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PubMed1988

Membrane voltage changes in passive dendritic trees: a tapering equivalent cylinder model.

An exponentially tapering equivalent cylinder model is employed in order to approximate the loss of the dendritic trunk parameter observed from anatomical data on apical and basilar dendrites of CA1 and CA3 hippocampal pyramidal neurons. This model allows dendritic trees with a relative paucity of branching to be treated. In particular, terminal branches are not required to end at the same electrotonic distance. The Laplace transform method is used to obtain analytic expressions for the Green's function corresponding to an instantaneous pulse of current injected at a single point along a tapering equivalent cylinder with sealed ends. The time course of the voltage in response to an arbitrary input is computed using the Green's function in a convolution integral. Examples of current input considered are (1) an infinitesimally brief (Dirac delta function) pulse and (2) a step pulse. It is demonstrated that inputs located on a tapering equivalent cylinder are more effective at the soma than identically placed inputs on a nontapering equivalent cylinder. Asymptotic solutions are derived to enable the voltage response behaviour over both relatively short and long time periods to be analysed. Semilogarithmic plots of these solutions provide a basis for estimating the membrane time constant tau m from experimental transients. Transient voltage decrement from a clamped soma reveals that tapering tends to reduce the error associated with inadequate voltage clamping of the dendritic membrane. A formula is derived which shows that tapering tends to increase the estimate of the electrotonic length parameter L.

Animals↗
PubMedDate not supplied

Determination of hepatic blood flow in the rat using sequential infusions of indocyanine green or galactose.

A method was developed for the estimation of hepatic blood flow in the rat using sequential infusions of one of two model substrates, indocyanine green or galactose. Either substrate was infused to steady state (achieved within 6 min of the start of indocyanine green infusion and within 40 min of the start of galactose infusion) through either the femoral or portal vein, and three steady state blood samples were obtained. Following a 30-min washout period, the same substrate was infused a second time through the alternate blood vessel. Using a pharmacokinetic approach, hepatic blood flow was estimated from the mean steady state concentrations during the two infusions and the infusion rate. The present method yielded hepatic blood flow estimates of 2.03 +/- 0.13 ml/min/g of liver (indocyanine green) and 2.28 +/- 0.49 ml/min/g of liver (galactose) in two groups of four adult male rats. A Monte-Carlo simulation experiment was conducted to assess the potential error introduced into the blood flow calculation by the moderate transhepatic extraction ratio of the two model substrates (0.386 +/- 0.049 for indocyanine green; 0.439 +/- 0.139 for galactose). The simulation experiment predicted calculational errors between 7.4% (indocyanine green) and 19.5% (galactose), based on the hepatic extraction ratio and the precision of the analytical method for the two compounds. The predicted errors were in good agreement with the variability in blood flow estimates observed experimentally (6.5% for indocyanine green; 21.4% for galactose). The steady state approach employed appears to be associated with superior reproducibility as compared to previously reported methods utilizing bolus dose administration of marker compounds and calculations based upon AUC estimates.

Animals↗
PubMed2000

An improved method for the determination of green and black tea polyphenols in biomatrices by high-performance liquid chromatography with coulometric array detection.

Tea polyphenols are strong antioxidants and are believed to have beneficial health effects. However, the blood and tissue levels of these compounds are not well characterized because of a lack of suitable analytical methods for the biological resolution of these compounds. Previously, we developed methods for the analysis of three green tea catechins. Now we report an improved method for the measurement of the levels of the different catechins and theaflavins in biological fluids and tissues. The method includes digestion of the plasma, urine, or tissue samples with beta-d-glucuronidase and sulfatase, followed by extraction with ethyl acetate and subsequent separation by reversed-phase high-performance liquid chromatography (HPLC). The polyphenols are identified on the basis of their retention times, spectral analysis, and electrochemical behavior across an array of electrodes. In a single HPLC run, it is possible to determine the major catechins and theaflavins as well as some of the catechin metabolites. The detection limits for catechins and theaflavins are from 5 to 10 ng/ml of saliva, plasma, or urine.

