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K Pfeiffer

Publications and source records attributed to K Pfeiffer.

At least 19 recordsLinked to original sources
PubMed2004

Neurobiology of polarization vision in the locust Schistocerca gregaria.

The polarization pattern of the blue sky serves as an important reference for spatial orientation in insects. To understand the neural mechanisms involved in sky compass orientation we have analyzed the polarization vision system in the locust Schistocerca gregaria. As in other insects, photoreceptors adapted for the detection of sky polarization are concentrated in a dorsal rim area (DRA) of the compound eye. Stationary flying locusts show polarotactic yaw-torque responses when illuminated through a rotating polarizer from above. This response is abolished after painting the DRAs. Central stages of the polarization vision system, revealed through tracing studies, include dorsal areas in the lamina and medulla, the anterior lobe of the lobula, the anterior optic tubercle, the lateral accessory lobe and the central complex. Physiological analysis of polarization-sensitive (POL) neurons has focussed on the optic tubercle and on the central complex. Each POL neuron was maximally excited at a certain e-vector (phimax) and was maximally inhibited at an e-vector perpendicular to phimax. The neurons had large visual fields, and many neurons received input from both eyes. The neuronal organization of the central complex suggests a role as a spatial compass within the locust brain.

Animals↗
PubMed2001

The ratio of oxidative phosphorylation complexes I-V in bovine heart mitochondria and the composition of respiratory chain supercomplexes.

The ratios of the oxidative phosphorylation complexes NADH:ubiquinone reductase (complex I), succinate:ubiquinone reductase (complex II), ubiquinol:cytochrome c reductase (complex III), cytochrome c oxidase (complex IV), and F1F0-ATP synthase (complex V) from bovine heart mitochondria were determined by applying three novel and independent approaches that gave consistent results: 1) a spectrophotometric-enzymatic assay making use of differential solubilization of complexes II and III and parallel assays of spectra and catalytic activities in the samples before and after ultracentrifugation were used for the determination of the ratios of complexes II, III, and IV; 2) an electrophoretic-densitometric approach using two-dimensional electrophoresis (blue native-polyacrylamide gel electrophoresis and SDS-polyacrylamide gel electrophoresis) and Coomassie blue-staining indices of subunits of complexes was used for determining the ratios of complexes I, III, IV, and V; and 3) two electrophoretic-densitometric approaches that are independent of the use of staining indices were used for determining the ratio of complexes I and III. For complexes I, II, III, IV, and V in bovine heart mitochondria, a ratio 1.1 +/- 0.2:1.3 +/- 0.1:3:6.7 +/- 0.8:3.5 +/- 0.2 was determined.

Animals↗
PubMed2001

Association of soluble HLA-G plasma levels with HLA-G alleles.

Soluble HLA-G (sHLA-G) molecules are found in the peripheral blood of healthy females and males, in cord blood and in amniotic fluids and discussed to be a mediator in maternal-fetal tolerance. In this study we investigated whether there are allele-specific differences in expression of sHLA-G molecules. For this, the sHLA-G plasma concentrations of 94 healthy unrelated individuals were measured by ELISA and correlated to their HLA-G genotypes, as determined by sequence analysis of exon 2 and 3 of the HLA-G gene. Mean sHLA-G levels in individuals with the most common HLA-G alleles G*01011 (27.0+/-2.1 SEM ng/ml, n=66), G*01012 (28.4+/-3.2 SEM ng/ml, n=34) were very similar. In contrast, individuals carrying the HLA-G*01013 (8.1+/-1.7 SEM ng/ml, n=17) or the "null" allele HLA-G*0105N (8.2+/-3.2 SEM ng/ml, n=7) presented significantly (P(c)=0.001 and P(c)<0.01, resp.) reduced sHLA-G levels. Furthermore, individuals with the HLA-G*01041 allele had significantly (P(c)=0.004) increased sHLA-G levels (42.5+/-4.6 SEM ng/ml, n=14). These results demonstrate that the generation of sHLA-G molecules is associated to certain HLA-G alleles and imply that sHLA-G levels are under genetic control. As low and high sHLA-G plasma levels did not segregate with HLA haplotypes including the HLA-G*01013 or *01041 allele, additional mechanisms may be involved in the regulation of the individual sHLA-G levels. Nevertheless, the existence of "low" and "high secretor" HLA-G alleles further suggests different levels of functionality in immune regulation.

Alleles↗
PubMed2001

Real-time dose calculation and visualization for the proton therapy of ocular tumours.

