RESUMO Neste artigo, estamos apresentando os resultados de um estudo sobre a influência de efeitos hidrodinâmicos sobre os potenciais superficiais da membrana do eritrócito, comparando dois modelos diferentes formulados para simular o movimento eletroforético de uma célula biológica: o modelo clássico de Helmholtz-Smoluchowski e um modelo apresentado por Hsu et al. (1996). Este modelo considera efeitos hidrodinâmicos para descrever a distribuição da velocidade do fluido. A equação do potencial eletrônico foi obtida da equação não linear de Poisson-Boltzmann, considerando a distribuição espacial das cargas elétricas fixas no glicocálix e nas proteínas citoplasmáticas, assim como as cargas eletrolíticas e as fixas nas superfícies da bicamada. Nossos resultados mostram que o modelo de Helmholtz-Smoluchowski não é capaz de refletir as forças reais responsáveis pelo comportamento eletroforético de células, pois este não leva em conta os efeitos hidrodinâmicos do glicocálix. Esta rede carregada que cobre a superfície celular constitui um sistema físico complexo cujas características eletromecânicas que não podem ser desprezadas. Assim, corroborando a hipótese de outros autores, sugerimos que, em análises de movimento eletroforético de células, o modelo clássico representa um caso limite de modelos que levam em conta os efeitos hidrodinâmicos para descrever a distribuição de velocidade do fluido.

ABSTRACT In this paper, we present the results of a study on the influence of hydrodynamic effects on the surface potentials of the erythrocyte membrane, comparing two different models formulated to simulate the electrophoretic movement of a biological cell: the classical Helmholtz-Smoluchowski model and a model presented by Hsu et al. (1996). This model considers hydrodynamic effects to describe the distribution of the fluid velocity. The electric potential equation was obtained from the non-linear Poisson-Boltzmann equation, considering the spatial distribution of electrical charges fixed in glycocalyx and cytoplasmic proteins, as well as electrolyte charges and ones fixed on the surfaces of lipidic bilayer. Our results show that the Helmholtz-Smoluchowski model is not able to reflect the real forces responsible to the electrophoretic behavior of cell, because it does not take account the hydrodynamic effects of glycocalyx. This charged network that covers cellular surface constitutes a complex physical system whose electromechanical characteristics cannot be neglected. Then, supporting the hypothesis of other authors, we suggest that, in electrophoretic motion analyses of cells, the classical model represents a limiting case of models that take into account hydrodynamic effects to describe the velocity distribution of fluid.

PURPOSE: The aim of this work was to analyze the bladder wall modifications after a chronic treatment with high doses of corticosterone in prepubertal rats. METHODS: This study included 26 male rats assigned into four groups: T30 was treated with corticosterone until 29 days of age and killed at day 30, while T65 group received the same treatment but was killed at day 65. Each group had its own control group (C30 and C65). For treated animals, daily intraperitoneal injections of corticosterone (20 mg/Kg) were administered between 7th and 29th day of life. Bladders were removed and collagen, smooth muscle, elastic fibers system, vascular density and epithelium were analyzed by morphometrical methods, immunofluorescence, and biochemistry. RESULTS: Vascular density in lamina propria was reduced by 40% (p<0.05) in group T65. Collagen organization was altered in T30 and T65, although total collagen concentration was unchanged. The T65 group had an increase in elastic system fibers. There was no difference in epithelial height and cell density between the groups. Concerning the smooth muscle fibers density we observed a 19% increase (p<0.05) in the T65 group. CONCLUSION: Prepubertal administration of corticosterone induces structural modifications in the bladder of rats in a medium term analysis.

The space-dependent electric potential equations were determined by solution of non-linear Poisson-Boltzmann equation, which decribes an erythrocyte membrane model which takes into account the charges of molecules associated with lipidic bilayer (glycocalyx molecules, outer side, and spectrin, inner side). It was assumed that on both sides of the membrane the charges are homogeneously distributed. Therefore, the potential was dependent on the z-coordinate only. Thus, we obtained the potential profile curve. The results are compared to previous ones obtained from more simple membrane model (Bioelectroch. Bioenerg. 1993, 32:305-315).