Adult↗
PubMed1991

Overestimation of albumin in heparinized plasma.

Monochromatic measurement of albumin by the bromcresol green method leads to overestimation of albumin in the presence of heparin. The interference seems to be caused by fibrinogen, which, in the presence of heparin, produces an almost constant increase of the measuring signal over the whole range of suitable wavelengths (550 to 700 nm). The albumin overestimation can be eliminated by using a bichromatic modification. An application of this procedure for the automated analyzer RAXT, RA-1000 (Bayer Diagnostik, Technicon) is presented. We recommend using only bichromatic methods for albumin determination with bromcresol green to avoid unexpected analytical artifacts.

Bromcresol Green↗
PubMed1999

Spectrophotometric quantitation of antioxidant capacity through the formation of a phosphomolybdenum complex: specific application to the determination of vitamin E.

A spectrophotometric method has been developed for the quantitative determination of antioxidant capacity. The assay is based on the reduction of Mo(VI) to Mo(V) by the sample analyte and the subsequent formation of a green phosphate/Mo(V) complex at acidic pH. The method has been optimized and characterized with respect to linearity interval, repetitivity and reproducibility, and molar absorption coefficients for the quantitation of several antioxidants, including vitamin E. The phosphomolybdenum method, in combination with hexane monophasic extraction, has also been adapted for the specific determination of vitamin E in seeds. The results obtained with the proposed method were validated by comparison with a standard HPLC method. The phosphomolybdenum method is routinely applied in our laboratory to evaluate the total antioxidant capacity of plant extracts and to determine vitamin E in a variety of grains and seeds, including corn and soybean.

Antioxidants↗
PubMed2002

A new green analytical procedure for monitoring sub-nanogram amounts of chlorpyrifos on fruits using flow injection chemiluminescence with immobilized reagents.

A novel green method using flow injection chemiluminescence with controlled-reagent-release technology has been investigated for the rapid and sensitive monitoring of sub-nanogram amounts of chlorpyrifos. The analytical reagents involved in chemiluminescence (CL) reaction, luminol and periodate, were both immobilized on an anion-exchange column. The CL signals produced by the reaction between luminol and periodate, which were eluted from the column through water injection, were decreased in the presence of chlorpyrifos. The decrease of CL intensity was linear over the logarithm of concentration of chlorpyrifos ranging from 0.48 to 484.0 ng x mL(-1) (r(2) = 0.9969), and the limit of detection was 0.18 ng x mL(-1) (3sigma). At a flow rate of 2.0 mL x min(-1), the determination of chlorpyrifos, including sampling and washing, could be performed in 0.5 min with a relative standard deviation of less than <3.0%. The proposed method was applied successfully in an assay of remnant chlorpyrifos on fruits such as orange and shaddock with the recovery of 94.4-107.4%. The change of the concentration of chlorpyrifos in a water sample was also investigated, and the variation rate was 99.96% during 35 h in the open air.

Chlorpyrifos↗
PubMed1990

Hepatic blood flow and splanchnic oxygen consumption measurements in clinical sepsis.

In an effort to characterize the hemodynamic response of the liver to sepsis, hepatic blood flow (HBF) was measured in 10 normal volunteers and compared with that of 9 patients with sepsis. Flow was determined according to two different indicators and three methods of analysis including indocyanine green dye clearance (HBFICG), galactose clearance (GC), and galactose clearance with splanchnic galactose gradient measurement (HBFGG). For normal subjects, these three analytic methods provided essentially identical results (HBFICG = 0.74 +/- 0.18, GC = 0.72 +/- 0.14, and HBFGG = 0.76 +/- 0.16 L/min-m2). With hepatic venous sampling, HBF in patients with sepsis was significantly higher than normal levels (HBFICG = 1.28 +/- 0.50 and HBFGG = 1.17 +/- 0.52 L/min-m2) (p less than 0.025), but HBF by the GC technique (0.89 +/- 0.41 L/min-m2), which uses peripheral venous sampling, was not significantly increased because of reduced splanchnic galactose extraction, which appears to be characteristic of sepsis. Thus HBF estimates based on peripheral venous sampling must be interpreted with caution in view of the reduced extraction fraction in sepsis. HBF in clinical sepsis tends to increase in response to this inflammatory stress.

