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PubMed1983

Repulsive stabilization in black lipid membranes. A hydrodynamic model.

A linear stability analysis is performed for a black lipid membrane. The hydrodynamic model consists of a viscous hydrocarbon film sandwiched between two aqueous phases. Attractive forces (van der Waals and electrical) and repulsive forces (steric) are expressed as body forces in the equations of fluid motion in the three phases. The steric repulsion due to overlap of the hydrocarbon chains of the lipids at small film thicknesses is described via an exponentially decaying interaction potential. The dispersion equation displays two modes of vibrations: the bending mode with the two Film surfaces transversely in phase, and the squeezing mode with the two surfaces 180 degrees out of phase. For symmetrical films, these two modes are uncoupled, and the squeezing mode (with thickness variations) is stabilized by the repulsive interactions. For nonsymmetrical films (different surface tensions, surface charges, etc.). these two modes are coupled and the asymmetry induces a shift of the marginal stability curve to shorter wavelengths.

Journal Article↗
PubMed1986

Changes in the hydrodynamic properties of microtubules induced by taxol.

Microtubule assembly was followed and monitored by (1) the turbidity at 350 nm, (2) the weight of the pelleted microtubules, (3) linear dichroism, LD tau, of the turbidity upon flow orientation, (4) the specific viscosity, eta spec, and (5) electron microscopy. These five methods showed the same features for normal microtubule assembly, but were different in the presence of taxol, a drug which binds to tubulin. The The apparent steady state of microtubule assembly in the presence of taxol as found by turbidity or the weight of pelleted polymer did not represent a stable state, as both LD tau and eta spec continued to change for a much longer time. Microtubules assembled in the presence of taxol from microtubule proteins as well as from purified tubulin were difficult to orient, as high flow gradients were needed and the maximal LD tau value represented only 20% of the LD tau for normal microtubules. In contrast to the slow relaxation of normal microtubules, rapid relaxation to random orientation was found in the presence of taxol. Low orientability was also indicated by electron micrographs, in which pelleted microtubules were seen to be randomly oriented in the presence of taxol. Taxol induced a very high eta spec, 4-times the steady-state value in the initial phase of assembly, which slowly declined again to a steady state, an effect which was also found for assembly of purified tubulin assembled in the absence of the microtubule-associated proteins. The presence of taxol did not change the relative amount and composition of the microtubule-associated proteins in the assembled microtubules. The results therefore suggest that taxol alters the hydrodynamic properties of the microtubules due to its interaction with tubulin and that this alteration is not an effect of the microtubule-associated proteins.

Alkaloids↗
PubMed1983

Rana catesbeiana tail fin lactogenic hormone receptor: hydrodynamic characterization.

The hydrodynamic properties of the 125I-hGH-receptor-detergent complex of the tadpole tail fin were determined. Based on the distribution coefficient from chromatography on Sepharose 6B the Stokes' radius of the complex was 5.03 nm. Using centrifugation through sucrose/H2O and sucrose/2H2O gradients the complex was determined to have a sedimentation coefficient of 4.05 S and a partial specific volume of 0.810 cm3/g. The 125I-hGH-receptor-detergent complex was calculated to have a mol wt of 121,000 and a frictional ratio of 1.38. Based on a calculated detergent content of 0.430 g/g complex the mol weight of the 125I-hGH-receptor was 69,100 and the mol wt of the receptor alone was 47,100.

Animals↗
PubMed1990

Hydrodynamic analysis of a two-dimensional model for micromechanical resonance of free-standing hair bundles.

To investigate the role of inner ear fluids and structures on mechanical stimulation of the hair bundles of hair cells, we analyzed a two-dimensional structure that consists of: a rectangular flap (which represents a hair bundle) attached to a flat basal plate (which represents the surface of the epithelium that contains the hair cells) with a spring-loaded hinge (that represents the compliant attachment of a hair bundle to the hair cell body) and surrounded by a viscous fluid (that represents endolymph). We computed the fluid velocity as well as the forces on and motion of the flap in response to sinusoidal vibration of the plate by numerical integration of the hydrodynamic equations, and--at asymptotically low and high frequencies--by analytic methods. The results suggest that: (1) the surface of the sensory epithelium, from which hair bundles project into fluid, plays an important part in the production of fluid forces on hair bundles; (2) both fluid inertia and viscosity play a key role in hair bundle mechanics; (3) passive mechanical resonances are likely to contribute to both frequency selectivity and frequency-to-place coding in the inner ear.

