Functional improvement and maturation of rat and human engineered heart tissue by chronic electrical stimulation

Spontaneously beating engineered heart tissue (EHT) represents an advanced in vitro model for drug testing and disease modeling, but cardiomyocytes in EHTs are less mature and generate lower forces than in the adult heart. We devised a novel pacing system integrated in a setup for videooptical recording of EHT contractile function over time and investigated whether sustained electrical field stimulation improved EHT properties. EHTs were generated from neonatal rat heart cells (rEHT, n=96) or human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes (hEHT, n=19). Pacing with biphasic pulses was initiated on day 4 of culture. REHT continuously paced for 16-18 days at 0.5Hz developed 2.2× higher forces than nonstimulated rEHT. This was reflected by higher cardiomyocyte density in the center of EHTs, increased connexin-43 abundance as investigated by two-photon microscopy and remarkably improved sarcomere ultrastructure including regular M-bands. Further signs of tissue maturation include a rightward shift (to more physiological values) of the Ca(2+)-response curve, increased force response to isoprenaline and decreased spontaneous beating activity. Human EHTs stimulated at 2Hz in the first week and 1.5Hz thereafter developed 1.5× higher forces than nonstimulated hEHT on day 14, an ameliorated muscular network of longitudinally oriented cardiomyocytes and a higher cytoplasm-to-nucleus ratio. Taken together, continuous pacing improved structural and functional properties of rEHTs and hEHTs to an unprecedented level. Electrical stimulation appears to be an important step toward the generation of fully mature EHT

Condensed matter and AdS/CFT

I review two classes of strong coupling problems in condensed matter physics, and describe insights gained by application of the AdS/CFT correspondence. The first class concerns non-zero temperature dynamics and transport in the vicinity of quantum critical points described by relativistic field theories. I describe how relativistic structures arise in models of physical interest, present results for their quantum critical crossover functions and magneto-thermoelectric hydrodynamics. The second class concerns symmetry breaking transitions of two-dimensional systems in the presence of gapless electronic excitations at isolated points or along lines (i.e. Fermi surfaces) in the Brillouin zone. I describe the scaling structure of a recent theory of the Ising-nematic transition in metals, and discuss its possible connection to theories of Fermi surfaces obtained from simple AdS duals.Comment: 39 pages, 12 figures; Lectures at the 5th Aegean summer school, "From gravity to thermal gauge theories: the AdS/CFT correspondence", and the De Sitter Lecture Series in Theoretical Physics 2009, University of Groninge

Determination of Myosin Filament Orientations in Electron Micrographs of Muscle Cross Sections

An automated image analysis system for determining myosin filament azimuthal rotations, or orientations, in electron micrographs of muscle cross sections is described. The micrographs of thin sections intersect the myosin filaments which lie on a triangular lattice. The myosin filament profiles are variable and noisy, and the images exhibit a variable contrast and background. Filament positions are determined by filtering with a point spread function that incorporates the local symmetry of the lattice. Filament orientations are determined by correlation with a template that incorporates the salient filament characteristics, and the orientations are classified using a Gaussian mixture model. The precision of the technique is assessed by application to a variety of micrographs and comparison with manual classification of the orientations. The system provides a convenient, robust, and rapid means of analysing micrographs containing many filaments to study the distribution of filament orientations

Aechmea rodriguesiana (L. B. Sm.) L. B. Sm. (Bromeliaceae) uma espécie endêmica da Amazônia brasileira Aechmea rodriguesiana (L. B. Sm.) L. B. Sm. (Bromeliaceae), an endemic species of the Brazilian Amazon

Aechmea subgênero Chevaliera (Gaudich. ex Beer) Baker está representado na Amazônia brasileira pelas espécies A. fernandae (E. Morren) Baker e A. rodriguesiana (L. B. Sm.) L. B. Sm., sendo a última restrita para esta região. A. rodriguesiana se caracteriza pelas flores dispostas em racemo de espigas, com brácteas florais ovais, margens inteiras, envolvendo o ovário e pelas pétalas alvas e cuculadas. O presente trabalho apresenta a complementação da descrição e ilustrações desta espécie. São apresentados dados de distribuição geográfica, hábitats e fenológicos.<br>Aechmea subgenus Chevaliera (Gaudich. ex Beer) Baker, is represented in the Brazilian Amazon by two species: A. fernandae (E. Morren) Baker and A. rodriguesiana (L. B. Sm.) L. B. Sm., the latter being restricted to this region. A. rodriguesiana is characterized by flowers arranged on racemes of spikes, oval floral bracts with entire margins that completely surround the ovary, and by cuculate white petals. The present work has as main goal to complement the description and illustration of this species, exclusive to the Brazilian Amazon, allowing its recognition and conservation. Data on geographical distribution, habitat, and phenology are presented