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Biomedical subjects

A Ludwig

Publications and source records attributed to A Ludwig.

At least 127 records · Page 7Linked to original sources
PubMed1992

Relationship between precorneal retention of viscous eye drops and tear fluid composition.

The influence of viscolysers on the precorneal residence of a fluorescent tracer was determined, using slit lamp fluorophotometry. The solution acceptability was evaluated by the volunteers by answering a standard questionnaire. The relationship between precorneal retention of viscous eye drops, discomfort and tear fluid composition after instillation of various cellulosic solutions was examined. Irritating hydroxypropylcellulose solution increases the total protein concentration of tears, without change in the ratio of lysozyme to total protein.

Cellulose↗
PubMed1992

Determination of a "critical shear stress level" applied to adherent mammalian cells.

An apparatus for the detailed investigation of the influence of shear stress on adherent BHK cells was developed. Shear forces between 0.0 and 2.5 N m-2 were studied. The influence on cell viability, cell morphology, cell lysis, and cell size was determined. Increasing shear forces as well as increasing exposure duration caused increasing changes in cell morphology and cell death. A "critical shear stress level" was determined.

Animals↗
PubMed1992

Haemolysin of Escherichia coli: comparison of pore-forming properties between chromosome and plasmid-encoded haemolysins.

Lipid bilayer experiments were performed with chromosome-encoded haemolysin of Escherichia coli. The addition of the toxin to the aqueous phase bathing lipid bilayer membranes of asolectin resulted in the formation of transient ion-permeable channels with two states at small transmembrane voltages. One is a prestate (single-channel conductance 40 pS in 0.15 M KCl) of the open state, which had a single-channel conductance of 420 pS in 0.15 M KCl and a mean lifetime of 30 s. Membranes formed of pure lipids were rather inactive targets for this haemolysin. Experiments with different salts suggested that the haemolysin channel was highly cation-selective at neutral pH. The mobility sequence of the cations in the channel was similar if not identical to their mobility sequence in the aqueous phase. The single-channel data were consistent with a wide, water-filled channel with an estimated minimal diameter of about 1 nm. The pore-forming properties of chromosome-encoded haemolysin were compared with those of plasmid-encoded haemolysin. Both toxins share common features, oligomerize probably to form pores in lipid bilayer membranes. Both types of haemolysin channels have similar properties but different lifetimes.

Amino Acid Sequence↗
PubMed1992

A comparative rheological study on carbopol viscous solutions and, the evaluation of their suitability as the ophthalmic vehicles and artificial tears.

The rheological behaviours of different types of Carbopol (Carbopol 940, 934, 941 and 910) were investigated in the present work. Viscous solutions of these polymers were prepared in the range of concentration between 0.01-0.25% (w/w). 10% aqueous solution of sodium hydroxide was used for the neutralization procedure. Mannitol, sorbitol, sodium chloride and borate were tested to make the isotonic solutions. The viscosities of the solutions decreased dramatically with sodium chloride and sodium borate. Mannitol had no effect on the pH values of the solutions while sorbitol has showed a small effect. The solution prepared were sterilized by autoclaving and stored at 4 degrees C for 3 months. The pH value, viscosity and osmolality measurements were made after neutralization and sterilization, at the end of 1 and 2 weeks, 1, 2 and 3 months of storage. It could be concluded that four types of Carbopol are suitable for ophthalmic use. The aqueous vehicles of Carbopol 940 had an excellent appearance and clarity when compared with the other types of polymer.

Acrylic Resins↗
PubMed1991

Mutations affecting pore formation by haemolysin from Escherichia coli.

