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Biomedical subjects

G Drews

Publications and source records attributed to G Drews.

At least 55 records · Page 3Linked to original sources
PubMed1995

The light-harvesting complex II (B800-850) of Rhodobacter sulfidophilus: characterization and formation under different growth conditions.

The photosynthetic bacterium Rhodobacter sulfidophilus is able to grow chemotrophically and phototrophically at a broad range of light intensities. In contrast to other facultative phototrophs, R. sulfidophilus synthesizes reaction center and light-harvesting (LH) complexes, B870 (LHI) and B800-850 (LHII) even under full aerobic conditions in the dark. The content of bacteriochlorophyll (BChl) varied from 3.8 micrograms Bchl per mg cell protein when grown at high light intensity (20,000 lux) to 60 micrograms Bchl per mg cell protein when grown at low light intensities (6 lux). After a shift from high light to low light conditions, the size of the photosynthetic unit increased by a factor of 4. Chromatographic analysis of the LHII complex, isolated and purified from cells grown phototrophically (at high and low light intensities) and chemotrophically, could resolve only one type of alpha and one type of beta polypeptide in the purified complex, of which the N-terminal sequences have been determined.

Aerobiosis↗
PubMed1995

The effects of nitric oxide on the membrane potential and ionic currents of mouse pancreatic B cells.

Nitric oxide (NO) is considered to contribute to the impairment of B cell function in insulin-dependent diabetes mellitus. The effects of compounds that release NO were tested on the membrane potential and ionic currents of mouse pancreatic B cells using intracellular microelectrodes and the whole-cell patch-clamp technique. S-Nitrosocysteine led to a concentration-dependent reduction of electrical activity induced by 15 mM glucose. At a concentration of 1 mM, S-nitrosocysteine cause a hyperpolarization of the plasma membrane with complete suppression of electrical activity. In about half of the cells tested, electrical activity reappeared during treatment with S-nitroso-cysteine or after wash-out. However, in the other cells the hyperpolarization was followed by a slow depolarization and electrical activity did not reappear. The perforated-patch whole-cell K+ATP current first increased and subsequently decreased again during exposure to 1 mM S-nitroso-cysteine. With 0.1 and 0.01 mM S-nitroso-cysteine, only the rise of the current amplitude was observed. S-nitroso-cysteine (1 mM) almost completely abolished the current through voltage-dependent Ca2+ channels (measured with Ba2+ as charge carrier). Like S-nitroso-cysteine, 100 microM sodium-nitroprusside, another donor, evoked a marked hyperpolarization of the membrane potential that was at least in part reversible. To further ascertain that the effect of S-nitroso-cysteine was mediated by NO, we tested the decomposition products of S-nitroso-cysteine. Nitrite and denitrosylated S-nitroso-cystein (1 mM) did not alter electrical activity of B cells, whereas cysteine (1 mM) caused a slight depolarization. It is concluded that exogenous NO evokes rapid changes of B cell function by influencing the activity of ion channels.

Animals↗
PubMed1995

Effects of membrane-permeant and -impermeant thiol reagents on Ca2+ and K+ channel currents of mouse pancreatic B cells.

The membrane permeant thiol reagent diazene dicarboxylic acid bis-(N'-methylpiperazide) (DIP) has been shown to inhibit insulin secretion and Ca2+ uptake in pancreatic B cells in the presence of a stimulating glucose concentration (20 mM), whereas the nonpenetrating analog of DIP (bis-N'-methyliodide; DIP + 2) stimulates insulin release and Ca2+ uptake at a low glucose concentration (3 mM). The effects of DIP and DIP + 2 were tested on currents through ATP-sensitive K+ (K+ATP) channels and voltage-dependent Ca2+ channels (with Ba2+ as the charge carrier) in mouse pancreatic B cells in the whole-cell mode of the patch-clamp technique. DIP (0.1 mM) almost completely inhibited both the K+ATP and Ca2+ channel currents. In contrast, DIP + 2 (0.1 mM) did not affect the Ca2+ channel current but reduced the whole-cell K+ATP current by about 40%. The data strongly suggest that the suppression of insulin secretion previously observed with DIP is due to a reduction of the current through voltage-dependent Ca2+ channels, whereas the stimulation of hormone release induced by DIP + 2 is caused by the partial inhibition of K+ATP channel current.

