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W Walz

Publications and source records attributed to W Walz.

At least 19 recordsLinked to original sources
PubMed1992

Bradykinin receptors in cultured astrocytes from neonatal rat brain are linked to physiological responses.

Specific binding sites for bradykinin (BK) have recently been demonstrated on astrocytes of primary cultures from neonatal rat brain. In this study we demonstrate that BK induces membrane currents in concert with an elevation of [Ca2+]i. In 67% of astrocytes, BK induced an inward current as determined with the perforated patch-clamp technique in the whole-cell recording configuration. In a small population of astrocytes (20%), a BK-activated outward current was observed, while in the remainder of the cells (13%) no apparent current responses were detected. As recorded by fura-2 microfluorimetry, the peptide induced a transient rise of [Ca2+/bdi even when the extracellular calcium was removed. In the majority of astrocytes, the selective B1-agonist des-Arg9-BK elicited physiological responses with a much lower potency, indicating that the BK receptors are predominantly of the B2 subtype. A minor population of astrocytes was present which only responded to des-Arg9-BK.

Animals↗
PubMed1992

Mechanism of rapid K(+)-induced swelling of mouse astrocytes.

Cultured astrocytes from newborn mouse cortex were impaled with double-barrelled ion-sensitive microelectrodes to investigate their response following a 5 min exposure period to saline containing 60 mM K+. The membrane potential decreased from -74 to -11 mV, the intracellular K+ concentration increased from 102 to 145 mM and the intracellular pH increased from 7.05 to 7.60 indicating an increase in the HCO3- concentration from 9 to 31 mM. All changes were reversible. In additional series of experiments the cells were loaded with choline and the application of a bias current to electrodes containing the Corning 477317 resin made them more sensitive to choline than to K+. This resulted in a decrease of the ion potential during K+ exposure, which stabilized within 2 min. It is assumed that this is due to a dilution of intracellular choline by water intake. Thus, the early K(+)-evoked swelling response can be explained by a fast (approx. 2 min) swelling induced by K+ and HCO3- (and Cl-) influx.

Animals↗
PubMed1992

GABA- and glutamate-activated currents in glial cells of the mouse corpus callosum slice.

Whole-cell transmitter-activated currents were recorded with the patch-clamp technique from glial cells in thin frontal brain slices of the corpus callosum. In slices from 6- to 8-day-old mice, glioblasts were predominantly found, while oligodendrocytes were predominant in slices from 10- to 13-day-old mice. These developmental stages could be readily distinguished by their K+ channel pattern and their morphology and ultrastructural features. Both cell types expressed GABA and glutamate receptors in this in situ preparation. GABA responses showed similarities to those described for GABAA receptors, i.e., they were mimicked by muscimol, blocked by bicuculline, and enhanced by pentobarbital. Glutamate responses showed similarities to those of the kainate/quisqualate receptor subtype. The amplitude of GABA-activated currents recorded in oligodendrocytes was significantly smaller than that from glioblasts, while glutamate responses did not show marked differences in either cell type.

Action Potentials↗
PubMed1992

Ionic dependence of a P2-purinoceptor mediated depolarization of cultured astrocytes.

The membrane potential of cultured mouse astrocytes was recorded to assess the effects of extracellular adenosine 5'-triphosphate (ATP) and related H purines on astrocyte electrophysiology. The purines were applied with or without the presence of barium, which blocks the high resting K+ conductance in astrocytes. The response to ATP alone was a moderate depolarization; however, the response to ATP in the presence of barium was a large, dose dependent depolarization. The ED50 was approximately 10 microM. The effect of adenosine 5'-diphosphate (ADP) or adenosine 5'-monophosphate (AMP), in the presence of barium, on membrane potential was less than that of ATP. Adenosine, with or without barium, had no effect on membrane potential; furthermore, adenosine agonists in barium produced no response. The results of applying various ATP analogues indicate that the response is mediated via a P2-purinoceptor. Ion replacement studies reveal a complicated response to ATP that has several components and involves Na+ and K+. These results show that astrocytes respond with ionic changes to very small, physiological concentrations of extracellular ATP. We suggest that ATP plays a role in interactions between neurons/endothelial cells and glial cells.

