Effects of acute ischemia,early extrabeats and propafenone on complex activation patterns in intact and ischemic canine hearts

Although, sodium channel blockers have the ability to suppress nonsustained ventricular arrhythmias, an excessive drug-associated arrhythmic death rate has been reported in patients with coronary heart disease (CHD). Sodium channel blockers should prevent initiation of reentry activation by reducing directional differences in cardiac conduction (anisotropy). However, in vitro data demonstrated, that reduction of membrane excitability, e.g. by lowering the inward Na+ current, increases the risk for conduction failure and associated reentry arrhythmias. In 11 dogs the effects of myocardial ischemia, premature epicardial stimulation (PES) and propafenone on anisotropic conduction properties were tested using three-dimensional mapping techniques. The epicardial (longitudinal and transverse to fiber orientation) and transmural (oblique and straight) spread of activation was reconstructed during constant and PES. At baseline, conduction velocities (CV) were higher along (1.20 +/- 0.41 m/s) than across (0.91 +/- 0.19 m/s; p < 0.05) epicardial muscle fibers as well as along oblique (1.77 +/- 0.75 m/s) compared to straight (0.39 +/- 0.09 m/s, p < 0.05) transmural pathways. Acute ischemia did not significantly reduce tissue anisotropy. PES and additional administration of propafenone epicardially eliminated and transmurally profoundly reduced tissue anisotropy (longitudinal 0.58 +/- 0.09 m/s, transverse 0.69 +/- 0.08 m/s, oblique 0.69 +/- 0.28 m/s, straight 0.27 +/- 0.07 m/s). However, reduced anisotropy was associated with a higher probability for conduction block along myocardial fibers in the epicardium and along oblique transmural pathways. Our data show, that propafenone exhibits both potential pro- and antiarrhythmic effects in dogs with acute myocardial ischemia. These results possibly provide more insights in mechanisms underlying the excessive drug-associated arrhythmic death rate in patients with CHD.     

Resolving the predator first paradox: Arthropod predator food webs in pioneer sites of glacier forelands

Primary succession on bare ground surrounded by intact ecosystems is, during its first stages, characterized by predator‐dominated arthropod communities. However, little is known on what prey sustains these predators at the start of succession and which factors drive the structure of these food webs. As prey availability can be extremely patchy and episodic in pioneer stages, trophic networks might be highly variable. Moreover, the importance of allochthonous versus autochthonous food sources for these pioneer predators is mostly unknown. To answer these questions, the gut content of 1,832 arthropod predators, including four species of carabid beetles, two lycosid and several linyphiid spider species caught in early and late pioneer stages of three glacier forelands, was screened molecularly to track intraguild and extraguild trophic interactions among all major prey groups occurring in these systems. Two‐thirds of the 2,310 identified food detections were collembolans and intraguild prey, while one‐third were allochthonous flying insects. Predator identity and not successional stage or valley had by far the strongest impact on the trophic interaction patterns. Still, the variability of prey spectra increased significantly from early to late pioneer stage, as did the niche width of the predators. As such the structure of pioneer arthropod food webs in recently deglaciated Alpine habitats seems to be driven foremost by predator identity while site and early successional effects contribute to a lesser extent to food web variability. Our findings also suggest that in these pioneer sites, predatory arthropods depend less on allochthonous aeolian prey but are mainly sustained by prey of local production.     

View-Angle Tilting and Slice-Encoding Metal Artifact Correction for Artifact Reduction in MRI: Experimental Sequence Optimization for Orthopaedic Tumor Endoprostheses and Clinical Application

Background

MRI plays a major role in follow-up of patients with malignant bone tumors. However, after limb salvage surgery, orthopaedic tumor endoprostheses might cause significant metal-induced susceptibility artifacts.

Purposes

To evaluate the benefit of view-angle tilting (VAT) and slice-encoding metal artifact correction (SEMAC) for MRI of large-sized orthopaedic tumor endoprostheses in an experimental model and to demonstrate clinical benefits for assessment of periprosthetic soft tissue abnormalities.

Methods

In an experimental setting, tumor endoprostheses (n=4) were scanned at 1.5T with three versions of optimized high-bandwidth turbo-spin-echo pulse sequences: (i) standard, (ii) VAT and (iii) combined VAT and SEMAC (VAT&SEMAC). Pulse sequences included coronal short-tau-inversion-recovery (STIR), coronal T1-weighted (w), transverse T1-w and T2-w TSE sequences. For clinical evaluation, VAT&SEMAC was compared to conventional metal artifact-reducing MR sequences (conventional MR) in n=25 patients with metal implants and clinical suspicion of tumor recurrence or infection. Diameters of artifacts were measured quantitatively. Qualitative parameters were assessed on a five-point scale (1=best, 5=worst): “image distortion”, “artificial signal changes at the edges” and “diagnostic confidence”. Imaging findings were correlated with pathology. T-tests and Wilcoxon-signed rank tests were used for statistical analyses.

Results

The true size of the prostheses was overestimated on MRI (P<0.05). A significant reduction of artifacts was achieved by VAT (P<0.001) and VAT&SEMAC (P=0.003) compared to the standard group. Quantitative scores improved in the VAT and VAT&SEMAC group (P<0.05). On clinical MR images, artifact diameters were significantly reduced in the VAT&SEMAC-group as compared with the conventional-group (P<0.001). Distortion and artificial signal changes were reduced and diagnostic confidence improved (P<0.05). In two cases, tumor-recurrence, in ten cases infection and in thirteen cases other pathologies were diagnosed.

