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C Eder

Publications and source records attributed to C Eder.

At least 55 records · Page 3Linked to original sources
PubMed1997

Age-dependent variations in potassium sensitivity of A-currents in rat hippocampal neurons.

Hippocampal pyramidal neurons were either cultured from prenatal rats or acutely isolated from the brain of newborn and juvenile rats. The influence of lowering the concentration of the extracellular potassium concentration ([K+]o) on isolated fast transient outward K+ currents (I(A)) was studied in these neurons using the patch clamp technique in the whole cell configuration. With respect to the response of I(A) to lowering [K+]o, three types of cells were observed. The first subpopulation of neurons was characterized by a complete suppression of I(A) over the whole voltage range under potassium-free solutions (type A neurons). A second proportion of cells showed an increase of I(A) at test pulses below -0 mV and a decrease of I(A) at voltages above -0 mV (type B neurons). In a third group of neurons, amplitudes of I(A) increased at all potentials tested during omission of potassium ions from the extracellular superfusate (type C neurons). Whereas type A and type B neurons were preferentially found in freshly plated cultures and newborn rats, the majority of type C cells was detected in long-term cultures and in animals of older ages. Thus, hippocampal A-currents lose their sensitivity to extracellular potassium ions during early ontogenesis.

Aging↗
PubMed1996

Blockade of voltage-gated outward K+ currents of ramified murine microglia by scorpion peptide toxins.

Microglial cells were cultured from murine neonatal brain. Ramification of isolated microglia could be induced by the application of astrocyte-conditioned medium (ACM). Voltage-gated outward potassium currents (IK) were measured in ramified microglial cells 12-24 h after their treatment with ACM. The effects of the specific K+ channel blockers charybdotoxin (CTX), noxiustoxin (NTX) and kaliotoxin (KTX) on IK of ramified microglia were studied. All these peptide toxins blocked IK in a concentration-dependent manner, while showing a high sensitivity for IK. A half-maximal effective concentration (IC50) of CTX was estimated to be 1.13 nM, while IC50 values of 1.24 nM and of 0.81 nM were calculated for KTX and for NTX, respectively. In contrast, dendrotoxin (DTX) did not show any effect on IK. It is suggested that ramified microglial cells express outward K+ currents exhibiting pharmacological properties similar to that of outward K+ currents in cytokine-activated ameboid microglia.

Animals↗
PubMed1996

Modulation of A-currents by [K+]o in acutely isolated pyramidal neurones of juvenile rat entorhinal cortex and hippocampus.

Pyramidal neurones of the entorhinal cortex and of hippocampal areas CA1 and CA3 were acutely isolated from juvenile rats. The effect of lowering the concentration of extracellular potassium ions ([K+]o) on fast transient A-currents (IA) was studied using the whole-cell configuration of the patch-clamp technique. Upon lowering [K+]o from 5.4 to 0 mM amplitudes of IA in all pyramidal neurones were reduced only at test potentials positive to -20 mV, but were increased at potentials below -20 mV. Omission of magnesium ions from the intracellular perfusate resulted in an increase of IA in external K+-free solution at any potential tested. Moreover, when [K+]o was reduced steady-state activation and inactivation curves of IA were shifted in the hyperpolarizing direction.

Animals↗
PubMed1996

Proton modulation of outward K+ currents in interferon-gamma-activated microglia.

Whole-cell outward potassium currents (IK) were measured in interferon (IFN)-gamma-activated cultured murine microglial cells. Acidification of the external milieu moved the threshold of activation of IK in a depolarizing direction, while alkalinization showed the opposite effect. A shift of more than 20 mV of the steady-state activation and inactivation curves of IK in hyperpolarizing direction was measured when pH was changed from 5.8 to 7.8. The time-dependent inactivation of IK was slower when superfusing cells with acid solutions than with alkaline ones. In contrast, variations in the pH of the intracellular solution did not alter kinetics of IK. However, alkalinization of the internal solution from a pH of 5.8 to 7.8 led to a two-fold increase in the current density of IK.

Animals↗
PubMed1996

Potassium currents in acutely isolated neurons from superficial and deep layers of the juvenile rat entorhinal cortex.