Adenosine Monophosphate↗
PubMed1992

Identification of mouse type-2-like astrocytes: demonstration of glutamate and GABA transmitter activated responses.

We have identified mouse type-2-like astrocytes and examined some of their electrophysiological properties. Cultures were prepared from P4 mouse neopallia. We demonstrate that mouse type-2-like astrocytes can be identified using the following criteria: presence of glial fibrillary acidic protein (GFAP), presence of chondroitin sulfate polysaccharide, and presence of gamma-aminobutyric acid (GABA). A2B5-binding is not a sufficient criterion to identify O2A lineage cells in mouse neopallial glial cultures since the monoclonal antibody A2B5 binds not only to O2A lineage cells but also to a subpopulation of large, flat type-1-like astrocytes. Mouse type-2-like astrocytes have resting membrane potentials of -76.2 +/- 2.1 mV-i.e., similar to that of mouse type-1-like astrocytes. The input resistance of 44.2 +/- 0.5 M omega is an order of magnitude greater than that of type-1-like astrocytes suggesting the type-2-like astrocytes are not extensively electrically coupled either to each other or to type-1-like astrocytes. Glutamate application caused an 8.8 +/- 1.7 mV depolarization of type-2-like astrocytes. Application of glutamate to barium treated astrocytes caused a fast depolarization with a peak amplitude of 21.4 +/- 1.8 mV; the cells repolarized from this peak by about 10 mV and upon removal of glutamate returned to its pre-glutamate value. Application of GABA caused a transient depolarization of 14.0 +/- 1.7 mV. The presence of barium resulted in a steady-state GABA-induced depolarization of 10.3 +/- 2.0 mV. Neither SITS nor beta-alanine interfered with the amplitude of the glutamate and GABA responses.

Animals↗
PubMed1992

Metabolic inhibition and electrical properties of type-1-like cortical astrocytes.

Type-1-like cortical mouse astrocytes were studied in homogeneous cultures. Membrane input resistance and membrane potential were measured during drug-induced inhibition of glycolysis (sodium fluoride), mitochondrial respiration (antimycin-a) and Na+/K+ pump activity (ouabain). It was found that the electrical properties of the astrocytes recovered after a 60 min period with inhibited glycolysis or mitochondrial respiration, exhibiting only small reversible depolarizations. A 60 min period of high K(+)-induced depolarization, of cell swelling or of Na+/K+ pump inhibition does not lead to irreversible changes. Total block of energy metabolism, however, causes (1) a large depolarization, which is mainly mediated by external calcium, and (2) a 10-fold increase in input resistance, suggestive of an uncoupling of gap junctions. After an exposure period ranging between 45 and 60 min these conditions lead to irreversible damage. This damage appears to be independent of extracellular calcium and the degree of depolarization and to be specifically mediated by events occurring after the 60-min period of inhibited cell metabolism, that is during the recovery period.

Animals↗
PubMed1992

Anoxia-induced changes in extracellular K+ and pH in mammalian central white matter.

