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Biomedical subjects

K Stock

Publications and source records attributed to K Stock.

At least 19 recordsLinked to original sources
PubMed2003

Variable-angle total internal reflection fluorescence microscopy (VA-TIRFM): realization and application of a compact illumination device.

A novel compact illumination device in variable-angle total internal reflection fluorescence microscopy (VA-TIRFM) is described. This device replaces the standard condensor of an upright microscope. Light from different laser sources is delivered via a monomode fibre and focused onto identical parts of a sample under variable angles of total internal reflection. Thus, fluorophores in close proximity to a cell-substrate interface are excited by an evanescent wave with variable penetration depth, and localized with high (nanometre) axial resolution. In addition to quantitative measurements in solution, fluorescence markers of the cytoplasm and the plasma membrane, i.e. calcein and laurdan, were examined using cultivated endothelial cells. Distances between the glass substrate and the plasma membrane were determined using the mathematical algorithm of a four-layer model, as well as a Gaussian-shaped intensity profile of the illumination spot on the samples. Distances between 0 and 30 nm in focal contacts and between 100 and 300 nm in other parts of the cell were thus determined. In addition to measurements of cell-substrate topology, the illumination device appears appropriate for numerous applications in which high axial resolution is required, e.g. experiments on endocytosis or exocytosis, as well as measurements of ion concentrations proximal to the plasma membrane. The compact illumination device is also suitable for combining TIRFM with further innovative techniques, e.g. time-resolved fluorescence spectroscopy, fluorescence lifetime imaging (FLIM) or fluorescence resonance energy transfer (FRET).

2-Naphthylamine↗
PubMed2003

Time-gated total internal reflection fluorescence spectroscopy (TG-TIRFS): application to the membrane marker laurdan.

A novel setup for total internal reflection fluorescence microscopy with spectral and temporal (nanosecond) resolution was used to measure the emission spectra of the membrane marker laurdan either selectively within the plasma membrane or in whole living cells, depending on the incident angle of the excitation light. With increasing temperature, the intensity of the fluorescence band around 490 nm increased in comparison with the band around 440 nm, which has previously been assigned to a phase transition of membrane lipids from gel to liquid crystalline phase. For a better separation of the overlapping spectral bands, time-gated detection with a delay of 10-15 ns with respect to the exciting laser pulse was used. As a parameter of membrane dynamics the so-called generalized polarization GP = (I440 - I490)/(I440 + I490) was evaluated at temperatures between 24 and 41 degrees C and variable angles of the incident light permitting to excite laurdan molecules either within the plasma membrane or in the whole cell. A decrease of the GP values by approximately 0.2 units between 28 and 41 degrees C indicated an increase in membrane fluidity or a decrease in membrane stiffness with increasing temperature. In addition, higher GP values were observed for the plasma membrane as compared with intracellular membranes, probably due to a higher amount of cholesterol. Because properties of the plasma membrane have a large influence on the uptake or release of certain pharmaceutical agents or metabolites, the direct assessment of the dynamics of the plasma membrane by total internal reflection fluorescence spectroscopy appears to be important for pharmacology.

2-Naphthylamine↗
PubMed2002

[Bilateral carotid dissection. A not to underestimate cause of neurological loss after road accident].

The dissection of the internal carotid artery is a rare complication of acceleration traumas of the upper spine. 30% of these dissections are caused by road accidents and again less than 30% of these occur bilateral as shown here. The symptoms are fronto-temporal and periorbital starting headaches spreading out to the occiput and Horner's syndrome. Complete hemiplegia as in our case is an impressive exception but the doctor in attendance should think of the carotid dissection. The exclusion of this complication is obligatory because treatment and outcome depend on it.The dynamic effects of bilateral carotid dissections may, as shown here, lead to relapsing cerebral infarctions with persisting neurologic deficits up to manifest hemiparesis. But restitution can be accomplished if early diagnosed by DSA and/or MRI. Therapy of choice is early prevention of persisting neurologic deficits using effective dosed heparin and depending on the residual lumen of the vessel oral anticoagulants or platelet antagonists for one year.

Accidents, Traffic↗
PubMed2002

[Intracanalicular trabeculostomy with the Er:YAG laser].

