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M Burg

Publications and source records attributed to M Burg.

At least 55 records · Page 3Linked to original sources
PubMed1994

Amino acids 327-350 of the human C5a-receptor are not essential for [125I]C5a binding in COS cells and signal transduction in Xenopus oocytes.

The anaphylatoxic peptide C5a is an important inflammatory mediator of the complement system. We have generated human C5a-receptor (hC5aR) mutants with truncation of its cytosolic carboxyl-terminus (C-terminus). Both mutants were analysed for C5a-binding in transiently expressing COS cells, and one mutant additionally for GTP-binding regulatory protein (G-protein) coupling in cRNA-injected Xenopus oocytes. Our data suggest that (a) amino acids (aa) 314 to 326 as part of the C-terminus are necessary for proper receptor folding or expression and (b) the receptor C-terminus distal from position 327 is not critical for receptor expression, folding, binding and G-protein coupling.

Animals↗
PubMed1994

Effects of long duration space flight on rice seed (or embryo) radiation sensitivity and element microlocalizations.

In long duration space experiments Rice caryopses and embryos, which are able to remain alive 10 years (or more) and tolerate extreme physical conditions (temperature, few water content) during irradiation and post-irradiation storage, were used (8, 40, 201 and 457 days on board of Salyut 7, 2107 days on LDEF). In certain experiments (Salyut 7), samples were irradiated either before or after the flight. Effects of the flight and radiosensitivity were observed in Rice seedlings cultivated in in vitro conditions. Statistical results indicate an increase in radiosensitivity when irradiations occur before the flight. Microanalyses were made in different parts of one caryopsis and of one embryo, and the results compared with those of control samples. With caryopses and embryos of the same Rice varieties, but from LDEF, we made the same kinds of experiments to compare results.

Free Radicals↗
PubMed1993

The competitive NMDA antagonist CPP protects substantia nigra neurons from MPTP-induced degeneration in primates.

Degeneration of nigrostriatal dopaminergic neurons is the primary histopathological feature of Parkinson's disease. The neurotoxin MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) induces a neurological syndrome in man and non-human primates very similar to idiopathic Parkinson's disease by selectively destroying dopaminergic nigrostriatal neurons. This gives rise to the hypothesis that Parkinson's disease may be caused by endogenous or environmental toxins. Endogenous excitatory amino acids (EAAs) such as L-glutamate could be involved in neurodegenerative disorders including Parkinson's disease. We report in this study that the competitive NMDA antagonist CPP (3-((+/-)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid) protects nigral tyrosine hydroxylase (TH) positive neurons from degeneration induced by systemic treatment with MPTP in common marmosets. This indicates that EAAs are involved in the pathophysiological cascade of MPTP-induced neuronal cell death and that EAA antagonists may offer a neuroprotective therapy for Parkinson's disease.

Animals↗
PubMed1992

C3a receptor on dibutyryl-cAMP-differentiated U937 cells and human neutrophils: the human C3a receptor characterized by functional responses and 125I-C3a binding.

The anaphylatoxic peptide C3a is part of a basic immunological defense mechanism, the complement system. Research on the human C3a receptor and signal transduction is hampered by the lack of a suitable human cell or cell line. We screened tumor cell lines and human blood cells for a C3a-dependent increase in cytosolic Ca2+ ([Ca2+]i) and analyzed this reaction in a fura-2/AM fluorescence assay for cells in suspension. U937 cells, when differentiated with dibutyryl-cAMP (Bt2cAMP), and purified human neutrophils reacted in a dose-dependent fashion to C3a and a C3a analogue synthetic peptide. We found complete homologous desensitization of this response and no heterologous desensitization to human C5a. Pertussis toxin totally blocked the increase in [Ca2+]i, indicating the possible involvement of a G-protein. Single-cell analysis by digital imaging fluorescence microscopy indicated that neutrophilic granulocytes responded to C3a. In binding studies with Bt2cAMP-differentiated U937 cells and human granulocytes, the 125I-C3a binding was displaced by C3a, yielding one class of C3a binding sites with dissociation constants (Kd) in the low nanomolar range. We identified myo-inositol 1,4,5-trisphosphate (IP3) as the second messenger possibly causing the [Ca2+]i increase and the release of N-acetyl-beta-D-glucosaminidase as one secretory cell response. By functional and binding studies we demonstrated the expression of the C3a receptor on Bt2-cAMP-differentiated U937 cells and human neutrophils and characterized parts of the C3a signal pathway. Our data support a physiological concept in which C3a might be more important than presently thought.