Algorithms↗
PubMed1992

The hydrodynamic function and leaflet dynamics of aortic and pulmonary roots and valves: an in vitro study.

Fresh homograft aortic and pulmonary roots were tested in a pulsatile flow simulator to assess their hydrodynamic function and leaflet opening characteristics. Simultaneous flow and pressure measurements were obtained for a range of cardiac outputs. The effective orifice area and regurgitant volumes were calculated. The mean pressure difference across the pulmonary roots was obtained under both left and right side pressures. A video recording of valve leaflet function was also obtained for each valve. A comparison was made with four porcine bioprosthetic heart valves (21 and 23 mm). The mean pressure difference with respect to flow for the 21 mm Hancock II and Intact porcine bioprostheses was significantly higher than that for all aortic roots tested. The 24 mm aortic root showed significantly lower pressure drop compared to all porcine valves tested. The mean pressure difference across each pulmonary root at pulmonary pressures was significantly greater than at systemic pressures. At systemic pressures the fully open leaflets had a triangular orifice with low leaflet open bending strains at the commissures. At the lower internal pressures, with reduced dilation of the root, higher bending strains were noted. These were not as severe as seen in porcine valves.

Adult↗
PubMed2004

On the hydrodynamics and temperature dependence of the solution conformation of human serum albumin from viscometry approach.

The paper presents the results of viscosity determinations on aqueous solutions of human serum albumin (HSA) at a wide range of concentrations and at temperatures ranging from 5 to 45 degrees C. On the basis of a modified Arrhenius formula and Mooney's equation, the viscosity-temperature and viscosity-concentration dependence of the solutions are discussed. The effective specific volume, the activation energy and entropy of viscous flow for hydrated HSA were calculated. Different models of HSA molecule are discussed and the best one-from the hydrodynamic point of view-was established. At low concentration limit, such rheological quantities as the intrinsic viscosity and Huggins coefficient were obtained. Using the dimensionless parameter [eta]c, the existence of three characteristic ranges of concentrations: diluted, semi-diluted and concentrated, was shown.

Humans↗
PubMed2005

A comparison of solution conformation and hydrodynamic properties of equine, porcine and rabbit serum albumin using viscometric measurements.

This paper presents the results of viscosity determinations on aqueous solutions of equine, porcine and rabbit serum albumin over a wide range of concentrations and at temperatures ranging from 5 degrees C to (42-45) degrees C. The results are compared with human and bovine serum albumin previously studied. Viscosity-temperature dependence is discussed on the basis of the modified Arrhenius formula. The effective specific volume, the activation energy and entropy of viscous flow for all investigated albumins are compared. Viscosity-concentration dependence, in turn, is discussed on the basis of Mooney equation. Based on the assumption that theoretical and experimental values of Simha factor--at high temperature limit--are equal to each other, the hydrodynamic volume of the studied albumins has been calculated. The numerical values of a self-crowding factor were also obtained. At low concentration limit, the numerical values of the intrinsic viscosity and of Huggins coefficient were compared.

Animals↗
PubMed2006

Hydrodynamically coupled water in surface adsorbed amino acids as a tool to study hydrated peptides.

The influence of different amino acid residues on properties of a protein surface is of great interest and importance. Hydrodynamically coupled water in the amino acids has the potential to be used as a tool to study surface properties of proteins. The contribution of this coupled water fraction in design of a hydropathy scale in surface adsorbed amino acid films on solid using quartz crystal microbalance is presented in this work. This scale compares well with the hydropathy scale of Guy reported in the literature and can be correlated with the solid/liquid interfacial tension and work of adhesion of the adsorbed amino acid films. Using Graphical Representation and Analysis of Surface Properties (GRASP) the free energy of transfer from Octanol to water for the amino acids has been estimated and shows approximately an inverse relationship with the coupled water fraction. This scale has been applied in a benchmark test for a native Laminin peptide YIGSR and its mutated sequences (with mutations carried out at 'Y and 'R' positions). The experimentally measured coupled water fractions seem to compare well with that obtained from the present scale assuming the total solvent fraction to be a linear function of the amino acids in the sequence. A survey of the protein data bank showed that sets of sequences based on this scale occur in membrane insertion domain or in trans-membrane proteins suggesting that the scale is suitable to study structure-function correlation in proteins.

