Search PubMed⌕ Search

Biomedical subjects

W Walz

Publications and source records attributed to W Walz.

At least 73 records · Page 4Linked to original sources
PubMed1985

Occurrence of phenolsulfotransferase in primary glial culture cells of rat.

Phenolsulfotransferase (PST) activity towards phenol and monoamines was determined in rat brain and in primary cultures of rat astrocytes. The pH requirement, Km values and the proportion of PST activity with respect to phenol and dopamine as substrates were similar between PST from the glial cells and the rat cortex. The enzyme activity increased with age in the brain of older animals, and also with increasing incubation time in the primary culture of astroglia. The specific PST activity of the astroglia appeared to be higher than that of the brain enzyme. In glial cultures treated with 0.25 mM dibutyryl cyclic AMP in the same culture conditions, PST activity is suppressed to about 25% of its untreated counterpart, even though dibutyryl cyclic AMP at concentrations of ImM only slightly inhibited PST activity in vitro.

Age Factors↗
PubMed1985

Genetic organization of the afimbrial adhesin operon and nucleotide sequence from a uropathogenic Escherichia coli gene encoding an afimbrial adhesin.

The uropathogenic Escherichia coli KS52 strain expresses a mannose-resistant hemagglutinin AFA-I, which recognizes a human erythrocyte site distinct from the alpha-digalactoside glycosphingolipid receptor common to uropathogenic E. coli strains specifying a P adhesin. A 6.7-kilobase chromosomal DNA fragment was cloned from KS52 into pBR322 and was shown to be necessary for host cell mannose-resistant hemagglutination expression and uroepithelial cell adherence (Labigne-Roussel et al., Infect. Immun. 46:251-259, 1984). The genetic organization of the 6.7-kilobase DNA fragment was investigated by generating derivative plasmids, and the polypeptides encoded by those plasmids in isolated minicells were analyzed on polyacrylamide gel. The 6.7-kilobase insert expresses five polypeptides of molecular mass 13,000, 16,000, 18,500, 30,000, and 100,000 daltons encoded, respectively, by the afaA, afaE, afaD, afaB, and afaC genes. The five genes were localized and were shown to belong to the same transcriptional unit. The afaB, afaC, and afaE gene products are required for mannose-resistant hemagglutination expression, whereas mutations in or deletions of either afaA or afaD do not modify host mannose-resistant hemagglutination expression. The afaE gene was identified as the structural gene encoding hemagglutinin. The gene has been sequenced; it encodes a 152-residue protein containing a typical 21-residue procaryote signal sequence and a 131-residue mature polypeptide, the AFA-I adhesin.

Adhesiveness↗
PubMed1984

Astrocytes in primary cultures: membrane potential characteristics reveal exclusive potassium conductance and potassium accumulator properties.

Mouse astrocytes in homogenous primary cultures were used to study the membrane potential response, measured with intracellular microelectrodes, to alterations of external ion composition and to certain drugs, and the observations were correlated with radiotracer measurements of equilibrated K+ content. The membrane potential was--92 mV at 3 mM K+, and reduction of external Na+ and Cl-concentration, as well as addition of furosemide, which acts on Cl- and Na+ fluxes, had no effect, showing that there is no other ion than K+ which significantly contributes to membrane conductance. Addition of ouabain showed that there is no electrogenic component of the membrane potential at either 'resting' conditions or during stimulation. Nevertheless, the behavior of the membrane potential was found to deviate from a Nernst potential for K+ when extracellular K+ was changed (the slope was linear from 1.5 to 100 mM K+ with 51 mV/10-fold change compared with 61 mV for a Nernstian behavior at 37 degrees C). The radioisotope measurements at different external K+ showed that this was due to accumulation of intracellular K+. We conclude that these astrocytes have spatial buffer and active accumulator properties towards the K+ ion.

Animals↗
PubMed1984

Sodium transport in astrocytes.

