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Biomedical subjects

C Eder

Publications and source records attributed to C Eder.

At least 37 records · Page 2Linked to original sources
PubMed2000

Upregulation of Kv1.3 K(+) channels in microglia deactivated by TGF-beta.

Microglial activation is accompanied by changes in K(+) channel expression. Here we demonstrate that a deactivating cytokine changes the electrophysiological properties of microglial cells. Upregulation of delayed rectifier (DR) K(+) channels was observed in microglia after exposure to transforming growth factor-beta (TGF-beta) for 24 h. In contrast, inward rectifier K(+) channel expression was unchanged by TGF-beta. DR current density was more than sixfold larger in TGF-beta-treated microglia than in untreated microglia. DR currents of TGF-beta-treated cells exhibited the following properties: activation at potentials more positive than -40 mV, half-maximal activation at -27 mV, half-maximal inactivation at -38 mV, time dependent and strongly use-dependent inactivation, and a single channel conductance of 13 pS in Ringer solution. DR channels were highly sensitive to charybdotoxin (CTX) and kaliotoxin (KTX), whereas alpha-dendrotoxin had little effect. With RT-PCR, mRNA for Kv1.3 and Kir2.1 was detected in microglia. In accordance with the observed changes in DR current density, the mRNA level for Kv1.3 (assessed by competitive RT-PCR) increased fivefold after treatment of microglia with TGF-beta.

Animals↗
PubMed2000

Identification of the Arabidopsis thaliana flavonoid 3'-hydroxylase gene and functional expression of the encoded P450 enzyme.

The phenylpropanoid pathway results in the synthesis of thousands of compounds, including flavonoids like flavonols, anthocyanidins and tannins. In Arabidopsis thaliana, the lack of tannins in the seed coat (testa) causes the transparent testa (tt) phenotype. In the present study, we identified the gene responsible for the tt7 mutation. We show that TT7 encodes the enzyme flavonoid 3'-hydroxylase (F3'H), and demonstrate that this P450-dependent monooxygenase has F3'H activity. The availability of the AtF3'H gene and promoter sequence will allow us to study the coregulation of a complete set of flavonol and anthocyanidin biosynthesis genes in A. thaliana, and makes in vitro synthesis of hydroxylated flavonoids more feasible.

Amino Acid Sequence↗
PubMed1999

GLI gene expression in bone and soft tissue sarcomas of adult patients correlates with tumor grade.

The GLI gene encodes a transcription factor harboring five zinc finger motifs that bind to DNA in a sequence-specific manner. The gene was originally identified because of its amplification in a human glioblastoma, and previous studies have shown it to be amplified in a significant proportion of mesenchymal tumors, such as childhood sarcomas. Here we evaluate GLI gene expression in bone and soft tissue sarcomas of adult patients. Samples from 40 patients (37 sarcomas and 3 benign mesenchymal tumors) and samples of 15 normal mesenchymal tissues were examined for GLI gene amplification and expression by Southern hybridization, reverse transcription-PCR of tissue RNA, and immunohistochemistry, using a new polyclonal GLI antibody developed against an epitope outside of the zinc finger region. In contrast to childhood sarcomas, amplification of the GLI gene was not observed in sarcomas of adult patients. Although GLI gene expression in sarcomas was significantly higher than that in normal mesenchymal tissues (P < 0.0001), the levels were very variable. Attempts to correlate the expression data with different pathophysiological parameters only showed a significant relationship to tumor grade. Based on these data, increased levels of GLI gene expression may be indicative of the aggressiveness of the tumor.

Adult↗
PubMed1999

Voltage-gated proton currents in microglia of distinct morphology and functional state.