Adsorption↗
PubMed2003

Hydrodynamics-based transfer of PCR-amplified DNA fragments into rat liver.

A high level of plasmid DNA expression in rat liver can be achieved by the rapid injection of a large volume of a naked DNA solution into the tail vein, called the 'hydrodynamics-based procedure.' The preparation of PCR-amplified DNA fragments is easier than that of naked DNA. In this paper we evaluated the effects of expressing the erythropoietin (Epo) gene in the rat liver by injecting fCAGGS-Epo, an Epo-expressing PCR-amplified DNA fragment, via the tail vein. After injection of 5 pmol fCAGGS-Epo (10 microg) or pCAGGS-Epo (18.4 microg), plasmid DNA, the serum Epo levels peaked at week 1, then persisted for at least 12 weeks. Transgene-derived Epo secretion resulted in significant erythropoiesis. These results demonstrated that transfer of PCR-amplified DNA fragments into the rat liver via rapid tail vein injection can be achieved. This method may provide a useful means for studying the physiologic function of a putative gene.

Animals↗
PubMed2006

Use of hydrodynamic forces to engineer cartilaginous tissues resembling the non-uniform structure and function of meniscus.

The aim of this study was to demonstrate that differences in the local composition of bi-zonal fibrocartilaginous tissues result in different local biomechanical properties in compression and tension. Bovine articular chondrocytes were loaded into hyaluronan-based meshes (HYAFF-11) and cultured for 4 weeks in mixed flask, a rotary Cell Culture System (RCCS), or statically. Resulting tissues were assessed histologically, immunohistochemically, by scanning electron microscopy and mechanically in different regions. Local mechanical analyses in compression and tension were performed by indentation-type scanning force microscopy and by tensile tests on punched out concentric rings, respectively. Tissues cultured in mixed flask or RCCS displayed an outer region positively stained for versican and type I collagen, and an inner region positively stained for glycosaminoglycans and types I and II collagen. The outer fibrocartilaginous capsule included bundles (up to 2 microm diameter) of collagen fibers and was stiffer in tension (up to 3.6-fold higher elastic modulus), whereas the inner region was stiffer in compression (up to 3.8-fold higher elastic modulus). Instead, molecule distribution and mechanical properties were similar in the outer and inner regions of statically grown tissues. In conclusion, exposure of articular chondrocyte-based constructs to hydrodynamic flow generated tissues with locally different composition and mechanical properties, resembling some aspects of the complex structure and function of the outer and inner zones of native meniscus.

Animals↗
PubMed2004

Hydrodynamic bead modelling of the 2:1 p50-IkappaBgamma complex.

NFkappaB is an important and ubiquitous transcription factor formed by various homo- and heterodimers of the NFkappaB family. The active transcription factor regulates genes involved in immune, inflammatory and survival responses. Specificity in gene regulation is achieved, at least in part, by the distinct DNA binding preferences of the various homo- and heterodimers and by the complex pathways that lead to signal-induced degradation of the IkappaB inhibitors. Analytical ultracentrifugation and hydrodynamic bead modelling were used to model the solution structures of the NFkappaB family member p50, its inhibitor IkappaBgamma and their complex. Sedimentation equilibrium (SE) and sedimentation velocity (SV) data show that p50 is a dimer in solution with a sedimentation coefficient consistent with a conformation intermediate between the closed conformation observed in the crystal structure of the p50 (N-terminal domain)-p65 heterodimer complexed with IkappaBalpha and the open conformation adopted by p50 when bound to DNA. SE and SV data show that IkappaBgamma is a monomer in solution and is prone to aggregation over time. p50 forms a 2:1 stoichiometric complex with IkappaBgamma in solution with a sedimentation coefficient consistent with a closed conformation for the p50 dimer.

Attention↗
PubMed2005

Expression of foreign genes in chicks by hydrodynamics-based naked plasmid transfer in vivo.