Using the whole-cell configuration of the patch-clamp technique, outward K+ currents were recorded from acutely isolated stellate cells from superficial layers, and pyramidal cells from deep layers, of the entorhinal cortex of juvenile rats. In both cell types a fast transient and a slowly inactivating outward K+ current were obtained. Whereas the fast transient current (IA) activated at potentials beyond -50 mV, the activation threshold of the slowly inactivating current (IK) was measured at -40 mV in stellate and pyramidal cells. In stellate cells a half-maximal inactivation was estimated for IA at -80.4 mV and for IK at -74.6 mV, and in pyramidal cells at -81.1 mV and -71.8 mV, respectively. IK of both cell types were reduced by tetraethylammonium (TEA) in a concentration-dependent manner. IC50 values were 0.8 mM TEA for stellate cells and 1.1 mM TEA for pyramidal cells. Superfusion of 4-aminopyridine resulted in a reduction of the amplitudes of IA and IK as well as in an acceleration of the inactivation time constants of IA. Extracellularly applied dendrotoxin did not have any effect on entorhinal cortex K+ currents. In summary, kinetic and pharmacological properties of IA as well as of IK are rather similar in superficial-layer stellate and deep-layer pyramidal cells acutely isolated from the entorhinal cortex of juvenile rats.

4-Aminopyridine↗
PubMed1996

Macronucleus structure and macronucleus development in hypotrichous ciliates.

In the course of macronuclear development of the hypotrichous ciliates all genetic information not required for normal growth of the cell is removed from the new macronucleus. This differentiation process involves DNA-splicing, excision of transposons, DNA-fragmentation, selective gene amplification and telomere addition. Since many of the processes observed during macronuclear development, such as DNA-transposition, DNA-rearrangement or selective DNA-amplification, may occur in differentiating cells of higher organisms, this biological system provides an unusual opportunity to study the ways in which DNA-sequences can be manipulated in a differentiating cell.

Animals↗
PubMed1995

Voltage-gated K+ currents of mouse dendritic cells.

Dendritic cells (DC) were enriched from murine spleen by exploring their intermediate density and transient weak adherence. The isolated population contained excellent antigen presenting cells with high surface expression of major histocompatibility complex (MHC) class II determinants thus exhibiting crucial immunofunctional characteristics of DC. Cells of typical dendritic shape were electrophysiologically analysed using the whole cell configuration of the patch clamp technique. All 26 cells expressed only outward K+ currents comparable to those detected in cytokine-activated microglia. Co-purified splenic macrophages, in contrast, displayed an inward rectifying K+ current.

Animals↗
PubMed1995

The processing of macronuclear-destined DNA sequences microinjected into the macronuclear anlagen of the hypotrichous ciliate Stylonchia lemnae.

We describe the construction of a vector carrying the micronuclear versions of two macronuclear DNA molecules, one of which was modified by the insertion of a polylinker sequence. This vector was injected into the polytene chromosomes of the developing macronucleus of Stylonychia and its processing during further macronuclear development and its fate in the mature macronucleus were analyzed. In up to 30% of injected cells the modified macronuclear DNA sequence could be detected. While the internal eliminated sequences (IES) present in the macronuclear precursor DNA sequence are still retained in the mature macronucleus, the modified macronuclear DNA sequence is correctly cut out from the vector, telomeres are added de novo and it is stably retained in the macronucleus during vegetative growth of the cells. This vector system represents an experimental system that allows the identification of DNA sequences involved in the processing of macronuclear DNA sequences during macronuclear development.

Animals↗
PubMed1995

Properties of voltage-gated potassium currents of microglia differentiated with granulocyte/macrophage colony-stimulating factor.

