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G Schwarz

Publications and source records attributed to G Schwarz.

At least 19 recordsLinked to original sources
PubMed1992

Kinetics of melittin induced pore formation in the membrane of lipid vesicles.

We have investigated the permeabilization of POPC unilamellar vesicle bilayers upon the addition of melittin. This process was measured in an early time range of a few minutes by means of monitoring the release of an entrapped marker, the self-quenching fluorescent dye carboxyfluorescein. Pore formation is indicated by an apparent 'all-or-none' efflux out of individual vesicles and a higher than linear dependence on melittin concentration. Applying a recently developed evaluation procedure, the data are readily converted into the gross number of pores per vesicle formed within the elapsed measuring time t. The results can be generally described in terms of a fast initial rate of pore formation that slows down to a much lower value after a period of about 1 to 2 minutes, following a single exponential time course. The three rate parameters involved are shown to be power functions of the concentration of melittin that is actually associated with the vesicle membrane. These findings are in excellent quantitative agreement with a proposed scheme of reaction steps where the formation of lipid associated peptide dimers becomes rate determining once an initial fast deposit is exhausted.

Ion Channel Gating↗
PubMed1992

Shear stress induced membrane currents and calcium transients in human vascular endothelial cells.

We have measured membrane currents induced by shear stress together with intracellular calcium signals in endothelial cells from human umbilical cord veins. In the presence of extracellular calcium (Ca2+]o), shear stress induced an inward current at a holding potential of 0 mV which is accompanied by a rise in intracellular Ca2+ ([Ca2+]i). In the absence of extracellular calcium shear stress was unable to evoke a calcium signal but still induced a membrane current. The voltage dependence of the shear stress induced current was obtained from difference currents evoked by linear voltage ramps before and during application of shear stress. Its reversal potential Erev shifted from -2.3 +/- 0.8 mV (n = 4) in a nominally Ca2+ free solution to +1.5 +/- 1.6 mV at 1.5 mM [Ca2+]o (n = 4) and to +21.9 +/- 4.4 mV (n = 7) at 10 mM [Ca2+]o. From our data we conclude that shear stress opens an ion channel that is 12.5 +/- 2.9 (n = 7) times more permeable for calcium than for sodium or cesium.

Calcium↗
PubMed1992

Brain death: timing of apnea testing in primary brain stem lesion.

In a 73-year-old patient complete areflexia of the cerebral and peripheral nerves following the rupture of an aneurysm of the basilar artery was diagnosed. During apnea testing the spectral analysis of electroencephalography (EEG) revealed an irreversible shift of peak from 6 to 3 Hz within the low-frequency bands. These findings suggest that apnea testing in patients with primary lesion of the brain stem should be carried out only after an isoelectric EEG.

Aged↗
PubMed1992

HLA and immunoglobulin polymorphisms in idiopathic dilated cardiomyopathy.

Dilated cardiomyopathy (DCM) is an idiopathic heart muscle disorder. The presence of circulating cardiac antibodies and the association with HLA-DR4 are consistent with autoimmune pathogenesis in a subset of patients. Sixty-eight DCM patients and 277 controls were typed for IgG heavy-chain constant region (Gm) and kappa light-chain (Km) allotypes. All patients and 210 of the 277 controls were HLA-DR typed. The Gm (1, 3, 17; 23; 5*, 21, 28) phenotype was overrepresented in DCM compared with controls (25% vs 13%, p = 0.0139, pc = NS, RR = 2.23). The frequency of this phenotype was higher in patients with younger age at onset, shorter symptom duration, and among those who were positive for cardiac as well as for non-organ-specific autoantibodies than in controls. A higher frequency of the Gm (1, +/- 2, 3, 17; +/- 23; 5*, 21, 28) heterozygous phenotypes was also found in DCM compared to controls (40.91% vs 26.89%; p = 0.02, pc = 0.04, RR = 1.88). The finding of Gm heterozygosity in DCM was associated with serum positivity for cardiac antibodies. A higher proportion of DCM patients were positive for both the Gm (1, 3, 17; 23; 5*, 21, 28) phenotype and HLA-DR4 compared to normals (3/68 vs 0/210; p = 0.04, RR = 22.50).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Kinetics of pore-mediated release of marker molecules from liposomes or cells.