Acetylglucosaminidase↗
PubMed1992

Do NMDA receptor antagonists protect against MPTP-toxicity? Biochemical and immunocytochemical analyses in black mice.

We investigated whether excitatory amino acids acting at the N-methyl-D-aspartate (NMDA) subtype of the L-glutamate receptor contribute to the dopaminergic neurotoxicity induced by systemic administration of the Parkinson's syndrome-inducing toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in C57Bl/6 mice. The MPTP-regimen chosen (30-40 mg/kg body weight subcutaneously) resulted a 60-70% depletion of striatal dopamine (DA) content and a 20% reduction of tyrosine hydroxylase immunoreactive (TH-IR) cells in the substantia nigra pars compacta 20 days after administration. Repeated systemic coadministration of the non-competitive NMDA receptor antagonist MK-801 or of the novel competitive NMDA receptor antagonist CGP 40116 did not protect against MPTP-induced striatal DA depletion 20 days after toxin administration. Additionally, no short-term protective effects of MK-801 on striatal DA content were observed 24, 48, and 96 h, respectively, after exposure to MPTP. A slight and non-significant attenuation (approximately 10%) of the MPTP-induced decrease in the number of nigral TH-IR cells was observed after MK-801- and CGP 40116-treatment. We conclude that neurotoxicity of systemically administered MPTP is not substantially antagonized by NMDA receptor antagonists in mice.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1990

Characterization of cell-associated proteoglycans synthesized by embryonic neural retinal cells.

To begin to understand the properties of the neuronal heparan sulfate proteoglycan (HSPG) that interacts with the neural cell adhesion molecule (NCAM), we have analyzed proteoglycans synthesized by dissociated embryonic retinal cells in culture. Because NCAM plays an integral role in cell-cell interactions, we have focused on cell-associated HSPGs. Proteoglycans were isolated from embryonic Day 10 retinal cell cultures labeled with 35SO4 and separated into fractions that either flowed through or were retained on phenyl-Sepharose. Molecules binding phenyl-Sepharose have been proposed to be capable of insertion into the plasma membrane, and thus may be involved in binding to NCAM. Proteoglycans binding to phenyl-Sepharose had an estimated molecular mass of 400-500 kDa, and contained 60% HSPG and 40% chondroitin sulfate proteoglycan (CSPG). The putative membrane-associated HSPGs, with an average molecular weight of 360 kDa, were shown to contain heparan sulfate chains of 40 and 20 kDa, and multiple core proteins with the major core protein having a molecular weight of approximately 130 kDa. The membrane-associated CSPGs also exhibited multiple core proteins, with sizes ranging from 120 to 220 kDa. These data suggest that multiple membrane-associated HSPGs and CSPGs are synthesized by embryonic neural retina cells, which may explain the diversity in function of this class of proteoglycans.

Animals↗
PubMed1989

Characterization of a heparan sulfate proteoglycan that copurifies with the neural cell adhesion molecule.

