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S Thompson

Publications and source records attributed to S Thompson.

At least 19 recordsLinked to original sources
PubMed1992

Effects of endothelin-1 on signal transduction in UMR-106 osteoblastic cells.

Endothelin-1 is now recognized to affect the functions of a number of tissues and to activate calcium/phospholipid second messenger pathways in target cells. In the present study, we characterized its effects on signal transduction in UMR-106 cells. To study calcium transients elicited by endothelin-1, cells were loaded either with fluo-3 (for the measurement of cytosolic free calcium) or chlortetracycline (for the measurement of intracellularly stored calcium) as fluorescent probes. Intracellular production of inositol phosphates and cyclic AMP was also measured. Endothelin-1 elicited dose-dependent cytosolic calcium transients with an ED50 of 20 nM. This effect was also seen in EGTA-containing or calcium-free medium; however, the signals were reduced in magnitude. The dihydropyridine calcium channel antagonist nifedipine did not affect the response. Repeated administration of endothelin-1 resulted in homologous desensitization of the response. A 4 minute pretreatment with phorbol ester reduced the initial response to endothelin-1 in both calcium-containing and calcium-free media. A 24 h pretreatment with indomethacin had no effect on response. Using chlortetracycline as an indicator, a significant reduction in intracellularly stored calcium by endothelin-1 was observed. This was prevented by 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate, a blocker of calcium release from internal stores. Endothelin-1 also stimulated the dose-dependent production of inositol phosphates by UMR-106 cells. Indomethacin was also without effect on this process. The increase in inositol trisphosphates was seen within the same time frame as the increase in cytosolic calcium. Endothelin-1 did not influence cyclic AMP production over 5 minutes in these cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium↗
PubMed1992

A-type potassium channel clusters revealed using a new statistical analysis of loose patch data.

The spatial distribution of ion channels over the surface of a neuron is an important determinant of its excitable properties. We introduce two measures of channel clustering for use in patch-clamp experiments: a normalized chi-squared statistic (eta) and the number of zero-channel patches in a data set (Z). These statistics were calculated for data sets describing the distribution of A-type potassium channels on neurons of the nudibranch Doriopsilla and measurements of Ca-dependent outward current channels on bullfrog hair cells, as well as simulated channel distributions. When channels are clustered, eta is approximately equal to the amount of current in a cluster. The analysis shows that somatic A-channels in the nudibranch are distributed in clusters of approximately 50 channels each. The clusters are < 2 microns wide and are separated, on average, by 3.2 microns. Outward current channels on hair cells occur in clusters of approximately 27 channels each, in agreement with the original analysis. Channel clustering may reflect properties of the insertion or regulation of channels in the membrane.

Animals↗
PubMed1979

Human erythrocyte fraction in "Percoll" density gradients.

A new rapid method for the age fractionation of human erythrocytes by centrifugation through a "Percoll" density gradient is described. The fractionation is demonstrated by density-related changes in the volume, haemoglobin concentration, pyruvate kinase and acetylcholine esterase activities and potassium contents of the erythrocytes, and the distribution of reticulocytes on the gradients.

Acetylcholinesterase↗
PubMed1979

A question of choice.

Explore the source record for details and available documents.

Education, Nursing, Diploma Programs↗
PubMed1978

Late effect of bacteriophage T4D on the permeability barrier of Escherichia coli.

Cold centrifugation of lysis-inhibited Escherichia coli B infected with wild-type T4D results in extensive lysis beginning around 20 min after infection at 37 degrees C. Infection with an e mutant, which fails to make lysozyme, prevents lysis, but does not prevent a marked loss of K+ and Mg3+. The t gene product, thought to disrupt the cytoplasmic membrane in natural lysis, is not required for this handling-induced cation loss or lysis. Three lines of evidence argue that late protein synthesis is required to develop this potential for cation loss; the potential does not develop in infections by: (i) mutants defective in DNA synthesis, (ii) mutants defective in gene 55, and (iii) wild-type T4 when chloramphenicol is added at 6 min after infection. All late mutants examined, which are blocked in the major pathways of morphogenesis, do not prevent development of the potential. The evidence argues for a new, late effect of T4 infection on the cytoplasmic membrane.

Cell Membrane Permeability↗
PubMed1978

Evaluation of the in vivo function of the Hancock porcine xenograft in the aortic position.

We evaluated the vivo hemodynamic function of the stent-mounted glutaraldehyde-fixed porcine xenograft in 23 patients who had undergone aortic valve replacement from 2 days to 24 months prior to the study. Functional aortic valve orifice areas for the porcine xenograft ranged from 0.58 to 3.0 sq. cm., the average area being 1.36 sq. cm. Six patients had calculated prosthetic valve orifice areas less than 1.0 sq. cm. Valve orifice area did not correlate significantly with valve size or the time interval from surgery to postoperative study. Left ventricular stroke volume showed a significant, positive correlation with calculated xenograft orifice area. Systemic thromboembolism was not encountered. One patient required reoperation for xenograft stenosis caused by dense fibrin deposition on the aortic leaflets. We conclude that use of the stent-mounted glutaraldehyde-fixed porcine xenograft can be associated with significant functional stenosis which may be related to annulus size or inertial properties of the valve. These factors should be taken into consideration when considering use of the stent-mounted glutaraldehyde-fixed porcine xenograft in individual patients.

Adult↗
PubMed1978

Ultrastructure of the foveal glands of the ticks, Dermacentor andersoni Stiles and D. variabilis (Say).