Animals↗
PubMed1994

Effects of osmotic changes in extracellular solution on electrical activity of mouse pancreatic B-cells.

The influence of changes in the osmolarity of the extracellular solution on electrical activity of mouse pancreatic B-cells was studied with intracellular microelectrodes. In the presence of 15 mmol/l glucose the membrane potential of B-cells oscillates. A reduction of the osmolarity by 40 mosmol/l caused a small temporary hyperpolarization in six out of eight cells. After 2 to 3 min electrical activity was increased in all cells. However, this effect was also transient. 5 to 8 min after onset of exposure to hypotonic solution the cells repolarized again and electrical activity decreased. Increasing the osmolarity of the extracellular solution by 40 mosmol/l led to a sustained and reversible depolarization of the membrane potential. However, the electrical activity was transiently suppressed. The changes in electrical activity observed in hypotonic solution might explain the previously described transient rise in insulin secretion provoked by osmotic cell swelling.

Animals↗
PubMed1994

Effects of SH-group reagents on Ca2+ and K+ channel currents of pancreatic B-cells.

The whole-cell patch-clamp technique has been applied to elucidate the effects of H2O2 and the SH-group reagent 2,2'-dithio-bis(5-nitropyridine) (DTBNP) on Ca2+ currents of mouse pancreatic B-cells. We also tested the effect of DTBNP on the whole-cell K+ ATP current. DTBNP (20 and 100 mumol/l) blocked both the current through Ca2+ channels (with Ba2+ as the charge carrier) and the K+ATP current in a concentration-dependent manner. The results suggest that the channels themselves or regulating proteins possess free SH-groups which may be of functional relevance. However, H2O2 did not influence the Ca2+ channel currents under standard whole-cell conditions as well as when recorded with the perforated patch technique. These results indicate that the two agents act differently on ion channel currents in B-cells although both are known to oxidize SH-groups.

Adenosine Triphosphate↗
PubMed1994

H2O2 induced hyperpolarization of pancreatic B-cells.

Conventional electrophysiology and the whole-cell patch-clamp technique have been applied to elucidate the effects of H2O2 on pancreatic B-cells of the mouse. In these cells, addition of 15 mmol/l glucose leads to depolarization and oscillation of the cell membrane potential. Subsequent addition of H2O2 (1 mmol/l) in the presence of glucose was followed by a marked and rapid hyperpolarization of the cell membrane with suppression of the electrical activity. Accordingly, in slow whole-cell patch-clamp experiments (with nystatin in the pipette solution) H2O2 induced a marked increase of cell membrane conductance. Tolbutamide, a blocker of K+ ATP channels, only partially blocked the effect of H2O2 even at high concentrations. The H2O2-induced, tolbutamide-insensitive current component, however, was largely abolished by a high concentration of TEA+ (80 mmol/l) or BaCl2 (10 mmol/l). It is concluded that in B-cells H2O2 stimulates a K+ current and that this effect leads to marked hyperpolarization and reversal of glucose-induced oscillations of cell membrane potential.

Animals↗
PubMed1994

Significance of membrane repolarization and cyclic AMP changes in mouse pancreatic B-cells for the inhibition of insulin release by galanin.

It is unclear whether the inhibition of insulin release by galanin is entirely explained by an interference with the secretory process at a step distal to the rise of cytoplasmic Ca2+ and to the action of second messengers in pancreatic B-cells. In this study, normal mouse islets were used to assess the functional significance of the effects of galanin on other signalling pathways. In the presence of 15 mM glucose, galanin caused a small repolarization of the B-cell membrane and a sustained decrease in the Ca(2+)-dependent electrical activity. These changes were largely prevented by tolbutamide and by arginine. Under these conditions the concentration-dependence curve of galanin inhibition of insulin release was shifted to the right. The IC50 was increased 4-5-fold from a control value of 1.8 nM in the presence of glucose alone. This was not the case when insulin release was increased by cytochalasin B, an agent that acts on the filamentous cell web. We also evaluated the role of the changes in cAMP. To bypass the inhibition of adenylate cyclase produced by galanin, the islets were provided with exogenous, membrane permeant cAMP. When 10 mM glucose and 0.25 mM dibutyryl cAMP were combined, control insulin release was similar to that produced by 15 mM glucose alone. Neither the repolarization of the membrane nor the inhibition of insulin release by galanin were affected. A higher concentration of dibutyryl cAMP (0.5 mM) depolarized the B-cell membrane in the presence of 15 mM glucose and partially antagonized the effects of galanin on membrane potential and insulin release.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenylyl Cyclases↗
PubMed1994

Phylogenetic positions of novel aerobic, bacteriochlorophyll a-containing bacteria and description of Roseococcus thiosulfatophilus gen. nov., sp. nov., Erythromicrobium ramosum gen. nov., sp. nov., and Erythrobacter litoralis sp. nov.