PURPOSE: To develop a new ab externo technique for glaucoma trabecular surgery using the infrared Er:YAG laser radiation (2.9 micrometer) guided into Schlemm's canal by an optical fiber. MATERIAL AND METHODS: In order to create a drainage canal to the anterior chamber, a quartz fiber (core diameter: 100 micrometer) coupled to an Er:YAG laser was shielded by a metal canula (diameter: 280 micrometer) bent in conformance to the curvature of Schlemm's canal. A 45 degrees -mirror enabled the laser radiation to exit the canula perpendicular to the fiber axis. The complete surgery device was tested on agar medium and enucleated human eyes. RESULTS: Using the unshielded quartz fiber, eight pulses of 8 mJ (frequency: 7 Hz, pulse duration: 150 microseconds) were sufficient to perforate the trabecular meshwork of the human eye. Histology showed a rippled canal with 50 micrometer average diameter and a surrounding necrosis zone of 15-35 micrometer. The complete device could be easily inserted into Schlemm's canal similar to the classic trabeculostomy probe and a conical-shaped canal with a length of 2-3 mm could be created in agar medium within a few seconds. CONCLUSIONS: Initial experience in an experimental set-up show the ab externo creation of a draining canal between Schlemm's canal and the anterior chamber with only minimal irritation of the surrounding tissue. Further refinements of the laser parameters and the biomechanical set-up resulted in a new hand-held device with improved function. The Er:YAG laser intracanalicular trabeculostomy could become a new ab externo technique for minimal invasive therapy of open angle glaucoma.

Equipment Design↗
PubMed2001

Pitfalls in imaging Hodgkin's disease with computed tomography and positron emission tomography using fluorine-18-fluorodeoxyglucose.

We report on a patient with Hodgkin's disease who presented with hypodense splenic lesions and corresponding increased glucose metabolism in FDG-PET imaging, four months after completion of initial treatment, suggestive of early relapse. Serological testing for toxoplasma gondii, however, showed evidence of a recently reactivated or newly acquired infection. Three weeks after immediate antibiotic treatment with Daraprime and Sulfadiazin, the splenic lesions had completely resolved. Additionally, serological titers for toxoplasma gondii were normalized and whole body FDG-PET imaging showed no metabolic activity. Although the positive predictive value of PET imaging to indicate lymphoma is reported to be higher than CT, hypermetabolic lesions are not specific for malignant tissue. Whereas benign tumors typically show low glucose metabolism, activated granulocytes and macrophages may display significantly increased glucose consumption. In conclusion, our case report shows that although therapeutic decisions are often based on the results of imaging modalities, the taking of a detailed history and the acquisition of histological confirmation of the suspected lymphoma relapse are also advisable where possible. Cellular immunodeficiency can result in severe infections even in patients with intermediate stage Hodgkin's lymphoma in remission after combined modality treatment. Therefore, despite the high sensitivity of FDG-PET imaging for the detection of recurrent lymphoma, the differential diagnosis of infectious lesions should be kept in mind, in particular in immunocompromised patients.

Adult↗
PubMed2001

A cardiac prevention and rehabilitation programme for all patients at first presentation with coronary artery disease.

OBJECTIVE: To develop and test a cardiac prevention and rehabilitation programme for achieving sustained lifestyle, risk factor, and therapeutic targets in patients presenting for the first time with exertional angina, acute coronary syndromes, or coronary revascularisation. DESIGN: A descriptive study. SETTING: A hospital based 12 week outpatient programme. INTERVENTIONS: A multiprofessional family based programme of lifestyle and risk factor modification. MAIN OUTCOME MEASURES: Non-smoking status, body mass index, blood pressure, plasma cholesterol, use of prophylactic drugs. RESULTS: 158 patients (82% of 194 possible cases) were recruited over 15 months, with 72% completing the programme. Targets for achieving non-smoking status, blood pressure < 140/90 mm Hg, and total cholesterol < 4.8 mmol/l were achieved in 92%, 73%, and 62%, respectively, and the proportion on aspirin, beta blockers, and lipid lowering treatment was 95%, 58%, and 64% on referral back to general practice for continuing care. CONCLUSIONS: A comprehensive cardiac prevention and rehabilitation programme can be offered to all patients presenting for the first time with coronary heart disease, including those with exertional angina who are normally managed in primary care. Lifestyle, risk factor, and therapeutic targets can be successfully achieved in most patients with such a hospital based programme.