The foveal glands of Dermacentor variabilis appear to consist of 2 cell types. The outer cells (Type I) are active, with large areas of abundant finely granular material, apparently precursors of the mature secretory granules. The inner cells (Type II) are apparently storage cells. They are highly vacuolated and contain coarsely granular material as well as presumably mature secretory granules. The foveal glands of D. andersoni contain only Type II cells with extensive accumulations of presumably mature secretory granules.

Animals↗
PubMed1977

Osmotic properties of human lymphocyte.

The osmotic properties of human lymphocytes isolated from 15 ml of venous blood were examined. Measurements of the permeability of the membrane to water under an osmotic gradient were also made. The Boyle-Van't Hoff relation held very well for the human lymphocyte when the cells were shrunken in hyperosmotic media to concentrations twice isosmotic. The volume of osmotically inactive material or "b" value averaged 32% of the mean corpuscular volume. These values were independent of temperature. Ponder's R ranged between 0.8 and 0.9. The average value for Lp, the hydralic coefficient was 0.46 mu/min atm +/- 0.02 (S.E.M.) at 25 degrees C. No significant effect of age, sex, or race was noted. The effect of temperature between 10 degrees C and 37 degrees C was measured and heats of activation between 11.1 and 17.4 kcal/mole were calculated with a mean of 14.1 kcal/mole +/- 1.6 (S.E.M.). Concanavalin A at 10 microgram/1.5 X 10(6) lymphocytes produced blastogenesis of 25% or more of the lymphocytes without clumping, agglutination, or toxicity. The mean corpuscular volume increased by 21% after 72 hours due to an increase in the "b" value which increased by 80%. The volume of free water remained constant. Histograms of the distribution of cell volumes showed that volume changes were uniform throughout the population with no evidence of agglutination of clumping. The significance of these results is discussed in the context of membrane fluidity and the state of intracellular water.

Cell Membrane Permeability↗
PubMed1977

The effects of benzoflavones on polycyclic hydrocarbon metabolism and skin tumor initiation.

The effects of benzoflavones on skin tumor initiation by polycyclic hydrocarbons and epidermal aryl hydrocarbon hydroxylase were investigated. 7,8-Benzoflavone (7,8-BF) was found to be a potent inhibitor of the inhibition of skin tumors by 3-methylcholanthrene (MC) as well as 7,12-dimethylbenz(a)anthracene (DMBA). 5,6-Benzoflavone(5,6-BF) inhibited tumor initiation by MC and DMBA, but to a lesser degree than 7,8-BF. Dose-response studies of the capacity of 7,8-BF to inhibit DMBA tumor initiation revealed that 7,8-BF was an effective inhibitor at 2.5 microgram and a maximum inhibition of 90% occurred at 100 microgram of 7,8-FB. The tumor initiating ability of 7-hydroxymethyl-12-methylbenz(a)anthracene (7-OHMe-12MeBA) was not inhibited by 7,8-BF. Epidermal aryl hydrocarbon(benzo(a)pyrene hydroxylase(AHH) was increased by 5,6-BF and either had no effect or was slightly inhibited by 7,8-BF when given either topically or i.p. Both flavones when added directly to the assay tubes inhibited the in vitro epidermal AHH activity from control and MC pretreated mice by greater than 75%. When added in vitro, 7,8-BF and 5,6-BF inhibited epidermally mediated covalent binding of radioactive DMBA and dibenz(a,h)anthracene to DNA by 50% or more. The inhibition of skin tumor initiation by 7,8-BF and 5,6-BF appears to be partially related to its ability to inhibit the formation of electrophilic intermediates.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1977

Mutagenicity of anti-cancer nitrobenzofuroxans.

Anti-leukaemically active benzofuroxans were tested for mutagenicity in Salmonella typhimurium. Mutagenicity was not found to be correlated to the previously established anti-leukaemic activity. One anti-leukaemically inactive compound after exposure to liver microsomal enzymes proved the most mutagenic of the derivatives for TA100, whereas after similar treatment, the mutagenicity of the most potent anti-leukaemic compound was reduced. All twelve derivatives tested were mutagenic in a base-substitution strain which was defective in excision-repair and also carried a plasmid-linked repair deficiency. Mutagenicity of five dervatives was undetectable in strains proficient for one or the other of the above repair pathways. Nine of the benzofuroxans could also be detected as mutagens in the frameshift tester strain TA98.

Animals↗
PubMed1977

Binding of dexamethasone by the subcellular fractions of mouse epidermis and dermis.

The binding of the potent anticarcinogenic agent, dexamethasone, to mouse epidermal and dermal subcellular fractions was investigated. When applied to mouse skin, 3H-labeled dexamethasone remained associated, after extensive dialysis, with epidermal and dermal cytosol, microsomes, microsomes, mitochondria, and chromatin. The specific activity of dexamethasone binding to these fractions was from 2 to 5 times as high in the epidermis as in the dermis. Epidermal chromatin had the highest specific activity fo binding. Dexamethasone was not associated with the cytosol protein receptor which was previously found to specifically bind tumor promoters and polycyclic hydrocarbon carcinogens.

Animals↗
PubMed1977

Cobb syndrome.

Cobb syndrome consists of a vascular skin nevus associated with an angioma in the spinal cord. We describe a young man with this condition. To our knowledge, this is the 28th case reported. Cobb syndrome must be differentiated from other syndromes characterized by vascular cutaneous lesions associated with central nervous system abnormalities, such as Sturge-Weber, Osler-Weber-Rendu, Fabry-Anderson, von Hippel-Lindau, and ataxia telangiectasia.

Adolescent↗