[Lipid pore states in bilayer lipid membranes at phase transition in LiCl solution with addition of polyethylene glycols].

Statistics on open and closed states of the lipid pores was experimentally investigated in planar lipid bilayer membranes from dipalmitoylphosphatidylcholine at the phase transition temperature in LiCl solution (1 M). Polyethylene glycol of different molecular mass was added to the solution. Transmembrane current pulses were measured at voltage-clamp conditions (50 mV). The histograms of the pore lifetime and the pulse interval have no exponential shape but the pronounced maximum. It means that the pulse sequence of the transmembrane current measured in the phase conditions is dependent. The emergence of the new pulses depends on the emergence time of the previous pulses. The time of the pulse end depends on the time of the pulse start. The proposed Erlang model approximates the experimental histograms quite accurately. According to the model the lipid pore can have several open and closed states.

[Orientation hypercolumns of the visual cortex: ring model].

A hypercolumn of the visual cortex is a functional unit formed of the neighbouring columns whose neurons respond to a stimulus of particular orientation. The function of the hypercolumn is to amplify the orientation tuning of visually evoked responses. According to the conventional simple model of a hypercolumn, neuronal populations with different orientation preferences are distributed on a ring. Every population is described by the frequency (FR) model. To determine the limitations of the FR-ring model, it was compared with a more detailed ring model, which takes into account the distribution of neurons of each population according to their voltage values. In the case of the leaky integrate-and-fire neurons, every neural population is described by the Fokker-Planck (FP) equation. The mapping of parameters was obtained. The simulations revealed differences in the behaviour of the two models. Contrary to the FR model, the model based on the Fokker-Planck equation reacts faster to a change in stimulus orientation. The Fokker-Planck ring model gives a steady-state solution in the form of waves of activity travelling on the ring, whereas the FR ring model presents amplitude instability for the same parameter set. The FR ring model reproduces the characteristic effects of the ring model: the virtual rotation and the symmetry breaking.

["Blocking" by polyethyleneglycol of single lipid pores arising in unmodified bilayer lipid membranes during phase transitions].

Changes in the ionic permeability of bilayer lipid membranes from dipalmitoyl phosphatidylcholine at temperatures of phase transition in LiCl (1 M) solution after the addition of polyethyleneglycols of different molecular masses have been studied. The transition of ionic membrane channels from the conducting state to a blocking nonconducting state using polymers makes it possible to calibrate lipid pores. It was shown that low-molecular-weight glycerol, polyethyleneglycols with molecular masses of 300 and 600 decrease the amplitude of fluctuations of the current through the membrane, the decrease being proportional to the size of the polymer molecule being incorporated. The addition of polyethyleneglycols with molecular masses of 1450, 2000, and 3350 decrease the current fluctuations to the basal noise level. This result is considered as a complete blockade of ion channel conductivity. In the presence of rather large polymers, such as polyethyleneglycols with molecular masses of 6000 and 20000, which are practically not incorporated into the pore, single current fluctuations occur again; however, their amplitudes are somewhat smaller than in the absence of polyethyleneglycol. It is assumed that the complete blockade of the conductivity of lipid ionic channels by polyethyleneglycols with molecular masses of 1450, 2000, and 3350 is due to the dehydration of the pore gap and the conversion of the hydrophilic pore to a hydrophobic pore.

[A soft poration of planar bilayer lipid membranes from dipalmitoylphosphatidylcholine at the temperature of the phase transition from the liquid crystalline to the gel state].

A method of soft poration of lipid bilayer was suggested, which is based on the structural rearrangement of lipid bilayer formed from disaturated phospholipids on the phase transition from liquid crystalline state to the gel. As opposed to the widely used method of electropbration, this method allows one to obtain a lipid pore population without application of high electric field. In the case of soft poration, the electric field does not exceed the physiological level of 10-100 mV. It was shown that, in planar bilayer lipid membranes formed from dipalmitoylphosphatidylcholine in water solution of 1 M LiCl, there appear up to 10 lipid pores in 1 min per 1 mm of membrane surface with an average conductivity of a pore of 31 +/- 13 nS. The average pore radius estimated using soluble polyethylene glycols ranged between 1.05-1.63 nm. Monovalent cation conductivity of a single lipid pore on soft poration was shown to decrease in the order Li+ > or = Na+ > K+ = Rb+ > or = Cs+. This order coincides with that observed by Marra and Israilashvili for dipalmitoylphosphatidylcholine-water interbilayer where the repulsive hydration force contribution is significant.

