in plasma.

Animals↗
PubMed1985

Demonstration of kallikrein in a rat pancreatic acinar cell carcinoma.

Kallikrein was identified immunohistochemically and biochemically in a transplantable pancreatic acinar cell carcinoma of the rat. The concentration of immunoreactive kallikrein in tumor homogenates was the same as in the pancreas. Kallikrein in tumor cells exists as a proenzyme and is released into blood in high concentrations. The impact of the presence of a kallikrein-producing tumor on other kallikrein-containing organs and other possibly interrelated systems was investigated. The concentration of kallikrein in the submandibular gland and pancreas of host rats was not significantly different from that of control rats. Urinary kallikrein secretion was significantly increased, although this may be a result of the high plasma glandular kallikrein concentration combined with kidney damage. The plasma concentration of kininogen, kininase, and renin was not significantly different from control rats. Rats with tumor had significantly lower blood pressure than did control animals, and blood pressure was inversely related to the concentration of glandular kallikrein in plasma. However, it was not proven that the low blood pressure was due to the high concentration of kallikrein. Nephrectomized tumor rats gave a smaller hypotensive response to kininase inhibition than was expected from their high concentration of circulating kallikrein. This may be explained by the absence of the "free kallikrein" fraction in plasma of host rats.

Amylases↗
PubMed1985

Hepatic uptake of circulating IgG immune complexes.

IgG antibodies were found to increase the uptake of circulating dinintrophenylated human serum albumin (DNP-HSA) preparations by the nonparenchymal liver cells in rats. Highly DNP-conjugated HSA was taken up by the Kupffer cells both when given alone and when complexed by IgG. More lightly DNP-conjugated HSA was taken up mainly by the liver endothelial cells. Here, IgG promoted the antigen uptake both by the Kupffer cells and by the endothelial cells. Uptake of IgG immune complexes (IgG-ICs) by the sinusoidal endothelial cells of the liver is a new aspect on the function of these cells. Whether or not this phenomenon is Fc receptor-mediated is discussed. A heat-labile serum factor was found to direct the ICs to the Kupffer cells. This implies that serum complement and hepatic C3 receptors are essential for the physiological clearance of circulating immune complexes.

Animals↗