Galactose↗
PubMed2004

Analysis of hydroxide, inorganic sulphur species and organic anions in kraft pulping liquors by capillary electrophoresis.

A new method has been developed for the determination of hydroxide, sulphide, thiosulphate, sulphate, sulphite, chloride, oxalate and formate in kraft green, white and black liquors by capillary electrophoresis. The method provides baseline resolution of all analytes of interest using an electrolyte composed of 10 mM sodium chromate and 2 mM tetradecyltrimethylammonium hydroxide. Separations are conducted under constant current conditions at 25 degrees C and analytes are quantified by indirect UV-detection at 275 nm. A brief, post run wash of the capillary with 0.5 M NaOH and water gave improved inter- and intra-run repeatability of both migration times and peak areas. Sulphide and other oxysulphur species were relatively stable in white and green liquors diluted in helium-sparged water. However, sulphide present in black liquor samples diluted in the same solvent underwent rapid oxidation to form sulphite and thiosulphate. thereby precluding the measurement of all three anions. We discovered that quinone-type compounds present in black liquor catalyze the oxidation of sulphide and that the addition of reduced glutathione at a concentration of I mg/mL during black liquor dilution completely stabilized sulphide, sulphite and thiosulphate for at least one hour, thus allowing for quantitative analysis of the analytes. A mechanism is proposed to explain the action of both quinones and that of glutathione. Results obtained by the new method compared well with those obtained by ion chromatography, titrimetry, and from spike-recovery experiments.

Anions↗
PubMed1998

Electrostatic Interaction and Hindered Diffusion of Ion-Penetrable Spheres in a Slit Pore.

Electrostatic interaction and hindered diffusion of ion-penetrable spheres in a slit pore filled with an electrolyte solution are investigated theoretically. The concentration of the particles is assumed sufficiently low so that the interactions between the particles can be neglected. The slit pore comprises two parallel infinite plates, which can be either permeable or impermeable to the electrolyte. The electrostatic interaction energy is obtained analytically by adopting an integral of Green's function and an image method. It is found that for impermeable plates having constant surface charge densities, the electrostatic interaction can be attractive or repulsive for a particle with charge of opposite sign, depending on the relative magnitudes of charge densities and particle location. Similar behavior is predicted for plates with constant surface potential and a particle with charge of like sign. The interaction energy is used to determine the spatial distribution of the particle in the pore and the partition coefficient, and then to calculate the average and apparent diffusivities. The average diffusivity calculated from the average mobility in the pore is always smaller than that in the bulk solution because of greater drag the particle experiences in the presence of the plates. This mean diffusivity is larger than that in the corresponding neutral system for repulsive electrostatic interaction, but becomes smaller for attractive interaction. The apparent diffusivity defined from the flux based on the bulk concentration of the particle depends strongly on the ion concentration, as does the partition coefficient when the double layer is sufficiently thick. Copyright 1998 Academic Press.

Journal Article↗
PubMed1991

Using the correct regression analysis technique in method comparison studies.

Regression analysis frequently is used to evaluate a new clinical laboratory method. Results from the new method are compared to results from an existing more established method. If measurement error exists in the established method, then least squares may not be an appropriate statistical method to use for the regression analysis. An errors variable regression analysis model was used to evaluate data from five method comparison studies. Results were compared to least squares analyses performed on the same data. When significant measurement error existed in the "reference" method, the errors variable analysis provided a less biased estimate of the regression statistics, which differed markedly from the least squares results. Inappropriate use of least squares in method comparison studies can lead to erroneous conclusions about the relationship of a new analytical method to an existing method.

Journal Article↗
PubMedDate not supplied

Lack of effect of histamine H2-receptor antagonists on indocyanine green disposition measured by two methods.

