Numerical simulation of the dynamics of a bileaflet prosthetic heart valve using a fluid-structure interaction approach

The main purpose of this study is to reproduce in silico the dynamics of a bileaflet mechanical heart valve (MHV; St Jude Hemodynamic Plus, 27mm characteristic size) by means of a fully implicit fluid-structure interaction (FSI) method, and experimentally validate the results using an ultrafast cinematographic technique. The computational model was constructed to realistically reproduce the boundary condition (72 beats per minute (bpm), cardiac output 4.5l/min) and the geometry of the experimental setup, including the valve housing and the hinge configuration. The simulation was carried out coupling a commercial computational fluid dynamics (CFD) package based on finite-volume method with user-defined code for solving the structural domain, and exploiting the parallel performance of the whole numerical setup. Outputs are leaflets excursion from opening to closure and the fluid dynamics through the valve. Results put in evidence a favorable comparison between the computed and the experimental data: the model captures the main features of the leaflet motion during the systole. The use of parallel computing drastically limited the computational costs, showing a linear scaling on 16 processors (despite the massive use of user-defined subroutines to manage the FSI process). The favorable agreement obtained between in vitro and in silico results of the leaflet displacements confirms the consistency of the numerical method used, and candidates the application of FSI models to become a major tool to optimize the MHV design and eventually provides useful information to surgeons.     

Identification of a posttranslational mechanism for the regulation of hERG1 K+ channel expression and hERG1 current density in tumor cells

A common feature of tumor cells is the aberrant expression of ion channels on their plasma membrane. The molecular mechanisms regulating ion channel expression in cancer cells are still poorly known. K(+) channels that belong to the human ether-a-go-go-related gene 1 (herg1) family are frequently misexpressed in cancer cells compared to their healthy counterparts. We describe here a posttranslational mechanism for the regulation of hERG1 channel surface expression in cancer cells. This mechanism is based on the activity of hERG1 isoforms containing the USO exon. These isoforms (i) are frequently overexpressed in human cancers, (ii) are retained in the endoplasmic reticulum, and (iii) form heterotetramers with different proteins of the hERG family. (iv) The USO-containing heterotetramers are retained intracellularly and undergo ubiquitin-dependent degradation. This process results in decreased hERG1 current (I(hERG1)) density. We detailed such a mechanism in heterologous systems and confirmed its functioning in tumor cells that endogenously express hERG1 proteins. The silencing of USO-containing hERG1 isoforms induces a higher I(hERG1) density in tumors, an effect that apparently regulates neurite outgrowth in neuroblastoma cells and apoptosis in leukemia cells.     

Thrips (Thysanoptera: Thripidae, Phlaeothripidae) damaging peach in Paranapanema, São Paulo State, Brazil

Seeking to identify thrips species associated to peach and the injuries they cause, plants of Aurora and Tropic Beauty cultivars were weekly monitored, from May to August of 2005, in Holambra II district, in Paranapanema, SP. Flowers and fruits from six plants per hectare were sampled by the hitting technique. Frankliniella occidentalis (Pergande), F. schultzei (Trybom), F. gardenia (Moulton), F. condei John, F. insularis (Franklin) and Thrips tabaci Lindeman, in Thripidae, and Haplothrips gowdeyi (Franklin), in Phlaeothripidae were identified. F. occidentalis was dominant, comprising 55.7% of the total specimens sampled. Slight and severe injuries were registered in fruits.     

Genetics of gliadins coded by the group 1 chromosomes in the high-quality bread wheat cultivar Neepawa

Summary The inheritance and biochemical properties of gliadins controlled by the group 1 chromosomes of the high-quality bread wheat cultivar Neepawa were studied in the progeny of the cross Neepawa x Costantino by six different electrophoretic procedures. Chromosome 1B of Neepawa contains two gliadin loci, one (Gli-B1) coding for at least six - or -gliadins, the other (Gli-B3) controlling the synthesis of gliadin N6 only. The map distance between these loci was calculated as 22.1 cM. Amongst the chromosome 1A gliadins, three proteins are encoded at the Gli-A1 locus whereas polypeptides N14-N15-N16 are controlled by a remote locus which recombines with Gli-A1. Six other gliadins are controlled by a gene cluster at Gli-D1 on chromosome 1D. Canadian wheat cultivars sharing the Gli-B1 allele of Neepawa were found to differ in the presence or absence of gliadin N6. The electrophoretic mobilities of proteins N6 and N14-N15-N16 were unaffected by the addition of a reducing agent during two-dimensional sodium dodecyl sulphate polyacrylamid-gel electrophoresis, suggesting the absence of intra-chain disulphide bonds in their structure.Research supported by a grant from the Commission of the European Communities, ECLAIR programme, Contract AGRE 0052     

