Impedance spectroscopy of bilayer lipid membranes self-assembled on agar support - interaction with HDL.

The electrical properties of the supported lipid bilayer membrane (s-BLM) of egg phosphatidylcholine (PC) self-assembled on agar surface were examined. To characterize the insulating properties of s-BLMs, electrochemical impedance spectroscopy (EIS) was used. The analysis of impedance spectra in terms of an equivalent circuit of agar/electrolyte and agar/s-BLM/electrolyte in the frequency range of 0.1 Hz-10 kHz was performed. The high-density lipoproteins (HDL)/s-BLM interaction in the concentration range from 20 microg/ml to 80 microg/ml of HDL was investigated. It is evident that treatment of s-BLM with HDL resulted in an increase of the lipid film resistance and a decrease of membrane capacitance.

Cyclic voltammetry study of glucose and insulin interactions with supported lipid membrane.

The effect of D-glucose and insulin on conducting properties of supported bilayer lipid membranes (s-BLM) modified by anthraquinone-2-sulphonic acid (AQS) at the presence of potassium ferricyanide was studied by means of cyclic voltammetry (CV). Both the oxidation and the reduction current peaks were found to decrease at the presence of glucose in concentration range varying from 10 to 320 mM. The influence of insulin on membrane properties is ambiguous. While the pretreatment of membrane with 20 mU l(-1) of insulin evoked slight increase of the current with unchanged course of the dependence of peak current on glucose, the decrease of conductance was observed above 10(5) mU l(-1) of insulin.

Angiotensin II-induced formation of ionic channels in bilayer lipid membranes.

The interaction of angiotensin II (ANG II) with membrane was studied by measuring conductance and current-voltage characteristics (IVC) of bilayer lipid membranes (BLM) prepared of a mixture of egg lecithin with cholesterol, and of gramicidin D-modified membranes of the same composition. Addition of physiological concentrations of ANG II (approx. 15 mumol/l) into the electrolyte (1 mol/l KCl, pH = 7) in contact with one side of BLM resulted in the appearance of discrete membrane conductance (symbol; see text) = (39.5 +/- 1.07) pS with a duration of the conductivity state tau = (52.15 +/- 6.44) s. Raising ANG II concentration to 75 mumol/l resulted in an additional conductance level of approx. 130 pS with a lifetime of approx. 1s. The electrolyte pH markedly influenced ANG II modified BLM conductance. A decrease of the electrolyte pH to 2.8 resulted in a reduction of the discrete conductance level to approx. 14 pS, whereas ANG did not induce any conductivity at pH = 11.5. The results obtained suggest that ion channels are formed consisting at least of two ANG II molecules. IVC of ANG II-modified BLM are superlinear within the range of electrolyte concentrations studied (between 0.01 and 3 mol/l KCl), i.e, the limiting stage of ion transport is the internal area of the conducting pore. ANG II affects in a cooperative manner the gramicidin D (GRD)-mediated transport, most likely by forming ANG II aggregates in the area of local inhomogeneities in the BLM structure of GRD channels.

Rimantadine effects on the elasticity of bilayer lipid membranes and on ion transport through gramicidin D channels.

The effect of the antiviral preparation rimantadine on lipid bilayer membranes (BLM) was studied by measuring the modulus of elasticity in the direction normal to the surface (E perpendicular) and by estimating the conductance lambda, the lifetime tau of single gramicidin D channels (GRD), and the coefficient of nonlinearity beta of current voltage characteristics (IVC) of GRD-modified BLM. Rimantadine induced a nonmonotonic change in E perpendicular of BLM prepared from a mixture of egg lecithin with cholesterol: at relatively low rimantadine concentrations (0-40 micrograms/ml) E perpendicular first increased, reached a maximum and started to decrease. The effectivity of rimantadine was dependent on the cholesterol concentration in the BLM. Changes in E perpendicular suggest an increased ordering of the lipid bilayer at low rimantadine concentrations and formation of clusters of the preparation at concentrations exceeding those necessary to obtain maximal values of E perpendicular for the given BLM lipid composition. Rimantadine concentrations lifetime by approximately 20 percent, affected the degree of IVC nonlinearity and superlinearity of GRD-modified membranes, which suggests some effect on the height of the barrier at the ionic channel mouth and in its centre.

[Relation between gramicidin D and valinomycin-induced conductivity of lipid bilayer and cholesterol levels]. / Zavisimost' indutsirovannoi gramitsidinom D i valinomitsinom provodimosti lipidnogo bisloia ot soderzhaniia kholesterina.

Kinetics of conductance and current-voltage characteristics (VACH) were studied on the bilayer lipid membranes from egg lecithin and cholesterol modified by gramicidin D and valinomycin. There were found significant changes of ionic channels conductance g, lifetime tau and non-linearity coefficient beta of VACH of modified membranes dependent on cholesterol content. In the region of high cholesterol concentrations, more than 20 mol%, there were observed abrupt changes of the ionic channels parameters: tau increased more than ten times, conductance decreased two times and beta greater than 0 in the whole region of electrolyte concentration.