We present a general mathematical treatment of marker efflux from liposomes or cells mediated by pore formation with the idea of using it in practice to obtain basic information about the underlying rates and mechanism. The approach encompasses permeation of molecules through any kind of pore-like defects in a cell membrane as they are induced by the action of some external agent. The approach broadens an earlier treatment to the more realistic general case in which a distribution of pore lifetimes must be taken into account. We derive a theoretical retention function describing the amount of marker remaining in the cells, formulated in terms of the pore activation and inactivation kinetics. The phenomenological efflux function evaluated directly from experimental data, is directly comparable with this retention function so long as the experimental signal is linearly related to the marker concentration. With the use of self-quenching dyes the relationship between signal and concentration is not, in general, linear, so that a more complicated treatment may be required. Even for these dyes, however, linearity holds under the frequently encountered condition of "all-or-none" release of dye from vesicles, a condition that can itself be verified experimentally.

Fluorescent Dyes↗
PubMed1992

Idiopathic dilated cardiomyopathy: lack of association between circulating organ-specific cardiac antibodies and HLA-DR antigens.

Organ-specific cardiac antibodies are serological markers of autoimmunity in dilated cardiomyopathy (DCM). HLA-DR4 and possibly DR5 are immunogenetic markers of susceptibility in DCM, but it is not known whether they are associated with autoantibody production. We studied the frequency of HLA-DR antigens and the presence of organ-specific cardiac antibodies in 80 DCM Caucasian patients from Northern Italy. HLA-DR typing was performed by serology; 289 healthy blood donors from the same region were tested as controls. HLA-DR frequencies in DCM were also compared with VIII International Workshop control data for Italy. Cardiac antibodies were detected by indirect immunofluorescence on human heart. Skeletal muscle was used to identify cross-reacting antibodies. The prevalence of cardiac antibodies in DCM was: organ-specific 34% and skeletal muscle cross-reactive 30%. The previously reported positive association between DCM and HLA-DR4 was confirmed using either the controls from the same region (21.25% vs 10.73% p = 0.02, relative risk = 2.30) or from all of Italy (21.25% vs 12.3%, p = 0.03). HLA-DR5 frequency was slightly but not significantly higher in DCM than in controls from the same region (46.25% vs 31.49% p = 0.02, relative risk of 1.87, p corrected = NS) or from all of Italy (46.25% vs 35.8% p = NS). HLA-DR3 frequency was lower in DCM than in controls from the same region (12.50% vs 29.41% p = 0.003, relative risk of 0.36, p corrected = 0.03). This negative association was not confirmed using the control data from the whole of Italy (12.50% vs 16.5% p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Shear stress-induced calcium transients in endothelial cells from human umbilical cord veins.

1. Changes of the free cytosolic Ca2+ concentration induced by shear stress were measured in Fura-2 acetoxymethyl ester-loaded endothelial cells from human umbilical cord veins. 2. We were able to induce Ca2+ transients in almost every cell by blowing a stream of physiological solution onto a single endothelial cell thereby inducing shear stress between 0 and 50 dyn cm-2. The Ca2+ response could be graded by varying the shear stress, and reached a half-maximal value at a shear stress of 30 dyn cm-2. 3. The shear stress responses critically depended on the extracellular Ca2+ concentration and were absent in a Ca(2+)-free solution. Repetitive application of short pulses of shear stress induced cumulative effects because of the slow decay of the shear stress Ca2+ responses (time constants 82.3 +/- 17.8 s from twenty-five cells). Application of a depolarizing high potassium solution to reduce the driving force for Ca2+ entry decreased the Ca2+ transients in some of the cells. 4. Application of shear stress in the presence of other divalent cations, such as nickel, cobalt or barium, always produced substantial changes in the ratio of the 390/360 nm fluorescence signal, indicating influx of these cations and subsequent quenching of the Fura-2 fluorescence. 5. Shear stress responses in the presence of 10 mM Ca2+ were completely blocked by application of 1 mM La3+. 6. Incubation of the cells with the phorbol ester 12-O-tetradecanoyl phorbol-13-acetate (TPA) did not alter the shear stress response, but completely blocked histamine-induced Ca2+ transients. 7. Small submaximal shear stress potentiated the Ca2+ transients induced by histamine. 8. We conclude that shear stress-dependent Ca2+ signals are induced by an influx of calcium that is not modulated via protein kinase C and not activated by membrane depolarization. The influx pathway is also permeable to divalent cations such as Ni2+, Co2+ and Ba2+, but is blocked by La3+.