In gray matter (GM), anoxia induces prominent extracellular ionic changes that are important in understanding the pathophysiology of this insult. White matter (WM) is also injured by anoxia but the accompanying changes in extracellular ions have not been studied. To provide such information, the time course and magnitude of anoxia-induced changes in extracellular K+ concentration ([K+]o) and extracellular pH (pHo) were measured in the isolated rat optic nerve, a representative central WM tract, using ion-selective microelectrodes. Anoxia produced less extreme changes in [K+]o and pHo in WM than are known to occur in GM; in WM during anoxia, the average maximum [K+]o was 14 +/- 2.9 mM (bath [K+]o = 3 mM) and the average maximum acid shift was 0.31 +/- 0.07 pH unit. The extracellular space volume rapidly decreased by approximately 20% during anoxia. Excitability of the rat optic nerve, monitored as the amplitude of the supramaximal compound action potential, was lost in close temporal association with the increase in [K+]o. Increasing the bath glucose concentration from 10 to 20 mM resulted in a much larger acid shift during anoxia (0.58 +/- 0.08 pH unit) and a smaller average increase in [K]o (9.2 +/- 2.6 mM). The increased extracellular glucose concentration presumably provided more substrate for anaerobic metabolism, resulting in more extracellular lactate accumulation (although not directly measured) and a greater acid shift. Enhanced anaerobic metabolism during anoxia would provide energy for operation of ion pumps, including the sodium pump, that would result in smaller changes in [K+]o. These effects were probably responsible for the observation that the optic nerve showed significantly less damage after 60 min of anoxia in the presence of 20 mM glucose compared to 10 mM glucose. Under normoxic conditions, increasing bath K+ concentration to 30 mM (i.e., well beyond the level shown to occur with anoxia) for 60 min caused abrupt loss of excitability during the period of application but minimal change in the amplitude of the compound action potential following the period of exposure. The anoxia-induced increase in [K+]o, therefore, was not itself directly responsible for irreversible loss of optic nerve function. These observations indicate that major qualitative differences exist between mammalian GM and WM with regard to anoxia-induced extracellular ionic changes.

Action Potentials↗
PubMed1992

Gene expression of aromatic L-amino acid decarboxylase in cultured rat glial cells.

Northern blot hybridization was performed to detect aromatic L-amino acid decarboxylase (AADC) mRNA in primary cultures of astrocytes and C6 glioma cells. The cDNA probe for rat AADC was generated by reverse transcription from rat adrenal gland total RNA and was amplified by the polymerase chain reaction method. AADC mRNA from cultured astrocytes and C6 glioma cells was present as a single band, 2.2 kbp in size, that comigrated with the RNA from rat kidney. Western immunoblot showed a single protein band at 52 kDa for AADC enzyme protein. These findings demonstrate that AADC is expressed in rat glial cells.

Animals↗
PubMed1992

Coupling of metabolism and electrical activity in cortical astrocytes.

Cortical mouse astrocytes in culture were impaled with two-channel microelectrodes. These mouse astrocytes have the same responses to different K+ concentrations, ouabain, and glutamate as cultured rat astrocytes, with the exception that a large barium-sensitive K+ conductance clamps the membrane potential at the K+ equilibrium potential. Glycolytic and mitochondrial inhibitors have little effect on the mouse astrocytes. Total blockade of energy metabolism leads to an irreversible, calcium-dependent depolarization, but only if applied for longer than 45 min. Increasing the extracellular K+ concentration to 60 mM increases the intracellular K+ concentration by 43 mM and the bicarbonate concentration by 22 mM and leads to a concomitant fast swelling. Together with the 20 mM increase in Cl- concentration reported in the literature this is a good indication for a Boyle- and Conway-mediated K(+)-anion influx with water. This influx is accomplished by the depolarization-induced opening of Cl- channels as reported in the literature. In conclusion, ischemia-like conditions have little direct, immediate impact on astrocytes. In contrast, ischemia-induced release of substances from neurones, such as K+, produces an immediate and fast response.

Animals↗
PubMed1992

Role of Na/K/Cl cotransport in astrocytes.