Production and genetic characterization of near-isogenic lines in the bread-wheat cultivar Alpe

Two biotypes of the bread-wheat cultivar Alpe were shown to possess contrasting alleles at each of the glutenin (Glu-B1, Glu-D1, Glu-B3 and Glu-D3) and gliadin (Gli-B1 and Gli-D1) loci on chromosomes 1B and 1D. Fourteen near-isogenic lines (NILs) were produced by crossing these biotypes and used to determine the genetic control of both low-molecular-weight (LMW) glutenin subunits and gliadins by means of one-dimensional or two-dimensional electrophoresis. Genes coding for the B, C and D groups of EMW subunits were found to be inherited in clusters tightly linked with those controlling gliadins. Southern-blot analysis of total genomic DNAs hybridized to a -gliadin-specific cDNA clone revealed that seven NILs lack both the Gli-D1 and Glu-D3 loci on chromosome 1D. Segregation data indicated that these null alleles are normally inherited. Comparison of the null NILs with those possessing allele b at the Glu-D3 locus showed one B subunit, seven C subunits and two D subunits, as fractionated by two-dimensional A-PAGExSDS-PAGE, to be encoded by this allele. Alleles b and k at Glu-B3 were found to code for two C subunits plus eight and six B subunits respectively, whereas alleles b and k at Gli-B1 each controlled the synthesis of two -gliadins, one and two -gliadins. The novel Gli-B5 locus coding for two -gliadins was shown to recombine with the Gli-B1 locus on chromosome 1B. The two-dimensional map of glutenin subunits showed -gliadins encoded at the Gli-A2 locus on chromosome 6A. The use of Alpe NILs in the study of the individual and combined effects of glutenin subunits on dough properties is discussed.Research supported by a grant from the Commission of the European Communities, ECLAIR programme, Contract AGRE 0052     

Estimation of the binding force of the collagen molecule-decorin core protein complex in collagen fibril

Decorin belongs to the small leucine proteoglycans family and is considered to play an important role in extracellular matrix organization. Experimental studies suggest that decorin is required for the assembly of collagen fibrils, as well as for the development of proper tissue mechanical properties. In tendons, decorins tie adjoining collagen fibrils together and probably guarantee the mechanical coupling of fibrils. The decorin molecule consists of one core protein and one glycosaminoglycan chain covalently linked to a serine residue of the core protein. Several studies have indicated that each core protein binds to the surface of collagen fibrils every 67 nm, by interacting non-covalently to one collagen molecule of the fibril surface, while the decorin glycosaminoglycans extend from the core protein to connect to another decorin core protein laying on adjacent fibril surface. The present paper investigates the complex composed of one decorin core protein and one collagen molecule in order to obtain their binding force. For this purpose, molecular models of collagen molecules type I and decorin core protein were developed and their interaction energies were evaluated by means of the molecular mechanics approach. Results show that the complex is characterized by a maximum binding force of about 12.4 x 10(3) nN and a binding stiffness of 8.33 x 10(-8) N/nm; the attained binding force is greater than the glycosaminoglycan chain's ultimate strength, thus indicating that overloads are likely to damage the collagen fibre's mechanical integrity by disrupting the glycosaminoglycan chains rather than by causing decorin core protein detachment from the collagen fibril.     

PIXE technique for calcium analysis of human bone

The determination of calcium content in human bone tissue is very useful in metabolic diseases of bone, such as renal osteodystrophy, osteoporosis, hyperparathyroidism, and osteomalacia of diverse etiology. The PIXE technique allows calcium to be directly determined in bioptic tissue sections properly, sampled for histological optical and/or electron microscopy examination. Bone semithin sections (3 μm thick, 4×4 mm² dimensions), cut by ultramicrotome and deposited onto polyvinyl acetate films, underwent PIXE analysis using the CISE set-up. Histomorphometric (after standard staining), evaluation of calcified bone volume (CBV) in absolute value allows calcium density to be determined. A total of nine bone biopsies were analyzed (three sections each) obtaining values ranging between 352 and 482, with an average value of 421.5±15.3 (M±SE) μg/μL, in good agreement with literature data (obtained by AAS technique on dissected bone samples). The aim of this paper is to emphasize the usefulness, of combined PIXE and histomorphometric techniques for the study of calcium content in bone tissue in both healthy and diseased bones.     

中国金线鲃属一新种(鲤形目:鲤科:鲃亚科)

作者于1986年5月在广西凌云县的溶洞内(属右江水系)采到鱼类一新种,命名为小眼金线鲃,新种 Sinocyclocheilus microphthalmus sp.nov.