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Biomedical subjects

P Pohl

Publications and source records attributed to P Pohl.

At least 55 records · Page 3Linked to original sources
PubMed1997

The effect of a transmembrane osmotic flux on the ion concentration distribution in the immediate membrane vicinity measured by microelectrodes.

The osmotically induced transmembrane water flow is accompanied by solute concentration changes within the unstirred layer adjacent to membranes. Experimental concentration profiles, measured by means of microelectrodes in the immediate vicinity of a planar lipid bilayer, are compared with theoretical ones predicted from the standard physiological model in which the osmotic advection is countered by back-diffusion of the solute only. An increase of the apparent osmotic flow rate is induced by an increase of the osmotic gradient and by rigorous stirring. The polarization effect decreases in the latter case due to an increase of the transfer rate of solutes between the bulk solutions and the membrane surfaces, whereas it increases in the former case. The observations show that the concentration profile is not well described by the standard approximation. The discrepancy becomes increasingly large with increased volume flow. Based on a modified theoretical description of the interaction between water flux and diffusion, the hydraulic conductivity of the bilayer is calculated from the measured uniexponential concentration profiles. The common approximation that there is a discrete boundary between the stirred and unstirred regions adjacent to the membrane is substituted by the model of a stagnant point flow that takes into account a gradual change of the stirring velocity in the immediate membrane vicinity. Supported by experimental observations, this approach predicts a shortening of the unstirred layer if the transmembrane osmotic gradient is increased under gentle stirring conditions.

Chemical Phenomena↗
PubMed1997

Permeation of ammonia across bilayer lipid membranes studied by ammonium ion selective microelectrodes.

Ammonium ion and proton concentration profiles near the surface of a planar bilayer lipid membrane (BLM) generated by an ammonium ion gradient across the BLM are studied by means of microelectrodes. If the concentration of the weak base is small compared with the buffer capacity of the medium, the experimental results are well described by the standard physiological model in which the transmembrane transport is assumed to be limited by diffusion across unstirred layers (USLs) adjacent to the membrane at basic pH values (pH > pKa) and by the permeation across the membrane itself at acidic pH values. In a poorly buffered medium, however, these predictions are not fulfilled. A pH gradient that develops within the USL must be taken into account under these conditions. From the concentration distribution of ammonium ions recorded at both sides of the BLM, the membrane permeability for ammonia is determined for BLMs of different lipid composition (48 x 10(-3) cm/s in the case of diphytanoyl phosphatidylcholine). A theoretical model of weak electrolyte transport that is based on the knowledge of reaction and diffusion rates is found to describe well the experimental profiles under any conditions. The microelectrode technique can be applied for the study of the membrane permeability of other weak acids or bases, even if no microsensor for the substance under study is available, because with the help of the theoretical model the membrane permeability values can be estimated from pH profiles alone. The accuracy of such measurements is limited, however, because small changes in the equilibrium constants, diffusion coefficients, or concentrations used for computations create a systematic error.

Ammonia↗
PubMed1997

Chicken egg yolk antibodies against F18ab fimbriae of Escherichia coli inhibit shedding of F18 positive E. coli by experimentally infected pigs.

F18ab and F18ac are antigenic variants of a colonizing fimbria commonly found on E. coli associated with postweaning diarrhea and edema disease in pigs. Chicken F18ab antibodies were obtained by immunising hens with purified F18ab fimbriae. For their in vitro characterisation antibodies were isolated from diluted egg yolks by ammonium sulfate precipitation. In vitro adhesion tests demonstrated that the chicken F18ab antibodies inhibited attachment of F18ab positive E. coli bacteria to the intestinal mucosa. Just weaned piglets were experimentally infected with an F18ab positive edema disease strain of E. coli, or with an F18ac positive postweaning diarrhea E. coli strain. The animals were infected on the second day of a period during which chicken F18ab antibodies were added to their feed. During the same period, pigs of the control group received commercial eggs in which no F18 antibodies were detected. In both experimental infections the excretion of the F18 positive strain was reduced in pigs that received the F18ab antibodies as compared to the control animals. The F18ab antibodies diminished the cases of diarrhea and death in animals infected with F18ac positive E. coli.