Eleven healthy male volunteers were treated according to a randomized, crossover design with ranitidine (300 mg/day), cimetidine (1200 mg/day), or nothing for 48 hours. Ninety minutes after the 48-hour dose, each volunteer was given 0.5 mg/kg indocyanine green by iv bolus. Indocyanine green plasma concentrations were measured by the traditional spectrophotometric method at 800 nm and by HPLC simultaneously monitored at 214 and 656 nm. Neither histamine H2-receptor antagonist altered the disposition of indocyanine green. The mean (+/- S.D.) plasma clearance by the spectrophotometric method was 7.48 +/- 2.07 (control), 7.15 +/- 3.07 (ranitidine), and 6.88 +/- 1.35 ml/min/kg (cimetidine). The power to detect a 20 per cent change is 0.87. The spectrophotometric method generally produced a biexponential plasma concentration decay, whereas the HPLC method resulted in a monoexponential decay. Analysis of the 5- to 15-minute data by the conventional technique showed that although indocyanine green total plasma clearance was not significantly different for the two methods (P greater than 0.10), the volume of distribution was significantly greater (P less than 0.001) and the elimination rate constant was significantly smaller (P less than 0.001) for the spectrophotometric than the HPLC method. Although neither ranitidine nor cimetidine chronic administration alters indocyanine green disposition by either method, the absolute values of the pharmacokinetic parameters are dependent upon the analytical technique employed.

Adult↗
PubMed2006

Preliminary evaluation of flow-through immunocapture followed by real-time PCR for the detection of Salmonella serovars on tomato surfaces within 8 hours.

This study reports a preliminary evaluation of flow-through immunocapture (FTI) followed by real-time PCR (FTI-PCR) for the detection of Salmonella serovars on tomato surfaces within 8 h. The FTI-PCR method was compared with real-time PCR, direct plating of FTI beads on xylose lysine desoxycholate (XLD), and the conventional culture method for Salmonella found in the U.S. Food and Drug Administration's (FDA) Bacteriological Analytical Manual (BAM). Unwaxed green tomatoes were spot inoculated with a five-serovar Salmonella cocktail on smooth surfaces at levels of 10(0) to 10(4) CFU per tomato and washed in lactose broth (LB) using a shake-rub method. The resulting LB rinse was incubated at 37 degrees C for 4 h prior to analysis by FTI-XLD, real-time PCR, or FTI-PCR and for 24 h as the first step in the BAM Salmonella culture method. For FTI-XLD, the observed lowest detection level (LDL) was 4.6 x 10(1) CFU per tomato. There was no significant difference in performance between the FTI-XLD method and the BAM Salmonella culture method (P > 0.05); however, the FTI-XLD method reduced the overall assay time by 48 h. For real-time PCR and FTI-PCR, the observed LDLs were 4.6 x 10(1) and 9.2 x 10(0) CFU per tomato, respectively. The FTI-PCR method was superior to the BAM Salmonella culture method (P < 0.05) for the detection of Salmonella serovars on tomato surfaces and was completed within 8 h.

Bacteriological Techniques↗
PubMed2001

Biosynthesis and release of methylarsenic compounds during the growth of freshwater algae.

Arsenic transformations by freshwater algae have been studied under laboratory conditions. By the use of a new analytical method, we identified methylarsenic(III) species in the growth medium of green-alga Closterium aciculare incubated under axenic conditions. The arsenate concentration in the experimental medium began to decrease just after inoculation, and the levels of arsenite and methylarsenicals increased with the growth of C. aciculare. Initially, most of the arsenate was converted into arsenite, which peaked in concentration during the exponential phase. Methylarsenicals accumulated rapidly in the stationary phase. DMAA(V) production was enhanced when the ratio of phosphate to arsenate decreased in the culture medium. The levels of DMAA(V) increased continuously toward the end of the experiment. On the other hand, methylarsenic(III) species remained relatively steady during the stationary phase. Methylarsenic(III) species accounted for 0-35% of methylarsenicals. These results suggest that arsenite and methylarsenicals (containing methylarsenic(III) species) are supplied by phytoplankton, and serve as evidence of the origin of methylarsenic(III) species in natural waters.