By introduction of site-specific deletions, three regions in HlyA were identified, which appear to be involved in pore formation by Escherichia coli haemolysin. Deletion of amino acids 9-37 at the N-terminus led to a haemolysin which had an almost threefold higher specific activity than wild-type and formed pores in an artificial asolectin lipid bilayer with a much longer lifetime than those produced by wild-type haemolysin. The three hydrophobic regions (DI-DIII) located between amino acids 238-410 contributed to pore formation to different extents. Deletion of DI led to a mutant haemolysin which was only slightly active on erythrocyte membranes and increased conductivity of asolectin bilayers without forming defined pores. Deletions in the two other hydrophobic regions (DII and DIII) completely abolished the pore-forming activity of the mutant haemolysin. The only polar amino acid in DI, Asp, was shown to be essential for pore formation. Removal of this residue led to a haemolysin with a considerably reduced capacity to form pores, while replacement of Asp by Glu or Asn had little effect on pore formation. A deletion mutant which retained all three hydrophobic domains but had lost amino acids 498-830 was entirely inactive in pore formation, whereas a shorter deletion from amino acids 670-830 led to a mutant haemolysin which formed abnormal minipores. The conductivity of these pores was drastically reduced compared to pores introduced into an asolectin bilayer by wild-type haemolysin. Based on these data and structural predictions, a model for the pore-forming structure of E. coli haemolysin is proposed.

Amino Acid Sequence↗
PubMed1991

Formulation of Carbopol 940 ophthalmic vehicles, and in vitro evaluation of the influence of simulated lacrimal fluid on their physico-chemical properties.

Carbopol 940 ophthalmic vehicles were prepared in order to investigate the interaction between the simulated lacrimal fluid and the polymer, and to examine the influence of sodium fluorescein - a tracer for the fluorophotometric studies - on the physico-chemical properties of the polymer vehicles. Four kinds of vehicles containing mannitol (5%), sodium fluorescein (0.05%) and disodium edetate (0.01%) were formulated. Physicochemical properties of the preparations including pH, osmolality, surface tension and viscosity were measured after neutralization and sterilization, and also after 1 and 2 weeks, 1, 2 and 3 months of storage at 4 degrees C. The viscosity significantly decreased by adding sodium fluorescein and disodium edetate to Carbopol 940 vehicles. It was observed no significant effect of sterilization and storage on the viscosity, pH and osmolality. Significant change in the flow property of the vehicles was observed when the simulated lacrimal fluid was added. Three concentrations of Carbopol 940 vehicles (0.20%, 0.15% and 0.10%) both containing and not containing disodium edetate were proposed for in vivo evaluation.

Acrylic Resins↗
PubMed1990

Nicotinamide and nicotinamide analogues as antitumor promoters in mouse skin.

Phorbol ester-induced promotion of initiated NMRI mouse skin keratinocytes to papillomas could be largely prevented when nicotinamide-like inhibitors of poly(ADP-ribose)polymerase (nicotinamide, benzamide, 3-aminobenzamide) were applied simultaneously with 12-O-tetradecanoylphorbol-13-acetate (TPA). A similar suppression of tumor promotion by nicotinamide analogues was demonstrated in clone 41 JB6 epidermal cells which are promotable by TPA to anchorage-independent growth. The antipromotion effect of nicotinamide analogues, however, does not appear to come about by an inhibition of poly(ADP-ribose)polymerase. Acid analogues of nicotinamide, such as benzoic acid or 3-aminobenzoic acid which do not inhibit the polymerase, showed antipromotion activity similar to that of their corresponding amides. It could also be ruled out that these antipromoters mediate their effect on keratinocytes by a cytostatic action, by scavenging the promoter TPA in a chemical reaction, or by inhibiting protein kinase C. In initiated mouse skin, nicotinamide analogues strongly suppressed TPA-induced accumulation of inflammatory cells and vascular permeability, while epidermal hyperplasia was not significantly affected.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1990

Preservation of P300 event-related potential topographic asymmetries in schizophrenia with use of either linked-ear or nose reference sites.

Previous studies of the auditory P300 event-related potential (ERP) from our laboratory have reported a left- greater than right-sided attenuation in medicated chronic schizophrenics compared with normal controls. A possible confound in these studies has been the use of the linked-ear reference (LER), which has been criticized on the grounds that it might either induce or suppress topographic asymmetries. To test the effects of LER on P300 asymmetries in schizophrenia, we recorded ERPs with both LER and a nose reference (NR) in a group of 20 chronic medicated schizophrenics and in group of 20 age-matched normal controls. We here report: (1) confirmation of our previous P300 findings of left temporal scalp region deficit using both LER and NR with a 28-electrode montage; this feature was prominent in the wave form associated with the target stimulus, without the use of the wave form subtractions of our previous studies; (2) no statistically significant topographic differences between the LER and NR for either the schizophrenic or normal subjects; and (3) better performance of the LER in differentiating schizophrenics versus normal controls, due to lower wave form variability. We conclude that the LER is preferable for studies using subject groups and methodology similar to the present study.