Whole-cell patch-clamp measurements were performed to investigate voltage-gated proton currents (I(PR)) in cultured murine microglia of distinct morphology and functional state. We studied I(PR) in ameboid microglia of untreated cultures, in ameboid microglia which had been activated by lipopolysaccharide, and in ramified microglia which had been exposed to astrocyte-conditioned medium. Proton currents of these three microglia populations did not differ regarding their activation threshold or the voltage dependence of steady-state activation. Moreover, pharmacological properties of I(PR) were similar: proton currents were sensitive to extracellularly applied Zn2+ or La3+, and could be abolished by each of those at a concentration of 100 microM. In the presence of extracellular Na+, I(PR) was decreased to a similar small extent due to activity of the Na+/H+ exchanger in all microglial populations. In contrast, proton currents of microglia differed between the three cell populations with respect to their current density and their time-course of activation: in comparison with untreated microglia, the current density of I(PR) was reduced by about 50% in microglia after their treatment with either lipopolysaccharide or astrocyte-conditioned medium. Moreover, I(PR) activated significantly more slowly in cells exposed to lipopolysaccharide or astrocyte-conditioned medium than in untreated cells. It can be concluded that the distinct H+ current characteristics of the three microglial populations do not correlate with the functional state of the cells.

Animals↗
PubMed1999

New alkaloids from the indopacific sponge Stylissa carteri.

Two samples of the marine sponge Stylissa carteri collected in Indonesia yielded two new bromopyrrole alkaloids: debromostevensine (1) and debromohymenin (2), as well as nine other known congeners (3-11). The structures of the new compounds were unambiguously established on the basis of their NMR and mass spectra.

Alkaloids↗
PubMed1999

Staurosporine derivatives from the ascidian eudistoma toealensis and its predatory flatworm pseudoceros sp

Two new indolocarbazole alkaloids, 3-hydroxy-3'-demethoxy-3'-hydroxystaurosporine (5) and 11-hydroxy-4'-N-demethylstaurosporine (6), were isolated from the marine ascidian Eudistoma toealensis and its predator, the marine flatworm Pseudoceros sp. In addition, five known derivatives were isolated in their protonated states, which caused the pyran-ring system to adopt a boat conformation. The structures were determined by 1D and 2D homonuclear and (1)H-detected heteronuclear NMR spectroscopy and from comparisons with published data. The heteronuclear correlations were necessary to establish reliable data for the structure elucidation.

Journal Article↗
PubMed1999

New bromopyrrole alkaloids from the Indopacific sponge Agelas nakamurai.

Two new dimeric bromopyrrole alkaloids, nakamuric acid (1) and its corresponding methyl ester (2), have been isolated from the Indopacific sponge Agelas nakamurai along with the known metabolites sceptrin (3), debromosceptrin (4), and ageliferin (5). Their structures were identified by analysis of spectral data. All compounds inhibited the growth of several Gram-positive and Gram-negative bacteria in the agar plate diffusion assay.

Alkaloids↗
PubMed1999

Morphological, immunophenotypical and electrophysiological properties of resting microglia in vitro.

Morphological, immunophenotypical and electrophysiological properties were investigated in isolated cultured murine microglia before and after exposure to astrocyte-conditioned medium (ACM). Following application of ACM, microglial cells underwent a dramatic shape transformation from an amoeboid appearance to a ramified morphology. In parallel to morphological changes, a downregulation of macrophage surface antigens was observed in microglia exposed to ACM. Staining intensities for major histocompatibility complex (MHC) class II molecules and for the adhesion molecules leukocyte function-associated antigen-1 (LFA-1) and intercellular adhesion molecule-1 (ICAM-1) were significantly decreased in ramified microglia 5 days after exposure to ACM. In microglial cells treated daily with ACM over a period of 5 days, the smallest staining intensities for all surface antigens as well as the smallest ramification index as a measure for the highest degree of ramification were determined. In addition, upregulation of delayed rectifier K + currents was observed in microglia exposed to ACM for 1 day or treated daily with ACM for 5 days. In contrast, untreated amoeboid microglia or ramified microglia analysed 5 days after exposure to ACM did not express delayed rectifier K + currents. Analyses of the resting membrane potential and expression levels and properties of inward rectifier K + currents did not reveal any differences between untreated and ACM-treated microglia. It is suggested that electrophysiological properties of microglia do not strongly correlate with the morphology or the immunophenotype of microglial cells.

