Estimates of the intramembrane field through the harmonics of capacitive current in inhomogeneous bilayer lipid membranes

Intramembrane field gives information about localisation of fixed charges o r dipoles inside the lipid bilayer, There is systematic discrepancy between field estimates made by various methods. The possible reason of this discr epancy can be attributed to the misinterpretation of the data in the frames of the methods used. It stands for the method that is based on the compens ation of the 2nd harmonic of capacitive current generated due to electrostr iction phenomenon if sine voltage is applied to the bilayer. The theoretica l grounds of the method mentioned are oversimplified because membrane heter ogeneity has not been taken into consideration. The purpose of the work is the analysis of the generation of harmonics of capacitive current in inhomo geneous bilayer if intramembrane charges are located at different depth. Th e results of the study enable one to determine the position of intramembran e charges. The theoretical methods are used. The bilayer electrostriction i nduced by the electric field in the presence of intramembrane charges is co mputed. The intramembrane field depends upon localisation of the charges in side the bilayer like a sine curve; it goes to zero if the charges are loca ted in the centre of the membrane. The charge discreteness affects the valu e of the compensation voltage due to nonlinearity of the bilayer deformatio ns close to the charge. The probable appendices of outcomes are discussed f or problems of intramembrane dye localisation and ion transport in the chan nel of sodium/potassium ATPase. (C) 2001 Elsevier Science B.V. All rights r eserved.