Biomedical subjects

S Bals

Publications and source records attributed to S Bals.

5 recordsLinked to original sources

PubMed2006

An efficient way of including thermal diffuse scattering in simulation of scanning transmission electron microscopic images.

We propose an improved image simulation procedure for atomic-resolution annular dark-field scanning transmission electron microscopy (STEM) based on the multislice formulation, which takes thermal diffuse scattering fully into account. The improvement with regard to the classical frozen phonon approach is realized by separating the lattice configuration statistics from the dynamical scattering so as to avoid repetitive calculations. As an example, the influence of phonon scattering on the image contrast is calculated and investigated. STEM image simulation of crystals can be applied with reasonable computing times to problems involving a large number of atoms and thick or large supercells.

Journal Article↗

PubMed2005

Nonlinear imaging using annular dark field TEM.

Annular dark field TEM images exhibit a dominant mass-thickness contrast that can be quantified to extract single atom scattering cross sections. On top of this incoherent background, additional lattice fringes appear with a nonlinear information limit of 1.2A at 150 kV. The formation of these fringes is described by coherent nonlinear imaging theory and good agreement is found between experimental and simulated images. Calculations furthermore predict that the use of aberration corrected microscopes will improve the image quality dramatically.

Journal Article↗

PubMed1992

Spare receptors for beta-adrenoceptor-mediated positive inotropic effects of catecholamines in the human heart.

We studied whether the human heart has spare receptors for beta-adrenoceptor-mediated positive inotropic effects. Thus, we assessed in right atria and left papillary muscles of patients with different degrees of heart failure under identical experimental conditions affinity (pKI values from (-)-[125I]iodocyanopindolol binding) and potency (pD2 values from contractile responses) for isoprenaline, adrenaline, and noradrenaline in comparison with rat heart. Plots of beta-adrenoceptor occupancy versus responses constructed from these data revealed that rat left atria and papillary muscles had a large receptor reserve for all three beta-adrenoceptor agonists: 50% of maximal response was produced with only 1-3% of beta-adrenoceptor occupancy. In human heart, however, receptor reserve was considerably lower: 50% of maximal response required 8-10% (in right atria) and 20-25% (in left papillary muscles) occupation of beta-adrenoceptors. Receptor reserve declined further with an increasing degree of heart failure (and decreasing beta-adrenoceptor number): in end-stage heart failure (New York Heart Association class IV) both in right atria and left papillary muscles a 1:1 ratio between beta-adrenoceptor occupancy and responses was observed. These data show that the human heart has only a small receptor reserve for beta-adrenoceptor agonists. This may explain why a decrease in beta-adrenoceptor number leads to a decrease in beta-adrenoceptor function early in the development of heart failure.

Adenylyl Cyclases↗

PubMed1992

Characterization of the beta adrenoceptor subtype(s) mediating the positive inotropic effects of epinine, dopamine, dobutamine, denopamine and xamoterol in isolated human right atrium.

In patients with chronic heart failure cardiac beta-1 adrenoceptors are reduced, whereas beta-2 adrenoceptor changes vary depending on the etiology of the disease. Beta Adrenoceptor agonists can be used for short-term inotropic support in chronic heart failure; their clinical efficacy might depend on which beta adrenoceptor subtype(s) mediates their positive inotropic effect. Thus, the beta adrenoceptor subtype(s) involved in the positive inotropic effects of clinically used beta adrenoceptor agonists was characterized on isolated electrically driven human right atria by the use of the selective beta-1 adrenoceptor antagonist CGP 20712 A (300 nmol/l) and/or the selective beta-2 adrenoceptor antagonist ICI 118,551 (30 nmol/l). Epinine evoked positive inotropic effects through stimulation of beta-1 and beta-2 adrenoceptors to about the same degree, whereas dobutamine acted mainly at beta-1 adrenoceptors but had a significant beta-2 adrenoceptor component. Both agonists were full agonists causing the same maximum increase in contractile force (Emax) as did isoprenaline or Ca++ (Emax = 1.0). In contrast, denopamine was a partial selective beta-1 adrenoceptor agonist (Emax = 0.75-0.85). Dopamine was in the presence of uptake1-blockade (by 5 mumol/l phenoxybenzamine) a partial agonist (Emax = 0.60-0.70) acting selectively at beta-1 adrenoceptors; in the absence of uptake1-blockade, however, dopamine was a full agonist, indicating that part of its positive inotropic effect is indirect via the release of endogenous noradrenaline. Xamoterol did not exert positive inotropic effects, but concentration-dependently slightly decreased basal force of contraction.

Adrenergic beta-Agonists↗

PubMedDate not supplied

Spontaneous and experimentally evoked [Ca2+]i-transients in cardiac myocytes measured by means of a fast Fura-2 technique.

A setup for dual wavelength-excitation fluorescence measurements is introduced which permits a temporal resolution of up to 1 KHz, using the Ca2(+)-sensitive fluorescent dye Fura-2. The system makes use of a novel technical solution for chopping between two excitation wavelengths which does not move any optical components. Two beams, which are alternatively opened or shut by a rotating chopper wheel, are united by a dichroic mirror and are used for low-noise epifluorescence microscopy. The system includes a device for fast changes of extracellular solution that can be used for studying various components of [Ca2+]i-regulation in excitable and non-excitable cells. Sample recordings of spontaneous and experimentally-evoked [Ca2+]i-transients from cardiac myocytes are presented. Cardiac myocytes are a cell species that produces particularly fast [Ca2+]i-transients and therefore, a high temporal resolution is required in order to study physiological and/or pharmacological properties of these transients.

Animals↗