We analyzed the 16S ribosomal DNAs of three obligately aerobic, bacteriochlorophyll a-containing bacteria, "Roseococcus thiosulfatophilus," "Erythromicrobium ramosum," and new isolate T4T (T = type strain), which was obtained from a marine cyanobacterial mat. "Roseococcus thiosulfatophilus" is a member of the alpha-1 subclass of the Proteobacteria and is moderately related to Rhodopila globiformis, Thiobacillus acidophilus, and Acidiphilium cryptum (level of sequence similarity, 90%). "Erythromicrobium ramosum" and isolate T4T are closely related to Erythrobacter longus and Porphyrobacter neustonensis (level of sequence similarity, 95%). These organisms are members of the alpha-4 subclass of the Proteobacteria. Strain T4T is a motile, red or orange bacterium. The major carotenoids are bacteriorubixanthinal and erythroxanthin sulfate. In vivo measurements revealed bacteriochlorophyll absorption maxima at 377, 590, 800, and 868 nm. Strain T4T grows in the presence of 5 to 96/1000 salinity and uses glucose, fructose, acetate, pyruvate, glutamate, succinate, and lactate as substrates. On the basis of its distinct phylogenetic position and phenotypic characteristics which are different from those of Erythrobacter longus, we propose that strain T4T should be placed in a new species of the genus Erythrobacter, Erythrobacter litoralis. The descriptions of "Roseococcus thiosulfatophilus" and "Erythromicrobium ramosum" are emended.

Bacteria, Aerobic↗
PubMed1993

Molecular cloning, sequence analysis and expression of the gene for catalase-peroxidase (cpeA) from the photosynthetic bacterium Rhodobacter capsulatus B10.

The gene encoding catalase-peroxidase was cloned from chromosomal DNA of Rhodobacter capsulatus B10. The nucleotide sequence of a 3.7-kb SacI-HindIII fragment, containing the catalase-peroxidase gene (cpeA) and its flanking regions were determined. A 1728-bp open reading frame, coding for 576 amino acid residues (molecular mass 61516 Da) of the enzyme, was observed. A Shine-Dalgarno sequence was found 5 bp upstream from the translational start site. The deduced amino acid sequence coincides with that of the amino terminus and of four peptides derived from trypsin digestion of the purified catalase-peroxidase of R. capsulatus B10. The amino acid sequence of R. capsulatus catalase-peroxidase shows interesting similarities to the amino acid sequences of the hydroperoxidases of Escherichia coli (42.7%) and Salmonella typhimurium (39.9%), the peroxidase of Bacillus stearothermophilus (32.1%) and the catalase-peroxidase of Mycobacterium intracellulare (42.2%). As shown by a cpeA::lacZ fusion in trans in R. capsulatus, the expression of the catalase-peroxidase gene is regulated by oxygen. The promoter of the cpeA gene was localized within 320 bp upstream of the ATG start codon.

Amino Acid Sequence↗
PubMed1993

Non-additivity of adrenaline and galanin effects on 86Rb efflux and membrane potential in mouse B-cells suggests sharing of common targets.

