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W Schwarz

Publications and source records attributed to W Schwarz.

At least 55 records · Page 3Linked to original sources
PubMed1999

Inhibition of uptake, steady-state currents, and transient charge movements generated by the neuronal GABA transporter by various anticonvulsant drugs.

1. We have expressed the GABA transporter (GAT1) of mouse brain in Xenopus oocytes and have investigated the effects of four antiepileptic drugs, tiagabine (TGB), vigabatrin (VGB), gabapentin (GBP) and valproate (VAL), on GAT1 transporter function by measurements of 3H-labelled GABA uptake and GAT1-mediated currents. 2. Not only TGB, a well-known inhibitor of GAT1-mediated transport, but also the other drugs efficiently inhibit the uptake of [3H]-GABA by GAT1. Inhibition at 50% is obtained for VGB, TGB, GBP, and VAL at concentrations of about 1 nM, 1 microM, 50 microM and 100 microM, respectively. 3. However, GAT1-mediated steady-state and transient currents are nearly unaffected by VGB, GBP, and VAL at even five times higher concentrations. Only TGB blocks the uptake and steady-state and transient currents at micromolar concentrations. 4. VGB exhibits a complex interaction with GAT1; at concentrations about 1 nM, the inhibition of uptake is released, but at millimolar concentrations the uptake is inhibited again, and also the GAT1-mediated current is finally inhibited at these concentrations with a KI value of 0.5 mM. The concentration dependency of inhibition of uptake can be explained by two interaction sites with different affinities, a blocking site and a transport site. 5. The differences in effects of VAL, GBP, and VGB on uptake and currents can be attributed to the fact that GAT1 has the capability to operate in an electrogenic mode without uptake of GABA. We suggest that inhibition occurs only when GAT1 operates in the GABA-uptake mode. 6. The inhibition of GABA uptake by these four drugs will result in an elevation of the GABA concentration in the synaptic cleft, which will enhance synaptic inhibition and thereby contribute to their antiepileptic effects.

Acetates↗
PubMed1998

Effect of mutation of glycosylation sites on the Na+ dependence of steady-state and transient currents generated by the neuronal GABA transporter.

The GABA (gamma-aminobutyric acid) transporter (GAT1) belongs to a superfamily of secondary active uptake systems for neurotransmitters that depend on the electrochemical gradients for Na+ and Cl-. In the GAT1, two Na+ ions and one Cl- ion are co-transported with one GABA molecule. Steady-state transport activity and transient charge movements during partial reactions of the transport cycle of the GAT1 of mouse brain expressed in Xenopus oocytes were investigated by two-electrode voltage clamp. Functional expression was demonstrated by Na+-dependent [3H]GABA uptake. Effects of mutation of two out of three N-glycosylation sites located in the extracellular loop between transmembrane domains 3 and 4 (Asn176, Asn181, Asn184) were analysed. Simultaneous substitution of two Asn by Asp leaves the transport system intact but leads to a reduction in turnover and complex changes in the interaction of external Na+ with the transport protein. If Asn176 is mutated to Asp and simultaneously Asn181 to Gly, no transport and no charge movements can be detected. In conclusion, mutations of the glycosylation sites result in altered transport, and the local conformation at Asn181 is critical for expression of transport activity.

Animals↗
PubMed1998

Voltage-dependent inhibition of the Na+,K+ pump by tetraethylammonium.

Tetraethylammonium (TEA+) is an effective inhibitor of a variety of K+ channels, and has been widely used to reduce K+-sensitive background conductances in electrophysiological investigations of the Na+,K+-ATPase. Here we demonstrate by combination of two-electrode voltage clamp (TEVC) and giant patch clamp of Xenopus oocytes, and measurements of the activity of purified ATPase of pig kidney that TEA+ directly inhibits the Na+,K+-ATPase from the outside. The KI value in TEVC experiments at 0 mV is about 10 mM increasing with more negative potentials. A similar voltage-dependent inhibition by TEA+ was observed in the excised membrane patches except that the apparent KI value at 0 mV is about 100 mM, a value nearly identical to that found for inhibition of purified kidney ATPase. The voltage-dependent inhibition can be described by an effective valency of 0.39 and is attributed to an interference with the voltage-dependent binding of K+ at an external access channel. The apparent dielectric length of the access channel for K+ is not affected by TEA+.

