Search PubMed⌕ Search

Biomedical subjects

K Keller

Publications and source records attributed to K Keller.

At least 37 records · Page 2Linked to original sources
PubMed2000

Cysteine scanning mutagenesis of helices 2 and 7 in GLUT1 identifies an exofacial cleft in both transmembrane segments.

Cysteine scanning mutagenesis in conjunction with site-directed chemical modification of sulfhydryl groups by p-chloromercuribenzenesulfonate (pCMBS) or N-ethylmaleimide (NEM) was applied to putative transmembrane segments (TM) 2 and 7 of the cysteine-less glucose transporter GLUT1. Valid for both helices, the majority of cysteine substitution mutants functioned as active glucose transporters. The residues F72, G75, G76, G79, and S80 within helix 2 and G286 and N288 within helix 7 were irreplaceable because the mutant transporters displayed transport activities that were lower than 10% of Cys-less GLUT1. The indicated cluster of glycine residues within TM 2 is located on one face of the helix and may provide space for a bulky hydrophobic counterpart interacting with another transmembrane segment or lipid side chains. Characteristic for helix 7, three glutamine residues (Q279, Q282, and Q283) played an important role in transport activity of Cys-less GLUT1 because an individual replacement with cysteine reduced their transport rates by about 80%. ParaCMBS-sensitivity scanning of both transmembrane segments detected several membrane-harbored residues to be accessible to the extracellular aqueous solvent. The pCMBS-reactive sulfhydryl groups were located exclusively in the exofacial half of the plasma membrane and, when presented in a helical model, lie along one side of the helices. Taken together, transmembrane segments 2 and 7 form clefts accessible to the extracellular aqueous solvent. The lining residues are however excluded from interaction with intracellular solutes, as justified by microinjection of pCMBS into the cytoplasm of Xenopus oocytes.

4-Chloromercuribenzenesulfonate↗
PubMed1999

A Model for Metal Adsorption on Montmorillonite.

A consistent thermodynamic model is developed for metal sorption on expanding 2:1 layer clays such as montmorillonite. The particle of clay, including lamellae and interlayers, is represented as a porous solid bearing a permanent negative charge (resulting from isomorphic substitution) with an infinite plane interface (i.e., edges) with the solution. Cation exchange occurs inside the clay particle as the result of the negative potential of the clay. Surface complexation reactions take place at the interface whose surface charge and potential are pH dependent. The potential in the bulk of the clay and near the interface, as well as the surface potential-surface charge density relation, are calculated taking into account the effect of the permanent negative charge. The results are discussed and compared with the classic Gouy-Chapman theory. A subroutine (Clayeql) with the new potential-charge relationships is implemented in the thermodynamic equilibrium program Mineql +3.0 and is used to fit an extensive published experimental data set on adsorption of transition metals on montmorillonite. The model is shown not only to fit satisfactorily all the data, but also to explain specific features of adsorption on clays compared to oxides. In particular, the increase in the surface concentration of protons with decreasing ionic strength is successfully reproduced and the weaker dependence of metal sorption on pH compared to oxides is correctly fitted. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Effects of dietary fat type, pentosan level and xylanase supplementation on digestibility of nutrients and metabolizability of energy in male broilers.

A complete two by two by four factorial design was used to examine the main effects of dietary fat type (10% soya oil or 10% beef tallow), xylanase supplementation (with or without Avizyme 1300 at 1 g/kg diet) and pentosan level (7.7 g/kg, 11.0 g/kg, 14.3 g/kg and 17.6 g/kg soluble pentosans, respectively, by varying wheat/rye proportions) as well as their interactions on intestinal chyme conditions, nutrient digestibility and nutrient utilization in male broilers. Nutrient digestibilities for the total digestive tract and at various sites of small intestine were measured during the period from day 18 to 20 of age and at day 21 of age, respectively, using a marker technique. Jejunal and ileal supernatant viscosity increased in an exponential manner as dietary pentosan concentration was increased. This increase was more pronounced in tallow fed birds but was also found in enzyme treated groups albeit at a much lower level. Xylanase activity was still detectable in the ileum of birds fed enzyme supplemented diets but its activity was found to decrease as dietary pentosan content increased. Digestibility of crude protein and that of some amino acids at the terminal ileum was decreased as dietary pentosan content was increased and significantly improved by xylanase addition. No fat effect and no interactions were detected at this site. In contrast, measurements made over the whole gastrointestinal tract showed significantly lower protein and amino acid digestibility values for tallow fed birds, and significant higher enzyme effects especially in diets with higher pentosan concentrations. Nitrogen-corrected apparent metabolizable energy (AMEN) content and net protein utilization decreased with increasing dietary pentosan content and were significantly improved by xylanase addition and were lower in tallow fed birds. Again, xylanase effects were found to be more pronounced for tallow fed birds and at higher pentosan concentrations.