Sodium transport in astrocytes in homogeneous primary cultures from mouse brain cortex were investigated with radiotracer (22Na) and electrophysiological methods. The equilibrated Na+ content was 190 nmol X mg-1 protein and the influx and efflux rates were identical at about 560 nmol X mg-1 X min-1. No significant change was observed in Na+ efflux or influx when external K+ was raised from 5.4 to 12 or 54 mM, but the Na+ content decreased. Intracellular Na+ loading, evoked by previous exposure to ice-cold K+-free medium, double the Na+ efflux. Ouabain, a Na+-K+ exchange inhibitor, exerted a small, nonsignificant inhibition of Na+ efflux at both 5.4 and 12 mM K+ and caused a large increase in Na+ content. At 5.4 mM K+, amiloride, a Na+-H+ exchange inhibitor, decreased both influx and efflux of Na+ and caused an increase in Na+ content. Furosemide, an inhibitor of a cation-Cl- carrier, decreased both content and influx of Na+ slightly but had no significant effect on Na+ efflux. The effects of amiloride or furosemide on Na+ influx were abolished at elevated (12 and 54 mM) K+. Attempts to stimulate the Na+-K+ pump with elevated external K+ or internal Na+ produced no electrogenic component of the membrane potential, probably owing to the high K+ permeability. Based on the present results and earlier experiments on K+ influx, it is concluded that 1) the Na+-K+ pump of astrocytes under normal conditions transports more K+ than Na+; 2) intracellular Na+ loading increases Na+ efflux; 3) some Na+-H+ exchange and cotransport of Na+ and Cl- seem to occur at 5.4 mM K+; and 4) neither of the latter two transport mechanisms is enhanced at elevated K+ concentrations.

Animals↗
PubMed1984

Barium-induced inhibition of K+ transport mechanisms in cortical astrocytes--its possible contribution to the large Ba2+-evoked extracellular K+ signal in brain.

Homogenous mouse astrocytes in primary cultures were used to investigate the action of different Ba2+ concentrations on 42K transport, membrane potential and Na+,K+-adenosine triphosphatase activity. Five millimolar Ba2+ reduced total K+ influx and efflux (each by 83%) and ouabain-sensitive net K+ uptake (by 80%); it decreased the K+ content, depolarized the membrane potential reversibly and completely inhibited the Na+,K+-adenosine triphosphatase activity. The concentration dependence of these effects was biphasic. Concentrations between 2 and 20 microM affected only the passive K+ fluxes (IC50: 6 microM). Concentrations between 50 microM and 5 mM inhibited the Na+,K+-adenosine triphosphatase and had no further effect on passive fluxes, but inhibited the ouabain-sensitive net uptake of K+ (IC50: 3.1-0.6 mM). It is suggested that the large evoked extracellular K+ increase in the brain observed in Ba2+-treated preparations in vivo or in brain slices to a large extent is due to the impairment of passive and active K+ clearance by glial cells.

Animals↗
PubMed1984

Intense furosemide-sensitive potassium accumulation in astrocytes in the presence of pathologically high extracellular potassium levels.

An intense K+ accumulation in primary cultures of astrocytes, occurring when external K+ was increased from 5.4 to 54 mM, was investigated. This increase resulted in a doubling of the K+ content within 10 s. Thirty percent of the accumulation was inhibited by furosemide (2 mM). This drug had no effect on the unidirectional influx of K+ at 5.4 mM K+, but when the extracellular K+ concentration was increased, there appeared to be a furosemide-sensitive component of the influx. This component increased with increasing external K+ levels, reaching 44% of the total influx at 72 mM. These results show that astrocytes exhibit an intense furosemide-sensitive K+ accumulation which is activated by K+ levels resembling those occurring in the extracellular compartment during pathological events. Previous studies on a furosemide-sensitive Cl- pump in cultured astrocytes suggest that this accumulation might be via KCl cotransport, which in other systems is involved in volume control.

Animals↗
PubMed1984

Antibody-dependent cellular cytotoxicity and chemiluminescence as a tool for studying the mechanism of anti-glomerular basement membrane nephritis. The role of the cytotoxic potential of polymorphonuclear granulocytes and monocytes.

An in vitro system was elaborated to study the mechanisms inducing tissue injury in anti-glomerular basement membrane (GBM) nephritis. Collagenase-digested GBM (CGBM) was covalently attached to Fab' specific for chicken red blood cells (CRBC). The preparation of the CGBM-Fab' conjugate was effected by using iodoacetyl chloride coupling in analogy to a procedure described by Chiang & Koshland (1979). This conjugate was used for coating CRBC (CGBM-CRBC). In this system the antibody-dependent cellular cytotoxicity (ADCC) and the chemiluminescence mediated by purified bovine polymorphonuclear (PMN) and mononuclear cells (MNC) as well as rabbit MNC against CGBM-CRBC were compared in the presence of sheep anti-GBM IgG. All three cell populations were potent effectors in ADCC and chemiluminescence and evidence was obtained that the cytotoxic potential of MNC has to be attributed to monocytes. If compared at low effector target cell ratios in a 2 hr assay bovine PMN, however, were significantly more efficient than bovine MNC. The extent of both ADCC and chemiluminescence was directly related to the amount of anti-GBM IgG present in the system. Based on the inhibition experiments with oxygen intermediate scavengers, both ADCC and chemiluminescence by bovine PMN is dependent on generation of reactive oxygen species indicating that such radicals could play a role in vascular (endothelial) injury as documented in the loss of structural integrity of GBM.