We have demonstrated previously that the neural cell adhesion molecule (NCAM) interacts with a neuronal heparan sulfate proteoglycan. The binding of this proteoglycan(s) by NCAM appears to be required for NCAM-mediated cell adhesion, although the mechanism is unclear. In the present study we show that a heparan sulfate proteoglycan copurifies with NCAM, and provide an initial biochemical characterization of the proteoglycan. The copurification of a heparan sulfate proteoglycan with NCAM was demonstrated following immunopurification of NCAM from a detergent extract of cell membranes derived from Na2(35)SO4-labeled neural retinal cells. A large-molecular-weight, 35SO4-labeled molecule copurified with NCAM isolated from these neural cell cultures, and was resistant to chondroitinase ABC treatment, but degraded completely by nitrous acid treatment. These results indicate that the molecule is a heparan sulfate proteoglycan. Although this proteoglycan copurifies with NCAM, it is not detected when the neuron-glia cell adhesion molecule (NgCAM) is immunopurified using the 8D9 monoclonal antibody. The heparan sulfate proteoglycan may also be a membrane-associated proteoglycan since it interacts with phenyl-Sepharose. Molecular weight characterization of the proteoglycan by gel filtration chromatography indicates a molecular weight of 400-520 kDa. The heparan sulfate glycosaminoglycan chains were shown to have an average molecular weight of approximately 40 kDa, and the polypeptide backbone was estimated to be 120 kDa by polyacrylamide gel electrophoresis. These data therefore demonstrate that a neuronal heparan sulfate proteoglycan copurifies with NCAM.

Animals↗
PubMed1989

Signal for induction of aldose reductase in renal medullary cells by high external NaCl.

GRB-PAP1 is a continuous line of epithelial cells derived from rabbit renal inner medulla. These cells accumulate large amounts of sorbitol when extracellular NaCl concentration is elevated. The accumulation involves an increase in aldose reductase, an enzyme that catalyzes production of sorbitol from glucose. The purpose of the present studies was to investigate the mechanism by which high NaCl triggers an increase in aldose reductase activity. When NaCl was added to increase medium osmolality from 300 to 500 mosmol/kg, enzyme activity began to increase after 12-24 h, was half-maximal in 2 days, and was maximal by 4 days. To test the effect of other solutes, medium osmolality was increased to 500 mosmol/kg by adding raffinose, urea, or glycerol. Raffinose increased aldose reductase activity as much as NaCl did. In contrast, neither urea nor glycerol affected the enzyme activity. NaCl and raffinose caused a sustained decrease in cell water content and an increase in cell sodium and potassium concentration, but urea did not. In some experiments, ouabain was added either with or without an increase in osmolality. Taking into account all of the experiments, with and without ouabain, we found that aldose reductase activity did not correlate with either cell sodium concentration or cell water content alone. It did correlate, however, with cell potassium concentration and even more strongly with the sum of cell sodium plus potassium concentration. We conclude that the signal by which hyperosmolality triggers an increase in aldose reductase activity most likely involves an increase in intracellular ionic strength.

Aldehyde Reductase↗
PubMed1987

High NaCl induces stable changes in phenotype and karyotype of renal cells in culture.

Extracellular fluid in the renal medulla normally is hyperosmotic. To test adaptation to such an environment, a continuous line of rabbit renal inner medullary epithelial cells (GRB-PAP1), which had been established in isosmotic medium, was switched to a medium containing high NaCl. The origin of these cells is described. When the osmolality was raised from 300 to 600 mosmol/kg by adding NaCl, cells eventually survived and proliferated, but unexpectedly, they underwent major changes in phenotype and karyotype that persisted during proliferation in isosmotic or hyperosmotic medium for at least 7 months. The threshold concentration for the changes was approximately 500 mosmol/kg. Cells of a typical strain (PAP-HT25) that formed in hyperosmotic medium were much larger and more often multinucleated than were GRB-PAP1. GRB-PAP1 cells were near diploid; PAP-HT25 cells were polyploid. The changes, since they occurred in most clones, were due to adaptation of the majority of cells and not to selection of a minority of cells already having these characteristics. Cloning efficiency was higher for GRB-PAP1 than PAP-HT25 in isosmotic medium, but the reverse occurred in hyperosmotic medium. Thus exposure to the hyperosmotic medium induced greater ability to clone in it. We suggest that these changes may involve persistent alterations in gene regulation, possibly like those previously reported in chicken embryo fibroblast cells after hyperosmotic NaCl (Cell 30: 131-139, 1982).

Animals↗
PubMed1986

Predominant osmotically active organic solutes in rat and rabbit renal medullas.