Amino Acids↗
PubMed1999

Comparison of four methods for assessing airway sealing pressure with the laryngeal mask airway in adult patients.

We have compared four tests for assessing airway sealing pressure with the laryngeal mask airway (LMA) to test the hypothesis that airway sealing pressure and inter-observer reliability differ between tests. We studied 80 paralysed, anaesthetized adult patients. Four different airway sealing pressure tests were performed in random order on each patient by two observers blinded to each other's measurements: test 1 involved detection of an audible noise; test 2 was detection of end-tidal carbon dioxide in the oral cavity; test 3 was observation of the aneroid manometer dial as the pressure increased to note the airway pressure at which the dial reached stability; and test 4 was detection of an audible noise by neck auscultation. Mean airway sealing pressure ranged from 19.5 to 21.3 cm H2O and intra-class correlation coefficient was 0.95-0.99. Inter-observer reliability of all tests was classed as excellent. The manometric stability test had a higher mean airway sealing pressure (P < 0.0001) and better inter-observer reliability (P < 0.0001) compared with the three other tests. We conclude that for clinical purposes all four tests are excellent, but that the manometric stability test may be more appropriate for researchers comparing airway sealing pressures.

Adolescent↗
PubMed1999

Liability of laryngeal mask airway devices to thermal damage from KTP and Nd:YAG lasers.

We have compared the liability of four laryngeal mask airway (LMA) devices (standard, flexible, intubating and reusable) and a tracheal tube to thermal damage from KTP and Nd:YAG lasers at two power densities used commonly in airway surgery: 570 W cm-2 and 1140 W cm-2. Eighty-five airway devices were tested: 24 standard LMA (silicone-based), 12 flexible LMA (silicone-based, metal wires), 24 disposable LMA (PVC-based), one intubating LMA (silicone and steel-based) and 24 PVC-based tracheal tubes. Comparisons were made during laser strike to eight different targets: the unmarked and marked part of the airway device tube; the unmarked part of the airway device tube after application of blood; the cuff filled with air or methylene blue dye; the unmarked flexible LMA tube on or between the metal wires; and the epiglottic elevator bar of the intubating LMA. The laser strike was continued for 30 s and each target was tested three times. Three different, but identical, impact sites were used for each target. There was no ignition of any airway device with either power density or laser type. The silicone-based LMA were generally more resistant to flaring and penetration than the PVC-based LMA and tracheal tube, but the intubating LMA tube flared more rapidly with the KTP laser, and the disposable LMA cuff was more resistant to penetration. Print markings, blood and the metal wires of the flexible LMA reduced the thermal resistance of the tube. Filling the cuff with methylene blue dye increased the thermal resistance of all airway devices. We conclude that the silicone-based LMA devices were more thermal resistant to KTP and Nd:YAG laser strike than PVC-based devices with the exception of the disposable LMA cuff and the intubating LMA tube.

Equipment Failure↗
PubMed1999

Intestinal mucins in colonization and host defense against pathogens.

Intestinal mucins are key components of the first line of host defense against intestinal pathogens. These large glycoconjugates secreted by specialized exocrine goblet cells form viscous gels that trap microorganisms and irritants and limit their diffusion to the intestinal epithelium. Moreover, they allow for colonization by indigenous bacterial flora that prevents attachment of pathogenic microbes. The interaction between microbes and mucins involves mucin carbohydrate side chains and microbial adhesin molecules. Certain microorganisms and disease states may alter mucin biochemistry or expression. Although these alterations most likely contribute to disease processes, the full impact of these phenomena are still unclear. The development of mucin-secreting cell lines has facilitated the study of mucin biology and aided our understanding of mucin-microbial interactions.

Animals↗
PubMed1999

Pressures exerted against the cervical vertebrae by the standard and intubating laryngeal mask airways: a randomized, controlled, cross-over study in fresh cadavers.

