scholarly journals Evidence that the uptake of tri-iodo-l-thyronine by human erythrocytes is carrier-mediated but not energy-dependent

1982 ◽  
Vol 208 (1) ◽  
pp. 27-34 ◽  
Author(s):  
Roelof Docter ◽  
Eric P. Krenning ◽  
Greetje Bos ◽  
Durk F. Fekkes ◽  
George Hennemann
Keyword(s):  
Contrast Agents ◽  
Rat Hepatocytes ◽  
Human Erythrocytes ◽  
Uptake System ◽  
Erythrocyte Ghosts ◽  
Intact Cells ◽  
X Ray ◽  
Dose Dependent Fashion ◽  
Uptake Studies ◽  
Energy Dependent

We investigated 3,3′,5-tri-iodo-l-thyronine transport by human erythrocytes and by ‘ghosts’ prepared from these cells. Uptake of tri-iodothyronine by erythrocytes at 37°C was time-dependent with a maximum reached after 60min. Tracer analysis after incubation for 1min revealed only one saturable binding site, with Km 128±19nm (mean±s.e.m.; n=7) and Vmax. 4.6±0.7pmol of tri-iodothyronine/min per 6×107 cells. After 10min incubation Km 100±16nm (n=10) was found with Vmax. 7.7±1.2pmol of tri-iodothyronine/10min per 6×107 cells. At 0°C the uptake system is still active, with Km 132±26nm and Vmax. 1.8±0.3pmol of tri-iodothyronine/10min per 6×107 cells. The Vmax. with intact cells is 5-fold greater than the Vmax. with membranes derived from the same amount of cells when uptake studies are performed in media with similar free tri-iodothyronine concentrations. This indicates that at least 80% of tri-iodothyronine taken up by the intact erythrocytes enters the cell. This saturable uptake system can be inhibited by X-ray-contrast agents in a dose-dependent fashion. (±)-Propranolol, but not atenolol, has the same effect, indicating that the membrane-stabilizing properties of (±)-propranolol are involved. Furthermore, there is no inhibition by ouabain or vanadate, which indicates that tri-iodothyronine uptake is not dependent on the activity of Na++K+-dependent adenosine triphosphatase. We have prepared erythrocyte ‘ghosts‘, resealed after 2.5min with 0mm-, 2mm- or 4mm-ATP inside. Inclusion of ATP and integrity of the membrane of the erythrocyte ‘ghosts’ were verified on the basis of an ATP-concentration-dependent functioning of the Ca2+ pump. No difference was found in the uptake of tri-iodothyronine by erythrocyte ‘ghosts’ with or without ATP included, indicating that uptake of tri-iodothyronine is not ATP-dependent. The following conclusions are drawn. (1) Tri-iodothyronine enters human erythrocytes. (2) There is only one saturable uptake system present for tri-iodothyronine, which is neither energy (i.e. ATP)-dependent nor influenced by the absence of an Na+ gradient across the plasma membrane. This mode of uptake of tri-iodothyronine by human erythrocytes is in sharp contrast with that of rat hepatocytes, which uptake system is energy-dependent and ouabain-sensitive [Krenning, Docter, Bernard, Visser & Hennemann (1978) FEBS Lett.91, 113–116; Krenning, Docter, Bernard, Visser & Hennemann (1980) FEBS Lett.119, 279–282]. (3) X-ray-contrast agents inhibit tri-iodothyronine uptake by erythrocytes in a similar fashion to that by which they inhibit the uptake of tri-iodothyronine by rat hepatocytes [Krenning, Docter, Bernard, Visser & Hennemann (1982) FEBS Lett.140, 229–233].

scholarly journals The effects of Ca2+ and Sr2+ on Ca2+-sensitive biochemical changes in human erythrocytes and their membranes

1981 ◽  
Vol 198 (3) ◽  
pp. 441-445 ◽  
Author(s):  
D Allan ◽  
P Thomas
Keyword(s):  
Direct Interaction ◽  
Human Erythrocytes ◽  
Biochemical Changes ◽  
Intracellular Concentration ◽  
Ionophore A23187 ◽  
Erythrocyte Ghosts ◽  
High Concentration ◽  
Intact Cells ◽  
Whole Cells