The mechanism that concentrates the urine to an osmolality several times that of systemic plasma results in high concentrations of solutes (particularly NaCl and urea) in extracellular fluid of renal medulla, but not in the labyrinth of the renal cortex. Intracellular and extracellular osmolality must be equal in animals, but the known intracellular levels of Na and K salts and urea in renal medullas are much too low to balance the high extracellular osmolality. The purpose of these studies was to identify the other intracellular osmolytes that must be present. Cortexes and medullas from rabbit and rat kidneys were analyzed by proton nuclear magnetic resonance, mass spectrometry, and chemical assays to determine the identity and amount of organic solutes. Large amounts of glycerophosphorylcholine, betaine, sorbitol, and inositol were found in both species localized almost exclusively to the inner medulla. In rabbits during antidiuresis glycerophosphorylcholine, betaine, and sorbitol were present in the inner medulla, at concentrations of 21.1, 34.8, and 20.8 mumol/g wet weight, respectively, but were not detected in the cortex. Inositol was present in rabbit inner medulla at 10.7 mumol/g wet weight and was also present in the cortex, but at lower concentration. None of the above metabolites was present in measurable amounts in urine or peripheral plasma. The accumulation in the cells of the inner medulla of relatively large amounts of betaine, sorbitol, glycerophosphorylcholine and inositol during antidiuresis suggests that they may play a significant role in the maintenance of intracellular osmotic balance.

Animals↗
PubMed1985

Differentiated lines of cells from rabbit renal medullary thick ascending limbs grown on amnion.

Previously we grew differentiated primary epithelial tissue cultures from rabbit renal medullary thick ascending limbs but were unable to subculture them into lines. Now, following the use of amnion as a support during the initial passages, two cell lines have grown from single fragments of medullary thick ascending limbs. Cells have now been in culture past 12 passages over more than 2 yr. On confluence they formed morphologically differentiated epithelial monolayers with polarization of the cells visible on electron microscopy. They had apical zonula occludens and microvilli, lateral cellular interdigitations, and basal membranes flat against the support. "Domes" often were visible when the epithelia formed on dishes, indicative of salt and water transport. Other functional differentiation in some passages of one line or the other included presence of Tamm-Horsfall protein (demonstrated by immunofluorescence) or transepithelial voltage oriented apical surface positive. Both the Tamm-Horsfall protein and the voltage are normally expressed by intact medullary thick ascending limbs and are characteristic of this particular nephron segment.

Amnion↗
PubMed1985

Lactate production in isolated segments of the rat nephron.

Lactate production was measured directly in individual segments of the rat nephron. Tubules were dissected and then incubated in vitro with glucose as the only metabolic substrate. Each segment was incubated with and without antimycin A, an inhibitor of oxidative metabolism. Proximal tubules produced no lactate with or without antimycin A. The distal segments all produced lactate. The rate of lactate production without antimycin A ranged from 0.4 to 0.9 pmol X min-1 X mm-1 in all distal segments except one, the inner medullary collecting duct, which produced lactate at the significantly higher rate of 2.8 pmol X min-1 X mm-1. Antimycin A increased lactate production significantly in all of the distal segments. The increase was largest in medullary thick ascending limbs (1,400%) and cortical (798%) and outer medullary collecting ducts (357%). Increments were smaller in cortical thick ascending limbs (98%) and distal convoluted tubules (98%) and least in the inner medullary collecting ducts (28%). We conclude that lactate production occurs only in distal segments of the nephron and that under anoxic conditions significant amounts of ATP are produced by anaerobic glycolysis in these segments.

Animals↗
PubMed1984

Methylation increases sodium transport into A6 apical membrane vesicles: possible mode of aldosterone action.

