Membranes breakdown

It follows from previous discussion that the destabilizing electrostatic contribution grows in absolute value with x (with increasing A.). But the influence of the nonuniform electrical force is overwhelmed by the stabilizing bending and stretching contributions. As a result, the traditional smectic model cannot explain how a small transmembrane voltage can lead to membrane breakdown. The obvious solution is to abandon this approach and to develop an alternative, such as the pore formation model. However, as we noticed before, this approach postulates rather than proves the appearance of hydrophobic pores. 

In our approach to membrane breakdown we have only taken preliminary steps. Among the phenomena still to be understood is the combined effect of electrical and mechanical stress. From the undulational point of view it is not clear how mechanical tension, which suppresses the undulations, can enhance the approach to membrane instability. Notice that pore formation models, where the release of mechanical and electrical energy is considered a driving force for the transition, provide a natural explanation for these effects [70]. The linear approach requires some modification to describe such phenomena. One suggestion is that membrane moduli should depend on both electrical and mechanical stress, which would cause an additional mode softening [111]. We hope that combining this effect with nonlocality will be illuminating. 

Wasserman, W. J., and Smith, L. D. (1978). The cyclic behavior of a cytoplasmic factor controlling nuclear membrane breakdown. J. Cell Biol. 78 R15-R22. 

Figure 4 Transfer of DNA from cytoplasm into the nucleoplasm. The DNA-containing complex can enter the nucleus by (1) crossing the membrane during mitotic nuclear membrane breakdown (2) diffusion through nuclear pore for small particles and (3) targeted uptake through the nuclear pore, facilitated by a nuclear localization sequence. Abbreviations NLS, nuclear localization sequence IMP, importin.

The relative importance of hepatic microsomal lipid peroxidation versus covalent binding of carbon tetrachloride-derived radicals has been the subject of considerable debate. Since cytochrome P-450 loss has been shown to be related to lipid peroxidation and to covalent binding, each in the absence of the other, both of these early consequences of carbon tetrachloride metabolism may contribute to P-450 destruction. Nevertheless, it is still not clear how these initial events are related to subsequent triglyceride accumulation, polyribosomal disaggregation, depression of protein synthesis, cell membrane breakdown and eventual death of the hepatocytes. Carbon tetrachloride... 

Sulfur mustard-induced lipid peroxidation is a function of glutathione (GSH) depletion. For this mechanism, depletion of GSH results in an accumulation of reactive oxygen species via hydrogen peroxide-dependent processes (Miccadei et al., 1988). The oxygen radicals react with membrane phospholipids forming lipid peroxides that alter membrane structure resulting in membrane breakdown. 

The ability to enzymically remove fungal cell walls and produce a protoplast has been exploited to generate strains capable of enhanced ethanol production or the metabolism of novel combinations of carbohydrates. Once protoplasts are formed they may be fused by incubation in polyethylene glycol (PEG) and calcium ions, which induces membrane breakdown. Selection of the resulting... 

R408 J. Klein, Membrane Breakdown in Acute and Chronic Neurodegeneration Focus on Choline-Containing Phospholipids , J. Neural Transm., 2000,107, 1027... 

The stability of bilayers in the presence of polyene antibiotics has been investigated [199]. Pure lecithin bilayers were found to be stable in the presence of 40 /xM filipin or nystatin in contrast, bilayers consisting of equal parts cholesterol and lecithin were disrupted rapidly by filipin but considerably more slowly by nystatin. Bilayers consisting exclusively of cholesterol or bilayers with phospholipid sterol ratios of 10 1 were stable in the presence of filipin. When added to a sterol-containing lecithin bilayer, filipin removed the sterol from the membrane by non-polar association, changing the fluidity of the lipid chains in the bilayer, and ultimately caused membrane breakdown [200],... 

The first workers to carry out such experiments (Crane and Davies ) found current-potential curves that were not linear. They interpreted it as a result of membrane breakdown (electrostriction ). Mandel, developing a suggestion due to Bockris, took data for currents caused to pass across pig s bladder membranes by means of the bielectrode technique and found that the logarithm of current varies linearly with the potential applied across the membrane. 

H. D. Hurwitz Professor Chismadjev did not limit himself to the problem of membrane breakdown and membrane fusion which is also tackled by Professor Berg s contribution. Other important aspects of bioelectrochemistry have been treated by Professor Chimadjev, like, for example, the determination of membrane potential, also considered in Professor Adams contribution, the electric field across membrane, the influence of antibiotics and of other vectors for the ion transport. I wish to ask the audience if there are any comments which concern such aspects of the selectivity of cell membranes to ions and the role of peptides. 

The treatment involves the application of very short electric pulses (1-100 ps) at electric field intensities in the range of 0.1-1 kVcm for the reversible permeabilization by means of stress induction in plant cells, 0.5-3 kVcm for the irreversible permeabilization of plant and animal tissues, and 15—40kVcm for the irreversible permeabilization of microbial cells. The aforementioned field intensities lead to the formation of a critical transmembrane potential, which is regarded as being the precondition for cell membrane breakdown and electroporation (Tsong, 1996). 

Tsong, T. Y., 1996. Electrically stimulated membrane breakdown, in Electrical manipulation of cells, (eds. P. T. Lynch, M. R. Davey), pp. 15-36. Chapman Hall, New York, USA. 

Klein, J. (2000) Membrane breakdown in acute and chronic neurodegeneration Focus on choline-containing phospholipids. J. Neural Transm. 107, 1027-1063. 

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