Računalniški sistem za določanje porazdelitve tlaka v kolčnem sklepu s pomočjoantero-posteriornega rentgenograma okolčja

Background. A computer system HIPSTRESS is described. The system can be used for the determination of the contact stress distribution in the hip joint for a known body weight and some characteristic pelvic and hip geometrical parameters which can be determined directly from the standard antero-posteriorradiograph. Conclusions. The system can be applied in clinicalpractice to predict an optimal stress distribution in different operative interventions in the hip.Izhodišča. V članku je opisan računalniški sistem HIPSTRESS, s katerim lahko določimo razdelitev tlaka v kolčni sklepni površini. Pri tem moramo poznati težo telesa in nekatere karakteristične geometrijske parametre medenice in kolka, ki jih lahko določimo neposredno iz antero-posteriornega rentgenograma.Zaključki. Sistem je uporaben v klinični praksi za določanje optimalne porazdelitve kolčnega sklepnega tlaka pri operativnem posegu v kolku

Determination of the Strength of Adhesion between Lipid Vesicles

A commonly used method to determine the strength of adhesion between adhering lipid vesicles is measuring their effective contact angle from experimental images. The aim of this paper is to estimate the interobserver variations in vesicles effective contact angle measurements and to propose a new method for estimating the strength of membrane vesicle adhesion. Theoretical model shows for the old and for the new measure a monotonic dependence on the strength of adhesion. Results obtained by both measuring techniques show statistically significant correlation and high interobserver reliability for both methods. Therefore the conventional method of measuring the effective contact angle gives qualitatively relevant results as the measure of the lipid vesicle adhesion. However, the new measuring technique provides a lower variation of the measured values than the conventional measures using the effective contact angle. Moreover, obtaining the adhesion angle can be automatized more easily than obtaining the effective contact angle

Razporejanje mikrotubulov v celicah V-79 po delovanju citohalazina B

Background. The aim of this work was to study the configuration of the microtubules in the cytochalasin B treated V-79 cells in connection to the cell shape and to see whether there are any similarities to the phenomena taking place in phospholipid vesicles. Subjects and methods. An experiment wasperformed where cytochalasin B was added to the V-79 cells (lung fibroblasts of Chinese hamster). Results. The cell shape changed from an elongated one into the shape with a profile resembling the Greek letter phi. The microtubules were found to be organized into a rod within the symmetry axis of the cell. Conclusion. As similar shapes were previously observed also in the phospholipid vesicles with entrapped microtubule rods, our results support the hypothesis that similar physical mechanisms may pertain in simple systems as well as in living cells.Izhodišča. V tej raziskavi smo proučevali razporeditev mikrotubulov celicah V-79 po delovanju citohalazina B. Poleg njihove oblike smo poskušali ugotoviti, ali je ta pojav v čemer koli podoben dogajanjem v fosfolipidnih mehurčkih. Material in metode. Opravili smo preiskus s citohalazinom B, ki smoga dodali celicam V 79 (pljučni fibroblasti kitajskega hrčka). Rezultati. Oblika celice se je spremenila iz podolgovate v obliko, katere profil je podoben grški črki fi. Mikrotubuli so se uredili v palico v simetrijski osi celice. Zaključek. Ker so podobne oblike pred tem opazili tudi pri fosfolipidnih mehurčkih, ki so vsebovali paličasto strukturo iz mikrotubulov, prikazani rezultati podpirajo hipotezo, da so podobni fizikalni mehanizmi prisotni v preprostih sistemih kot tudi v živih celicah

Modelling how curved active proteins and shear flow pattern cellular shape and motility