When isolated apical membrane vesicles prepared from cultured A6 epithelia were incubated in vitro with the methyl donor S-adenosylmethionine, the control rate of amiloride-inhibitable sodium transport was doubled. The methylation inhibitors 3-deazaadenosine and S-adenosyl homocysteine returned the S-adenosyl-methionine-stimulated sodium transport to control levels. Neither these agents nor adenosine affected sodium transport into control vesicles. In vesicles incubated with S-adenosyl-[3H-methyl]methionine, both membrane phospholipids and proteins were labeled, and this labeling was inhibited by deazaadenosine. In vesicles prepared from A6 cells treated with aldosterone, sodium transport was twice the control value and S-adenosylmethionine did not cause any further stimulation of transport. In those vesicles, both lipid and protein methylation were increased. These results suggest that methylation, which increases the rate of amiloride-sensitive sodium transport is involved in the action of aldosterone at the apical membrane level in epithelia.

Aldosterone↗
PubMed1984

Biological changes observed on rice and biological and genetic changes observed on tobacco [correction of tabacco] after space flight in the orbital station Salyut-7 (Biobloc III experiment).

Caryopses and isolated embryos from Rice (Oryza sativa L.) and Tobacco seeds (Nicotiana tabacum L. variety Xanthi) were studied in the Biobloc III container aboard the Soviet orbital space station SALYUT 7. The recovery from radiation damage under conditions of space flight was observed for rice caryopsis and embryos gamma irradiated (Co 60, 50 grays) prior to launch. There was a large decrease in the percentage of germinating seeds from the Tobacco strain tested when the seeds were exposed to heavy ions. Among the germinating plantlets there were few morphological anomalies. Furthermore, there was a significant greater amount of genetic change in those samples held in grids as compared to those in bags.

Cosmic Radiation↗
PubMed1983

Sodium chloride coupled transport in mammalian nephrons.

A number of possible modes of coupling of sodium chloride transport have been considered, and their roles in the various parts of the renal tubule have been reviewed. Many modes of coupling have been found in various combinations in one or another of the segments. Of special interest are the observations of carrier coupling of sodium to chloride transport in some of the segments, such as the thick ascending limbs of Henle's loop.

Animals↗
PubMed1983

Organization of nephron function.

Recent studies of mammalian nephron segments have revealed an unexpected diversity of renal transport functions. Most substances are transported by several segments, and the transport mechanisms differ from segment to segment. In this paper we review some of these findings in order to fit them into an integrated picture of kidney function. The main question we ask is what is the advantage of spatial separation of the various transporters along the nephron. We propose that spatial separation of transport functions allows independent and efficient control of the excretion of substances whose renal handling is interdependent. The organization of sodium and water handling along the nephron is considered in the greatest detail. Sodium and water play central roles in controlling the renal excretion of many other substances. Yet the excretion rates of sodium and water themselves are independently controlled. The intricate anatomical structure of the kidney not only provides spatial separation of transport processes along the nephron but also couples the function of different segments by juxtaposing them in specialized regions within the medulla and cortex. These anatomical arrangements provide a framework for integrating the complex array of renal functions.

Animals↗
PubMed1982

Heterogeneity in the distal nephron of the salamander (Ambystoma tigrinum): a correlated structure function study of isolated tubule segments.

Studies on isolated perfused tubules of the tiger salamander (Ambystoma tigrinum) have shown that the distal nephron is heterogeneous with respect to function (Stoner, 1977). In this study, the initial portion of the distal tubule (diluting segment) exhibited a voltage, positive in the lumen, and a net absorption of chloride. Since the chloride was transported against an electro-chemical gradient, its transport was active. More distad, the junctional segment exhibited a lumen-negative voltage and sodium, rather than chloride, was transported actively. More recently Delaney and Stoner (1981) have demonstrated in vitro that the collecting duct of this species also has a lumen-negative voltage which is probably associated with active sodium reabsorption. The primary objective of the present paper was to correlate the morphology of the diluting and junctional segments of the Ambystoma distal tubules with the physiologic data from the same isolated perfused tubules. The results indicate that the morphological heterogeneity previously demonstrated in distal tubules of Necturus exists with respect to both structure and function in Ambystoma. The cell types found in the amphibian distal nephron appear to be homologous to those seen in the mammalian nephron.

Animals↗