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Biomedical subjects

S A Jackson

Publications and source records attributed to S A Jackson.

At least 19 recordsLinked to original sources
PubMed1992

Aerobic heat shock activates trehalose synthesis in embryos of Artemia franciscana.

Encysted embryos (cysts) of the brine shrimp, Artemia franciscana, contain large amounts of trehalose which they use as a major substrate for energy metabolism and biosynthesis for development under aerobic conditions at 25 degrees C. When cysts are placed at 42 degrees C (heat shock) these pathways stop, and the cysts re-synthesize the trehalose that was utilized during the previous incubation at 25 degrees C. Glycogen and glycerol, produced from trehalose at 25 degrees C, appear to be substrates for trehalose synthesis during heat shock. Anoxia prevents trehalose synthesis in cysts undergoing heat shock. These results are consistent with the view that trehalose may play a protective role in cells exposed to heat shock, and other environmental insults, in addition to being a storage form of energy and organic carbon for development.

Animals↗
PubMed1992

Identification of novel peptide antagonists for GPIIb/IIIa from a conformationally constrained phage peptide library.

Methods have recently been developed to present vast libraries of random peptides on the surface of filamentous phage. To introduce a degree of conformational constraint into random peptides, a library of hexapeptides flanked by cysteine residues (capable of forming cyclic disulfides) was constructed. This library was screened using the platelet glycoprotein, IIb/IIIa, which mediates the aggregation of platelets through binding of fibrinogen. A variety of peptides containing the sequence Arg-Gly-Asp or Lys-Gly-Asp were discovered and synthesized. The cyclic, disulfide-bonded forms of the peptides bound IIb/IIIa with dissociation constants in the nanomolar range, while reduced forms or an analogue in which Ser replaced the Cys residues bound considerably less tightly. These results demonstrate the feasibility for introducing conformational constraints into random peptide libraries and also demonstrates the potential for using phage peptide libraries to discover pharmacologically active lead compounds.

Amino Acid Sequence↗
PubMed1992

Regional observer performance variation in the evaluation of gated cardiac blood pool studies.

Receiver operating characteristic (ROC) analysis demonstrated that regional variations of sensitivity exist in the detection of wall motion abnormality in cardiac blood pool imaging studies. The observer response is significantly better in the apex than either the septum or posterolateral wall segments. The observer errors tend to be false-negative in the posterolateral wall segment and false-positive in the other two segments. Image presentation can make a significant difference to the overall sensitivity, and the monochrome cine-sequence performed best in this study.

Gated Blood-Pool Imaging↗
PubMed1992

Evaluation of a personal computer-based quantitative coronary analysis system for rapid assessment of coronary stenoses.

Quantitative coronary analysis (QCA) is a technique that is rarely used because of the complexity and expense of existing systems. We studied a new personal computer-based QCA system that is capable of both geometric and densitometric analysis and compared it to a previously validated QCA system. Both systems performed extremely well in phantom analysis with 11 phantoms filmed in both 5-inch and 7-inch magnifications (R greater than 0.97 and SEE less than 0.33 mm for all modes). In 28 abnormal coronary angiograms analyzed at end diastole, stenosis and reference diameter correlations between the two systems were excellent (R = 0.90 and 0.96 and SEE = 0.43 and 0.33 mm for densitometric and geometric modes, respectively). Intraobserver and interobserver correlation was also excellent for both analysis modes. The new QCA system was able to perform analysis in approximately one third the time required by previously validated system and was much less expensive. We conclude that personal computer-based coronary analysis is an accurate, quick, and relatively inexpensive means for performing QCA that may help to make this technique feasible for nonresearch settings.

Constriction, Pathologic↗
PubMed1992

Estimating radon potential from an aerial radiometric survey.

A radon screening survey of 719 residences in Nova Scotia was performed using liquid scintillation charcoal canisters. The readings have been correlated with an aerial radiometric survey map of the 1.76-MeV gamma emission of 214Bi, which is plotted in terms of uranium parts per million equivalent. A good correlation exists, suggesting that this particular map could be used to indicate the potential for radon problems in particular geographic areas.

Air Pollutants, Radioactive↗
PubMed1990

Glucose metabolism and the channeling of glycolytic intermediates in permeabilized L-929 cells.