Animals↗
PubMed1998

The Na+,K+-ATPase carrying the carboxy-terminal Ca2+/calmodulin binding domain of the Ca2+ pump has 2Na+,2K+ stoichiometry and lost charge movement in Na+/Na+ exchange.

An altered ion-transport stoichiometry from 3Na+,2K+ to 2Na+,2K+ is observed in a chimeric Na+,K+ATPase, which carries the Ca2+/calmodulin binding domain (CBD) of the plasma membrane Ca2+-ATPase at its carboxy-terminus [Zhao et al., FEBS Lett. 408 (1997) 271-2751. The ouabain-resistant mutant of this chimera (ORalpha1-CBD) was constructed to further investigate the effect of the CBD on ion-transport properties. The ORalpha1-CBD still shows the 2Na+,2K+ stoichiometry. The loss of electrogenicity is accompanied by the disappearance of transient charge movements in the Na+/Na+ exchange mode. We conclude that the binding of the third Na+ ion, but not of the two others, in 3Na+,2K+ transport mode apparently senses the electric field, and that the voltage-dependent Na+ binding is likely to be lost in the chimera with CBD.

Animals↗
PubMed1998

Significance of the glutamic acid residues Glu334, Glu959, and Glu960 of the alpha subunits of Torpedo Na+, K+ pumps for transport activity and ouabain binding.

Glutamic acid residues in transmembrane segments of the alpha subunit of the Na+,K+-ATPase have been discussed as possible candidates for the binding sites of the transported cations. Here we report on effects of mutations of Glu334, Glu959, and Glu960 to alanine in ouabain-sensitive (OS) as well as ouabain-resistant (OR) ATPases of Torpedo electroplax expressed in Xenopus oocytes. All mutants are incorporated to about the same extend as the wild-type ATPases into the plasma membrane. None of the mutations produces complete inhibition of transport activity as judged from measurements of 86Rb+ uptake, membrane current, and ATPase activity. After conversion of OS to OR by mutation of the bordering residues of the first extracellular loop Gln118 to Arg and Asp129 to Asn, the Km value for inhibition by ouabain increases to 59 microM. Substitution of Glu334 to Ala in the OR pump variant restores ouabain sensitivity with a Km value of 0.12 microM, which is similar to that of the endogenous Xenopus pump. After substitution of Glu960 by Ala in the OR pump, ouabain sensitivity is partially restored. The Km values for pump stimulation by external K+ appear to be reduced in the OR compared to the OS pump. Mutation of Glu959 and Glu960 to Ala has no pronounced effects on the potential-dependent Km values at external pH 7.8; only in the Glu959-mutated OR pump, the apparent Km at 0 mV is raised. We conclude that none of the mutated glutamic acid residues is essential for cation coordination, but that GIu334, and in part also Glu960, seems to be involved in preserving the ouabain-resistant conformation of the enzyme.

Animals↗
PubMed1998

Inhibition of the Na+,K+ pump by the epileptogenic pentylenetetrazole.

Pentylenetetrazole (PTZ) is a convulsant drug used in animal experiments to induce epileptic activity. It is known to interact with a variety of channels and neurotransmitter receptors. We investigated the effects of PTZ on the Na+,K+ pump by measuring pump-mediated current, 86Rb+ uptake and [3H]ouabain binding using the Xenopus oocytes as a model system. PTZ inhibits Rb+ uptake with a KI value of about 10 mM, and the number of pump molecules is not altered as judged by the number of ouabain-binding sites. The measurements of pump current under voltage-clamp conditions revealed voltage-dependent inhibition with KI values increasing with depolarization. Reduced sensitivity to PTZ in the presence of ouabain and at reduced external K+ suggests that PTZ directly interacts with the transport ATPase and binds preferentially to the E1 form. Development of inhibition and recovery have time constants of about 10 min, which suggests that the externally applied PTZ acts on the pump from the cytoplasmic or membrane phase. Since inhibition of the Na+,K+ pump is accompanied by membrane depolarization, PTZ should promote the generation of discharges and contribute to the epileptogenic effects through pump inhibition.