The kinetic characterization of the Na/K/Cl cotransport of cultured astrocytes and evidence for its involvement in volume regulation and K+ net uptake during K+ clearance are reviewed. Emphasis is put on experimental evidence for a proposed sodium cycle in astrocytes; this cycle involves a Na(+)-K+ ATPase that is stimulated by both a high external K+ and intracellular Na+. Elevated external K+ also stimulates the Na/K/Cl carrier, transporting these ions inward. As a result Na+ is cycled across the membrane, carried inward by the Na/K/Cl carrier, and returned by the Na(+)-K+ ATPase. Both functionally coupled mechanisms lead to intracellular KCl accumulation and inward movements of water to compensate for increased osmolarity. The combined cycle is expected to play a major role in the regulation of physiological K+ levels in the brain.

Animals↗
PubMed1991

Short-circuiting effects of K+ currents on electrical responses of type-1-like astrocytes from mouse cerebral cortex.

The membrane potential and membrane input resistance of cortical astrocytes from newborn mice were recorded with and without exposure to 1 mM barium. Barium treatment drastically decreased the membrane response to 0 and 35 mM K+. It also revealed an electrogenic component of the Na+,K(+)-ATPase as evident by a biphasic depolarization as a response to ouabain, which was monophasic without barium presence. Untreated mouse astrocytes reacted with small monophasic depolarizations to GABA and glutamate exposure. Barium-treated astrocytes exhibited additional transient responses to both transmitters, similar to those responses of rat astrocytes as found in the literature. The transmitter responses were not changed by exposure to uptake blockers for both transmitter substances. Thus, this electrophysiological study confirms earlier studies with radioactive K+ fluxes in showing that astrocytes derived from mouse brain are capable of short-circuiting electrogenic components and transmitter responses. This extreme high K+ permeability resembles the one reported for endfeet of retinal Muller cells and dissociated astrocytes from optic nerve.

Animals↗
PubMed1990

Sodium- and bicarbonate-independent regulation of intracellular pH in culture mouse astrocytes.

The intracellular pH (pHi) of cultured mouse astrocytes was measured with double-barrelled pH-sensitive microelectrodes. In bicarbonate-buffered saline pHi was 7.05 and in HEPES-buffered saline 6.68. In both solutions H+ was not in electrochemical equilibrium; pHi was 0.7-1 pH unit more alkaline than expected from passive H+ distribution. Cells were acidified by applying NH4+ and the subsequent regulation of pHi was studied in bicarbonate-free saline. The mean rate of pHi recovery was 0.2 pH units min-1 which was not changed by amiloride or by removal of external Na+. Thus, the cells recovered from an acid load independently of Na(+)-H+ exchange, Na(+)-HCO3- cotransport or any other bicarbonate- or Na(+)-dependent mechanism.

Amiloride↗
PubMed1990

Simulation of aspects of ischemia in cell culture: changes in lactate compartmentation.

Aspects of hyperglycemic ischemia were simulated in cultures of astrocytes and of neurons by high glucose and dinitrophenol exposure. Lactate release increased almost sevenfold and it was found that astrocytes were responsible for 92% of the release. There was no significant increase in internal lactate content. Experiments involving loading of astrocytes with lactate at different external pH values showed that lactate accumulation was increased by an increased inward proton gradient. This inward transport of lactate probably consists of two transport components, a passive diffusion of its neutral form and transport via a recently described monocarboxylic acid carrier. It was found that lactate did not get trapped in astrocytes, despite the fact that loading of astrocytes with lactic acid by exposure to 30 mM lactic acid increased the membrane input resistance dramatically. We conclude that lactate is released as lactic acid from astrocytes and equilibrates quickly with all CNS compartments. Thus we argue against a role of lactate accumulation in cytotoxic swelling.

Animals↗
PubMed1990

Acidosis and blockade of orthodromic responses caused by anoxia in rat hippocampal slices at different temperatures.

