A study of the inhomogeneity of bilayer lipid membranes by measurements of higher harmonics of transmembrane current

Higher harmonics of alternating current in bilayer lipid membranes caused by sinusoidal voltage applied to the membrane were measured. The bilayer lipid membranes were prepared from diphytanoylphosphatidylcholine in n-decane and n-tetradecane, and measurements were conducted with the aid of an analog-to-digital converter of 16th category. Sinusoidal voltage was formed using a digital-to-analog converter of the 16th category. The dynamic region of measurements was up 90 dB. The results of measurements were used to determine the alpha and beta coefficients of the expansion of membrane capacity C in terms of membrane voltage U C = C0 (1 + alphaU2 + betaU4). We showed in the framework of the electrostriction model that the relation between the alpha and beta coefficients characterizes the inhomogeneity of bilayer lipid membrane with respect to its thickness and Young modulus of elasticity.     

Thermal acoustic radiation from multilamellar vesicles in lipid phase transition

A new acoustical method for the investigation of lipid phase transition is introduced based on the measurement of the thermal acoustic radiation (TAR) inherent in lipids. The TAR of multilamellar vesicles from dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylcholine (DMPC) was measured in the megahertz range and the variations in the radiation intensity during the lipid phase transition were recorded. Two types of variations are possible: if the temperature of the vesicles decreases (in the process of transition from the liquid crystalline state to the gel state) then the TAR intensity increases, and if the temperature increases (in the reverse transition) then the TAR intensity decreases. These effects are connected with an increase in the ultrasonic absorption in the vesicles under lipid phase transition. Basing on the results of the TAR investigation, a new theoretical estimate has been developed of the variation in the absorption coefficient during the lipid phase transition. In this estimate, the variation is equated to the ratio of the phase transition entropy to the gas constant.     

On measurements of the higher harmonics of transmembrane current

The higher harmonics of the current caused by an alternating voltage applied to bilayer lipid membranes made of diphytanoyl phosphatidylcholine (DPhPC) in decane and tetradecane were measured. A universal relation between the amplitudes of harmonics was proposed and experimentally verified. This allowed the coefficients of expansion of the capacitance in even powers of voltage to be calculated for the DPhPC membrane in tetradecane; it also permitted comparison of the inhomogeneity in the thickness of the DPhPC membranes in decane and tetradecane.     

A study of inhomogeneity of bilayer lipid membranes by measuring the higher harmonics of the transmembrane current

The higher harmonics of the alternating current in bilayer lipid membranes induced by a sinusoidal voltage applied to the membrane were measured. The bilayer lipid membranes were prepared from diphytanoylphosphatidylcholine in decane and tetradecane; a 16-bit analog-to-digital converter was used for the measurements. A sinusoidal voltage was formed with a 16-bit digital-to-analog converter. The dynamic measurement range reached 90 dB. The coefficients α and β of the expansion of capacitance C in terms of the membrane voltage U—C = C ₀(1 + αU ² + βU ⁴)—were determined from the measurement results. It was shown within the framework of the electrostriction model that a certain ratio of the coefficients α and β characterizes the inhomogeneity of the membrane with respect to its thickness and Young’s modulus of elasticity.     

On measurements of higher harmonics of transmembrane current

Measurements of higher harmonics of transmembrane current in bilayer lipid membranes from diphytanoyl phosphatidylcholine (DPhPC) in n-decane and n-tetradecane, caused by alternating voltage applied to the membrane, have been conducted. A universal relation between the amplitudes of harmonics was suggested and experimentally checked. This allowed one to calculate the coefficients of expansion of membrane capacity in series with even powers of membrane voltage and to compare the inhomogeneity of membranes from diphytanoyl phosphatidylcholine in n-decane and n-tetradecane with respect to thickness.