Animals↗
PubMed1997

A predictive parameter in patients with brain related complications after cardiac surgery?

OBJECTIVE: The prognostic estimation of cerebral complications after cardiac surgery is a major problem in the early postoperative period. Neuron specific enolase (NSE) is an enzyme involved in glycolysis, which is localized in neurons and axonal processes. It escapes into the blood and cerebrospinal fluid at the time of neural injury. Therefore we focused the study on the question of how far serum levels of neuron specific enolase can predict the neurological and neuropsychological outcome after cardiac surgery. METHODS: We determined, with a prospective study design of NSE serum levels in 200 patients undergoing cardiac surgery preoperatively, right after the operation and 48 h later. The NSE was measured with a solid phase enzyme immuno assay which utilized a highly specific monoclonal antibody to NSE. We evaluated the neurological and neuropsychological status before and 72 h after surgical intervention. As a control group we recruited 50 patients undergoing general surgical treatment. RESULTS: The preoperative serum levels of NSE are constantly low in all patients with a mean value of 11.1 ng/ml (8.3-13.6) and a mean +/- S.D. of 3.12 in the main group and a mean value of 9.6 ng/ml (7.8-10.3) and a mean +/- S.D. of 1.84 in the control group. The early postoperative measurements indicated a significant increase to a mean value of 19.7 ng/ml (8.7-70.9) with a mean +/- S.D. of 2.89 in the main group. In contrast there is no increase of NSE serum levels after general surgery. The 48 h postoperative mean levels declined to 14.2 ng/ml (9.9-26.2), S.D. of 3.23. In 17 out of the 200 patients a neurological complication occurred. Elevated NSE levels were found in 16 of these 17 patients. The highest concentrations of NSE were measured in 7 patients with the most severe neurological complications being transient ischemic attack and stroke. CONCLUSIONS: The early serum levels of NSE after cardiopulmonary bypass, in those patients with severe neurological deficits, indicate that NSE is a suitable marker for the detection and quantification of cerebral injury after open heart surgery. Therefore, in addition NSE seems to be of predictive value for the clinical outcome and gives implications for the treatment and prognosis of patients with brain related complications in cardiac surgery.

Adult↗
PubMed1997

The effect of AC voltage on the ionophore-induced steady-state flux across the bilayer lipid membrane.

Application of an AC voltage to a model bilayer lipid membrane in the presence of electrogenic ionophores (valinomycin, protonophores CCCP and TTFB) was shown to change the steady-state current across the membrane induced by a DC voltage. The change in the DC current was proportional to the magnitude of the DC voltage and to the amplitude of the AC voltage and depended on both the AC frequency and the ionophore used. Application of this new experimental approach to the estimation of kinetic constants at individual stages of ionophore functioning is discussed.

Benzimidazoles↗
PubMed1996

Visualization of the reaction layer in the immediate membrane vicinity.

Coupled processes of diffusion and chemical reaction are quantitatively analyzed by means of proton concentration profile measurements in the immediate membrane vicinity. Because mass transfer across the unstirred layer (USL) is thought to proceed via diffusion, only the size of the USL is used as a scale for diffusion restrictions. Limitations associated with the finiteness of the reaction rate are characterized by the size of the reaction layer (RL). The latter is defined as the distance from the membrane where equilibrium is reached if transmembrane diffusion is followed by chemical reactions proceeding in the solution layers adjacent to the membrane. The well-known reaction of acetaldehyde oxidation catalyzed by alcohol dehydrogenase in the presence of NADH was selected because it is accompanied by an easily measurable alkalinization of the solution. The enzyme/coenzyme and the substrate were added to opposite sides of the membrane. A theoretical model describing the reaction and diffusion kinetics enabled us to calculate the size of the RL from the pH profile within the USL of a planar bilayer membrane showing a high proton permeability. As the enzyme concentration increased, the initially reaction-limited kinetics of the total turnover became diffusion limited under our experimental conditions due to a dramatic shortening of the RL.

Acetaldehyde↗
PubMed1996

Immunotoxins containing A-chain of mistletoe lectin I are more active than immunotoxins with ricin A-chain.