Barium↗
PubMed1992

Tumor necrosis factor beta gene polymorphisms in Graves' disease.

The physical mapping of tumor necrosis factor alpha (TNF alpha) and lymphotoxin (TNF beta) genes to the short arm of chromosome 6 in man between the loci for histocompatibility leucocyte antigens (HLA)-B and the complement system focused attention to this genetic region that controls immune responses in many ways. It also holds susceptibility genes for a variety of autoimmune disorders that are linked to specific alleles of loci in the HLA D subregion. We have recently identified a TNF restriction fragment length polymorphism with the enzyme NcoI (K. Badenhoop, G. Schwarz, J. Trowsdale, et al. Diabetologia. 1989;32:445-8). The less frequent fragment of 5.5 kilobase (kb) is in strong linkage disequilibrium with the HLA haplotype A1B8DR3. Since Graves' disease is linked to A1B8DR3, we analyzed TNF gene polymorphisms in a large group of Graves' disease patients and normal controls derived from four Centers. We show here a significant association of TNF beta polymorphisms with Graves' disease. The patients have less homozygotes for the 10.5 kb band (60 of 174, 34%) and more heterozygotes 10.5/5.5 kb (96 of 174, 55%), than 173 controls (49% homozygotes 10.5 kb and 42% heterozygotes; chi 2 = 7.45, P less than 0.03). When DR3+ patients and controls were analyzed separately, heterozygotes were still significantly increased in DR3+ Graves' disease patients (54 of 77, 70%) compared to DR3+ controls (21 of 45, 47%; chi 2 = 6.6, P less than 0.04). Furthermore, TNF fragment heterozygotes were found predominantly in patients, who had TSH-receptor antibodies (29/45, 64%, P less than 0.007), implying that these patients might represent an immunogenetic subset of the disease. Although TNF beta polymorphisms are linked to A1B8DR3, these results suggest that they represent an additional susceptibility marker in Graves' disease.

Autoantibodies↗
PubMed1992

[Acoustic evoked brainstem potentials--patterns of stimulus artefacts in irreversible coma].

Brainstem auditory evoked potentials (BAEP) were performed in a total of 20 subjects (mean age 33.2 +/- 15.1 years; severe head injury in most cases) with the diagnosis of coma dépassé. The control group consisted of 33 healthy volunteers (mean age 26.9 +/- 5.3 years). The presence, latency and amplitude of the single BAEP-components and the variations of the stimulus artifact were evaluated. The mean amplitudes of the stimulus artifact of the brain dead subjects were calculated (means +/- SD) to be 0.26 +/- 0.12 microV (control group: 0.11 +/- 0.03 microV). Pathological alterations of the mechanics of the inner ear as well as extracerebral changes in conductivity or stimulus related depolarization processes in extracerebral parts of the auditory system were taken into consideration to be possible reasons for this significant (p less than 0.001; t-test) difference.

Adolescent↗
PubMed1991

A combined study of aggregation, membrane affinity and pore activity of natural and modified melittin.