Animals↗
PubMed1998

A nongenomic mechanism for progesterone-mediated immunosuppression: inhibition of K+ channels, Ca2+ signaling, and gene expression in T lymphocytes.

The mechanism by which progesterone causes localized suppression of the immune response during pregnancy has remained elusive. Using human T lymphocytes and T cell lines, we show that progesterone, at concentrations found in the placenta, rapidly and reversibly blocks voltage-gated and calcium-activated K+ channels (KV and KCa, respectively), resulting in depolarization of the membrane potential. As a result, Ca2+ signaling and nuclear factor of activated T cells (NF-AT)-driven gene expression are inhibited. Progesterone acts distally to the initial steps of T cell receptor (TCR)-mediated signal transduction, since it blocks sustained Ca2+ signals after thapsigargin stimulation, as well as oscillatory Ca2+ signals, but not the Ca2+ transient after TCR stimulation. K+ channel blockade by progesterone is specific; other steroid hormones had little or no effect, although the progesterone antagonist RU 486 also blocked KV and KCa channels. Progesterone effectively blocked a broad spectrum of K+ channels, reducing both Kv1.3 and charybdotoxin-resistant components of KV current and KCa current in T cells, as well as blocking several cloned KV channels expressed in cell lines. Progesterone had little or no effect on a cloned voltage-gated Na+ channel, an inward rectifier K+ channel, or on lymphocyte Ca2+ and Cl- channels. We propose that direct inhibition of K+ channels in T cells by progesterone contributes to progesterone-induced immunosuppression.

Amino Acid Sequence↗
PubMed1998

Involvement of stretch-activated Cl- channels in ramification of murine microglia.

A stretch-activated Cl- current (ICl) was investigated in cultured murine microglia using the whole-cell configuration of the patch-clamp technique. After application of membrane stretch, a Cl- current appeared within seconds, and its amplitude increased further within 3-8 min. ICl underwent rundown, which was prevented by addition of 4 mM ATP to the intracellular perfusing solution. The stretch-activated Cl- current exhibited outward rectification and did not show any voltage-dependent gating. Lowering the concentration of extracellular Cl- from 142 to 12 mM by equimolar substitution of Cl- with gluconate shifted the reversal potential of ICl by 41.6 +/- 1.8 mV in the depolarizing direction. 4, 4'-Diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) and 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid (SITS) blocked ICl in a voltage- and time-dependent manner. At a test potential of +40 mV, a half-maximal blockade at 16.1 microM DIDS and at 71.0 microM SITS was determined for ICl. At a concentration of 200 microM, 5-nitro-2-(3-phenylpropylamino)benzoic acid or flufenamic acid blocked ICl by 88% and 75%, respectively. Each of these four Cl- channel blockers reversibly inhibited the ramification process of microglia, whereas blockers of voltage-gated Na+ and K+ channels did not affect the transformation of microglia from their ameboid into the ramified phenotype. It is suggested that in microglia functional stretch-activated Cl- channels are required for the induction of ramification but not for maintaining the ramified shape.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1998

Changes in proton currents in murine microglia induced by cytoskeletal disruptive agents.

Voltage-gated proton currents (IPR) were investigated in cultured murine microglia using the whole-cell configuration of the patch clamp technique. At a gradient of 1.5 between intracellular (pHi = 6.0) and extracellular pH (pHo = 7.5) values, outward IPR were detected at depolarizing potentials, while the activation threshold of IPR was -40 mV. Time-dependent activation of IPR was fitted by a single exponential with a time constant of 661 ms at +40 mV. An increase in the activation time constant of IPR was seen after exposure of microglia to the cytoskeletal disruptive agents cytochalasin D or colchicine. Moreover, the current density of IPR was significantly reduced by 49% in cells treated with cytochalasin D and by 27% in cells treated with colchicine for 24 h. In contrast, voltage-dependence of steady-state activation of IPR was unchanged after disruption of the cytoskeleton. Exposure of microglia to the cytoskeletal stabilizers phalloidin and taxol did not affect IPR of microglia.