Conjugates of anti-CD25 monoclonal antibodies against cell surface IL-2 receptor with MLIA and RTA were prepared and investigated. Both of the immunotoxins had high specific cytotoxic activity on target cells. The IC50 value of the anti-CD25/MLIA immunotoxin was 15-fold greater than that of the anti-CD25/RTA. Previous studies of the anti-CD5 immunotoxins with MLIA and RTA showed that the anti-CD5/MLIA IT was 80-fold more active than anti-CD5/RTA IT [Tonevitsky et al. (1991) Int. J. Immunopharmacol. 13, 1037-1041]. The surface hydrophobicity of the MLI A-chain was 4-fold higher than that of the ricin A-chain as estimated by binding with ANS. In model experiments with small unilamellar DMPC liposomes, MLIA but not RTA increased the turbidity of liposome suspensions at pH 4.5. Our results indicate that the greater cytotoxic activity of the MLI A-chain immunotoxin probably provided a higher surface hydrophobicity of the protein and the ability to interact with phospholipid membranes.

Anilino Naphthalenesulfonates↗
PubMed1996

Characterization of F18 fimbrial genes fedE and fedF involved in adhesion and length of enterotoxemic Escherichia coli strain 107/86.

Infection of susceptible weaned pigs with oedema disease strains of E. coli is associated with bacterial adhesion to the small intestine. F18 fimbria (previously named F107) was the first colonisation factor described on oedema disease strains, and its genetic determinant was cloned. In the present study, genes fedE and fedF were positioned in the F18 gene cluster, downstream of the major structural subunit gene fedA. Two fedE and two fedF mutants were identified that had lost their capacity to adhere to isolated porcine villi. Moreover, these mutants produced significantly longer fimbriae. In vitro adhesion tests, electron microscopy study, transcomplementation tests, and nucleotide sequence analysis indicated that proteins FedE and FedF are F18 minor subunits essential for fimbrial adhesion and effecting fimbrial length.

Bacterial Adhesion↗
PubMed1996

Myasthenia gravis and primary biliary cirrhosis. Common immunological features and rare coincidence.

A 43-year-old woman with recently diagnosed primary biliary cirrhosis developed antibody-negative myasthenia gravis. She did not receive D-penicillamine therapy. Clinical and immunological features of this patient are discussed. In previous reports on an association between primary biliary cirrhosis and myasthenia D-penicillamine treatment was an obligate causal linkage between both disorders.

Adult↗
PubMed1995

Steady-state nonmonotonic concentration profiles in the unstirred layers of bilayer lipid membranes.

Catalytic reactions in the unstirred layers near bilayer lipid membranes can induce nonmonotonic concentration profiles near the membrane surface. In the case of transmembrane diffusion of a substrate immediately followed by its conversion due to the presence of an aqueous soluble enzyme the size of the unstirred layer defined in terms of the concentration gradient at the membrane surface does not correspond to the width of the aqueous layer adjacent to the membrane where the concentration differs from the bulk phase concentration. Deducing of flux values or convection parameters from the concentration gradient at zero distance from the membrane gives misleading results. An empirical equation for the estimation of the size of the concentration boundary layer is proposed. It was derived from pH profiles registered with the help of a microelectrode near a planar bilayer lipid membrane surrounded by a buffer solution containing at one side of the membrane acetaldehyde and sodium acetate and at the other side alcohol dehydrogenase. Since this parameter equals to the thickness of the unstirred layer in the case of exponential concentration profiles it may be applied to estimate both mass transfer restrictions and kinetic of diffusion limited reactions occurring in the immediate membrane vicinity regardless the complexity of the system under investigation.

Acetates↗
PubMed1995

Effects of ultrasound on agglutination and aggregation of human erythrocytes in vitro.

A new experimental approach has shown that human erythrocytes of different blood groups were induced to form more agglutinates at a sound pressure of 70-240 kPa in vitro than the control erythrocytes. Similar effects were observed for alcian blue and dextran stimulated aggregation and for spontaneous aggregation. The increase of agglutination or aggregation was reversible. Heating and acoustic cavitation were shown not to be responsible for this effect. Bulk fluid movement produced by ultrasound irradiation appeared to cause the described phenomenon. Possible underlying mechanisms connecting the acoustic streaming and agglutination or aggregation behaviour of the cells are proposed.