Arsenates↗
PubMed1981

Continuous-flow serum albumin determination by reaction with picrate ions, with use of a flow-through picrate ion electrode.

An automated potentiometric method for serum albumin determination by use of the picrate/albumin reaction is described. A continuous-flow system and a specially designed flow-through picrate ion electrode were used in making the measurements. Various factors affecting the reaction, such as pH, picrate ion concentration, and reaction time, were studied. Peak height in millivolts and albumin concentration were linearly related in the range 10-70 g/L. Both within-run and day-to-day, the CV for the method was about 2%. Analytical recovery of albumin added to serum samples ranged from 97.0 to 110.3%, averaging 102.2%. Results compare favorably with those by the established bromcresol green method. The proposed method is suitable for routine use and for screening tests.

Electrodes↗
PubMed2006

All-optical switching, bistability, and slow-light transmission in photonic crystal waveguide-resonator structures.

We analyze the resonant linear and nonlinear transmission through a photonic crystal waveguide side-coupled to a Kerr-nonlinear photonic crystal resonator. First, we extend the standard coupled-mode theory analysis to photonic crystal structures and obtain explicit analytical expressions for the bistability thresholds and transmission coefficients which provide the basis for a detailed understanding of the possibilities associated with these structures. Next, we discuss limitations of standard coupled-mode theory and present an alternative analytical approach based on the effective discrete equations derived using a Green's function method. We find that the discrete nature of the photonic crystal waveguides allows a geometry-driven enhancement of nonlinear effects by shifting the resonator location relative to the waveguide, thus providing an additional control of resonant waveguide transmission and Fano resonances. We further demonstrate that this enhancement may result in the lowering of the bistability threshold and switching power of nonlinear devices by several orders of magnitude. Finally, we show that employing such enhancements is of paramount importance for the design of all-optical devices based on slow-light photonic crystal waveguides.

Journal Article↗
PubMed2002

Surveillance for early detection and monitoring of infectious disease outbreaks associated with bioterrorism.

The appearance of "new" infectious diseases, the reemergence of "old" infectious diseases, and the deliberate introduction of infectious diseases through bioterrorism has highlighted the need for improved and innovative infectious disease surveillance systems. Traditional current surveillance systems are generally based on the recognition of a clear increase in diagnosed cases before an outbreak can be identified. For early detection of bioterrorist-initiated outbreaks, the sensitivity and timeliness of the systems need to be improved. Systems based on syndromic surveillance are being developed using technologies such as electronic reporting and the internet. The reporting sources include community physicians, public health laboratories, emergency departments, intensive care units, district health offices, and hospital admission and discharge systems. The acid test of any system will be the ability to provide analyses and interpretations of the data that will serve the goals of the system. Such analytical methods are still in the early stages of development.

Bioterrorism↗
PubMed2006

High-throughput analysis of catechins and theaflavins by high performance liquid chromatography with diode array detection.

Increased interest in potential health-protective activities of flavonoid-rich tea has created the need to take advantage of HPLC column and system advances in order to optimize methodologies for flavonoid analysis. Two new RP-C18 methods for HPLC-DAD analysis of tea flavonoids were developed to facilitate separation of catechins within 5 min and separation of catechins and theaflavins within 10 min total analysis time. Calibration results indicate that these methods have on-column limits of detection on the order of 1-10 pmol for most tea catechins, and method replication generally resulted in intraday and interday peak area variation of <5% for catechins and <9% for theaflavins in green and black tea infusions. These new methods are therefore sensitive, reproducible, and represent a 2-4-fold reduction in HPLC analysis time from existing analytical methods. These improvements are readily achievable with commonly used HPLC equipment, thus facilitating increased sample throughput and efficiency across a broad range of experimental applications.

Biflavonoids↗