L-929 cells (mouse fibroblasts) permeabilized with dextran sulfate (DSP cells) carry out vigorous and linear rates of glycolysis when supplied with a suitable incubation medium. Glycolysis in DSP cells is pH dependent, being strongly inhibited at pH 6.5. Compared to their nonpermeabilized counterparts, DSP cells exhibit faster glycolytic rates, but tend to convert a smaller proportion of the glucose utilized to lactate. [14C]Glucose is converted to lactate by DSP cells without dilution from endogenous substrates. When exogenous 12C-labeled glycolytic intermediates (12C-I) are added to glycolyzing DSP cells the [14C]lactate produced from [14C]glucose is diluted to varying extents, depending on the intermediate. However, the extent of that dilution (reduced specific activity) is not that expected from the complete mixing of exogenous 12C-I with their corresponding 14C-labeled intermediates coming from [14C]-glucose. DSP cells also respire and convert glucose to CO2. The amount of 14CO2 produced from [14C]glucose is also reduced by addition of most 12C-I, an interesting exception being pyruvate, which had no measurable effect on 14CO2 production and caused only a modest stimulation of respiration in glycolyzing DSP cells. These results suggest that channeling, or some other form of coupling, takes place between the glycolytic production of pyruvate and its further oxidation. These observations confirm previously published data and add further support to the proposition that channeling of glycolytic intermediates occurs in DSP cells but is of the "leaky" type. Although abundant evidence in the literature indicates that various glycolytic enzymes associate with F-actin, as well as other elements of the cytomatrix, we observed no effect of cytochalasin D on lactate production even at very high concentrations of this compound. Our results are compared with those from other laboratories and discussed in the context of metabolic organization.

Animals↗
PubMed1990

Glycolysis compared in intact, permeabilized and sonicated L-929 cells.

The effects of incubation time and cell density on glycolytic rate were examined in suspensions of intact, permeabilized and sonicated L-929 cells. Sonicates exhibited strong dependence on cell density and a distinct lag in glycolytic rate, while intact cells showed no cell density dependence and linear glycolytic rates. Permeabilized cells exhibited linear glycolytic rates, but sometimes showed dependence on cell density. Rates of lactate production (nmol at 30 min/10(6) cells) were highest in sonicates and lowest in intact cells. These results are interpreted as support for the previously proposed hypothesis that enzymes of the glycolytic pathway are highly organized in intact L-929 cells.

Animals↗
PubMed1990

Effects of reduced cell volume and water content on glycolysis in L-929 cells.

Mouse L-929 cells were subjected to increasing concentrations of sorbitol, which remove cell water and reduce volume osmotically. The rate of lactate production from glucose was significantly higher in osmotically perturbed cells than in controls, both in monolayers and in suspensions. L cells can apparently use sorbitol as a glycolytic substrate; however, studies using other solutes (trehalose and sucrose) and permeabilized cells showed that the major effect of sorbitol on glycolysis in intact cells is mediated through a reduction in cell water content and volume. It is possible to explain some of these results by an increase in the chemical potentials of dissolved components of the glycolytic pathway caused by water loss; however, the relationship between water loss and glycolytic rate increase in not a simple linear one, suggesting that the situation is more complex than would result merely from increased concentrations of pathway components. Whatever the complete explanation might be, these studies show that glycolysis continues in an orderly fashion in cells that have lost about 85% of their original water content, suggesting that the operation of this pathway is not unduly sensitive to events taking place in the bulk aqueous phase.

Animals↗
PubMed1990

A comparative study of the nephrotoxicity of iohexol, iopamidol and ioxaglate in peripheral angiography.

Iohexol (Omnipaque 350) and iopamidol (Isovue 370) are nonionic monomers; ioxaglate (Hexabrix 320) is an ionic dimer. We compared the nephrotoxicity of these three media by a prospective double-blind evaluation in 500 patients who underwent peripheral angiography during a 6-month period. Serum creatinine levels were determined before injection of the contrast medium and 72 hours after in 478 patients. In 308 (64%) patients there was an average increase in the serum creatinine level of 18.1 mumol/L after injection of an average volume of 123 ml of contrast medium. A subset of 80 patients who had an elevated baseline creatinine level (more than 110 mumol/L) had an average increase in the serum creatinine level of 40.45 mumol/L. Of patients who had arterial injections, 182 (72%) had an increase in serum creatinine level (20.7 mumol/L), but of those who had peripheral venous injections, only 43 (45%) had an elevated creatinine level (9.2 mumol/L), and of those who had central venous injections, 83 (63.8%) had an elevated level (17.0 mumol/L). In most patients elevation of the serum creatinine level was not of clinical importance. High-risk patients with an elevated serum creatinine level were found to be most vulnerable to contrast nephrotoxicity. Although mean differences were not statistically significant, there were consistent trends which suggested that ioxaglate was the least nephrotoxic of the three agents studied.