Animals↗
PubMed1983

Comparison between fluxes of potassium and of chloride in astrocytes in primary cultures.

Transport processes operating in astrocytes were examined by measuring unidirectional fluxes of 42K and 36Cl in primary cultures of mouse astrocytes, at steady-state with respect to ion composition. The total K+ uptake rate was 2025 nmol X mg-1 protein X min-1. This rate was not influenced by furosemide (2 mM), an inhibitor of Cl- uptake and K+-K+ exchange, or acetazolamide (0.1 mM), a carbonic anhydrase inhibitor. Ouabain (1 mM) inhibited the uptake rate by 541 nmol X mg-1 X min-1. The equilibrated K+ content was determined to be 696 nmol X mg-1. The rate constant for efflux was 2.76 min-1. This equals an efflux rate of 1921 nmol X mg-1 X min-1, i.e. a similar value as the influx. Furosemide and ouabain did not inhibit the efflux. The equilibrated Cl- content was found to be 167 nmol X mg-1 and it decreased in furosemide-treated cells to 68.1 nmol X mg-1. The total Cl- uptake was 35 nmol X mg-1 X min-1 and it was inhibited by furosemide or bumetanide by 27 nmol X mg-1 X min-1. The mean resting membrane potential was found to be -77.4 mV. From these data we conclude: (1) that the K+ uptake rates are high, as can be expected from estimates based on literature data for K+ conductance in mammalian glial cells in situ; and (2) that the cells possess a very low relative Cl- permeability.

Animals↗
PubMed1983

The Na+-K+ pump in neuropile glial cells of the medicinal leech.

The membrane potential of neuropile glial (NG) cells in the central nervous system of the medicinal leech and the K+ concentration in extracellular spaces (ECS) of the neuropile were measured under various experimental conditions to determine properties of a glial Na+-K+ pump. The ganglia were exposed to K+-free saline thereby loading the NG cells with intracellular Na+. Their membranes hyperpolarized transiently when the K+-free solution was replaced by a bathing medium with normal (= 4 mM) K+ concentration. The hyperpolarization increased in amplitude with time of exposure to K+ -free solution and could be abolished by ouabain or by replacing Na+ with Li+. The transient membrane hyperpolarization could not be attributed to K+ depletion in the ECS of the neuropile or to changes in membrane input conductance. In a (bathing) medium containing 5 X 10(-4) M ouabain, the K+ concentration in the ECS increased transiently, and the NG cell membrane depolarized rapidly. This short-term depolarization (duration 2-3 min) was followed by a second long-term depolarization (duration 15 min) of the NG cell membrane, which reached a steady-state 20 min after ouabain application. In a bathing medium with elevated external K+ concentrations, the amplitude of the membrane depolarization was enhanced by ouabain. This depolarizing ouabain effect was a result of K+ accumulation in the ECS. We conclude that the Na+-K+ pump does not contribute directly to the resting membrane potential of NG cells and is not directly involved in K+ homeostasis at the cellular level.

Animals↗
PubMed1983

Intracellular ion changes of astrocytes in response to extracellular potassium.

Intracellular changes of K+, Na+, and Cl- were investigated by the aid of radiotracers in primary cultures of astrocytes when extracellular K+ was (1) increased from 3 to 12 mM and subsequently again decreased to 3 mM; and (2) increased from 5.4 to 54 mM with subsequent decrease to 5.4 mM. In both situations the K+ content increased by 50% within seconds, and it doubled within 1-2 min. The increase must be carrier mediated, because keeping the K X Cl product (Donnan equilibrium) constant did not lower the K+ accumulation rates. The Na+ content decreased when K+ was increased to 12 mM, but the decrease corresponded only to 10% of the accumulated K+. When K+ was increased to 54 mM, the Na+ content increased transiently. Cl- increased by about 15-25% of the accumulated K+. Return of extracellular K+ to original levels evoked a very fast K+ release, reversing all ion changes. The Na+ content increased transiently during the release process. For an interpretation of these observations, it is necessary to postulate endogenous production of an anion and of H+, which in turn is partly exchanged with Na+.