Voltage-gated whole-cell currents were recorded from cultured microglial cells which had been developed in the presence of the macrophage/microglial growth factor granulocyte/macrophage colony-stimulating factor. Outward K+ currents (IK) were most prominent in these cells. IK could be activated at potentials more positive than -40 mV. Half-maximal activation of IK was achieved at -13.8 mV and half-maximal inactivation of IK was determined at -33.8 mV. The recovery of IK from inactivation was described by a time constant of 7.9 sec. For a tenfold change in extracellular K+ concentration the reversal potential of IK shifted by 54 mV. Extracellularly applied 10 mM tetraethylammonium chloride reduced IK by about 50%, while 5 mM 4-aminopyridine almost completely abolished IK. Several divalent cations (Ba2+, Cd2+, Co2+, Zn2+) reduced current amplitudes and shifted the activation curve of IK to more positive values. Charybdotoxin (IC50 = 1.14 nM) and noxiustoxin (IC50 = 0.89 nM) blocked IK in a concentration-dependent manner, whereas dendrotoxin and mast cell degranulating peptide had no effect on the current amplitudes. The outward K+ currents showed a frequency dependence when depolarizing pulses were applied at a frequency of 1 Hz. A frequency-independent outward current (IK') characterized by the same activation behavior as IK was detected. IK' was blocked completely by 10 nM charybdotoxin or by 10 nM noxiustoxin. In contrast to its effect on IK, 10 mM tetraethylammonium chloride did not reduce IK'.

4-Aminopyridine↗
PubMed1995

Properties of voltage-gated currents of microglia developed using macrophage colony-stimulating factor.

Microglia were isolated from a murine neonatal brain cell culture in which their development had been stimulated by supplementation with the macrophage/microglial growth factor macrophage colony-stimulating factor (M-CSF). Using the whole-cell configuration of the patch-clamp technique, voltage-gated membrane currents were recorded from these microglial cells. Hyperpolarization induced inward rectifying K+ currents, as described for microglia from untreated cultures. These currents activated negative to the K+ equilibrium potential and, with a strong hyperpolarization, displayed time-dependent inactivation. The inactivation was abolished when extracellular NaCl was replaced by N-methyl-D-glucamine (NMG), thereby indicating a partial block of this K+ conductance by Na+. Inward rectifying currents were also blocked by extracellularly applied Cs+ or Ba2+. They were slightly diminished following treatment with extracellular tetraethylammonium chloride (TEA) but were not affected by 4-aminopyridine (4-AP). Upon long lasting depolarizing voltage pulses to potentials positive to 0 mV, the cells exhibited a slowly activating H+ current which could be reduced by application of inorganic polyvalent cations (Ba2+, Cd2+, Co2+, La3+, Ni2+, Zn2+) as well as by 4-AP or TEA. Based on their kinetics and pharmacological characteristics, both currents detected on M-CSF-grown microglia are suggested to correspond to the inward rectifier and the H+ current of macrophages.

Animals↗
PubMed1995

Cytokine-dependent K+ channel profile of microglia at immunologically defined functional states.

Microglia were enriched in brain cell cultures from newborn mice as a result of supplementation with the growth factors macrophage colony-stimulating factor or granulocyte/macrophage colony-stimulating factor. When separately administered these two cytokines promote the outgrowth of loosely adherent cells with similar morphology which stained positive for CD11b and nonspecific esterase. Microglial cells isolated from both types of culture were electrophysiologically characterized using the whole cell configuration of the patch-clamp technique. Different resting membrane potentials were measured. In response to hyperpolarizing and depolarizing voltage commands 68 of 91 macrophage colony-stimulating factor-cultured microglial cells exhibited only an inward rectifying potassium current. By contrast, an outward potassium current was observed on 71 of 95 granulocyte/macrophage colony-stimulating factor-grown cells. Parallel testing of their capability for antigen presentation proved the activated functional state of these microglial cells. They induce antigen-specific T cell response without prior stimulus. In comparison, cells developed with macrophage colony-stimulating factor failed to present antigen. In such resting microglia a short-term treatment with granulocyte/macrophage colony-stimulating factor or interferon-gamma provoked a strong appearance of outward potassium currents, however, only the interferon-gamma-trigger resulted in efficient antigen presentation. The differential induction of both functional parameters suggests the detection of outward potassium currents to provide an electrophysiological activation marker of microglia which is subjected to cytokine regulation but not compellingly linked to antigen presentation.

Animals↗
PubMed1994

Current density analysis of outward currents in acutely isolated rat entorhinal cortex cells.