The study of gene function in vivo is considered one of the top achievements of modern biology, inasmuch as it provides tools to study gene function in the context of the whole animal. In chickens, techniques of DNA-mediated gene transfer are less advanced than in other animal or livestock models, and remain a significant challenge. The study presented here is the first to show that a hydrodynamics-based gene-transfer technique, originally developed for naked DNA transfer in mice, can be applied to chickens. Rapid injection of naked plasmids containing expression cassettes into the jugular vein of 6- to 10-day-old chicks resulted in specific expression of the transgenes. A CMV promoter-driven luciferase reporter gene was expressed at significant levels in the liver during the first 3 days post-injection with lower levels also detected in the kidney. Significantly, all injected birds showed detectable levels of luciferase expression. Similarly, injection of a plasmid containing the secreted human coagulation factor IX (hFIX) gene under the control of human alpha-1-anti-trypsin promoter resulted in detectable levels of the hFIX in the plasma during the first 2 days post-injection. The method described herein has the potential for a quick and simple route for gain and loss-of function experiments in chicken liver and kidney, as well as for studying systemic effects of secreted proteins and hormones.

Animals↗
PubMed2006

Polybrominated diphenyl ethers in surface sediments of the Yangtze River Delta: Levels, distribution and potential hydrodynamic influence.

A total of 32 surface sediments collected from the Yangtze River Estuary, Hangzhou Bay and the Qiantang River were analyzed for polybrominated diphenyl ethers (PBDEs). The concentrations of summation operatorPBDEs (sum of 12 PBDE congeners without BDE 209) and BDE 209 varied from n.d. to 0.55 and from 0.16 to 94.6 ng/g, respectively. The spatial variability of summation operatorPBDEs concentrations indicated that waste discharge from the urban areas might been the main source of PBDEs in the Yangtze River Delta. BDE 209 was the predominant congener (approximately 90-100%) detected among the 13 congeners, consistent with the fact that technical deca-BDE mixtures are presently the dominant technical PBDE mixtures used in China. Compared to published data acquired from other locales, PBDE congeners with less than four bromines were more abundant in the present study area. The hydrodynamic conditions may likely be a significant factor in dictating the observed levels and congener distribution patterns of PBDEs.

China↗
PubMed2006

Rapid detection of Salmonella from hydrodynamic pressure-treated poultry using molecular beacon real-time PCR.

A real-time polymerase chain reaction (PCR) assay was evaluated to detect Salmonella in hydrodynamic pressure (HDP)-treated chicken using molecular beacon probes available as a commercial kit (iQ-Check, Bio-Rad Laboratories). The sensitivity and accuracy of the assay were compared with the conventional USDA microbiological procedure using artificially contaminated minced chicken. Chicken fillets were irradiated at 10 kGy to completely destroy any naturally occurring Salmonella. These fillets were minced and inoculated with as low as 2+/-1 cfu of S. typhimurium per 25 g chicken. The minced chicken samples were vacuum packed in multi-layer barrier bags, heat shrunk, and treated with HDP. Results showed that all inoculated samples (n=36) were detected by the PCR assay and conventional USDA procedure. Similarly, all uninoculated controls (n=11) were negative by both PCR assay and USDA procedure. As few as 2+/-1 cfu could be detected from 25 g HDP-treated chicken following 16-18 h enrichment in buffered peptone water. Real-time PCR proved to be an effective method for Salmonella detection in HDP-treated chicken with high sensitivity and more importantly, a rapid and high-throughput detection in 18 h, compared to 3-8 days for the conventional microbiological methods. HDP treatment, which has been reported to reduce spoilage bacteria in various meats, was unable to kill pathogenic Salmonella in minced chicken.

Animals↗
PubMed2004

The effect of hair bundle shape on hair bundle hydrodynamics of non-mammalian inner ear hair cells for the full frequency range.