UNLABELLED: In this randomized, controlled, cross-over study, we measured the pressures exerted by the standard laryngeal mask airway (LMA) and the intubating laryngeal mask airway (ILM) against the cervical vertebrae during insertion, intubation, and maneuvers commonly used to facilitate intubation. We also assessed the effect of these pressures on cervical spine (C-spine) movement. Twenty cadavers (6-24 h postmortem) without cervical abnormality were initially studied. Three microchip pressure sensors were implanted into the pharyngeal surface of C2-3. The size 5 ILM and LMA were inserted in random order into each cadaver with the head-neck in the neutral position. Maximal cervical pressures (CPmax) were recorded for both devices during cuff inflation from 0-40 mL and with the intracuff pressure (ICP) at 60 cm H2O, insertion, fiberscope-guided intubation, partial withdrawal/reinsertion (ILM only), elevation/depression of the handle with 20 N of force applied (ILM only). In five additional matched cadavers, the effect of pressure on posterior displacement of C3 was assessed, and CPmax was measured during laryngoscope- and fiberscope-guided oro/nasotracheal intubation (controls). CPmax was higher for the ILM than the LMA over the inflation range (96 vs 15 cm H2O; P < 0.0001) and with the ICP at 60 cm H2O (95 vs 10 cm H2O; P < 0.0001). During cuff inflation, CPmax was generally unchanged for the ILM but was always increased for the LMA. CPmax for the LMA and ILM was similar during insertion (224 vs 273 cm H2O) but higher for the ILM during fiberscope-guided intubation (96 vs 43 cm H2O; P < 0.0001). At 60 cm H2O ICP, CPmax increased during LMA (224 cm H2O; P < 0.0001) and ILM insertion (273 cm H2O; P < 0.0001) and increased for the LMA (43 cm H2O; P < 0.0001) but was unchanged for the ILM (96 cm H2O) during fiberscope-guided intubation. For the ILM, CP-max increased during handle depression (394 cm H2O; P < 0.0001) and partial withdrawal/reinsertion (265 cm H2O; P < 0.0001) but decreased during handle elevation (6 cm H2O; P < 0.00001). CPmax for the controls was usually zero and was always less than the LMA/ ILM (P < 0.0001). The mean (range) for posterior displacement of C3 was 0.8 (0-2) mm at 100 cm H2O and 2.8 (1-5) mm at 400 cm H2O. Laryngeal mask devices exert greater pressures against the cervical vertebrae than established intubation techniques and can produce posterior displacement of the C-spine. IMPLICATIONS: Laryngeal mask devices exert greater pressures against the cervical vertebrae than established intubation techniques and can produce posterior displacement of the cervical spine. We recommend that laryngeal mask devices only be used in the unstable cervical spine if difficulties are anticipated or encountered with established techniques, pending the results of studies demonstrating its relative safety.

Aged↗
PubMed1998

Cysteine-scanning mutagenesis of flanking regions at the boundary between external loop I or IV and transmembrane segment II or VII in the GLUT1 glucose transporter.

To investigate local secondary structure of GLUT1, site-directed and cysteine-scanning mutagenesis were employed to probe p-chloromercuribenzenesulfonate sensitivity of flanking regions at the boundary of external loops (ELs) and transmembrane segments (TMs) and to check the compatibility of two alternative membrane topology models with the experimental data. In the Cys-less GLUT1, single serine residues located in external loops adjacent to putative transmembrane segments were replaced with cysteine. Transport activities of the cysteine-replacement mutants were comparable to that of the nonmutated Cys-less GLUT1. Only the cysteine residues inserted into the first or fourth EL contributed to transport inhibition by p-chloromercuribenzenesulfonate (pCMBS). Dependent on the pCMBS sensitivity of these residues, cysteine-scanning mutagenesis of flanking regions was performed, including EL I-TM II and TM VII-EL IV, respectively. Of the 27 amino acids changed, the majority of cysteine-substitution mutants displayed transport activities comparable to that of Cys-less GLUT1. Irreplaceable amino acids were Phe-72, Gly-286, Asp-288, Tyr-292, and Tyr-293. The pCMBS sensitivity of loop residues decreased when the distance between inserted thiol groups and the putative transmembrane limit increased. The mutants T62C, T63C, T295C, and I297C even exhibited transport stimulation after pCMBS treatment. Regarding putative membrane-harbored residues, a few thiol groups were involved in pCMBS-induced transport inhibition. Drawn on a helix wheel, these pCMBS-sensitive cysteine residues lie on the same facial half of the helix, shown for TM II and TM VII. With respect to EL-TM boundaries, the experimental data are consistent with the local secondary structure predicted from hydropathy profiles. Conversely, certain data obtained by pCMBS-sensitivity scanning are not consistent with either of the two recently published alternative GLUT1 topology models.