1. The Ca2+-dependency of K+ efflux, microvesiculation and breakdown of polyphosphoinositides and of ankyrin have been measured in intact human erythrocytes exposed to ionophore A23187 and HEDTA [N'-(2-hydroxyethyl)ethylenediamine NNN'-triacetate]-Ca2+ buffers. Half-maximal responses were observed at pCa values of 6.4, 4.1, 5.0 and 4.8 respectively. 2. The Ca2+ dependencies of K+ efflux and breakdown of polyphosphoinositides and ankyrin measured in erythrocyte ghosts without addition of ionophore showed almost identical values with those seen in whole cells treated with ionophore. 3. We conclude that ionophore A23187 is able to cause rapid equilibration of extracellular and intracellular [Ca2+] in intact cells and that in the presence of a suitable Ca2+ buffer, ionophore A23187 can be used to precisely fix the intracellular concentration of Ca2+ in erythrocytes. 4. The relatively high concentration of Ca2+ required to produce microvesiculation in intact cells may indicate that microvesiculation could be at least partly dependent on a direct interaction of Ca2+ with phospholipid. 5. Results obtained with Sr2+ paralleled those with Ca2+, although higher Sr2+ concentrations were required to achieve the same effects as Ca2+. Mg2+ produced none of the changes seen with Ca2+ or Sr2+.

scholarly journals The ß-Glucosidase of the Yeast Cell Surface

1966 ◽  
Vol 50 (1) ◽  
pp. 9-24 ◽  
Author(s):  
J. Gordin Kaplan ◽  
Wanda Tacreiter
Keyword(s):  
Transport System ◽  
Metabolic Energy ◽  
Uptake System ◽  
Entire System ◽  
Membrane Component ◽  
Intact Cells ◽  
Yeast Cell Surface ◽  
Dependent Transport ◽  
Energy Dependent ◽  
Rate Limiting

There are two distinct components of the system which limits the rate at which intact cells of S. cerevisiae C hydrolyze external ß-glucosides; one component requires metabolic energy and the other is stereospecific for ß-glucosides. The stereospecific component is localized at the cell membrane, as shown by its sensitivity to heavy metal inhibitors which did not penetrate the cell under the conditions used. It was shown that cellobiose-grown cells were able to remove cellobiose from the medium in which they were incubated, and that the cellobiose uptake system was identical to that which limits the patent ß-glucosidase activity. In order to test the hypothesis that the system in question was a transport system, for ß-glucosides the ability of cellobiose-grown cells to take up 14C-labeled methyl-ß-glucoside (MBG) was studied. The induced cells were able to take up MBG-14C and the label could be partially chased out by cold MBG and cellobiose; glucose-grown cells could not incorporate label. However, induced cells could not take up label when incubated with 14C-MBG, thus excluding the hypothesis of transport of intact ß-glucosides. It was concluded that the stereospecific membrane component was actually a ß-glucosidase, coupled to an energy-dependent transport system for the glucose moiety; the function of the latter was rate-limiting in the over-all activity of the entire system.

scholarly journals Cellular and lysosomal uptake of methylamine in isolated rat hepatocytes

1983 ◽  
Vol 210 (3) ◽  
pp. 929-936 ◽  
Author(s):  
A E Solheim ◽  
P O Seglen
Keyword(s):  
Rat Hepatocytes ◽  
Proton Pumping ◽  
Temperature Sensitive ◽  
Facilitated Diffusion ◽  
High Concentration ◽  
Isolated Rat Hepatocytes ◽  
Intact Cells ◽  
Total Cell Volume ◽  
Energy Inhibitors ◽  
Energy Dependent

Upon addition of methylamine to intact cells, this lysosomotropic weak base accumulates intracellularly as the result of at least two different mechanisms: (1) facilitated diffusion across the plasma membrane, i.e. a process which is carrier-mediated and subject to both trans-stimulation (accelerative exchange) and cis-inhibition (competition) by other amines (e.g. ammonia, methylamine and triethylamine); this transport process is furthermore non-concentrative, energy-independent, and (although moderately temperature-sensitive) operative even at 0 degrees C; (2) active uptake, i.e. an energy-dependent concentrative process which is inhibited by anoxia and energy inhibitors. With time, methylamine accumulates in lysosomes and gives rise to a lysosomal swelling which is easily visible by optical microscopy, and which causes the cells to appear coarsely granular. After a 1h incubation with 10mM-methylamine, the total cell volume is increased by about 12%. Under anoxic conditions or in the presence of energy inhibitors, lysosomal swelling is abolished regardless of there being a high concentration of methylamine intracellularly (taken up by facilitated diffusion). The continuous accumulation of methylamine in lysosomes therefore seems to depend on an energy-requiring process (such as continuous proton pumping), and not only on trapping by Donnan-equilibrium-generated protons.