A new real-time dose calculation and visualization was developed as part of the new 3D treatment planning tool OCTOPUS for proton therapy of ocular tumours within a national research project together with the Hahn-Meitner Institut Berlin. The implementation resolves the common separation between parameter definition, dose calculation and evaluation and allows a direct examination of the expected dose distribution while adjusting the treatment parameters. The new tool allows the therapist to move the desired dose distribution under visual control in 3D to the appropriate place. The visualization of the resulting dose distribution as a 3D surface model, on any 2D slice or on the surface of specified ocular structures is done automatically when adapting parameters during the planning process. In addition, approximate dose volume histograms may be calculated with little extra time. The dose distribution is calculated and visualized in 200 ms with an accuracy of 6% for the 3D isodose surfaces and 8% for other objects. This paper discusses the advantages and limitations of this new approach.

Algorithms↗
PubMed2000

The correlation of office blood pressure and 24-hour ambulatory measurements in hypertensive patients - comparison between non-pharmacological treatment and antihypertensive medication.

Blood pressure control in many hypertensive patients remains imperfect, also because routine office blood pressure can only give limited information about diurnal variations and nocturnal dipping. It was the aim of our evaluation to study the efficacy of antihypertensive therapy and the correlation between repeated office blood pressure values and 24-hour ambulatory measurements in hypertensive outdoor patients treated by life-style modification and antihypertensive medication. Clinical data and blood pressure values in 343 outdoor patients who were admitted to the medical centre for diagnostic and therapeutic procedures in hypertension were evaluated. Database was created from 1991 to 1998. The study population (mean age 59.5 +/- 11.6 years) comprised 153 men and 190 women, 141 (41%) were treated by life-style modification, 202 (59%) received antihypertensive medication. 57 patients showed symptoms of a metabolic syndrome, 62 suffered from manifest diabetes mellitus type 2. - Repeated office blood pressure measurements showed a significant positive correlation to the systolic and diastolic values obtained by 24-hour blood controls. While diastolic night minima revealed a positive correlation to office measurements (R = 0. 211; P <0.05), systolic night minima showed no correlation to office pressure control. In the whole study population and in subgroups (metabolic syndrome, diabetes mellitus) patients under antihypertensive medication still revealed significantly higher mean 24-hour systolic blood pressure values (140.5 +/- 16.9 mm Hg) than patients treated by life-style modification (133.0 +/- 14.4 mm Hg; P <0.001). Diastolic day- and night-time difference (dipping) was less pronounced in patients with antihypertensive medication. For appropriate antihypertensive therapy 24-hour blood pressure measurements are thus of advantage to repeated office controls especially to optimize medication for high systolic blood pressure values and adapt therapy to the nocturnal decrease of blood pressure values (dipping).

Aged↗
PubMed2000

Supercomplexes in the respiratory chains of yeast and mammalian mitochondria.

Around 30-40 years after the first isolation of the five complexes of oxidative phosphorylation from mammalian mitochondria, we present data that fundamentally change the paradigm of how the yeast and mammalian system of oxidative phosphorylation is organized. The complexes are not randomly distributed within the inner mitochondrial membrane, but assemble into supramolecular structures. We show that all cytochrome c oxidase (complex IV) of Saccharomyces cerevisiae is bound to cytochrome c reductase (complex III), which exists in three forms: the free dimer, and two supercomplexes comprising an additional one or two complex IV monomers. The distribution between these forms varies with growth conditions. In mammalian mitochondria, almost all complex I is assembled into supercomplexes comprising complexes I and III and up to four copies of complex IV, which guided us to present a model for a network of respiratory chain complexes: a 'respirasome'. A fraction of total bovine ATP synthase (complex V) was isolated in dimeric form, suggesting that a dimeric state is not limited to S.cerevisiae, but also exists in mammalian mitochondria.

ATP Synthetase Complexes↗
PubMed2000

[A 3-D capsular bag model for describing biomechanical properties of neu intraocular lenses].

BACKGROUND: This study quantified the geometric deformation of the capsular bag following implantation of various intraocular lenses (IOL) using a three-dimensional capsular bag model made of silicone caoutchouc. METHODS: After implantation of 13 different IOLs (polymethylmethacrylate, silicone acrygel) into the artificial bag, the induced capsular bag deformation was measured and analyzed. The posterior space between IOL and capsule was examined by ultrasonographic biomicroscopy. RESULTS: Polymethylmethacrylate IOLs with C-haptic design induced a greater deformation of the capsular bag than silicone lenses; however, both types showed a larger gap posterior to the IOL than acrygel lenses. Acrygel IOLs with different haptic design revealed only minimal deformation with close contact posteriorly. CONCLUSIONS: The presented three-dimensional model simulates the biomechanical and geometrical parameters of the vital capsular bag. Further investigations may determine a correlation of close posterior IOL contact and lens epithelial cell progression.