Cell spreading and motility on an adhesive substrate are driven by the active physical forces generated by the actin cytoskeleton. We have recently shown that coupling curved membrane complexes to protrusive forces, exerted by the actin polymerization that they recruit, provides a mechanism that can give rise to spontaneous membrane shapes and patterns. In the presence of an adhesive substrate, this model was shown to give rise to an emergent motile phenotype, resembling a motile cell. Here, we utilize this “minimal-cell” model to explore the impact of external shear flow on the cell shape and migration on a uniform adhesive flat substrate. We find that in the presence of shear the motile cell reorients such that its leading edge, where the curved active proteins aggregate, faces the shear flow. The flow-facing configuration is found to minimize the adhesion energy by allowing the cell to spread more efficiently over the substrate. For the non-motile vesicle shapes, we find that they mostly slide and roll with the shear flow. We compare these theoretical results with experimental observations, and suggest that the tendency of many cell types to move against the flow may arise from the very general, and non-cell-type-specific mechanism predicted by our model

Temperature and cholera toxin B are factors that influence formation of membrane nanotubes in RT4 and T24 urothelial cancer cell lines

The growth of membrane nanotubes is crucial for intercellular communication in both normal development and pathological conditions. Therefore, identifying factors that influence their stability and formation are important for both basic research and in development of potential treatments of pathological states. Here we investigate the effect of cholera toxin B (CTB) and temperature on two pathological model systems: urothelial cell line RT4, as a model system of a benign tumor, and urothelial cell line T24, as a model system of a metastatic tumor. In particular, the number of intercellular membrane nanotubes (ICNs; ie, membrane nanotubes that bridge neighboring cells) was counted. In comparison with RT4 cells, we reveal a significantly higher number in the density of ICNs in T24 cells not derived from RT4 without treatments (P = 0.005), after 20 minutes at room temperature (P = 0.0007), and following CTB treatment (P = 0.000025). The binding of CTB to GM1–lipid complexes in membrane exvaginations or tips of membrane nanotubes may reduce the positive spontaneous (intrinsic) curvature of GM1–lipid complexes, which may lead to lipid mediated attractive interactions between CTB–GM1–lipid complexes, their aggregation and consequent formation of enlarged spherical tips of nanotubes. The binding of CTB to GM1 molecules in the outer membrane leaflet of membrane exvaginations and tips of membrane nanotubes may also increase the area difference between the two leaflets and in this way facilitate the growth of membrane nanotubes

Numerical Study of Membrane Configurations

We studied biological membranes of spherical topology within the framework of the spontaneous curvature model. Both Monte Carlo simulations and the numerical minimization of the curvature energy were used to obtain the shapes of the vesicles. The shapes of the vesicles and their energy were calculated for different values of the reduced volume. The vesicles which exhibit in-plane ordering were also studied. Minimal models have been developed in order to study the orientational ordering in colloids coated with a thin sheet of nematic liquid crystal (nematic shells). The topological defects are always present on the surfaces with the topology of a sphere. The location of the topological defects depends strongly on the curvature of the surface. We studied the nematic ordering and the formation of topological defects on vesicles obtained by the minimization of the spontaneous curvature energy

The role of cholesterol-sphingomyelin membrane nanodomains in the stability of intercellular membrane nanotubes

Intercellular membrane nanotubes (ICNs) are highly curved tubular structures that connect neighboring cells. The stability of these structures depends on the inner cytoskeleton and the cell membrane composition. Yet, due to the difficulty in the extraction of ICNs, the cell membrane composition remains elusive. In the present study, a raft marker, ostreolysin, revealed the enrichment of cholesterol-sphingomyelin membrane nanodomains along ICNs in a T24 (malignant) urothelial cancer cell line. Cholesterol depletion, due to the addition of methyl-β-cyclodextrin, caused the dispersion of cholesterol-sphingomyelin membrane nanodomains and the retraction of ICNs. The depletion of cholesterol also led to cytoskeleton reorganization and to formation of actin stress fibers. Live cell imaging data revealed the possible functional coupling between the change from polygonal to spherical shape, cell separation, and the disconnection of ICNs. The ICN was modeled as an axisymmetric tubular structure, enabling us to investigate the effects of cholesterol content on the ICN curvature. The removal of cholesterol was predicted to reduce the positive spontaneous curvature of the remaining membrane components, increasing their curvature mismatch with the tube curvature. The mechanisms by which the increased curvature mismatch could contribute to the disconnection of ICNs are discussed