Adult↗
PubMed2001

Incidence of Salmonella in minced meat produced in a European Union-approved cutting plant.

Contamination of minced meat with Salmonella is still considered a major problem in food hygiene. Therefore, in this study the Salmonella incidence in minced meat produced in a European Union-approved slaughtering and cutting plant was investigated in detail. Throughout 21 months, 297 pool samples (1,485 individual samples) of mixed minced meat (beef and pork) were examined according to Council Directive 94/65/EC and to ISO 6579. Salmonellae were detected in 47 (15.8%) of the pool samples. After separation of the positive pools, 93 individual samples were determined to be Salmonella positive, representing 6.3% of the total 1,485 samples. Serotyping resulted in most isolates (69.6%) being identified as Salmonella Typhimurium. It was further shown that the incidence of Salmonella isolations varied during the year and that the isolation rate was higher on some days of the week compared with others.

Animals↗
PubMed2000

Time-resolved in situ measurement of mitochondrial malfunction by energy transfer spectroscopy.

To establish optical in situ detection of mitochondrial malfunction, nonradiative energy transfer from the coenzyme NADH to the mitochondrial marker rhodamine 123 (R123) was examined. Dual excitation of R123 via energy transfer from excited NADH molecules as well as by direct absorption of light results in two fluorescence signals whose ratio is a measure of mitochondrial NADH. A screening system was developed in which these signals are detected simultaneously using a time-gated (nanosecond) technique for energy transfer measurements and a frequency selective technique for direct excitation and fluorescence monitoring of R123. Optical and electronic components of the apparatus are described, and results obtained from cultivated endothelial cells are reported. The ratio of fluorescence intensities excited in the near ultraviolet and blue-green spectral ranges increased by a factor 1.5 or 1.35 after inhibition of the mitochondrial respiratory chain by rotenone at cytotoxic or noncytotoxic concentrations, respectively. Concomitantly the amount of mitochondrial NADH increased. Excellent linearity between the number of cells incubated with R123 and fluorescence intensity was found in suspension.

Animals↗
PubMed2000

Plasma membrane associated location of sulfonated meso-tetraphenylporphyrins of different hydrophilicity probed by total internal reflection fluorescence spectroscopy.

Sulfonated meso-tetraphenylporphyrins of different hydrophilicity were microspectrofluorimetrically examined in endothelial cells using total internal reflection (TIR) illumination or epi-illumination. Since the penetration depth of the evanescent field during TIR illumination is limited to a few hundred nanometers, photosensitizers were almost selectively examined in close vicinity to the plasma membrane. Pronounced fluorescence signals during TIR illumination were observed for the hydrophilic compounds meso-tetraphenylporphyrin tetrasulfonate (TPPS4) and meso-tetraphenylporphyrin trisulfonate (TPPS3), whereas the more lipophilic compounds meso-tetraphenylporphyrin disulfonate (TPPS2a) and meso-tetraphenylporphyrin monosulfonate (TPPS1) could only be detected under epi-illumination. Irradiation of TPPS1 and TPPS2a in the Soret band led to an increase in fluorescence intensity and formation of a photoproduct with an emission maximum around 610 nm, which was limited to intracellular compartments. In contrast, fluorescence spectra of TPPS3 and TPPS4 obtained by TIR and epi-illumination remained almost unchanged after irradiation in the Soret band. Extralysosomal location of TPPS3 and TPPS4 in close proximity to the plasma membrane was deduced from experiments with the lysosomal markers acridine orange (AO) or lysotracker yellow (LY), which were not detectable under TIR illumination. In conclusion, these results provide for the first time direct evidence for a plasma membrane-associated fraction of the hydrophilic compounds TPPS3 and TPPS4 in living cells.

Cell Membrane↗
PubMed1999

[Radiological evaluation of complications of implantable venous access port systems].