Entorhinal cortex stellate and pyramidal cells were acutely isolated from juvenile rats. Using the whole-cell configuration of the patch-clamp method outward potassium currents were recorded. A fast transient A-current and a sustained outward current could be measured in both stellate and pyramidal cells. The A-current density was significantly larger in pyramidal cells than in stellate cells. In contrast, stellate cells possessed a larger current density of the delayed rectifier current as well as the Ca2+ activated K+ current than pyramidal cells. Moreover, superficial stellate cells exhibited large delayed rectifier currents and only small A-currents while entorhinal cortex deep layer pyramidal cells displayed larger A-currents than delayed rectifier currents.

Animals↗
PubMed1993

The processing of macronuclear DNA sequences during macronuclear development of the hypotrichous ciliate Stylonychia lemnae.

The organization of two macronuclear DNA sequences in the polytene chromosomes of the hypotrichous ciliate Stylonychia lemnae and their processing from the micronucleus via the polytene chromosome stage up to the macronucleus was analyzed. The overall organization of these sequences in the polytene chromosomes resembles that described for the micronucleus of other hypotrichous ciliates, i.e. they are interrupted by internal eliminated sequences and not associated with telomeric sequences. The spacer region between the genes is bordered by direct repeats and inverted repeats are found at the termini of macronuclear sequences and in the spacer region. The organization of these macronuclear DNA sequences in the micronucleus was analyzed by polymerase chain reactions. The results obtained show that in the sequences analyzed no DNA reorganization occurs during polytene chromosome formation.

Animals↗
PubMed1992

Ultrastructure of normal and hepatitis virus infected human and chimpanzee liver: similarities and differences.

Ultrastructure of liver biopsy specimens obtained from normal and hepatitis B (HBV) and hepatitis C virus (HCV) infected livers of patients and chimpanzees were compared. Nuclear alterations (glycogen particles, nuclear bodies, "vermicellar bodies", etc.), intracytoplasmic crystalloid inclusions were observed before and after the HBV and HCV infections both in human and chimpanzee hepatocytes, however, some of them were more common during the viral infection. Extreme endoplasmic reticulum dilatation characterized the human, while the presence of membranous cytoplasmic inclusions the hepatocytes of chimpanzees during HCV infection. Interferon-associated membrane alterations were noted during acute or chronic hepatitis, however, in slightly different forms in humans and chimpanzees. Data suggest to be precautions in the interpretation of the ultrastructural alteration observed in different species even to be so closely related as humans and chimpanzees especially during infection with hepatotropic viruses.

Animals↗
PubMed1991

The cyclophilin multigene family of peptidyl-prolyl isomerases. Characterization of three separate human isoforms.

Cyclophilin (CyP), a major cytosolic protein possessing peptidyl-prolyl cis-trans isomerase activity, has been implicated as the specific receptor of the immunosuppressive drug cyclosporin A (CsA). To identify other potential CsA receptors related to CyP, two human cDNA libraries were screened under low stringency conditions using human CyP cDNA (encoding hCyP1) as a probe. Two cDNAs were identified which encode distinct proteins related to human hCyP1. These two novel proteins, designated hCyP2 and hCyP3, share 65 and 76% amino acid sequence homology with hCyP1, respectively. Both hCyP2 and hCyP3 contain NH2-terminal hydrophobic extensions of 32 and 42 amino acids, respectively. Protein-specific antibodies revealed the predominant association of hCyP2 and hCyP3 with membranes and subcellular organelles, which suggests that the amino-terminal leader sequences of the two CyP isoforms may act as signal peptides. In contrast to the results with hCyP1, Southern blot analysis indicated that both hCyP2 and hCyP3 gene sequences are represented infrequently in the human genome. Northern and Western blot analysis showed that the distribution of mRNA and proteins of the three hCyPs in differing tissues and cell types was similar. Each hCyP protein was expressed in Escherichia coli, purified, and shown to be an active peptidyl-prolyl isomerase. Substrate specificity was examined with 11 synthetic peptides (Suc-Xaa-Yaa-Pro-Phe-4-nitroanilide), and inhibition of the peptidyl-prolyl isomerase activities associated with hCyP1, hCyP2, and hCyP3 was studied with CsA, MeAla6-CsA and MeBm2t1-CsA. From both equilibrium considerations and the results of kinetic characterizations it is proposed that of these three CyP proteins, hCyP1 is the most likely intracellular target for CsA.

Amino Acid Isomerases↗