4-Chloromercuribenzenesulfonate↗
PubMed1998

Customized composite reconstruction of extensive midfacial defects.

We describe the treatment of 2 patients with extensive midfacial defects by using a customized composite flap. Autogenous bone was transferred from the iliac crest, revascularized by the rectus muscle, and then transferred as a complete unit by microvascular technique to provide a vascularized bone graft to this area of difficult reconstruction. The bone was shaped and customized to fit the osseous defect. Although the rectus muscle was relatively bulky at the time of harvest, its hearty blood supply permitted trimming and contouring to fit the gap. This technique was based on the principles proposed previously by other authors regarding the vascularization of a free bone graft and its transfer as a composite flap. This technique requires more research and refinement, however this clinical demonstration shows the feasibility of revascularizing a composite flap and the extent to which this technique can be performed.

Bone Transplantation↗
PubMed1998

The effects of a managed care educational program on faculty and trainee knowledge, attitudes, and behavioral intentions.

PURPOSE: To assess the state of managed care knowledge and attitudes and to evaluate the effects of a two-day course on participants' knowledge, attitudes, and behavioral intentions. METHOD: In 1996, the University of California, Davis, Medical School invited all medical students, residents, faculty, and administrators to participate in one of two sessions of a two-day course on managed care. Participants in the first session were given both pre- and post-course questionnaires. Participants in the second session were given only post-course questionnaires. The questionnaires measured objective knowledge, attitudes, and behavioral intentions. Participants (other than administrators) who completed the questionnaires also received a follow-up questionnaire six months after the seminar. RESULTS: The two sessions were attended by 818 UC Davis medical students, residents, faculty, and administrators: after excluding 33 non-physician administrators, 428 completed survey packets (55%) were available for full analysis. Before the course, participants in the first session correctly answered on average only 46% of 32 questions about managed care knowledge. Course attendance was associated with significant gains in knowledge (to 67% correct, p < .001) and a marked increase in appreciation for the cost-control effectiveness of managed care (from 3.35 to 3.98 on a five-point scale, p < .001). Knowledge gains were greatest among medical students; changes in attitudes and behavioral intentions were least among residents. Among respondents to a follow-up survey, the changes were partially sustained six months later. CONCLUSION: Within this academic medical center, baseline levels of managed care knowledge were low among faculty as well as among trainees, and attitudes reflected a blend of negativism and wishful thinking. An intensive two-day educational program effectively increased knowledge and changed selected attitudes among critical academic constituencies. Other academic medical centers may wish to consider presenting similar programs in order to orient their faculties and trainees to the economic realities of the foreseeable future.

Academic Medical Centers↗
PubMed1997

Heterologous expression of rab4 reduces glucose transport and GLUT4 abundance at the cell surface in oocytes.

To evaluate the role of the small rab GTP-binding proteins in glucose transporter trafficking, we have heterologously co-expressed rab4 or rab5 and GLUT4 or GLUT1 glucose transporters in Xenopus oocytes. Co-injection of rab4 and GLUT4 cRNAs resulted in a dose-dependent decrease in glucose transport; this effect was specific for rab4, since co-injection of an inactive rab4 mutant or rab5 cRNA did not have any effect on glucose transport. The effect of rab4 was selective for GLUT4, since no effect was detected in GLUT1-expressing oocytes. The inhibitory effect of rab4 on GLUT4-induced glucose transport was not the result of a change in overall cellular levels of GLUT4 glucose transporters. However, rab4 expression caused a marked decrease in the abundance of GLUT4 transporters present at the cell surface. Finally, rab4 and inhibitors of PtdIns 3-kinase showed additive effects in decreasing glucose transport in GLUT4-expressing oocytes. We conclude that rab4 plays an important role in the regulation of the intracellular GLUT4 trafficking pathway, by contributing to the intracellular retention of GLUT4 through a PtdIns 3-kinase-independent mechanism.