Adrenaline and galanin inhibit insulin release through strikingly similar mechanisms triggered by distinct receptors in pancreatic B cells. In this study we evaluated whether activation of alpha 2-adrenoceptors and galanin receptors use a common or only a similar transduction pathway. The membrane potential of B-cells was measured with intracellular microelectrodes and 86Rb efflux was monitored in normal mouse islets perifused with a medium containing 15 mM glucose. At a maximally effective concentration of 10 microM, adrenaline partially repolarized the membrane, inhibited but did not abolish electrical activity, and caused a decrease in 86Rb efflux (due to a lesser activation of Ca(2+)- and voltage-activated K+ channels). In the presence of 10 microM adrenaline, galanin had no effect on membrane potential, electrical activity and 86Rb efflux. Decreasing the concentration of glucose from 15 to 6 mM repolarized the B-cell membrane to the same extent as did adrenaline but did not prevent galanin from causing an additional hyperpolarization. In contrast to galanin, diazoxide, a selective opener of ATP-sensitive K+ channels still produced a small hyperpolarization and further decrease in 86Rb efflux when added at a low concentration (15 microM) to a medium containing 10 microM adrenaline. At a high concentration (250 microM), diazoxide repolarized the membrane to the resting potential and markedly accelerated 86Rb efflux both in the presence and absence of adrenaline. The non-additivity of the effects of adrenaline and galanin suggests that alpha 2-adrenoceptors and galanin receptors share common targets in pancreatic B-cells.

Animals↗
PubMed1992

Characterization of LHI- and LHI+ Rhodobacter capsulatus pufA mutants.

The NH2 termini of light-harvesting complex I (LHI) polypeptides alpha and beta of Rhodobacter capsulatus are thought to be involved in the assembly of the LHI complex. For a more detailed study of the role of the NH2-terminal segment of the LHI alpha protein in insertion into the intracytoplasmic membrane (ICM) of R. capsulatus, amino acids 6 to 8, 9 to 11, 12 and 13, or 14 and 15 of the LHI alpha protein were deleted. Additionally, the hydrophobic stretch of the amino acids 7 to 11 was lengthened by insertion of hydrophobic or hydrophilic amino acids. All mutations abolished the ability of the mutant strains to form a functional LHI antenna complex. All changes introduced into the LHI alpha protein strongly reduced the stability of its LHI beta partner protein in the ICM. The effects on the mutated protein itself, however, were different. Deletion of amino acids 6 to 8, 9 to 11, or 14 and 15 drastically reduced the amount of the LHI alpha protein inserted into the membrane or prevented its insertion. Deletion of amino acids 12 and 13 and lengthening of the stretch of amino acids 7 to 11 reduced the half-life of the mutated LHI alpha protein in the ICM in comparison with the wild-type LHI alpha protein. Under the selective pressure of low light, revertants which regained a functional LHI antenna complex were identified only for the mutant strain deleted of amino acids 9 to 11 of the LHI alpha polypeptide [U43 (pTPR15)]. The restoration of the LHI+ phenotype was due to an in-frame duplication of 9 bp in the pufA gene directly upstream of the site of deletion present in strain U43(pTPR15). The duplicated nucleotides code for the amino acids Lys, Ile, and Trp. Membranes purified from the revertants were different from that of the reaction center-positive LHI+ LHII- control strain U43(pTX35) in doubling of the carotenoid content and increase of the size of the photosynthetic unit. By separating the reaction center and LHI complexes of the revertants by native preparative gel electrophoresis, we confirmed that the higher amount of carotenoids was associated with the LHI proteins.

Amino Acid Sequence↗
PubMed1992

Ionic, electrical, and secretory effects of inhibitors of arachidonic acid metabolism in mouse pancreatic beta-cells.

Mouse islets were used to study the effects of inhibitors of cyclooxygenase and lipoxygenase pathways on insulin release, ionic fluxes, and beta-cell membrane potential. The cyclooxygenase inhibitors, Na-salicylate and Na-acetylsalicylate, potentiated glucose-induced insulin release, despite a decrease in Ca influx evidenced by inhibition of the Ca-dependent electrical activity in beta-cells and 45Ca efflux from islets perifused with a medium containing Ca. This paradox can probably be explained by a mobilization of intracellular Ca (acceleration of 45Ca efflux in the absence of Ca) with subsequent activation of K+ channels (acceleration of 86Rb efflux) and repolarization of the membrane. These effects of salicylate could not be ascribed to a change in intracellular pH because they were not mimicked by 2-Cl-benzoate, which has a similar pK as salicylate but increased insulin release by stimulating Ca influx in beta-cells. Among the other cyclooxygenase inhibitors tested, indomethacin caused a slight potentiation of insulin release accompanied by marginal increases in 45Ca efflux and electrical activity, whereas flurbiprofen and ibuprofen were ineffective. Among the lipoxygenase inhibitors, compound BW 755c reversibly decreased glucose-induced insulin release by inhibiting Ca influx in beta-cells, but nordihydroguaiaretic acid had no effect. Inhibitors of arachidonic acid metabolism have effects on ionic fluxes and beta-cell membrane potential, which may explain some of the changes in insulin release they produce.