Action Potentials↗
PubMed1998

Bioactive pyridoacridine alkaloids from the micronesian sponge Oceanapia sp.

The Micronesian sponge Oceanapia sp. afforded three pyridoacridine alkaloids: the known compounds kuanoniamine C (1) and kuanoniamine D (2), as well as the new N-deacyl derivative (3) of the kuanoniamines. Compounds 1 and 2 exhibited insecticidal activity toward neonate larvae of the polyphagous pest insect Spodoptera littoralis (LC50 of 156 and 59 ppm, respectively), when incorporated into artificial diet. Both compounds also showed toxicity in the brine shrimp lethality test with a LC50 of 37 micrograms/mL (compound 1) and 19 micrograms/mL (compound 2), respectively. The N-deacyl derivative did not show any remarkable effect in both bioassays. Cytotoxcity of the alkaloids was studied in vitro, using two human cell lines. The new derivative (3) appeared to be active in the same range of concentrations as kuanoniamine C (1) and D (2). The IC50 of 3 was 1.2 micrograms/mL toward HeLa cells and 2.0 micrograms/mL toward MONO-MAC 6 cells. In receptor binding assays compound 2 showed affinity to A1- and A2A-adenosine receptors with Ki values of 2.94 and 13.7 microM, respectively. Compound 1 was less active than compound 2, whereas compound 3 showed no affinity toward adenosine receptors. In addition, compounds 1-3 exhibited moderate affinity to benzodiazepine binding sites of GABAA receptors.

Acridines↗
PubMed1998

Ion channels in microglia (brain macrophages).

Microglia are immunocompetent cells in the brain that have many similarities with macrophages of peripheral tissues. In normal adult brain, microglial cells are in a resting state, but they become activated during inflammation of the central nervous system, after neuronal injury, and in several neurological diseases. Patch-clamp studies of microglial cells in cell culture and in tissue slices demonstrate that microglia express a wide variety of ion channels. Six different types of K+ channels have been identified in microglia, namely, inward rectifier, delayed rectifier, HERG-like, G protein-activated, as well as voltage-dependent and voltage-independent Ca2+-activated K+ channels. Moreover, microglia express H+ channels, Na+ channels, voltage-gated Ca2+ channels, Ca2+-release activated Ca2+ channels, and voltage-dependent and voltage-independent Cl- channels. With respect to their kinetic and pharmacological properties, most microglial ion channels closely resemble ion channels characterized in other macrophage preparations. Expression patterns of ion channels in microglia depend on the functional state of the cells. Microglial ion channels can be modulated by exposure to lipopolysaccharide or various cytokines, by activation of protein kinase C or G proteins, by factors released from astrocytes, by changes in the concentration of internal free Ca2+, and by variations of the internal or external pH. There is evidence suggesting that ion channels in microglia are involved in maintaining the membrane potential and are also involved in proliferation, ramification, and the respiratory burst. Further possible functional roles of microglial ion channels are discussed.

Adult↗
PubMed1997

Developmental changes of inward rectifier currents in neurons of the rat entorhinal cortex.

A slice preparation was used to investigate inward rectifier currents (I(H)) of entorhinal cortex (EC) neurons. Using the whole-cell configuration of the patch-clamp technique, I(H) was studied in pyramidal cells from layer IV of the rat EC and in stellate cells from layer II of the EC. Inward rectifier currents were analyzed in neurons of newborn (P1-3), juvenile (P8-14) and adult (>P28) rats. Pyramidal cells of juvenile rats possessed a significantly larger current density of I(H) than pyramidal cells of newborn rats, whereas no differences in the current density of I(H) were found between pyramidal neurons of juvenile and of adult animals. In contrast, the current density of I(H) of stellate cells was significantly increased in juvenile rats compared with newborn rats as well as in adult rats compared with juvenile rats. Moreover, in adult rats the current density of I(H) was larger in stellate cells than in pyramidal cells, whereas opposite data were obtained in juvenile animals.