Animals↗
PubMed1997

The tumor necrosis factor alpha-stimulating region of galactose-inhibitable lectin of Entamoeba histolytica activates gamma interferon-primed macrophages for amebicidal activity mediated by nitric oxide.

Entamoeba histolytica adheres via galactose-lectin (Gal-lectin) to human colonic mucins and intestinal epithelial cells as a prerequisite to amebic invasion. Native Gal-lectin is a protective antigen in the gerbil model of amebiasis. Amino acids 596 to 1082 of Gal-lectin mediate E. histolytica adherence to target cells and stimulate tumor necrosis factor alpha (TNF-alpha) production by naive murine bone marrow macrophages (BMM). Resistance to amebiasis requires an effective cell-mediated immune response against E. histolytica trophozoites mediated by nitric oxide (NO) released from activated macrophages. Herein, we determine whether the TNF-alpha-stimulating region of Gal-lectin can activate gamma interferon (IFN-gamma)-primed BMM for NO production and amebicidal activity. Native Gal-lectin (100 to 500 ng/ml) stimulated TNF-alpha and inducible nitric oxide synthase (iNOS) mRNA expression in IFN-gamma-primed BMM as did lipopolysaccharide (100 ng/ml). Primed BMM produced TNF-alpha and NO in response to Gal-lectin in a dose-dependent manner. Antilectin monoclonal antibody IG7, which recognizes a domain (amino acids 596 to 818) of the TNF-alpha mRNA-stimulating region of Gal-lectin, specifically inhibited TNF-alpha and iNOS mRNA induction and TNF-alpha and NO production by primed BMM in response to Gal-lectin (100 ng/ml). Simultaneous treatment of BMM with IFN-gamma and Gal-lectin (100 ng/ml) activated the cells to kill E. histolytica trophozoites, whereas IFN-gamma treatment alone had no effect. In the presence of monoclonal antibody 1G7 or aminoguanidine (an iNOS inhibitor), NO production and amebicidal activity were inhibited >80%. These results suggest that the TNF-alpha-stimulating region of native Gal-lectin is a potent stimulus of IFN-gamma-primed BMM for NO production, which is essential for host defense against amebiasis.

Animals↗
PubMed1997

[Special therapeutic guidelines from the viewpoint of BfArM (Federal Institute for Drug and Medical Products)].

Homeopathic, anthroposophic and phytotherapeutic drugs are subject to the German Medicines Act of 1976 (AMG). The relevant EU regulations also refer to this group of medicinal products. Definitions and requirements for proof of adequate quality, efficacy and safety are set out by regulations under national law, as well as EU and WHO regulations. Homeopathic products may be registered without statement of indication. It has become possible in the meantime that medicinal products belonging to these particular schools of therapy and groups of substances are critically reviewed and assessed without being blamed for bias in the sense of discrimination against one of these therapies or exaggerated criticism. The term of "particular schools of therapy and groups of substances" is different from what is understood by "traditional" products according to article 109a AMG. "Traditional" products are subject to reduced requirements and their documentation need not fulfil the assessment criteria established for particular schools of therapy.

Adverse Drug Reaction Reporting Systems↗
PubMed1996

Nonsteroidal antiinflammatory drugs inhibit cyclooxygenase-2 enzyme activity but not mRNA expression in human macrophages.

At present it is unclear whether nonsteroidal antiinflammatory drugs (NSAIDs) can inhibit cyclooxygenase (COX) gene expression. In some cells that express COX-2, NSAIDs can inhibit enzymatic activity and gene expression. In this study we evaluated the effect of several NSAIDs on COX-1 and COX-2 mRNA, protein expression and PGE2 production in PMA-differentiated THP-1 and U937 human macrophages stimulated with LPS. Macrophages pre-treated with acetylsalicylic acid, indomethacin, naproxen or NS-398 and stimulated with LPS showed a marked inhibition on PGE2 production but not on COX-1 or COX-2 mRNA and protein expression. Furthermore, COX-2 mRNA levels induced by LPS were transient (peak 3-4 h), suggesting that PGE2 was unable to regulate COX-2 expression in an autocrine manner. These results demonstrate that NSAID's action in human macrophages is not directed towards the transcription or translation of the COX genes but only to the enzymatic activity of the proteins.

Anti-Inflammatory Agents, Non-Steroidal↗