Adult↗
PubMed1990

A method for the study of fungal growth inhibition by plant proteins.

A bioassay is described for the study of inhibitory activity of plant proteins on fungal growth. Fungal spores were germinated in liquid growth medium and pipetted into wells of a microtitre plate. Fungal growth was followed spectrophotometrically. The bioassay was tested using crude protein extracts from plant tissues known to have high activities of chitinase and beta-1,3-glucanase, and with purified enzymes. Crude protein preparations and combinations of the purified enzymes produced a temporary reduction of growth but no permanent growth inhibition.

Fungi↗
PubMed1990

The dihydropyridine-sensitive calcium channel of the skeletal muscle: biochemistry and structure.

The dihydropyridine-sensitive calcium channel of the rabbit skeletal muscle is the first voltage-gated calcium channel which has been purified and biochemically characterized. The alpha 1-subunit, a 165 kDa protein, of the purified dihydropyridine receptor contains all regulatory sites of a L-type calcium channel and the calcium conducting unit. The purpose of this review is to summarize and discuss recent findings on the structure and possible function of the skeletal muscle calcium channel subunits.

Animals↗
PubMed1989

Difficulties of risk determination from the use of new contrast media.

The difficulties with comparing data on the risks involved in the use of conventional contrast media and new low-osmolar contrast media are presented. These difficulties are a result of the necessary size of the groups to be compared and the problems of obtaining data. Prospective studies, carried out by a single researcher, probably have the greatest reliability. In multicentered studies with a larger number of participants, a number of factors must be reckoned with. The assessment of the same reaction can vary considerably, depending on the initial illness and interest of the patient or physician. This will, of course, influence the collection of the data. Due to the fact that complications and side effects are more frequent than deaths, the reduction of the first two through the use of new contrast media is statistically easier to ascertain. It can be assumed from the studies performed thus far that the risk of mortality is also reduced. Definite statistical guarantees do not as yet exist, and it is possible that they will never be produced.

Contrast Media↗
PubMed1988

Immunoquantitation and size determination of intrinsic poly(ADP-ribose) polymerase from acid precipitates. An analysis of the in vivo status in mammalian species and in lower eukaryotes.

Antibodies against pig thymus poly(ADP-ribose) polymerase were obtained with enzyme-hemocyanin conjugates and used for immunoquantitation. The quick-blot procedure used allowed the determination of amounts as low as 1 ng of enzyme from whole cell trichloracetic acid precipitates. When applied to analysis of various human, rodent, and bovine cell types, surprisingly similar amounts of polymerase were found (1-5 ng of pig thymus polymerase equivalents/micrograms of DNA, 2 X 10(5) polymerase molecules/HeLa cell). Also, no significant difference was seen between normal and transformed cells. Polymerase tended to decline in several fibroblast cultures upon reaching confluency, which was not reflected by total polymerase activity. Divergence between total activity and immunogenic equivalents was also seen in alkylated cells and in rat liver treated with phenobarbital. Trichloroacetic acid-insoluble fractions dissolved in sodium dodecyl sulfate buffer could also be used to analyze, by Western blotting, the size distribution of poly(ADP-ribose) polymerase in vivo. Application to various cell types revealed that all mouse and rat cells tested had two immunogenic bands (116 and 98 kDa) of similar intensity. A highly conserved structure of poly(ADP-ribose) polymerase may be deduced from the existence of immunogenic and renaturable 116-kDa polypeptide bands even in the low eukaryotes Physarum polycephalum and Dictyostelium discoideum.

Animals↗
PubMed1988

The repeat domain of Escherichia coli haemolysin (HlyA) is responsible for its Ca2+-dependent binding to erythrocytes.