Biomechanical Phenomena↗
PubMed2000

Digoxin, flecainide, and amiodarone transfer across the placenta and the effects of an elevated umbilical venous pressure on the transfer rate.

Clinical observations suggest that flecainide might pass the placenta more easily than digoxin, and that its transfer is less disturbed in case of hydrops fetalis than that of digoxin. The purpose of the study was to compare the materno-fetal transplacental transfer of digoxin, flecainide, and amiodarone, another antiarrhythmic agent used in the treatment of fetal tachyarrhythmia, and to assess the effect of an elevated umbilical venous pressure (UVP) on the transfer rate. Isolated lobules of 16 human placentas were dually perfused after spontaneous delivery or caesarean section. The transplacental transfer (area under the curve in the maternal compartment [maternal AUC], area under the curve in the fetal compartment [fetal AUC], kinetic parameters) of digoxin, flecainide, and amiodarone was calculated after these drugs were added to the maternal circuit. In five experiments, the effect of increased UVP on the transplacental transfer rate was assessed by elevating the UVP by 10 cm H2O. Flecainide efflux out of the maternal compartment was significantly greater than that of digoxin (maternal AUC 57.4% +/- 5.1 %/min vs 73.9% +/- 1.5%/min), whereas the flecainide influx into the fetal circulation was smaller (fetal AUC 9.3% +/- 4.1%/min vs 11.5% +/- 2.0%/min). Only in 50% of the experiments were the smallest amounts of amiodarone detectable in the fetal compartment. An elevation of the UVP reduced the influx of digoxin and flecainide into the fetal compartment (fetal AUC) from 11.5% +/- 2.0%/min to 7.4% +/- 1.9%/min and from 9.3% +/- 4.1% to 4.7% +/- 1.4%/min, respectively. Materno-fetal transplacental transfer of digoxin, flecainide, and amiodarone decreases in this sequence. Fetal cardiac insufficiency accompanied by an elevation of the UVP might reduce the transplacental transfer of these drugs, although no significant difference could be found between the reduction of transfer of digoxin and flecainide.

Amiodarone↗
PubMed1999

ATP synthase of yeast mitochondria. Isolation of subunit j and disruption of the ATP18 gene.

The subunit composition of the mitochondrial ATP synthase from Saccharomyces cerevisiae was analyzed using blue native gel electrophoresis and high resolution SDS-polyacrylamide gel electrophoresis. We report here the identification of a novel subunit of molecular mass of 6,687 Da, termed subunit j (Su j). An open reading frame of 127 base pairs (ATP18), which encodes for Su j, was identified on chromosome XIII. Su j does not display sequence similarity to ATP synthase subunits from other organisms. Data base searches, however, identified a potential homolog from Schizosaccharomyces pombe with 51% identity to Su j of S. cerevisiae. Su j, a small protein of 59 amino acid residues, has the characteristics of an integral inner membrane protein with a single transmembrane segment. Deletion of the ATP18 gene encoding Su j led to a strain (Deltasu j) completely deficient in oligomycin-sensitive ATPase activity and unable to grow on nonfermentable carbon sources. The presence of Su j is required for the stable expression of subunits 6 and f of the F0 membrane sector. In the absence of Su j, spontaneously arising rho- cells were observed that lacked also ubiquinol-cytochrome c reductase and cytochrome c oxidase activities. We conclude that Su j is a novel and essential subunit of yeast ATP synthase.

Amino Acid Sequence↗
PubMed1999

Detection of soluble HLA-G molecules in plasma and amniotic fluid.