The pore activity of melittin and several chemically modified derivatives has been investigated using conductance measurements on planar lipid bilayers and marker release from small unilamellar vesicles. The modifications included N-terminal formylation, acetylation, succinylation and modification of the tryptophan residue. All of the compounds showed bilayer permeabilizing properties, though quantitative differences were evident. These comprised changes in the voltage dependence of the conductance, in the single-pore kinetics, in the concentration of aqueous peptide required to induce a given pore activity and in the apparent 'molecularity' reflected by the power law of its concentration dependence. A strong tendency for disrupting bilayers was not always correlated with strong pore activity. For a better understanding of these results, measurements of pore activity were complemented by studying the aggregation behavior in solution and the water-membrane partition equilibrium. Modifications of charged residues gave rise to significant changes in the aggregation properties, had virtually no influence on the partition coefficient. The latter decreased strongly, however, as a result of tryptophan modification. Analysis of the isotherms was consistent with the assumption that the arginine residues in melittin do not contribute very much to charge accumulation at the immediate membrane/water interface.

Acetylation↗
PubMed1991

Melittin induced voltage-dependent conductance in DOPC lipid bilayers.

Melittin-induced conductance was measured on planar bilayers made from dioleoylphosphatidylcholine. Upon application of a fixed voltage, the current response was monophasic and remained so even after prolonged observation times. The conductance of melittin-doped bilayers increased exponentially with voltage. In addition, an ohmic contribution appeared after some current had passed. The voltage-dependent conductance increased e-fold every 22 mV and was proportional to the fourth power of the aqueous monomeric peptide concentration, for all salt concentrations investigated (0.4-1.8 M NaCl). Discrete conductance steps could be resolved at all these salt concentrations. The amplitudes of these steps were highly variable. In each experiment, conductance was initially only observed for potentials which were positive on the side of peptide addition. As more and more current passed across the bilayer, the current-voltage curves became symmetric. The system needed some time to reach stationary current-voltage characteristics: about 50 min at pH 7 but only about 15 min at pH 8, suggesting involvement of the N-terminus (pK around 7.5) of melittin in the slow formation of a 'prepore'.

Amino Acid Sequence↗
PubMed1990

Primary structure of Torpedo marmorata chloride channel isolated by expression cloning in Xenopus oocytes.

A complementary DNA encoding a voltage-gated chloride channel from Torpedo marmorata electric organ was cloned by expressing hybrid-depleted messenger RNA in Xenopus oocytes. The predicted protein has a sequence of 805 amino acids containing several putative membrane-spanning domains. Expression of the protein in Xenopus oocytes shows that it is sufficient for channel function.

Amino Acid Sequence↗
PubMed1990

Electrostatics of a peptide at a membrane/water interface. The pH dependence of melittin association with lipid vesicles.

The association of the peptide melittin with small unilamellar DMPC vesicles was studied as a function of pH. The results are discussed quantitatively assuming a water-membrane partition equilibrium. Electrostatic surface charging is taken into account as more and more of the strongly basic peptide accumulates at the bilayer/water interface. The data could be well described in terms of a Gouy-Chapman approach involving an effective interfacial charge well below the actual physical charge carried by the individual peptide molecules. The partition coefficient turned out to be pH invariant, so that one can exclude deprotonation reactions upon insertion of the peptide into the bilayer. The effective interfacial charge per associated melittin molecule decreased over a broad range of pH (pH 7 to pH above 10). Contributions of the free amino terminus and of the arginine residues could be determined by comparing with results obtained using modified melittin (N-terminally formylated and fully acetylated). The data suggest approximately equal fractional contributions of the amino terminus and the three lysines to the effective interfacial charge. The two arginines contribute less. Thus, they may be located farther away from the interface or be closely associated with counter-ions. The analysis is extended to the effect of different ionic strengths.

Bee Venoms↗
PubMed1990

HLA associations in patients with polycystic ovaries and in patients with congenital adrenal hyperplasia caused by 21-hydroxylase deficiency.