The haemolysin protein (HlyA) of Escherichia coli contains 11 tandemly repeated sequences consisting of 9 amino acids each between amino acids 739 and 849 of HlyA. We removed, by oligonucleotide-directed mutagenesis, different single repeats and combinations of several repeats. The resulting mutant proteins were perfectly stable in E. coli and were secreted with the same efficiency as the wild-type HlyA. HlyA proteins which had lost a single repeat only were still haemolytically active (in the presence of HlyC) but required elevated levels of Ca2+ for activity, as compared to the wild-type haemolysin. Removal of three or more repeats led to the complete loss of the haemolytic activity even in the presence of high Ca2+ concentrations. The mutant haemolysins were unable to compete with the wild-type haemolysin for binding to erythrocytes at low Ca2+ concentrations but could still generate ion-permeable channels in artificial lipid bilayer membranes formed of plant asolectin, even in the complete absence of Ca2+. These data indicate that the repeat domain of haemolysin is responsible for Ca2+-dependent binding of haemolysin to the erythrocyte membrane. A model for the possible functional role of Ca2+ in haemolysis is presented.

Amino Acid Sequence↗
PubMed1988

Increased expression of Thomsen-Friedenreich antigens during tumor progression in breast cancer patients.

Paraffin-embedded tissue sections of primary tumors and lymph node metastases of 80 breast cancer patients were tested for the expression of Thomsen-Friedenreich (TF) antigens with the aid of a monoclonal IgM antibody (49H8) highly specific for phenyl-beta-galactoside. TF antigens were not expressed in 16 different normal tissues with the exception of some structures in the kidney. In tumor cells, two types of antigen expression were found; namely, cryptic and exposed. From stage T1/No to stages T2-4/N1,2 the number of cases expressing high amounts of TF antigens increased from 9% (2/22) to 22% (4/18) while the percentage of patients with low intensity of antibody binding was reduced from 59% (13/22) to 39% (7/18). The total amount of TF-positive primary tumors at stages T2-4/No increased from 42% (8/19) to 69% (18/26) when lymph nodes were infiltrated (T2-4/N1,2). At this stage 80% (21/26) of the patients with lymph node infiltration carried TF antigens in the nodes. The distribution of antigens was heterogeneous among the tumor cells and was expressed mainly in an apical or luminal position. The increased expression of antigens was attributed to exposed TF antigens, while cryptic antigens remained constant. When primary tumors expressed exposed TF antigens, the corresponding lymph nodes also contained exposed antigen. The same was true for the cryptic antigen. The data demonstrate an increase in the intensity of TF antigen expression during tumor progression and a spread of TF-positive tumor cells into the axillary lymph nodes with an increasing number of breast cancer patients being TF-positive at this stage.

Antigens, Tumor-Associated, Carbohydrate↗
PubMed1987

Mutations affecting activity and transport of haemolysin in Escherichia coli.

Temperature-sensitive mutants that exhibit an altered haemolytic phenotype were isolated from Escherichia coli harbouring the plasmid pHly152. Complementation with recombinant plasmids carrying one of the four hly genes (C, A, B or D) allowed localization of the hly(ts) mutations. A ts mutation in hlyC leads to a pro----leu exchange in amino acid position 53 of HlyC. Two ts mutations in HlyA were found in positions 312 (ser----pro) and 315 (thr----ile). Both amino acid exchanges are located in the same hydrophobic domain of HlyA which extends from amino acids 299 to 327. Two different mutations were introduced by site-specific mutagenesis in this hlyA domain: one by an exchange of ala, val to asp, glu (positions 313, 314) altering the hydrophobicity of this region and another which removes most of this hydrophobic portion. Both mutants have entirely lost the haemolytic activity but the mutant haemolysins are still efficiently transported across both membranes when hlyB and hlyD are provided. Functional HlyC is not required for the transport of the mutant haemolysins. Two site-specific mutations at the N-terminal end of hlyA (one at amino acid position 2 leading to a thr----pro exchange and another deleting ile and thr at positions 4 and 5) also do not affect the transport of the altered haemolysins. The thr----pro exchange enhances the haemolytic activity of the corresponding mutant, whereas the ile, thr deletion exhibits little or no effect on the haemolytic activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1987

The role of the psychiatrist in the practice of psychotherapy.

Historically, psychiatry has played a dominant role in psychotherapeutics, but recently, other mental-health professionals are challenging the role. This paper discusses psychiatrists' different conceptualization of problems and underlines the special contributions they are qualified to make because of their medical training. Patients should be free to choose the type of treatment approach--psychiatric or nonpsychiatric--that best serves their needs.

Humans↗