Conclusions

Significant reduction of metallic artifacts was achieved by VAT and SEMAC. Clinical results suggest, that these new techniques will be beneficial for detecting periprosthetic pathologies during postoperative follow-up.     

New C-5 substituted pyrrolotriazine dual inhibitors of EGFR and HER2 protein tyrosine kinases

Novel C-5 substituted pyrrolotriazines were optimized for dual EGFR and HER2 protein tyrosine kinase inhibition. The lead compound exhibited promising oral efficacy in both EGFR and HER2 driven human tumor xenograft models. It is hypothesized that its C-5 morpholine side chain binds in the ribose phosphate portion of the ATP binding pocket.     

Interactions between SQUAMOSA and SHORT VEGETATIVE PHASE MADS-box proteins regulate meristem transitions during wheat spike development

Inflorescence architecture is an important determinant of crop productivity. The number of spikelets produced by the wheat inflorescence meristem (IM) before its transition to a terminal spikelet (TS) influences the maximum number of grains per spike. Wheat MADS-box genes VERNALIZATION 1 (VRN1) and FRUITFULL 2 (FUL2) (in the SQUAMOSA-clade) are essential to promote the transition from IM to TS and for spikelet development. Here we show that SQUAMOSA genes contribute to spikelet identity by repressing MADS-box genes VEGETATIVE TO REPRODUCTIVE TRANSITION 2 (VRT2), SHORT VEGETATIVE PHASE 1 (SVP1), and SVP3 in the SVP clade. Constitutive expression of VRT2 resulted in leafy glumes and lemmas, reversion of spikelets to spikes, and downregulation of MADS-box genes involved in floret development, whereas the vrt2 mutant reduced vegetative characteristics in spikelets of squamosa mutants. Interestingly, the vrt2 svp1 mutant showed similar phenotypes to squamosa mutants regarding heading time, plant height, and spikelets per spike, but it exhibited unusual axillary inflorescences in the elongating stem. We propose that SQUAMOSA–SVP interactions are important to promote heading, formation of the TS, and stem elongation during the early reproductive phase, and that downregulation of SVP genes is then necessary for normal spikelet and floral development. Manipulating SVP and SQUAMOSA genes can contribute to engineering spike architectures with improved productivity.

Functional characterization of developmental genes reveals ways to modify the wheat spike architecture to increase the number of grains and improve productivity.     

Protein phosphatase 2A holoenzyme assembly: identification of contacts between B-family regulatory and scaffolding A subunits

Protein serine/threonine phosphatase (PP) 2A is a ubiquitous enzyme with pleiotropic functions. Trimeric PP2A consists of a structural A subunit, a catalytic C subunit, and a variable regulatory subunit. Variable subunits (B, B', and B" families) dictate PP2A substrate specificity and subcellular localization. B-family subunits contain seven WD repeats predicted to fold into a beta-propeller structure. We carried out mutagenesis of Bgamma to identify domains important for association with A and C subunits in vivo. Several internal deletions in Bgamma abolished coimmunoprecipitation of A and C subunits expressed in COS-M6 cells. In contrast, small N- and C-terminal Bgamma deletions had no effect on incorporation into the PP2A heterotrimer. Thus, holoenzyme association of B-family subunits requires multiple, precisely aligned contacts within a core beta-propeller domain. Charge-reversal mutagenesis of Bgamma identified a cluster of conserved critical residues in Bgamma WD repeats 3 and 4. Acidic substitution of paired basic residues in Bgamma (RR165EE) abolished association with wild-type A and C subunits, while fostering incorporation of Bgamma into a PP2A heterotrimer containing an A subunit with an opposite charge-reversal mutation (EE100RR). Thus, binding of A and B subunits requires electrostatic interactions between conserved pairs of glutamates and arginines. By expressing complementary charge-reversal mutants in neuronal PC6-3 cells, we further show that holoenzyme incorporation protects Bgamma from rapid degradation by the ubiquitin/proteasome pathway.     

Binding Specificity of Protein Phosphatase 2A Core Enzyme for Regulatory B Subunits and T Antigens

The core enzyme of protein phosphatase 2A is composed of a regulatory subunit A and a catalytic subunit C. It is controlled by three types of regulatory B subunits (B, B′, and B") and by tumor (T) antigens, which are unrelated by sequence but bind to overlapping regions on the A subunit. To find out whether the different B subunits and T antigens bind to identical or distinct amino acids of the A subunit, mutants were generated and their abilities to bind B subunits and T antigens were tested. We found that some amino acids are involved in the binding of all types of B subunits, whereas others are specifically involved in the binding of one or two types of B subunits. T-antigen-binding specificity does not correlate with that of a particular type of B subunit.     

In Vitro Calcite Crystal Morphology Is Modulated by Otoconial Proteins Otolin-1 and Otoconin-90

Otoconia are formed embryonically and are instrumental in detecting linear acceleration and gravity. Degeneration and fragmentation of otoconia in elderly patients leads to imbalance resulting in higher frequency of falls that are positively correlated with the incidence of bone fractures and death. In this work we investigate the roles otoconial proteins Otolin-1 and Otoconin 90 (OC90) perform in the formation of otoconia. We demonstrate by rotary shadowing and atomic force microscopy (AFM) experiments that Otolin-1 forms homomeric protein complexes and self-assembled networks supporting the hypothesis that Otolin-1 serves as a scaffold protein of otoconia. Our calcium carbonate crystal growth data demonstrate that Otolin-1 and OC90 modulate in vitro calcite crystal morphology but neither protein is sufficient to produce the shape of otoconia. Coadministration of these proteins produces synergistic effects on crystal morphology that contribute to morphology resembling otoconia.