4,5-Dihydro-1-(3-(trifluoromethyl)phenyl)-1H-pyraz↗
PubMed1992

[Malignant tumor of the autonomic nervous system of the stomach (GAN-tumor)--case report of a new entity].

Gastrointestinal autonomic nerve (GAN)-tumors are extremely rare. So far seven cases of intestinal and four of gastric GAN-tumors were reported. GAN-tumors, also termed plexosarcomas, arise from autonomic nervous system plexuses of the gastrointestinal tract such as those of Meissner or Auerbach. We report a case of a metastatic gastric GAN-tumor in a 40-year-old woman. A small, 1 cm in diameter, submucosal plexosarcoma located in the posterior gastric wall and a 1.5 kg, 23 x 15 x 11-cm metastasis located retroperitoneally behind the stomach between liver, spleen and pancreas without discernable invasion of any of these organs were found. En-bloc resection of the retroperitoneal mass, the spleen, the pancreatic tail, and a part of the posterior gastric wall adhering to the mass were performed. In addition, lymph node metastases in splenic hilum were noted, and resected. In CT scan liver metastases were detectable fourteen months after surgery. The diagnosis is based on light microscopical, ultrastructural, and immunhistochemical analyses. The prognosis of GAN-tumors is fatal. In spite of radical excision 8 of 11 reported patients died few month after surgery while local recurrences and/or metastases in regional lymph nodes and in the liver were found. The response to chemotherapy was poor.

Adult↗
PubMed1991

Vanadate stimulation of insulin release in normal mouse islets.

The effects of vanadate (Na3VO4) on pancreatic B-cell function were studied in normal mouse islets. Vanadate did not affect basal insulin release but potentiated the effect of 7-30 mM glucose at concentrations of 0.1-1 mM. This effect was progressive and slowly reversible. It was abolished by omission of extracellular Ca2+ but unaffected by blockers of adrenergic or muscarinic receptors. Comparison of the changes in membrane potential, 86Rb efflux and 45Ca efflux that vanadate and ouabain produced in B-cells made it possible to exclude the hypothesis that vanadate increases insulin release by blocking the sodium pump. Vanadate was also without effect on cAMP levels. On the other hand, it markedly changed the characteristics of the Ca(2+)-dependent electrical activity and of the oscillations of cytoplasmic Ca2+ recorded in B-cells stimulated by 15 mM glucose. In the steady state, Ca2+ influx was increased by vanadate, and this resulted in a rise in cytoplasmic Ca2+. The exact mechanisms underlying these changes could not be established but a blockade of K channels was excluded. In the presence of LiCl, vanadate markedly increased inositol phosphate levels in islet cells. This effect was attenuated but not suppressed by omission of Ca2+. A small increase in inositol bisphosphate was still produced by vanadate in the absence of LiCl. These results suggest that vanadate both stimulates phosphoinositide breakdown and inhibits inositol phosphate degradation. In conclusion, vanadate does not induce insulin release, but markedly potentiates the stimulation by glucose. This property is not due to an inhibition of the sodium pump or to a rise in cAMP concentration. It results from a complex interplay between changes in B-cell membrane potential, phosphoinositide metabolism and Ca2+ handling.

Animals↗
PubMed1991

Possible role of the highly conserved amino acids Trp-8 and Pro-13 in the N-terminal segment of the pigment-binding polypeptide LHI alpha of Rhodobacter capsulatus.

Trp-8 and Pro-13 of the Rhodobacter capsulatus light-harvesting (LH) I alpha polypeptide are highly conserved among LHI and LHII alpha proteins of several species of the Rhodospirillaceae. Exchange of Trp-8 and Pro-13 to other amino acyl residues similar in structure and/or hydrophobicity indicates that Trp-8 is involved in the insertion of the LHI alpha polypeptide into the intracytoplasmic membrane (ICM). Pro-13, however, seems not to participate in the integration process of the LHI alpha protein but seems to be important for stable insertion of the LHI beta partner protein in the ICM.

Amino Acid Sequence↗