Age Factors↗
PubMed1997

Distinct soluble astrocytic factors induce expression of outward K+ currents and ramification of brain macrophages.

Isolated cultured murine brain macrophages (BM) were treated with supernatants of enriched astrocytic cultures. The astrocyte-conditioned medium (ACM) induced ramification of BM. In parallel, BM expressed voltage-gated outward K+ currents (I(K)) during the first 2 days after the application of ACM. However, in ramified BM which were treated once with ACM, I(K) disappeared 5 days after that treatment. In contrast, BM expressed I(K) over a period of more than 5 days when cells were treated daily with ACM. A blockade of I(K) by charybdotoxin or by kaliotoxin did not inhibit ramification of the cells. Furthermore, after application of low-concentrated ACM BM exhibited I(K) but did not change their morphology. It is suggested that in murine BM the ramification and the expression of I(K) are induced by distinct soluble factors derived from astrocytes.

Animals↗
PubMed1997

Effects of colony-stimulating factors on voltage-gated K+ currents of bone marrow-derived macrophages.

Murine bone marrow macrophages had been grown using either macrophage colony-stimulating factor (M-CSF) or granulocyte/macrophage colony-stimulating factor (GM-CSF). The influence of these cytokines on appearance and properties of voltage-gated potassium currents was studied in the macrophages derived from both cultures. Potassium currents were recorded using the patch clamp technique in the whole cell configuration. Two different types of currents were investigated-inward rectifying (IKi) and outward K+ currents (IKo). Macrophages isolated from M-CSF or GM-CSF-supplemented culture exhibited either one of them or both currents simultaneously. However, a distinct distribution of these currents was observed: Whereas in the majority of M-CSF-cultured macrophages IKi were detected (94%; n = 63), development of macrophages with GM-CSF resulted in the expression of IKo in a large number of cells (97%; n = 69). When both currents were expressed together, in M-CSF-treated macrophages the amplitudes of most IKi were larger than those of IKo. Opposite data were measured in the majority of GM-CSF-cultured macrophages.

Animals↗
PubMed1997

Pharmacological properties of Ca2+-activated K+ currents of ramified murine brain macrophages.

Using the whole-cell configuration of the patch clamp technique, calcium-activated potassium currents (I(K,Ca)) were investigated in ramified murine brain macrophages. In order to induce I(K,Ca) the intracellular concentration of nominal free Ca2+ was adjusted to 1 microM. The Ca2+-activated K+ current of brain macrophages did not show any voltage dependence at test potentials between -120 and +30 mV. A tenfold change in extracellular K+ concentration shifted the reversal potential of I(K,Ca) by 51 mV. The bee venom toxin apamin applied at concentrations of up to 1 microM did not affect I(K,Ca). Ca2+-activated K+ currents of ramified brain macrophages were highly sensitive to extracellularly applied charybdotoxin (CTX). The half-maximal effective concentration of CTX was calculated to be 4.3 nM. In contrast to CTX, the scorpion toxin kaliotoxin did not inhibit I(K,Ca) at concentrations between 1 and 50 nM. Tetraethylammonium (TEA) blocked 8.0% of I(K,Ca) at a concentration of 1 mM, whereas 31.4% of current was blocked by 10 mM TEA. Several inorganic polyvalent cations were tested at a concentration of 2 mM for their ability to block I(K,Ca). La3+ reduced I(K,Ca) by 72.8%, whereas Cd2+ decreased I(K,Ca) by 17.4%; in contrast, Ni2+ did not have any effect on I(K,Ca). Ba2+ applied at a concentration of 1 mM reduced I(K,Ca) voltage-dependently at hyperpolarizing potentials.

Animals↗