OBJECTIVE: Clinical signs and symptoms sometimes throw suspicion on functional complications and venous thrombosis due to implantable venous access ports. Objective was to determine frequency of these problems using radiologic imaging. METHODS: 61 patients were examined by means of fluoroscopy. If indication was given we injected radiopaque (contrast) medium. In the case of suspected vascular thrombosis the radiological finding was verified by sonography, phlebography or by venous magnetic resonance imaging angiography. RESULTS: Altogether 46 complications were documented in 37 out of 61 examined patients (61%). Occlusions of port-catheter were proved in 24 cases. It was the radiologically most frequently recorded complication (52%;) and found coincident with other problems in 9 patients (37%;). Pain frequently indicates break of catheters. Implantation of catheters into jugular and axillary veins predisposes to break of catheters just as port-catheters lateral implanted into subclavian veins ("pinch-off-sign"). CONCLUSIONS: Functional tests of venous access systems using fluoroscopy and phlebography give information that helps to decide if clinically problematic port-systems should be used furthermore. Directions of catheter which are predestined to complications should be avoided.

Catheters, Indwelling↗
PubMed1998

[Intracanalicular trabeculostomy--a new approach to glaucoma surgery].

BACKGROUND: A new "ab externo" technique for glaucoma trabecular surgery creating multiple perforations of the trabeculum to improve outflow facility was tested. MATERIAL AND METHOD: In order to perform a draining canal to the anterior chamber, a quartz fiber (phi: 300 microns) with a side-firing tip, coupled to an Er:YAG laser (2.94 microns), was inserted into Schlemm's canal of an enucleated human eye. RESULTS: Eight pulses of 8 mJ each were sufficient to perforate the trabecular meshwork. Histologic analysis showed a rippled canal with 50 microns average diameter and a surrounding necrosis zone of 15-35 microns. CONCLUSIONS: The Er:YAG laser trabeculostomy, in conjunction with special fibers, shows promise as a new "ab externo" technique for minimally invasive therapy of open angle glaucoma.

Endoscopes↗
PubMed1996

Pancreatitis in children infected with human immunodeficiency virus.

The incidence of pancreatitis in HIV-infected children is not well known. Medical records of 42 children with HIV infection followed at Children's Hospital during a 6-year period were reviewed. Pancreatitis (elevated serum lipase levels) developed in 10 children (23.8%). Three children acquired HIV infection from vertical transmission and seven from contaminated blood products (hemophiliacs). Nine were severely immunosuppressed (CD4+ of < 100 cells/mm3). Lipase values were more often elevated than amylase values. The clinical course was protracted and severe in two children, one had four recurrences, and seven had only a single episode of pancreatitis lasting a few weeks. Opportunistic infections were present in four children and seven were receiving medications previously implicated as cause of pancreatitis. Discontinuation of dideoxynosine (ddI) in one child led to rapid resolution of pancreatitis, but continuation of medications in the other children did not alter the course. The etiology of pancreatitis may be multifactorial. Severe and prolonged clinical course is associated with advanced HIV infection. Determination of serum lipase is more useful than serum amylase for identifying those with pancreatitis.

AIDS-Related Opportunistic Infections↗
PubMed1976

Influence of papaverine derivatives on phosphodiesterase activity, cyclic 3',5'-AMP levels and relaxing effect on rabbit ileum.

The correlations between the relaxing effect of papaverine derivatives, inhibition of low Km-phosphodiesterase (cAMP-PDE = EC 3.1.4.17) activity and cyclic 3',5'-AMP (cAMP) levels in isolated rabbit ileum were investigated. There was a strong correlation between the relaxing effect, inhibition of PDE activity and cAMP content for eupaverine, ethylpapaverine and papaverine. Eupaverine was the most effective relaxing agent (I50 = 7.5 muM) and the most potent inhibitor of PDE activity (Ki = 0.6 muM), followed by ethylpapaverine (I50 = 10 muM;Ki 0.8 muM) and papaverine (I50 = 20 muM;Ki = 2 muM). In contrast, there was a strong relaxing effect (I50 = 6 muM) but only slight inhibition of PDE activity (Ki = 350 muM) by tetrahydropapaveroline (THP). The adenylate cyclase stimulating effect of THP which was shown by others is most likely the reason for comparatively higher cAMP levels, which were found to be elevated about seven times over basal levels of 0.35 nmoles/g wet weight, and effective relaxation. Relaxation could be induced by exogenously added cAMP (I50 = 45 muM) and dibutyryl-cAMP (I50 = 450 muM). Our results support the assumption that smooth muscle relaxation in rabbit ileum is mediated by cAMP. Some of these observations have been published in abstract form (Schulz and Berndt, 1972).

3',5'-Cyclic-AMP Phosphodiesterases↗