Alcian Blue↗
PubMed1994

Prevalence of F107 fimbriae on Escherichia coli isolated from pigs with oedema disease or postweaning diarrhoea.

The study comprises fifty 4 to 12 weeks old pigs that died from oedema disease or severe diarrhoea. Smears were prepared from the mucosa of duodenum, jejunum and ileum, and by immunofluorescence F107 fimbrial antigens were detected. E. coli strains were isolated from the intestines and were characterised by slide agglutination (serogroup and F107 fimbriae production), by their cytotoxicity for Vero cells, and by gene amplification (genes coding for the major F107 subunit FedA, the toxin causing oedema disease SLT-IIv, and enterotoxins LTI, STIa and STII). F107 fimbriae were demonstrated in association with E. coli of serogroups O139:K12 and O141:K85a,b but not of serogroup O149:K91:F4a,c. Expression in culture of F107 fimbriae by some isolates gave additional evidence for production of these fimbriae by ETEC strains. The genetic determinant of SLT-Ilv was found in association with F107, and could not be detected in serogroup O149:K91:F4a,c. Gene fedA was demonstrated in two isolates which were devoid of SLT-IIv. Most isolates from cases of oedema disease belonged to serogroup O139:K12 and did not contain enterotoxin genes. Isolates from pigs that suffered from diarrhoea were serotyped O141:K85a,b or O149:K91:F4a,c, and carried at least two enterotoxin genes in their genomes. In a small proportion of the cases F107 antigens were demonstrated in intestinal smears although gene fedA was not detected in the corresponding isolates. The results confirm the importance of F107 fimbriae as virulence factor in oedema disease E. coli strains, but also demonstrate that F107 fimbriae can be found in association with postweaning diarrhoea isolates. In these latter strains enterotoxins were always demonstrated, irrespective of the presence of toxin SLT-IIv.

Animals↗
PubMed1994

Steroids and opioid receptors.

The genomic mode of action is believed to represent the predominant effect of a steroid hormone. Recently, however, rapidly manifesting, non-genomic effects have also been observed. These are mediated mostly by allosteric interaction of a steroid with heterologous target structures such as membrane receptors, a prototype example being the GABAA. Here we describe our studies considering two interdependent questions: (1) do steroids also interact with opioid receptors in brain? Twenty different steroids, i.e. estrogens, androgens, glucocorticoids, mineralocorticoids, gestagens and a cardiac glycoside were tested with respect to their ability to compete for in vitro binding to rat brain membranes of 3H-ligands specific for delta, mu and kappa opioid receptors, respectively. Among all classes of steroids, only the estrogens were effective, all others were 20 to 100 times less effective or ineffective. The rank order among the estrogens was diethylstilbestrol > 17 alpha-estradiol > 17 alpha-ethinyl-estradiol > estriol > estrone > 17 beta-estradiol. Next potent to estrogens (although far less) were--on average as a group--glucocorticoids, followed by mineralocorticoids, androgens, gestagens and digoxin. This global as well as within-group rank order, was, with rare exceptions, qualitatively equal irrespective of which radioligand was used, yet displayed the various radioligands different sensitivities with respect of being inhibited by steroids (irrespective of kind), i.e. in the order [3H]naloxone > or = [3H]DAGO > or = [3H]DADL > [3H]DPDP >> [3H]etorphine. The IC50 of diethylstilbestrol for displacing [3H]DAGO was approximately 30 microM and that of 17 beta-estradiol was approximately 200 microM. (2) What are the concentrations of the major steroid hormones in the brain's extracellular fluid? We have analyzed in 56 matched (i.e. simultaneously withdrawn) peripheral serum and cerebrospinal fluid (CSF) samples (from endocrinologically grossly normal patients) the concentrations of the unconjugated steroid hormones testosterone, androstenedione, dehydroepiandrosterone (DHEA), progesterone and cortisol (all being more or less lipophilic) as well as those of their hydrophilic counterparts, i.e. DHEA-sulfate, or their hydrophilic binding proteins, i.e. sex hormone binding globulin, corticosterone binding globulin, and albumin. Total (i.e. free plus protein-bound) CSF levels of all these steroids were found to be in the 0.02-2 nM range except for cortisol (approximately 20-50 nM), thus 3 to 4 orders of magnitude lower than the IC50 of estrogens for [3H]DAGO (see above). These total CSF values were quite similar to the reported and calculated free serum levels of these steroids and no difference existed between those of patients with intact or with disturbed (abnormally leaky) blood-brain barrier function.(ABSTRACT TRUNCATED AT 400 WORDS)

Androgens↗
PubMed1994

Specific DNA probes to detect Escherichia coli strains producing cytotoxic necrotising factor type 1 or type 2.