Ninety-nine Caucasian patients with ultrasonically detected polycystic ovaries (PCO) were typed for human leucocyte (HLA) antigens. Fifty patients with congenital adrenal hyperplasia (CAH) caused by 21-hydroxylase deficiency were similarly typed. Among the patients with PCO, there was a significant increase in the frequency of HLA DRW6 (P = 0.0027) compared with that found in a control population, which remained significant (P = 0.027) when corrected for the number of antigens tested. This difference was reduced, but remained significant (P = 0.006), when the patients with CAH and PCO were added. There was also a significant decrease in the frequency of HLA DR7 (P = 0.017) among the patients with PCO compared with a control population, but there was no distortion of the frequencies of HLA A, B or Cw antigens. Among the patients with CAH, previously well documented associations of HLA B14 and DR1 with non-classical disease were confirmed. The frequency of HLA Bw47 was increased among the whole group of CAH patients (P = 0.05) but was not increased among those with classical salt-wasting (SW) or simple virilizing (SV) disease. Family studies were performed in close female relatives of 16 of the PCO patients and 21 of the CAH patients but no evidence for genetic linkage between HLA and PCO status could be found. These data suggest that there is no significant component of disturbed adrenal steroid 21-hydroxylase activity to account for the PCO morphology, although there may be some other genetic factor, more proximal to the centromere on chromosome 6, affecting the development of polycystic ovaries.

Adrenal Hyperplasia, Congenital↗
PubMed1990

Restriction fragment length polymorphism analysis of HLA haplotypes in families with type I diabetes mellitus.

HLA Class II polymorphisms were analysed in 27 families with at least one Type I diabetic proband using Southern blotting technique according to 10th Histocompatibility Workshop Standards. The probes used were DRB, DQA1, DQB1 and DOB. We have studied 108 haplotypes and performed segregation analysis with HLA serology and restriction fragment length polymorphism (RFLP) data and compared "affected" with "non-affected" haplotypes (not inherited by IDDM patients). RFLPs correlated well with DR and DQ serology and detected additional polymorphisms. In particular, DQB polymorphism analysis showed segregation of the DQw3 splits with 88.5% of the DR4 affected haplotypes bearing the DQw3.2 split (now DQw8) and 11.5% the DQw3.1 split (now DQw7) while in the non-affected DR4 haplotypes 33.3% were DQw3.2 and 66.6% were DQw3.1. Haplotype analysis showed that DR4-DQw3.2 was in strong linkage with the U fragment (2.1 kb Taq I) of DQA2 (DX alpha) and with the L fragment (5.4 kb BamH I) of DOB. This study confirms previous observations of DQB polymorphisms in heterozygous IDDM patients, supports the protective effect of DQw3.1 (DQw7) against the development of the disease and demonstrates the importance of DQw3.2 (DQw8) for susceptibility to Type I diabetes.

Diabetes Mellitus, Type 1↗
PubMed1990

Susceptibility to thyroid autoimmune disease: molecular analysis of HLA-D region genes identifies new markers for goitrous Hashimoto's thyroiditis.

Hashimoto's thyroiditis has been shown to be associated with the HLA-specificities DR4 and DR5. Since former association studies yielded variable results, we used novel molecular typing methods to assess predisposing immunogenetic factors. Gene analysis of the HLA-DR-DQ and tumor necrosis factor region was performed in a group of Hashimoto's thyroiditis patients and randomly chosen controls using standards and nomenclature of the 10th International Histocompatibility Workshop. Genomic DNA of patients and controls was analyzed using a cDNA probe of the DQB1 gene. The resulting restriction fragment patterns allowed the determination of newly defined DQw-types 1-9. We find the strongest relative risk conferred by DQw7 (RR = 4.7), that is observed in 36 of 64 patients (56%) and only 21 of 98 controls (21%) (P corr less than 0.002). Comparison of DNA sequence variation in the DQB1 gene, that is found predominantly in Hashimoto's thyroiditis patients, indicates that codons 45 and 57 are critical features in DQw7 which distinguish it from other DQw specificities. The adjacent DQA1 genes also display a significant association with Hashimoto's thyroiditis (DQA1*0201/*0301 heterozygotes were found in 37% of patients and 15% controls, P less than 0.03). No significant association could be found with polymorphisms of the tumor necrosis factor gene. These results provide a new basis for the concept of genetic susceptibility in Hashimoto's thyroiditis and will help to elucidate the underlying autoimmune mechanisms that lead to disease at the functional level.

Amino Acid Sequence↗