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At least 271 records · Page 15Linked to original sources
PubMed1994

Sources of errors in different single-electrode voltage-clamp techniques: a computer simulation study.

The use of voltage clamp with a single electrode has been useful in estimating kinetic parameters for a number of ionic whole-cell currents. There are two main types of such a technique: discontinuous voltage clamp (dSEVC) (Brennecke and Lindemann, 1974), and continuous voltage clamp (cSEVC) (Hamill et al., 1981). We have studied, by means of computer simulations, the performance of both types of clamp on estimating activation kinetics parameters of a typical neuronal Ca2+ current. Deviations from the theoretical values are shown to be sensitive on both set-up and cell properties. Both types of clamp are shown to lose voltage control when either access resistance or absolute membrane conductance are increased. In contrast, changes in membrane capacitance affect differently to the estimates obtained by the two types of clamp. Cell size is also shown to affect cSEVC performance but not that of dSEVC. The nature and magnitude of errors obtained by using both types of clamp in different situations are discussed.

Amplifiers, Electronic↗
PubMed1984

Sources of error in the registration of oral cancer.

The names of 102 patients with histologically confirmed squamous cell carcinoma of the oral cavity were checked against Cancer Registry data for the Trent Region. The study was carried out to determine the accuracy of site recording and the failure rate of registration. Although 94 of the patients were registered, 38 per cent of these were incorrectly coded with respect to site. The way in which such errors may occur is discussed and the procedure for registration of oral cancer is explained.

Carcinoma, Squamous Cell↗
PubMed1981

A source of error in mutagen testing of foods.

Mutagenic compounds reported to be present in foods may be forming during the extraction process rather than during cooking or baking. In this study, the formation of mutagenic substances in biscuits was examined using in the extraction procedure either ammonium sulfate and ammonium hydroxide or sodium sulfate and sodium hydroxide. Compounds producing high mutagenic activity in Salmonella strains 1538 and TA 98 obtained from aqueous biscuit extracts containing ammonium ions. No mutagenic activity was observed in extracts from aqueous biscuit extracts containing sodium ions until some ammonium ions (NH4OH) were added. We suggest that ammonium sulfate and ammonium hydroxide not be used in the extraction procedure of food when studying mutagen formation.

Bread↗
PubMed1993

Electrical field stimulation causes oxidation of exogenous histamine in Krebs-Henseleit buffer: a potential source of error in studies of isolated airways.

Electric field stimulation (EFS) relaxes human histamine-precontracted airways in vitro. This relaxation is only partly neurally mediated. Nonneural relaxation has been also shown in blood vessels and is due to the generation of oxygen radicals by EFS. In isolated airways the origin of the nonneural component of the relaxation is not clear. Because exogenous catecholamines are oxidized during EFS of carbogenated Krebs-Henseleit (K-H) buffer, we questioned whether this is also the case for exogenous histamine. Human airways precontracted with histamine or methacholine were exposed to either EFS-stimulated carbogenated K-H buffer that also contained histamine or methacholine or unstimulated buffer. Airways exposed to EFS-stimulated buffer that contained histamine relaxed, whereas airways exposed to buffer containing methacholine or exposed to unstimulated buffer did not. It appeared that the histamine concentrations in the organ baths decreased during 30 min of EFS. This decrease was significantly reduced in the presence of ascorbic acid. We conclude that EFS causes oxidation of histamine in carbogenated K-H buffer, and this may at least partly explain the nonneural component of EFS-induced relaxations of precontracted human isolated airways. Therefore, histamine should not be used to induce precontraction in EFS experiments.

Aged↗
PubMed1987

Solvent-induced photodegradation as a source of error in the analysis of polycyclic aromatic hydrocarbons.

The photodegradation of seven common polycyclic aromatic hydrocarbons (PAHs) has been examined in a range of organic solvents. Reactions followed a first order equation with benzo[a]pyrene and benzo[a]anthracene being the most rapidly photodegraded. Generally, the more polar the solvent the faster is the degradation process. A number of photodegradation products were identified by gas chromatography-mass spectrometry. The identification of compounds such as 4-amino-1-naphthalenecarbonitrile and 1H,3H-naphtho[1,8-cd]pyran-1-one clearly indicated that the solvent molecules have taken part in the formation of these compounds. Solvent-induced photodegradation is shown to be an important consideration in choosing the optimum solvent for the best analytical recoveries of PAHs from various matrices.

Chromatography, High Pressure Liquid↗
PubMed1988

S-100 immunoreactivity in primary and metastatic carcinoma of the breast: a potential source of error in immunodiagnosis.

Immunoreactivity for S-100 protein, typically a marker for malignant melanoma and neural-derived tumors, was observed in neoplastic cells of 57 of 68 cases (84%) of formalin-fixed, paraffin-embedded primary and/or metastatic carcinoma of the breast of various histologic types. The extent of S-100 immunoreactivity varied, with only a minor proportion of positive tumor cells noted in some cases. An awareness of this staining profile for S-100 protein, particularly in metastatic poorly differentiated neoplasms with unknown primaries, is imperative for accurate immunohistochemical interpretation. Using a panel of reagents which includes antibodies to keratin proteins and epithelial membrane antigen, the epithelial nature of S-100-positive carcinomas may be readily defined. Tumor cells in all cases of primary and metastatic carcinoma of the breast evaluated in this study exhibited strong staining for both of these tissue markers. To preclude misinterpretation of tumor type due to anomalous staining patterns for a specific antibody, eg, S-100 protein, a panel of antibodies is recommended for assessment of metastatic poorly differentiated tumors.

Breast Neoplasms↗