Acute Kidney Injury↗
PubMed1989

Evidence for intermediate channelling in the glycolytic pathway of permeabilized L-929 cells.

L-929 cells permeabilized by dextran sulfate (DSP cells) carry out vigorous and linear rates of glycolysis when supplied with a suitable incubation medium. Unlabeled 3-phosphoglycerate (PGA) added to DSP cells reduces the specific activity of lactate coming from [14C]glucose but the extent of this reduction can not be accounted for on the basis of free diffusion of PGA coming from [14C]glucose. Studies on other glycolytic intermediates, although preliminary, yield similar results. PGA also inhibits the production of lactate from glucose; however, this effect, like that of the reduction of lactate specific activity, becomes apparent only at concentrations of PGA well in excess of those considered to be physiological. We conclude that channelling of PGA, and probably other intermediates, occurs but is of the "leaky" type.

Animals↗
PubMed1988

Glycolysis in permeabilized L-929 cells.

Mouse L-929 cells permeabilized with dextran sulphate (DSP cells) carry out glycolysis when supplemented with glucose, ATP and NAD+ in a suitable incubation buffer. Glycolytic rates were linear and generally independent of cell density over the range examined (1 x 10(6)-10 x 10(6) cells/ml). Electron microscopy revealed characteristic changes in DSP cell ultrastructure, notably for nuclei and mitochondria. Some cells lacked plasma membranes, while others appeared intact. In the latter case, estimates of the lesion size in plasma membranes were obtained from volume of distribution studies using 14C-labelled proteins, and infiltration of fluorescein isothiocyanate dextran. The results indicated the presence of lesions large enough to allow globular proteins of about 400 kDa to cross the cell surface. In spite of that, only about 10% of total cell protein exited from DSP cells during a 30 min incubation period. We propose that none of the glycolytic enzymes in DSP cells can exist completely in solution in the 'cytosol', suggesting extensive enzyme organization. The results are interpreted within the broader picture of metabolic organization in animal cells and the nature of the 'cytosol'.

Adenosine Triphosphate↗
PubMed1986

The renal washout parameter as an indicator of transplant rejection.

The accumulation of intravascular fibrin thrombosis in both acute and chronic renal rejection leads to a delay in the transit of perfusion. This study examines the renal washout parameter as an indicator of transit time. By mathematical simulation of renal time-activity curves various factors which can influence this parameter are investigated, a simple analysis is proposed and clinical results are correlated with biopsy findings. A washout parameter greater than 28 s is found to be consistent with histologically diagnosed rejection over a range of bolus qualities.

Graft Rejection↗
PubMed1986

Emergency screening for ethylene glycol in serum.

We have exploited the "interference" of ethylene glycol in the Du Pont aca triglyceride method to develop a convenient and rapid screening method for detecting ethylene glycol in serum. Pretreatment of patient's serum with lipase, glycerol kinase, and other cofactors usually added for triglyceride analysis removes triglycerides and glycerol, but not ethylene glycol, from the sample. The aca triglyceride method may then be used to estimate the ethylene glycol concentration in serum.

Emergencies↗
PubMed1986

Graphical comparisons of interferences in clinical chemistry instrumentation.

Instrument- and analyte-specific interferences can be produced by adding known concentrations of potentially interfering substances to serum from healthy volunteers. Analytical results are expressed as a percentage of the original (unaffected) result. Graphical displays of the transformed data document the conditions under which erroneous results would be probable for specimens containing the additive. If several analytical systems are available, one can make an informed choice of which to use for a particular analysis by comparing the appropriate graphical information. Comparisons of such displays of data from newer systems being considered for purchase may facilitate decisions regarding laboratory instrumentation.

Bilirubin↗
PubMed1984

Effects of carbohydrates on membrane stability at low water activities.

The relative effectiveness of a variety of carbohydrates in preserving the structural and functional integrity of membranes at low water activities was studied, using Ca-transporting microsomes from muscle as a model membrane. The order of effectiveness (greatest to lowest) was: trehalose, lactose, maltose, cellobiose, sucrose, glucose, fructose, sorbitol, raffinose, myo-inositol, glycerol. At the highest concentrations of the most effective sugars tested, microsomes were obtained upon rehydration that were similar structurally and functionally to fresh membranes. The least effective carbohydrates, alcohol sugars, all appear to be fusogenic. A structural explanation for relative effectiveness of the sugars was sought, but no clear relationship was found, except that effectiveness does not appear to be related to the number of position of hydroxyl groups available for hydrogen bonding.

Animals↗