The effect of the size and the shape of the hair bundle of a hair cell in the inner ear of non-mammals on its motion for the full range of frequencies is determined thereby extending the results of a previous analysis of hair bundle motion for high and low frequencies [Hear Res. 141 (2000) 39-50]. A hemispheroid is used to represent the hair bundle because it can represent a full range of shapes, from thin, pencil-like shapes to wide, flat, disk-like shapes. Boundary element methods are used to approximate the solution for the hydrodynamics. For physiologically relevant parameters, an excellent match is obtained between the model's predictions and measurements of hair bundle motion in the free-standing region of the basilar papilla of the alligator lizard [Aranyosi, Measuring sound-induced motions of the alligator lizard cochlea. Massachusetts Institute of Technology, PhD Thesis, 2002]. Neither in the model's predictions nor in experimental measurements is sharp tuning observed. The model predicted the low frequency region of neural tuning curves for the alligator lizard and bobtail lizard, but could not predict the sharp tuning or the high frequency region. An element that represents an active mechanism is added to the hair bundle model to predict neural tuning curves, which are sharply tuned, and an excellent match is obtained for all the characteristics of neural tuning curves for the alligator lizard, and for the low and high frequency regions for the bobtail lizard. The model does not predict well the sharp tuning of the shorter hair bundles of the bobtail lizard, possibly because it does not represent tectorial sallets.

Animals↗
PubMed2006

Hydrodynamic properties of DNA and DNA-lipid complex in an elongational flow field.

The aim of this study was to determine the difference between hydrodynamic properties of DNA-cetyltrimethylammonium (CTA) complex and those of DNA, which may be related to the difference in fibre-forming ability of DNA-CTA from that of DNA. Responses of DNA and DNA-CTA complex to an elongational flow field were investigated. In both solution systems, results suggesting a coil-stretch transition were obtained. From a critical strain rate value, the radius of gyration of DNA-CTA molecules in ethanol-glycerol solution was revealed to be 0.3-0.5 times of that of DNA in aqueous NaCl solution. Shear viscosity of DNA-CTA solution was much smaller than that of DNA solution, also suggesting a smaller size of DNA-CTA in ethanol-glycerol solution than that of DNA in aqueous NaCl solution. The plateau birefringence value of the DNA-CTA system, a parameter that indicates the local molecular conformation and the molecular arrangement, was only about 1/10 of that of the DNA system. There is an empirically determined molecular model of DNA-CTA complex in which a DNA molecule is sheathed by a cylindrical crust made of CTA chains. This structure reduces the DNA molecular density in a pure elongational flow field region but cannot explain the observed reduction of birefringence intensity. The small plateau birefringence value of DNA-CTA compared with that of DNA was attributed to the reduced molecular polarizability by the particular conformation of DNA molecules and CTA chains in the DNA-CTA system such as that expected by the conformational models.

Animals↗
PubMed2005

Hydrodynamics-induced variability in the USP apparatus II dissolution test.

The USP tablet dissolution test is an analytical tool used for the verification of drug release processes and formulation selection within the pharmaceutical industry. Given the strong impact of this test, it is surprising that operating conditions and testing devices have been selected empirically. In fact, the flow phenomena in the USP test have received little attention in the past. An examination of the hydrodynamics in the USP apparatus II shows that the device is highly vulnerable to mixing problems that can affect testing performance and consistency. Experimental and computational techniques reveal that the flow field within the device is not uniform, and dissolution results can vary dramatically with the position of the tablet within the vessel. Specifically, computations predict sharp variations in the shear along the bottom of the vessel where the tablet is most likely to settle. Experiments in which the tablet location was carefully controlled reveal that the variation of shear within the testing device can affect the measured dissolution rate.

Chemistry, Pharmaceutical↗
PubMed2006

Lipid nanocapsule size analysis by hydrodynamic chromatography and photon correlation spectroscopy.

Particle size and the size distribution are known to be important factors in the overall behavior of nanoparticulate drug delivery systems and an exact determination of these parameters is highly important. Several techniques are applied in the size determination of nanoparticulates, particularly dynamic light scattering. Also other methods have been proposed, among them hydrodynamic chromatography (HDC). In order to characterize a HDC method for nanosized carriers, differently sized lipid nanocapsules having a diameter of 25-100 nm were analyzed and results were compared with measurements from photon correlation spectroscopy (PCS) and atomic force microscopy. Results from atomic force microscopy studies were generally not in line with determinations from the other techniques due to a particle shape loss by the drying step. PCS and HDC led to comparable results in simple size determination of lipid nanocapsules. However, slight differences were found during the characterization of more complex samples. HDC was able to detect micelles as a byproduct of nanocapsule preparation while in PCS the sample dilution turned micelles undetectable. HDC analysis was able to characterize mixed samples of particle batches differing in their average size similar to PCS. HDC was found to be an excellent tool for the determination of size and average size distribution of lipid nanocapsules.

Chromatography↗