Animals↗
PubMed1998

[Odontogenic focus as the etiology of cerebral ischemia].

Recent studies have shown that acute infections, especially of the respiratory tract, are an important risk factor for cerebral ischemia. Additionally we know that chronic dental infections may be a risk for myocardial infarction and artherosclerosis. However, the connection between stroke and dental infections has hardly been examined so far. Therefore we performed a case-control study using a standardized questionaire and examination. We investigated 66 patients consecutive to a acute cerebral ischemia/stroke and 60 age- and sex-matched nonstroke neurological patients as a control group. Dental status was determined by a so called total dental index (TDI) which reflects primarily caries, periodontitis, periapical lesions, devital and missing teeth as well as by a panoramic index (PI). Specifically, older patients with cerebrovascular ischemia tended to have a significantly worse dental status and had more severe periodontitis and periapical lesions than control subjects. A predefined poor dental status was associated with cerebrovascular ischemia independent from other vascular risk factors and social status. In conclusion, poor dental health, mainly resulting from chronic dental infections, may be associated with an increased risk for cerebrovascular ischemia. The results must now be verified in larger studies. As chronic dental infections are a common and also easily treatable factor, their identification as a risk factor for stroke would be quite important in the field of preventive medicine.

Adult↗
PubMed1998

On the interaction of numerical and size information in digit comparison: a behavioral and event-related potential study.

To investigate effects of dimensional congruity in digit comparison processes we recorded response latencies, error rates and event-related potentials (ERPs) in a situation when the relevant and the irrelevant dimension of judgement, the digit's physical size or its numerical value, varied unpredictably from trial to trial. Congruity effects may arise at early processing stages, where both numerical and size information are mapped onto a common, integrated representation. Alternatively, numerical and size information may be processed in functionally independent channels and interact only at a later stage of response activation. For both, numerical and size comparisons, reliable distance effects on ERPs (starting 224 ms post-stimulus at frontal electrode sites) and on behavioral data were observed. Congruity effects follow a timecourse that mirror-images the temporal pattern found for the distance effects: while distance effects on difference potentials start about 64 ms earlier for numerical comparisons, congruity effects due to the irrelevant attribute are seen about 88 ms earlier for size comparisons. While Lateralized Readiness Potentials (LRPs) for incongruent trials are shifted in time, there was no indication of an activation for the incorrect response in incongruent trials, as an account of congruity effects in terms of response competition would predict. The most parsimonious explanation of our results is that numerical and size information are extracted in parallel, are both converted into an integrated representation and potentially interact during these early parallel stages.

Adult↗
PubMed1998

Val 70, Phe 72 and the last seven amino acid residues of C-terminal are essential to the function of norepinephrine transporter.

The norepinephrine transporter(NET) is a member of the Na+/Cl- dependent neurotransmitter transporter family and constitutes the target of several clinically important antidepressants. To delineate the critical amino acid residues and the function of C-terminal in regulating transport activity of NET, here we constructed two site mutants (V70F, F72V; V70I, F72V) and one C-terminal truncated mutant (delta 611-617). The wild type and mutants of NET were expressed in Xenopus oocytes by injection of their cRNA. We found that all of these mutants lost their transport activity. These results indicate that the amino acid residues of V70 and F72, and the last seven amino acids of C-terminal are essential to the transport activity of NET.

Amino Acid Sequence↗
PubMed1998

Drainage systems in thyroid surgery: a randomised trial of passive and suction drainage.