Cytotoxic necrotising factors type 1 (CNF1) and type 2 (CNF2) are produced by many Escherichia coli strains isolated from man and animals with intestinal or extra-intestinal colibacillosis. In most laboratories, CNF-producing strains are detected by a cell cytotoxicity assay and confirmed with a neutralisation assay or a mouse footpad assay. In this study, we sought to determine whether DNA probes could detect clinical isolates of E. coli producing CNF2 or CNF1, or both, without the need for cell cultures or animal assays. Two internal fragments of the gene encoding CNF2 were used as DNA probes: a 875-bp XhoI-PstI DNA fragment and an adjacent 335-bp PstI-ClaI fragment. A positive response with both DNA probes was associated with CNF2-producing strains, whereas a positive response with only the 335-bp probe was associated with CNF1-producing strains. Results of colony hybridisation experiments with 185 clinical isolates of E. coli demonstrated that these DNA probes detected CNF2-producing strains with a sensitivity and specificity of 100% and CNF1-producing strains with a sensitivity and specificity of 99%. These two DNA probes should greatly facilitate epidemiological studies to assess the importance of CNF-producing strains as agents of diarrhoea and septicaemia.

Animals↗
PubMed1994

Acute cerebellar ataxia after immunisation with recombinant hepatitis B vaccine.

We report one woman with acute cerebellar ataxia (ACA), a well-defined clinical syndrome, which occurred 10 days after the second vaccination with recombinant hepatitis B vaccine. The patient had no previous symptoms or signs of neurological disease and there was no evidence of neurologic disease in the family history. Within nine months the symptoms remitted completely according to other reports of ACA. As there was a close temporal connection and no noticeable other cause we assume a causal link between the vaccination and the disease. As far as we known this is the first case of ACA after hepatitis B vaccination.

Acute Disease↗
PubMed1993

[Infectious diarrhea of calves: therapeutic and preventive possibilities based on etiological, pathophysiological and immunological data].

In this article the current knowledge on the development mechanisms of bacterial, viral and cryptosporidial neonatal calf diarrhoea are briefly reviewed as basis for an efficacious prophylaxis strategy. Hygienic measures will prevent the infection of the calf before colostrum intake and will diminish the infection pressure during the first weeks of life. Moreover, local intestinal immunity will be provided by early administration of immune colostrum for the prevention of E.coli diarrhoea and prolonged administration of colostrum or immune milk during the first weeks can protect against viral diarrhoea. To obtain a maximum level of E.coli antibodies in colostrum, the last vaccination has to be administered at least 8 weeks before parturition. Prolonged excretion of antiviral antibodies in the milk for several weeks, can be achieved by a 'priming' vaccination with an adjuvanted inactivated vaccine during pregnancy, followed by a booster vaccination within 24 hours after parturition. Cryptosporidium parvum diarrhoea can be prevented with halofuginone lactate.

Animals↗
PubMed1993

Effect of ultrasound on the pH profiles in the unstirred layers near planar bilayer lipid membranes measured by microelectrodes.

A pH shift in the unstirred layers (USLs) near a planar lipid bilayer membrane was induced by the diffusion of acetic acid along a concentration gradient. By means of a microelectrode technique it was shown that ultrasound decreases the thickness of the USL and that this reduction was much more pronounced on the side facing the ultrasound transducer than on the opposite side of the membrane. The effect depending on sound frequency and pressure is caused by the unidirectional fluid flow built up between transducer surface and membrane, the so-called quartz wind. Theoretical considerations based on the equations of the acoustic streaming near interfaces combined with the diffusion equation allow to predict the thickness of the USL if the sound field parameters are known.

Acetates↗