Biomedical subjects

S Samarin

Publications and source records attributed to S Samarin.

3 recordsLinked to original sources

PubMed2006

Energy- and momentum-resolved exchange and spin-orbit interaction in cobalt film by spin-polarized two-electron spectroscopy.

Spontaneous ordering of electronic spins in ferromagnetic materials is one of the best known and most studied examples of quantum correlations. Exchange correlations are responsible for long range spin order and the spin-orbit interaction (SOI) can create preferred crystalline directions for the spins, i.e., magnetic anisotropy. Presented experimental data illustrate how novel spin-polarized two-electron spectroscopy in-reflection mode allows observation of the localization of spin-dependent interactions in energy-momentum space. Comparison of spin-orbit asymmetries in spectra of Co film and clean W(110) may indicate the presence of interface specific proximity effects providing important clues to the formation of preferred orientations for the magnetic moment of the Co film. These results may help to understand the microscopic origin of interface magnetic anisotropy.

Journal Article↗

PubMed2001

Listeria protein ActA mimics WASp family proteins: it activates filament barbed end branching by Arp2/3 complex.

Actin-based propulsion of the bacteria Listeria and Shigella mimics the forward movement of the leading edge of motile cells. While Shigella harnesses the eukaryotic protein N-WASp to stimulate actin polymerization and filament branching through Arp2/3 complex, the Listeria surface protein ActA directly activates Arp2/3 complex by an unknown mechanism. Here we show that the N-terminal domain of ActA binds one actin monomer, in a profilin-like fashion, and Arp2/3 complex and mimics the C-terminal domain of WASp family proteins in catalyzing filament barbed end branching by Arp2/3 complex. No evidence is found for side branching of filaments by ActA-activated Arp2/3 complex. Mutations in the conserved acidic (41)DEWEEE(46) and basic (146)KKRRK(150) regions of ActA affect Arp2/3 binding but not G-actin binding. The motility properties of wild-type and mutated Listeria strains in living cells and in the medium reconstituted from pure proteins confirm the conclusions of biochemical experiments. Filament branching is followed by rapid debranching. Debranching is 3-4-fold faster when Arp2/3 is activated by ActA than by the C-terminal domain of N-WASp. VASP is required for efficient propulsion of ActA-coated beads in the reconstituted motility medium, but it does not affect the rates of barbed end branching/debranching by ActA-activated Arp2/3 nor the capping of filaments. VASP therefore affects another still unidentified biochemical reaction that plays an important role in actin-based movement.

Actin-Related Protein 2↗

PubMed2000

Spatial resolution of epicardial pace mapping using body surface potentials.

Body surface potential maps (BSPMs) recorded during pace mapping provide an important non-invasive means for identifying local cardiac events; recent clinical studies demonstrated that endocardial pacing sites can be resolved within less than 10 mm. We sought to determine whether similar spatial resolution could be achieved during epicardial pacing. Four patients who were undergoing either heart valve replacement (one), aortocoronary bypass graft (one), or both (two) were studied. In each patient, a pair of epicardial electrodes was placed intraoperatively at the middle aspect of the right ventricular free wall. The distance between the neighbouring electrodes was 10 mm. Five days after the surgery, ECGs were acquired from 35 leads during pacing from each epicardial electrode. We determined the distributions of QRS integrals (the net area under the ECG signal) and compared integrals corresponding to pacing from each of the adjacent electrodes using statistical indices. Student's t-test was applied to these indices and in all the patients revealed that differences in distributions of QRS integral maps were statistically significant (p < 0.01). Results of our study indicate that the non-invasive acquisition of body surface ECGs could resolve epicardial breakthrough sites within 10 mm, which may be useful in facilitating therapeutic ablations in patients with ventricular tachycardias.

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