OBJECTIVE: To investigate the effectiveness of high-vacuum and passive drainage systems after elective thyroid resection. DESIGN: Prospective randomised clinical study and multicentre postal survey. SETTING: Military hospital, Germany. PATIENTS: 80 patients, treated with passive closed drains (n = 40) or high-vacuum systems (n = 40). INTERVENTIONS: 1. Measuring the amount of blood collected during drainage and the extent of residual haematoma on ultrasonography. 2. Survey in Austria, Germany and Switzerland of annual number of bilateral thyroid resections, type of drainage used, and volume of postoperative drainage. RESULTS: 799 of the 1698 hospitals surveyed replied (47.2%). 785 (98.2%) of the 799 surgeons said that they used drainage systems of whom 766 (97.6%) used high-vacuum systems. In the 40 patients in whom passive closed drainage was used, the median volume drained was 34 ml (range 0-175) compared with 115 ml (40-346) in the high vacuum group (p < 0.01). In the passive drainage group the extent of residual haematoma measured by us was 4.4 ml (range 0-21.7) compared with 5.3 ml (0.6-24.9) in the high vacuum group. CONCLUSIONS: The high-vacuum drainage that is most commonly used in Austria, Germany, and Switzerland results in increased blood loss with no reduction in the extent of residual wound haematoma and offers no additional advantage over passive drainage systems in thyroid surgery.

Adult↗
PubMed1998

Experimental investigation of oscillatory flow through a symmetrically bifurcating tube.

To provide a quantitative description of the convection field of gas transport through the lung under both low and high-frequency ventilation conditions, volume-cycled, purely oscillatory flow has been investigated in a symmetrically bifurcating model bronchial bifurcation. Significant differences in the flow properties that developed as the Reynolds number varied from 750 to 950 and the dimensionless frequency varied from 3 to 12 are described. At low frequency, the axial velocity field was found to approximate closely that of a steady flow through a bifurcation. However, even at alpha = 3, secondary velocity fields were confined to within a few diameters of the bifurcation, with less than 10 percent of the magnitude of the axial velocity. At high frequency they were still slower and more limited. These secondary velocity observations are discussed in terms of a physical mechanism balancing inviscid centripetal acceleration with viscous retardation. As the dimensionless frequency increased but the flow amplitude decreased, the magnitude of the axial drift velocity field was found to decrease. In addition, a burst of high-frequency velocity fluctuations was detected in both the axial and secondary velocity measurements in the parent tube, in low-frequency flow, during the deceleration phase of expiration. The position and timing of this burst suggest that it derives from the free shear layer in the parent tube. Stability criteria for the flow were therefore evaluated.

Acceleration↗
PubMed1998

[Differential diagnosis and therapy of benign liver tumors].

Hemangioma, focal nodular hyperplasia (FNH) and hepatocellular adenoma represent the most common and clinically relevant benign liver tumors. Improved diagnostic imaging procedures as well as the broad use of oral contraceptives resulted in an increased detection rate during the past 25 years. Focal liver diseases are primarily diagnosed by ultrasonography, while a specific diagnosis can be established by contrast enhanced magnetic resonance imaging. Hepatocellular adenomas should be resected, since they bear the potential of a malignant transformation as well as the risk of rupture and intraperitoneal hemorrhage. Conversely, a conservative approach is advocated for hemangioma and FNH. However, surgical procedures may be justified when a mass becomes symptomatic, and should be applied liberally when the diagnosis remains uncertain.

Adenoma, Liver Cell↗
PubMed1998

Computer-assisted training program for simulation of triage, resuscitation, and evacuation of casualties.

The purpose of this paper is to introduce a multimedia computer software package that has been developed for the Federal Armed Forces of Germany to train military physicians in trauma management. The program presents different groups of casualties with characteristic wounds and multiple injuries on a CD-ROM and provides many clinical options at each decision point. Automatically evaluating the decisions for accuracy, the objective of the program is to train for triage, resuscitation, and evacuation of wounded in combat under pressure of time. The computer-assisted instruction program is inexpensive and allows easily accessible self-instruction as a supplement to formal classroom training. Using this teaching software, it may be possible to teach a standardized emergency case-management algorithm for battlefield trauma. There was a high level of acceptance for this type of instruction. This is encouraging for medical educators involved in producing multimedia packages for teaching emergency medicine.

CD-ROM↗
PubMed1997

Assembly of the chimeric Na+/K+-ATPase and H+/K+-ATPase beta-subunit with the Na+/K+-ATPase alpha-subunit.