1. Interstitial pH (pHo) and field responses (to stratum radiatum stimulation) were recorded simultaneously with double-barrelled microelectrodes in the CA1 region of hippocampal slices from Sprague-Dawley rats. 2. Both the relative acidity and amplitude of field responses increased with depth, reaching a maximum near the centre of the slice. When the temperature was raised from 22 to 37 degrees C, this pHo gradient was greater than 2 times steeper, but the field responses were much diminished. 3. Standard anoxic tests (substituting 95% N2 + 5% CO2 for 95% O2 + 5% CO2, for 2 min) tended to reduce pHo and population spikes, but these effects were highly temperature sensitive: at approximately 22 degrees C the blocking rate was only 12.3 +/- 4.6% and delta pHo -0.018 +/- 0.0157 units, both per minute; corresponding changes at 34-35 degrees C were 67.6 +/- 11.9% and -0.065 +/- 0.0046 units per minute. Highly significant linear correlations between rates of block and delta pHo gave a mean slope of 90.4 +/- 17.6% per 0.1 unit of acid change. 4. Anoxia caused similar temperature-dependent increases in acidity in stratum pyramidale and radiatum, but in the latter field responses (EPSPs) were much less depressed after 2 min of anoxia. 5. When slices were superfused with acid medium (low [HCO3-]), much greater reductions in pHo were needed to depress responses, giving a mean slope of 17.7% per 0.1 pH unit. 6. In glucose-free medium, there was a slow alkaline shift in pHo (0.13 +/- 0.036 units); population spikes and the acid transients evoked by anoxia disappeared. 7. It was concluded that acidosis cannot be the immediate cause of the similar depressions of postsynaptic excitability seen during anoxia and hypoglycaemia. 8. In further tests, DL-p-hydroxyphenyl-lactic acid, a blocker of lactate transport, failed to diminish acid transients evoked by anoxia, indicating that these are not mediated principally by lactate transport.

Action Potentials↗
PubMed1990

Brain lactic acidosis and synaptic function.

Measurements of the presynaptic fiber volley (PSFV), the population excitatory postsynaptic potential (EPSP), and the extracellular pH in the dendritic CA1 layer of rat hippocampal slices were used to evaluate the effects of lactacidosis on central synaptic transmission. Replacement of NaCl with sodium lactate (up to 30 mM) was found not to affect the PSFV; however, the EPSP was reversibly suppressed. Sodium citrate, with added CaCl2 to adjust for Ca2+ chelation, had the same effect as sodium lactate. Addition of lactic acid influenced the PSFV only when, at a concentration of 30 mM, the extracellular pH dropped to 6.6 or lower. With lactic acid concentrations of up to 20 mM, which produced pH levels of 6.8 in the slice, effects on the EPSP were reversible. However, 30 mM lactic acid suppressed both the PSFV and EPSP irreversibly. These results show that synaptic transmission is much more susceptible to lactacidosis than presynaptic axonal transmission. They also show that high levels of lactate, albeit causing suppression of synaptic transmission, do not cause irreversible damage. However, acidosis associated with lactic acid release may damage synaptic transmission irreversibly.

Acidosis, Lactic↗
PubMed1989

Resistance of astrocyte electrical membrane properties to acidosis changes in the presence of lactate.

The membrane potential and input resistance of mouse astrocytes in primary cultures were measured with two-channel microelectrodes. It was found that 30 mM sodium lactate (no pHo change) caused a hyperpolarization of 5 mV. A stepwise reduction in pH via HCl addition had no effect at pHo 6.5, at pHo 5.5 there was a 5 mV depolarization and at pHo 4.5 the membrane depolarized by 28 mV and the input resistance increased by 4.9-times. After 20 min this change was still reversible. If the pHo was lowered by the addition of lactic acid, a pHo of 4.5 (30 mM lactic acid) caused a 45 mV depolarization and a 4.3-times increase in input resistance. Exposure to these conditions caused irreversible effects. The exposure time for a 50% recovery of the membrane potential was 15 min. The results show that external acidification (for a period of 20 min) is only irreversible if lactate is present, probably due to excessive H+ shifts into the cells via the H+-lactate carrier. The results are of significance to explain glial damage during incomplete ischemia.

Animals↗