Animals↗
PubMed1983

Lithium-potassium interaction in acutely treated cortical neurons and astrocytes.

Pure mouse primary cultures of cortical astrocytes and of cortical neurons were exposed to 1 mM Li+, i.e., a therapeutically relevant concentration. The 42K uptake rates of neurons were not influenced, whereas those of astrocytes showed an 11% inhibition (P less than 0.01). Internal loading with Li+ did not change the K+ uptake rates in either cell type. Neurons, which had been exposed for 5 min to veratridine, a situation which mimics neuronal activity, showed also no change in K+ uptake rate when Li+ was present during this time. Na+-K+ ATPase activity from cell homogenates was not changed in neuronal preparations by exposure to Li+, but astrocytic preparations appeared to show a slight increase by 14%. These experiments point out that the Li+ effects on ion distribution of the brain which have been described in the literature, are due to partly impairment of astrocytic K+ uptake. The mechanism of action, underlying the Li+ effect is probably a competition with K+ for transport sites at the external site of the Na+-K+ ATPase. This leads to a decrease of K+ uptake, but an enhancement of ATPase activity in the presence of Li+.

Animals↗
PubMed1982

Ionic mechanism of a hyperpolarizing 5-hydroxytryptamine effect on leech neuropile glial cells.

The ionic mechanism of a membrane effect of 5-hydroxytryptamine (5-HT) on neuropile glial (NG) cells in ganglia of the medicinal leech was investigated with conventional single-barrelled microelectrodes. Control experiments were made with double-barrelled ion-selective microelectrodes. 5-Hydroxytryptamine hyperpolarized the NG-cell membrane and increased the conductance considerably. Methysergide, a potent 5-HT antagonist, blocked the 5-HT-induced hyperpolarization completely. When leech ganglia were superfused with physiological bathing media free of 5-HT, the NG-cell membrane conductance returned to the original value, but the membrane potential recovered only partially from the hyperpolarization in most experiments. In glial membranes artificially depolarized by means of constant-current injection, the amplitude of the 5-HT response increased. The amplitude decreased with membrane hyperpolarization and reversed at - 73 mV, close to the potassium equilibrium potential. The reversal potential changed by 52 mV when the extracellular potassium concentration was altered by a factor of 10. We conclude that 5-HT increases the potassium conductance of NG-cell membranes.

Animals↗
PubMed1982

External ions and membrane potential of leech neuropile glial cells.

In ion-substitution experiments supplemented by measurements of the membrane conductance, the membrane potential of neuropile glial (NG) cells in the CNS of th medicinal leech has exhibited a dependence of the external concentration of both potassium and chloride. The membrane potential was largely dependent on the external potassium concentration, as may be inferred from the change in potential as the potassium concentration of the bathing solution was changed. The external potassium concentrations had been corrected to allow for the discrepancy between intra- and extraganglionic levels found with ion-selective electrodes. A transient membrane depolarization was recorded when the chloride in the bathing medium was replaced by sulphate or glucuronate. The restoration of the normal membrane potential following the return to chloride-based saline was preceded by a transient hyperpolarization. After transfer to low-chloride solutions, the transient depolarization of the NG cell membrane was followed by a steady-state hyperpolarization. The amplitude of the steady-state hyperpolarization depended on the concentration of chloride in the bathing medium. The membrane conductance decreased in low-chloride solutions.

Animals↗
PubMed1982

Do neuronal signals regulate potassium flow in glial cells? Evidence from an invertebrate central nervous system.

Experiments were conducted with the aid of intracellular microelectrodes to study physiological properties of neuropile glial cells in the central nervous system of the medicinal leech. The results showed significant contributions of both K+ and Cl- ions to the membrane potential. The transmitter substance 5-hydroxytryptamine increased the K+ conductance of the cell membrane. On the basis of these experiments, a model for potassium homeostasis in leech neuropile is suggested, according to which excess K+ ions in the extracellular space lead to passive KCl fluxes across the glial cell membrane and the transmitter 5-hydroxytryptamine induces a K+ release from glial cells into the extracellular space. Since 5-hydroxytryptamine is known to be an inhibitory transmitter in the leech central nervous system, this release will occur in regions with inactive neurons, which may be specially well suited for neuronal reaccumulation of K+ ions.