Two sets of chimeric beta-subunits were constructed from subunits of Torpedo californica Na+/K+-ATPase and pig gastric H+/K+-ATPase. Five unique restriction sites (SnaBI, EcoRV, MunI, SphI and EcoT22I) were created at equivalent positions of the respective cDNAs and were used as joining points for the construction. One set of chimeras (HxN series) was made by exchanging the 5' portion of the Na+/K+-ATPase beta-subunit cDNA with the corresponding portion of the H+/K+-ATPase beta-subunit cDNA at the respective joining point. Complementary constructs were also prepared (NxH series). In the HxN series, the chimera joined at the SnaBI site formed a stable trypsin resistant complex with the Na+/K+-ATPase alpha-subunit, which was functional with respect to ATP hydrolysis and pump current generation, although the activities were less than those of the complex with the Na+/K+-ATPase beta-subunit. Trypsin resistance decreased for the complex of the chimera joined at the EcoRV site. In the NxH series, the chimeras joined at the SnaBI site and the EcoRV site formed rather trypsin-resistant complexes, but the expressions of the alpha-subunits were below 50% of the control. The chimeras joined at the MunI, SphI and EcoT22I site formed complexes susceptible to tryptic digestion. None of the chimeras in the NxH series were functional. These results suggest that at least two regions of the Na+/K+-ATPase beta-subunit [SnaBI site(Tyr40) to EcoRV site(Ile89) and EcoT22I site(Cys176) to C-terminus)] are involved in stable assembly with the Na+/K+-ATPase alpha-subunit and that the cytoplasmic domain [N-terminus to SnaBI site(Tyr40)] is functionally replaceable with the corresponding domain of the H+/K+-ATPase beta-subunit.

Amino Acid Sequence↗
PubMed1997

The Ca2+/calmodulin binding domain of the Ca2+-ATPase linked to the Na+,K+-ATPase alters transport stoichiometry.

Using Xenopus oocytes as an expression system, we have investigated ion-transport and ouabain-binding properties of a chimeric ATPase (alpha1-CBD; Ishii and Takeyasu (1995) EMBO J. 14, 58-67) formed by the alpha1-subunit of chicken Na+,K(+)-ATPase (alpha1) and the calmodulin binding domain (CBD) of the rat plasma membrane Ca2(+)-ATPase. alpha1-CBD can be expressed and transported to the oocyte plasma membrane without the beta-subunit, and shows ouabain binding. In contrast to ouabain binding, this chimera requires the beta-subunit for its cation (Na+ and K+) transport activity. alpha1-CBD exhibits an altered stoichiometry of Na(+)-K+ exchange. A detailed analysis of 22Na+ efflux, 86Rb+ uptake, pump current and ouabain binding suggests that the chimeric molecule can operate in an electrically silent 2Na(+)-2K+ exchange mode and, with much lower probability, in its normal 3Na(+)-2K+ exchange mode.

Animals↗
PubMed1997

[Manual ultrasound of the knee joint. A general practice method for diagnosis of fresh rupture of the anterior cruciate ligament].

A prospective, arthroscopic controlled study was performed to evaluate the usefulness of mancal sonometry of the knee in the diagnosis of acute rupture of the anterior cruciate ligament (ACL). In 58 patients with an acute knee injury, a maximum of 30 days elapsed between accident and clinical examination (Lachmantest, pivot-shift/ McIntosh, 90 degrees anterior translation), manual sonometry and functional X-ray examination. Afterwards all patients were examined by arthroscopy. Nine patients showed a partial, 38 patients a total rupture of the ACL. If the ACL was completely ruptured, the average difference in anterior translation between the contralateral and the injured knee was 3.3 mm (p < or = 0.001). Statistical analysis showed high sensitivity (85%), specificity (91%) and positive predictive value (98%) for manual sonometry. Clinical examination, apparative sonometry and functional X-ray were, overall, less effective than manual sonometry in detecting ligament rupture. Manual sonometry proved to be a good and practicable method for assessing acute rupture of the ACL.

Adult↗