Effects of cetyltrimethylammonium bromide (CTAB) surfactant upon the dielectric properties of yeast cells.

The dielectric properties of yeast cells in the absence and presence of cetyltrimethylammonium bromide (CTAB) were investigated. The surfactant concentration range was between 0.0 and 1.0 mM. The experimental permittivity and conductivity spectra of frequency were analyzed by means of the two-shell electrical cell model (Irimajiri et al., Bull. Inst. Chem. Res., Kyoto Univ. 69 (1991) 421-438), and the electrical phase parameters of cells were subsequently evaluated. The cytoplasm conductivity and the conductivity of the vacuole interior decreased drastically by treating the cells with surfactant. The apparent capacitance of the plasma membrane increased systematically from 0.65 microF/cm2, for untreated cells, up to about 0.75 microF/cm2, at 0.3 mM CTAB. This growth was ascribed to the increase in the folding of the membrane surface associated with the surfactant-induced cell shrinkage. A further addition of the surfactant entailed a gradual decrease of the capacitance that was assigned to the membrane solubilization by the surfactant molecules. Within the accuracy of the data, the specific capacitance of the vacuole membrane was nearly constant (0.544+/-0.021 microF/cm2) over the whole surfactant concentration range. Also, the cytoplasm permittivity remained constant at 64.3+/-4.5.

Selective association of phospholipids as a clue for the passive flip-flop diffusion through bilayer lipid membranes.

We showed that the investigation of the selective association of phospholipids might contribute to the insight of the flip-flop diffusion processes. The process of selective association was studied quantitatively by testing the association probabilities for both parallel and anti-parallel orientations of the polar headgroups. The model of double chain binary mixture confirms a high capacity of phospholipids for self-association in parallel configuration of the electric dipole moments whether the cross-sectional area of the polar headgroups are in an usual range of 25-55 A2. It is demonstrated that the aggregation of a class of phospholipids from a binary mixture is strongly dependent on the dipole-dipole interaction between the same phospholipids and is modulated by the magnitude of the electric dipole moment of the other phospholipids from that binary mixture. There are a great number of mechanisms involved in the transbilayer movement of phospholipids. We referred here only to the passive transport of lipids from one monolayer to the other. The flip-flop mechanisms raised in this paper are the breakdown of bilayer due to the increase of the packing density and the inversion of the coupled phospholipids from the opposite monolayers of the same bilayer. Thus, the pair formation promoting a drop in occupied volume decreases the packing pressure in the respective monolayer and consequently triggers a flip-flop into the other direction since the packing pressure in the other monolayer has not dropped. According to the present model for the binary mixtures of double-chain lipids, the rate of the flip-flop diffusion decreased by increasing the number of the methylene groups added to the acyl chain. This dependence may be perturbed whether the phospholipids possesses a very high cross-section area of the polar headgroups (a > 55 A2). We think that the selective association of phospholipids is neither exclusively, nor only involved in promoting the transbilayer diffusion of phospholipids. Most probably, the selective association determines some phospholipid domains that attract certain particular proteins so that it can modulate the protein activity.

Dielectric properties of yeast cells as simulated by the two-shell model.

The paper reports a re-evaluation of the previous studies on yeast by considering the influence of vacuole upon the dielectric properties of the cell. In this respect, relative permittivity and conductivity of yeast cells dispersed in KCI solutions of various concentrations were measured in the frequency range from 0.1 to 100 MHz. The analysis of data revealed that the beta-dielectric dispersion of yeast cell suspensions is a composite of three (or probably four) distinct sub-dispersions. Since the dielectric response of the cell wall was experimentally avoided (according to Asami et al. (1976) J. Membr. Biol. 28, 169-180), the two-shell model, related to the plasma membrane and the vacuolar membrane, respectively, appeared to be the best approximation for yeast cells. The most relevant parameters obtained with the aid of the two-shell model were as follows. Specific capacitance of the plasma membrane and the vacuolar membrane were 0.703 +/- 0.011 microF/cm2 and 0.483 +/- 0.029 microF/cm2, respectively; electrical conductivity of the cytoplasm and the vacuole interior were 0.515 +/- 0.028 S/m and 3.22 +/- 0.48 S/m; finally, the permittivity of the cytoplasm was 50.6 +/- 2.

Liposomes: presentation and actual applicative trends in medicine.

In this paper the main aspects of characterization, handling and applications of liposomes are presented. In the last 25 years much attention has been focused to liposomal systems for optimization of the drug targeting. Several pathways to optimize the drug action of liposomes in various situations as cancer, microbial therapy, vaccines, oral therapy and diagnosis were tested. Certain applications of liposomes especially those implying the phagocytic cells sustain a real interest for industrial applications.

[Role and value of the footprint in evaluation of the development of congenital talipes equinovarus]. / Rolul si valoarea plantogramei în aprecierea evolutiei piciorului strîmb congenital varus echin

The author points out the importance of the plantogram in appraising the evolution of the principal component deformities in congenital equinovarus tailipes, under treatment or not. There are two kinds of pantograms, "contact" plantogram orientative in the redressment of supination, and "necessarily contact" plantogram for the redressment of adduction.

Membrane damage in dehydrated bacteria and its repair.

The dehydration of bacteria by vacuum exposure results in damage to the cell membrane. This membrane damage does not necessarily lead to cell death. A part of the dehydrated bacteria is capable of eliminating the membrane damage by repair processes. Repair can proceed rapidly under conditions that permit synthesizing activities. The kinetics of this repair process were studied by means of the membrane-mediated biosynthesis of the cell wall as well as by the recovery of resistance to small concentrations of lysozyme. Repair is a precondition for cell proliferation. At low temperature cells can conserve their membrane damage and the repair process can be initiated when conditions become favourable.

Effects of simulated space vacuum on bacterial cells.

The effect of vacuum on bacterial cells is related to water desorption. Below water vapour pressure the inactivation remains constant, independent of total pressure and exposure time. In subsequent growth, the lag-phase of the survivors is delayed. Combined treatment with vacuum and radiation (X-rays or uv of 254 nm wavelength) results in synergistic effects, whereas vacuum and heat can act antagonistically. The vacuum inactivated cells (indicated as loss of colony-forming ability) are completely damaged. They do not show cellular elongation, phage production or respiration. The cellular membrane becomes permeable by vacuum exposure: biomolecules are released from the cells when re-suspended after vacuum treatment.