Although the cDNA sequence of HLA-G antigens is compatible with their expression as soluble molecules (sHLA-G), the determination of native sHLA-G levels in body fluids has not yet been described. The lack of this information is likely to reflect the difficulties in developing an assay suitable to measure sHLA-G antigens in the presence of soluble HLA-A, -B and -C (sHLA-I) antigens, since most of the available anti-HLA-G mAb do not detect soluble beta2-m associated HLA-G antigens or crossreact with sHLA-I antigens. Therefore, we have developed a two-step assay which eliminates the interference of classical HLA class I antigens. In the first step, the sample is depleted of sHLA-I antigens and of HLA-E antigens with mAb TP25.99. Then, HLA-G antigens are captured with mAb W6/32 and detected with anti-beta2-m mAb in ELISA. Utilizing this assay, sHLA-G antigen levels were measured in EDTA plasma from 92 controls with known HLA types, 28 women at delivery and the corresponding cord bloods and in 50 amniotic fluids. Mean sHLA-G plasma levels did not differ between males (24.9+/-3.0 SEM ng/ml; n=42) and females (20.1+/-2.1 SEM ng/ml; n = 50). However, sHLA-G levels in HLA-A11 positive probands (mean: 13.0+/-4.4 SEM ng/ml; n=12) were significantly (P<0.05) lower than in HLA-A11 negative ones (mean: 24.5+/-2.0 SEM ng/ml; n=80). sHLA-G levels in women at delivery (mean: 22.9+/-2.2 SEM ng/ml; n=28) were in the range of controls but were significantly (P<0.001) reduced in the corresponding cord bloods (mean: 13.8+/-1.5 SEM ng/ml; n=28). sHLA-G levels in amniotic fluids (mean: 15.5 + 1.0 SEM ng/ml; n=50) were significantly (P<0.001) lower than in plasma. sHLA-G levels were 5 and 11% of those of sHLA-I antigens in plasmas and amniotic fluids, respectively. Individual sHLA-G levels were not correlated with sHLA-I levels. SDS-PAGE analysis of plasma sHLA-G antigens revealed two molecular variants with a 35 kD and a 27 kD MW corresponding to the sizes of sHLA-G1 and -G2 isoforms. In conclusion, our study has shown that the two-step assay we have developed is reliable in measuring sHLA-G antigen levels. This assay will facilitate the analysis of the biological and clinical significance of sHLA-G antigens in plasma.

Adult↗
PubMed1998

Yeast mitochondrial F1F0-ATP synthase exists as a dimer: identification of three dimer-specific subunits.

Using the technique of blue native gel electrophoresis, the oligomeric state of the yeast mitochondrial F1F0-ATP synthase was analysed. Solubilization of mitochondrial membranes with low detergent to protein ratios led to the identification of the dimeric state of the ATP synthase. Analysis of the subunit composition of the dimer, in comparison with the monomer, revealed the presence of three additional small proteins. These dimer-specific subunits of the ATP synthase were identified as the recently described subunit e/Tim11 (Su e/Tim11), the putative subunit g homolog (Su g) and a new component termed subunit k (Su k). Although, as shown here, these three proteins are not required for the formation of enzymatically active ATP synthase, Su e/Tim11 and Su g are essential for the formation of the dimeric state. Su e/Tim11 appears to play a central role in this dimerization process. The dimer-specific subunits are associated with the membrane bound F0-sector. The F0-sector may thereby be involved in the dimerization of two monomeric F1F0-ATP synthase complexes. We speculate that the F1F0-ATP synthase of yeast, like the other complexes of oxidative phosphorylation, form supracomplexes to optimize transduction of energy and to enhance the stability of the complex in the membrane.

Amino Acid Sequence↗
PubMed1998

Identification and characterization of a novel 9.2-kDa membrane sector-associated protein of vacuolar proton-ATPase from chromaffin granules.

Vacuolar proton-translocating ATPase (holoATPase and free membrane sector) was isolated from bovine chromaffin granules by blue native polyacrylamide gel electrophoresis. A 5-fold excess of membrane sector over holoenzyme was determined in isolated chromaffin granule membranes. M9.2, a novel extremely hydrophobic 9.2-kDa protein comprising 80 amino acids, was detected in the membrane sector. It shows sequence and structural similarity to Vma21p, a yeast protein required for assembly of vacuolar ATPase. A second membrane sector-associated protein (M8-9) was identified and characterized by amino-terminal protein sequencing.

Amino Acid Sequence↗
PubMed1998

Diatomaceous earth lowers blood cholesterol concentrations.