[Electric capacitance of bilayer lipid membranes from hydrogenated egg lecithin during phase transition from liquid crystalline state to gel]. / Elektricheskaia emkost' bisloinykh lipidnykh membran iz gidrirovannogo iaichnogo letsitina pri fazovom perekhode iz zhidkokristallicheskogo sostoianiia v gel'.

The electrical capacity of planar bilayer lipid membranes (BLM) from natural hydrogenated egg lecithin (HEL) in n-decane at a temperature of phase transition was measured. The temperature of phase transition was determined calorimetrically to be 51 degrees C. The data obtained revealed a phase separation of HEL in BLM into two fractions, one freezing at 42-44 degrees C and one that is converted to a liquid-crystal state at 51-59 degrees C. It was assumed that the first fraction is rich in dipalmitoyl lecithin, and the second fraction is rich in distearoyl lecithin. Freezing and the transition to the liquid-crystal state were accompanied by an increase and decrease in membrane thickness, respectively, in part due to a displacement of the solvent from the torus to the planar part of the bilayer. The displacement of the solvent is explained by changes in the disjoining pressure in BLM, which arises across the lipid bilayer due to van der Waals forces of attraction between water layers on both sides of the BLM.

[Use ciprofloxacin in children with mucoviscidosis]. / Opyt primeneniia tsiprofloksatsina u detei, bol'nykh mukovistsidozom.

Ciprofloxacin was used in treatment of 13 children aged 6 to 18 years with mucoviscidosis and exacerbation of the bronchopulmonary process. The dose of the drug was 20 to 30 mg/kg a day when administered orally or 15 mg/kg a day when administered at first intravenously and then orally. The treatment course averaged 14 days. The indications to the drug use were: severe processes of mucoviscidosis and chronic colonization of the bronchial mucosa and lung tissues with Pseudomonas aeruginosa (mucoid or nonmucoid form) sensitive to ciprofloxacin and resistant to other antibiotics. The trials showed that ciprofloxacin was highly efficient: the state of the patients improved and the inflammation index of the total blood count normalized. However, eradication of P. aeruginosa from the respiratory tracts was not observed. The drug allergy in 1 patient and a transient increase in the level of transaminases in 5 patients as the adverse reactions were recorded.

[Formation of stabile cupola-like lipid bilayer membranes with a mobile plateau Gibbs boundary]. / Formirovanie stabil'nykh kupoloobraznykh bisloinykh lipidnykh membran s podvizhnoi granitsei plato-Gibbsa.

Stable bilayer lipid membrane with mobile Platear-Gibbs border have been formed. The predominant condition of the formation is the presence of lipid coverage on the teflon surface near the hole. The formation process includes transformation of the initial planar lipid bilayer into cupola-shaped one by bowing of the lipid bilayer due to hydrostatic pressure, movement of the PGb along the teflon surface. The bilayer area estimated by electric capacitance increases from 0.1 x 10(-8) F to 21 x 10(-8) F. Electric conductance of the lipid bilayer has not changed except for the phase transition and membrane collapse. The electric capacitance of the BLM formed from hydrogenated egg lecithin was changed by cooling between 60 degrees and 40 degrees C with the maximum at about phase transition range. The individual membrane sustains several scannings of the temperature without disruption which is an evidence of the stability of the cupola-shaped membranes.

[Conductivity of bilayer lipid membranes in phase transition: the role of intramolecular phosphate-phosphate hydrogen bonds]. / Provodimost' bisloinykh lipidnykh membran pri fazovom perekhode: rol' mezhmolekuliarnykh fosfat-fosfatnykh vodorodnykh sviazei.

pH effect on phase transition measured by jump of conductance in the BLM formed from DPPA and thio-DPPA was studied. The difference of pH dependence for these two lipids was shown. The corresponding calculation discovered significance of intermolecular phosphate-phosphate hydrogen bonds in induced conductance of BLM.

[Ca2+ ions induce successive capacity and ion currents in BLM from phosphatidic acid as a result of phase transition]. / Iony Ca2+ indutsiruiut posledovatel'noe poiavlenie emkostnogo i ionnogo tokov v BLM iz fosfatidnoi kisloty v rezul'tate fazovogo perekhoda.

Time dependence of Ca2+-induced electric current in BLM formed from DPPA was studied at constant temperature and pH. The phase transition in BLM is accompanied by capacity current and following appearance of single ionic channels. It was shown that transferred charge was 5 nC/F, conductivity of single ionic channels--500-100 pSm.