RESUMO
We report on the formation of tubular membrane protrusions from giant unilamellar vesicles in alternating electric fields. The construction of the experimental chamber permitted the application of external AC fields with strength of dozens of V/mm and kHz frequency during relatively long time periods (several minutes). Besides the vesicle electrodeformation from quasispherical to prolate ellipsoidal shape, the formation of long tubular membrane protrusions with length of up to several vesicle diameters, arising from the vesicular surface in the field direction, was registered and analyzed. The threshold electric field at which the electro-induced protrusions appeared was lower than the field strengths inducing membrane electroporation.
Assuntos
Fenômenos Eletromagnéticos , Lipossomas Unilamelares/química , Elasticidade , Bicamadas Lipídicas/química , Potenciais da Membrana , Modelos Biológicos , Fosfatidilcolinas/química , Propriedades de SuperfícieRESUMO
The dynamics of giant lipid vesicles under shear flow is experimentally investigated. Consistent with previous theoretical and numerical studies, two flow regimes are identified depending on the viscosity ratio between the interior and the exterior of the vesicle, and its reduced volume or excess surface. At low viscosity ratios, a tank-treading motion of the membrane takes place, the vesicle assuming a constant orientation with respect to the flow direction. At higher viscosity ratios, a tumbling motion is observed in which the whole vesicle rotates with a periodically modulated velocity. When the shear rate increases, this tumbling motion becomes increasingly sensitive to vesicle deformation due to the elongational component of the flow and significant deviations from simpler models are observed. A good characterization of these various flow regimes is essential for the validation of analytical and numerical models, and to relate microscopic dynamics to macroscopic rheology of suspensions of deformable particles, such as blood.
Assuntos
Lipossomos/química , Fluidez de Membrana , Lipídeos de Membrana/química , Modelos Químicos , Modelos Moleculares , Fosfatidilcolinas/química , Água/química , Simulação por Computador , Elasticidade , Conformação Molecular , Transição de Fase , Fosfatidilcolinas/análise , Resistência ao Cisalhamento , Estresse Mecânico , ViscosidadeRESUMO
An analysis of joint occurrence of tick-borne encephalitis and Lyme borreliosis in the Central Bohemian region of Czechoslovakia, based on clinical cases, showed a divergency in the dispersion patterns of the diseases. Whilst tick-borne encephalitis infections occurred in a few limited areas and its clinical cases tended to aggregate into well defined clusters, apparently following its natural focality, the cases of Lyme borreliosis were scattered +/- randomly over nearly all the region without forming such marked clusters and having little topographical correlation with tick-borne encephalitis. A computer model was applied to substantiate the observations.