SIGMAL: A Program for Calculating L-Shell lonization Cross-Sections

1981 ◽  
Vol 39 ◽  
pp. 198-199 ◽  
Author(s):  
R.F. Egerton
Keyword(s):  
Cross Sections ◽  
Fortran Program ◽  
Absorption Data ◽  
X Ray ◽  
Atomic Electrons ◽  
Energy Dependent ◽  
Hydrogenic Model ◽  
Electron Energy Loss ◽  
X Ray Absorption ◽  
Shell Ionization

SIGMAL is a short (∼ 100-line) Fortran program designed to rapidly compute cross-sections for L-shell ionization, particularly the partial crosssections required in quantitative electron energy-loss microanalysis. The program is based on a hydrogenic model, the L1 and L23 subshells being represented by scaled Coulombic wave functions, which allows the generalized oscillator strength (GOS) to be expressed analytically. In this basic form, the model predicts too large a cross-section at energies near to the ionization edge (see Fig. 1), due mainly to the fact that the screening effect of the atomic electrons is assumed constant over the L-shell region. This can be remedied by applying an energy-dependent correction to the GOS or to the effective nuclear charge, resulting in much closer agreement with experimental X-ray absorption data and with more sophisticated calculations (see Fig. 1 ).

Energy-dependent dead-time correction in digital pulse processors applied to silicon drift detector's X-ray spectra

2018 ◽  
Vol 25 (2) ◽  
pp. 484-495 ◽  
Author(s):  
Suelen F. Barros ◽  
Vito R. Vanin ◽  
Alexandre A. Malafronte ◽  
Nora L. Maidana ◽  
Marcos N. Martins
Keyword(s):  
Dead Time ◽  
Pulse Height ◽  
Height Distribution ◽  
Pulse Height Distribution ◽  
Dead Time Correction ◽  
Time Model ◽  
X Ray ◽  
Digital Pulse ◽  
Analytical Correction ◽  
Energy Dependent

Dead-time effects in X-ray spectra taken with a digital pulse processor and a silicon drift detector were investigated when the number of events at the low-energy end of the spectrum was more than half of the total, at counting rates up to 56 kHz. It was found that dead-time losses in the spectra are energy dependent and an analytical correction for this effect, which takes into account pulse pile-up, is proposed. This and the usual models have been applied to experimental measurements, evaluating the dead-time fraction either from the calculations or using the value given by the detector acquisition system. The energy-dependent dead-time model proposed fits accurately the experimental energy spectra in the range of counting rates explored in this work. A selection chart of the simplest mathematical model able to correct the pulse-height distribution according to counting rate and energy spectrum characteristics is included.

scholarly journals Performance and optimization of X-ray grating interferometry

2014 ◽  
Vol 372 (2010) ◽  
pp. 20130027 ◽  
Author(s):  
T. Thuering ◽  
M. Stampanoni
Keyword(s):  
Interference Fringe ◽  
Refraction Angle ◽  
Fringe Visibility ◽  
X Ray ◽  
Analytical Formulae ◽  
Grating Interferometer ◽  
Differential Phase Contrast ◽  
Energy Dependent ◽  
Application Specific ◽  
Contrast Image

The monochromatic and polychromatic performance of a grating interferometer is theoretically analysed. The smallest detectable refraction angle is used as a metric for the efficiency in acquiring a differential phase-contrast image. Analytical formulae for the visibility and the smallest detectable refraction angle are derived for Talbot-type and Talbot–Lau-type interferometers, respectively, providing a framework for the optimization of the geometry. The polychromatic performance of a grating interferometer is investigated analytically by calculating the energy-dependent interference fringe visibility, the spectral acceptance and the polychromatic interference fringe visibility. The optimization of grating interferometry is a crucial step for the design of application-specific systems with maximum performance.

Determining the energy-dependent X-ray flux variation of a synchrotron beamline using Laue diffraction patterns

2011 ◽  
Vol 44 (1) ◽  
pp. 177-183 ◽  
Author(s):  
Catherine Dejoie ◽  
Martin Kunz ◽  
Nobumichi Tamura ◽  
Colin Bousige ◽  
Kai Chen ◽  
...  
Keyword(s):  
Incident Energy ◽  
Flux Variation ◽  
Laue Diffraction ◽  
X Ray ◽  
Measured Flux ◽  
Highly Sensitive ◽  
Diffraction Patterns ◽  
Energy Dependent ◽  
Flux Curve

Although the spectrum originating from a superconducting bending magnet is quasi-continuous, it shows important intensity variations through its spectral range. A method to determine the incident energy-dependent flux variation based on the comparison between observed intensities and the calculated intensities of a well known structure (calcite) is presented here. It is found that the measured flux is highly sensitive to the use of correct Debye–Waller factors for the atoms of the standard crystal. By using the measured flux curve, it was possible to unambiguously index the Laue diffraction pattern of a trigonal crystal structure in its hexagonal setting. This is a crucial but difficult first step for the determination of strain and stress in materials with this symmetry, such as quartz, Mg, Ti, Znetc.

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