In this study a potential influence of diatomaceus earth to lower blood cholesterol was investigated. During 12 weeks we monitored serum lipid concentrations in 19 healthy individuals with a history of moderate hypercholesterinemia (9 females, 10 males, aged 35 - 67 years). Individuals administered orally 250 mg diatomaceous earth three-times daily during an 8 weeks observation period. Serum concentrations of cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol and triglycerides levels were measured before study entry, every second week during the period of diatomaceous earth intake and 4 weeks after stop of intake. Compared to baseline (285.8 +/- 37.5 mg/dl = 7.40 +/- 0.97 mM) diatomaceous earth intake was associated with a significant reduction of serum cholesterol at any time point, reaching a minimum on week 6 (248.1 mg/dl = 6.43 mM, -13.2% from baseline; p<0.001). Also low-density lipoprotein cholesterol (week 4: p<0.05) and triglycerides levels decreased (week 2: p<0.05, week 4: p<0.01). Four weeks after intake of diatomaceous earth was stopped, serum cholesterol, low-density lipoprotein cholesterol and triglycerides still remained low and also the increase of high-density lipoprotein cholesterol became significant (p<0.05). Diatomaceous earth, a bioproduct, is capable of reducing blood cholesterol and positively influencing lipid metabolism in humans. Placebo-controlled studies will be necessary to confirm our findings.

Adult↗
PubMed1998

Vibroacoustic Stimulation of the Fetus Using a Conventional Mechanical Alarm Clock.

> Objective: For more than 20 years, vibroacoustic stimulation testing (VAST) using an artificial larynx has been used worldwide when fetal heart rate monitoring produced patterns with absent or very low variability. In addition to the artificial larynx many other appliances have been used to stimulate a seemingly dormant fetus, but these have rarely been evaluated properly. In this study we tried to evaluate the use of standard mechanical wind-up alarm clocks for VAST. Methods: VAST with an alarm clock was performed successfully in 80 women with normal pregnancies from 36 weeks to term. It was tested by placing the alarm clock on the maternal abdomen just above the fetal head or on the controlateral side of the maternal abdomen to see whether position made any difference and whether coupling with ultrasound gel applied between the alarm clock and the maternal abdomen would affect the degree of fetal reaction to VAST as expressed in heart rate acceleration. Similarly, the effect of the alarm clock VAST on subjective and objective fetal movement patterns as registered by kineto-cardiotocotraphy (K-CTG) in addition to heart rate patterns was investigated. Results: All fetuses showed heart rate acceleration, an increase in heart variability, and increase in movement patterns in the 6 min after the application of alarm clock VAST. No statistically significant difference was found which would favor a particular placement of the alarm clock on the maternal abdomen or the use of ultrasound coupling gel. When K-CTG was performed, patient-perceived fetal movements as expressed with an event marker showed agreement with the machine-registered movements only when patients could see the tracing during registration and no accordance when the K-CTG was turned toward the wall during registation. Conclusion: In keeping with the ALARA principle a conventional wind-up alarm clock appears to be an inexpensive and effective alternative to the electrolarynx.

Journal Article↗
PubMed1997

The direct determination of urinary oxalate by non-suppressed ion chromatography.

In this paper we describe a simple ion chromatographic method for determination of oxalate in urine. Acidified urine was diluted 1:2 with 0.03 mol/l benzidine hydrochloride in 0.3 mol/l boric acid to precipitate sulphate. The supernatant was passed through a C18-cartridge and 100 microliters of eluant were injected into an ion chromatographic system. Oxalate was measured by nonsuppressed conductivity detection. The detection limit for urinary oxalate was 0.05 mmol/l. The recovery for spiked urine samples was 101.5% with a CV of 4.5%. The within- and between-assay coefficients of variation were less than 4.5% and 2.5%, respectively. We found the results obtained by this method to be statistically equivalent to an enzymatic assay and a different ion-chromatographic method.

Analysis of Variance↗
PubMed1996

Electrophoretic separation of multiprotein complexes from blood platelets and cell lines: technique for the analysis of diseases with defects in oxidative phosphorylation.

A two-dimensional electrophoretic technique combining blue native polyacrylamide gel electrophoresis (BN-PAGE) with Tricine sodium dodecyl sulfate (SDS)-PAGE was previously used for the localization of oxidative phosphorylation (OXPHOS) defects in human diseases starting from biopsy or autopsy tissues (Schägger, H., Electrophoresis 1995, 16, 763-770). In the present work the technique was extended for the resolution of OXPHOS enzymes from platelets and tissue-cultured cells. Silver staining is required to detect the protein subunits of OXPHOS complexes in two-dimensional gels. However, the use of cultured cells has major implications for patients with mitochondrial encephalomyopathies since it will reduce the number of invasive muscle biopsies. The ease of isolating the platelet membrane glycoprotein complex from a few milliliters of blood makes it possible to analyze this complex and its protein subunits in bleeding disorders like Glanzmann's thrombasthenia.

3T3 Cells↗