No abstract

No abstract

Cell membrane microfragments called microvesicles (MV) originating from different cells are circulating in the blood of healthy subjects and their elevated numbers are found in different diseases, including cancer. This study was designed to characterise MV present in plasma of gastric cancer patients. Since majority of MV in blood are platelets-derived (PMV), plasma samples deprived of PMV were used. In comparison to control, the number of MV in patients was significantly elevated in all stages, higher in more advanced disease. Patients' MV showed an increased membrane expression of CCR6 and HER-2/neu. The proportion of MV carrying some leucocyte determinants was low and similar in patients and control. Transmission electron microscopy showed their substantial heterogeneity in size and shape. The size determined by dynamic light scattering analysis confirmed this heterogeneity. The MV size distribution in patients was broader within the range of 10-800 nm, while in control MV showed 3-mode distribution within the range of 10-400 nm. Atomic force microscopy confirmed MV size heterogeneity with implication that larger objects represented aggregates of smaller microparticles. Patients' MV exhibited increased absolute values of zeta potential, indicating a higher surface charge. Tumour markers HER-2/neu, MAGE-1, c-MET and EMMPRIN were detected both in control and patients' samples with stronger expression in the latter. Significantly higher expression of MAGE-1 and HER-2/neu mRNA was observed in individual patients. All together, it suggests that at least some MV in plasma of gastric cancer patients are tumour-derived. However, their role in cancer requires further studies.

The zeta potentials of natural mica, bare and covered by positively charged latex particles of micrometer size range, were determined by the streaming potential method. Measurements were carried out using the parallel-plate channel formed by clamping together two mica sheets separated by a Teflon spacer. The dependence of streaming potential on surface coverage (ϑ) of adsorbed particles was determined for various ionic strengths and particle sizes. The coverage was determined directly by optical and electron microscope counting procedures. It was found that the negative streaming potential for bare mica E s was significantly increased by the presence of adsorbed particles. The dependence of the reduced streaming potential E s p /E s (where E s p is the zeta potential in the presence of particles) on ϑ exhibited an universal behavior being independent of particle size and ionic strength. These experimental data were interpreted in terms of a theoretical model postulating that the streaming potential change was due to flow damping over the interface and by charge transport from the double-layer surrounding adsorbed particles. In contrast with previous approaches no assumption of the slip (shear) plane shift upon particle adsorption was made. By exploiting the experimental results it was suggested that colloid and bioparticle adsorption kinetics can be studied in situ using the streaming potential method.

No abstract

Polyelectrolyte multilayer adsorption on mica was studied by the streaming potential method in the parallel-plate channel setup. The technique was calibrated by performing model measurements of streaming potential by using monodisperse latex particles. Two types of polyelectrolytes were used in our studies: poly(allylamine) hydrochloride (PAH), of a cationic type, and poly(sodium 4-styrenesulfonate) (PSS) of an anionic type, both having molecular weight of 70,000. The bulk characteristics of polymers were determined by measuring the specific density, diffusion coefficient for various ionic strengths, and zeta potential. These measurements as well as molecular dynamic simulations of chain shape and configurations suggested that the molecules assume an extended, wormlike shape in the bulk. Accordingly, the diffusion coefficient was interpreted in terms of a simple hydrodynamic model pertinent to flexible rods. These data allowed a proper interpretation of polyelectrolyte multilayer adsorption from NaCl solutions of various concentrations or from 10(-3) M Tris buffer. After completing a bilayer, periodic variations in the apparent zeta potential between positive and negative values were observed for multilayers terminated by PAH and PSS, respectively. These limiting zeta potential values correlated quite well with the zeta potential of the polymers in the bulk. The stability of polyelectrolyte films against prolonged washing (reaching 26 h) also was determined using the streaming potential method. It was demonstrated that the PSS layer was considerably more resistant to washing, compared to the PAH layer. It was concluded that the experimental data were consistent with the model postulating particle-like adsorption of polyelectrolytes with little chain interpenetration. It also was concluded that due to high sensitivity, the electrokinetic method applied can be effectively used for quantitative studies of polyelectrolyte adsorption, desorption, and reconformation.

No abstract

Statistical properties of surfaces covered by particles deposited under the influence of gravity are investigated by means of optical microscopy and image analysis. The radial distribution function of the particle configurations is determined over a wide coverage range. Special attention is paid to the fluctuations of the number of particles on small surfaces which contain information upon the deposition process. A first analysis of these fluctuations is presented within a mean field approximation. All results are compared to the ballistic process which proves to be a good model. On the contrary, the observations are not compatible with a simple random sequential adsorption model.