Animals↗
PubMed1982

Acute and chronic effects of lithium in therapeutically relevant concentrations on potassium uptake into astrocytes.

Potassium uptake into astrocytes in primary cultures was measured by the aid of 42K. Acute application of lithium in concentrations of 1 and 5 mM, but not 0.5 und 0.25 mM, exerted a significant inhibition of the potassium uptake rates. This effect is due to a partial impairment of the ouabain-sensitive part of the uptake into the cells caused by a lithium interaction with the extracellular K+-activated site of the Na+, K+-ATPase. After 14 days of exposure of the astrocytes to 1 mM lithium, the potassium uptake remained lower in the presence of lithium than in its absence. However, the cells had adjusted to the chronic presence of lithium by increasing their potassium uptake to such an extent that, during the exposure to 1 mM lithium, it was indistinguishable from that in cultures from the same batches grown in the absence of lithium and measured in the absence of this compound. The interference by lithium with potassium uptake into astrocytes may well be related to the inhibition of potassium clearance in the CNS described in the literature.

Astrocytes↗
PubMed1982

Ouabain-sensitive and ouabain-resistant net uptake of potassium into astrocytes and neurons in primary cultures.

Inhibition of net uptake of 42K by different concentrations of ouabain was studied in primary cultures of astrocytes and in primary cultures of neurons in order to investigate whether there is a pronounced difference between ouabain sensitivity in the two cell types and to determine the genuine magnitudes of the ouabain-sensitive and the ouabain-resistant potassium uptakes. In morphologically differentiated astrocytes, obtained after treatment with dibutyryl cyclic AMP (dBcAMP), the sensitivity to ouabain was slightly lower than in neurons, but astrocytes which had not been treated with dBcAMP showed sensitivity similar to the neurons (which likewise were not treated). In the presence of elevated potassium concentrations (12 and 24 mM) ouabain sensitivity was decreased, although only by a factor of 2-3. Accordingly, maximum inhibition of the uptake required under all conditions studied, at most, 1.0 mM ouabain. Like total uptake, this ouabain-sensitive uptake was several times less intense in neurons than in astrocytes, where it reached its maximum value at an external potassium concentration of 12 mM. Subtraction of the ouabain-sensitive uptake from the total uptake revealed a considerable ouabain-resistant uptake. This ouabain-resistant uptake was studied in detail in the astrocytes, where it was found to increase with increasing potassium concentration over the whole concentration range 3-24 mM and to exceed substantially the maximum amount that can be accumulated by diffusion.

Animals↗
PubMed1980

Fluorescence marking of neuropile glial cells in the central nervous system of the leech Hirudo medicinalis.

Neuropile glial (NG) cells in the central nervous system of the medicinal leech, Hirudo medicinalis L., were studied by histological and intracellular electrophysiological methods. Potential profiles of single leech ganglia were mapped by advancing an electrolyte-filled microelectrode into the ganglion as far as the NG cell. A small negative potential usually appeared during or immediately after penetration of the ganglion sheath. Most of the ganglia in the chain (ganglia 1-4 and 7-21) have Retzius-cell-bodies of normal size; in these, the potential associated with the ganglion sheath was followed by a jump to a more negative potential. Superimposed action potentials were associated with entry of the electrode into a Retzius cell. When the electrode tip passed out of the cell into the center of the ganglion, another potential change was observed, namely that to the membrane potential of the anterior NG cell. This membrane potential averaged -60.2mV and ranged from -50 to -73mV. In ganglia 5 and 6 the Retzius-cell-bodies are particularly small, and no changes of potential associated with these cells were observed; the first potential to appear after the electrode passed through the sheath of the ganglion was the membrane potential of the NG cell. Potential profiles like those of ganglia 5 and 6 are recorded in the posterior parts of all ganglia. Potential profiles of single leech ganglia were also recorded with microelectrodes filled with the fluorescent dye Procion Yellow M4-RAN. When the presumed membrane potential of an NG cell appeared, the dye was injected into the gaglion. Subsequent histological examination with the fluorescence microscope revealed that all of the dye was contained in NG cells.

Animals↗