GIULIO MILAZZO SCHOOL ON BIOELECTROCHEMISTRY
September 12-19, 1997, Szeged, Hungary


ELECTROCOMPRESSIBILITY OF BILAYER LIPID MEMBRANES

 Slawomir Kalinowski* , Grazyna Ibron**

 * University of Warsaw, Bialystok Branch, Al. J. Pilsudskiego 11/4, 15-443 Bialystok, Poland
** University of Agriculture and Technology, 10-957 Olsztyn Kortowo, Poland

 The bilayer lipid membranes formed by the Mueller-Rudin method usually contain remains of solvent inside the bilayer. Applying the voltage to the membrane causes relocation of this solvent between the bilayer and the Plateau-Gibbs border, surrounding the bilayer. The thickness of the membrane changes, causing change of the membrane capacitance. The main reason of this phenomenon is an electrocompression. The membrane capacitance can be described by the approximated equation:

eq. 1
Where: C0 - minimum membrane capacitance, U - potential applied to the membrane, delta - difference of the membrane surface potentials, alpha - the factor which indicates the susceptibility of the capacitance to the potential. This parameter may be named as the membrane electrocompressibility. It describes the mebrane elasticity.

 The parameters of the equation (1) were estimated by measurements of the membrane capacitance during polarization by the linear sweep potential. The least square method was used for calculation of this parameters. The experimental points were fitted to the quadratic equation and on the basis of obtained factors the parameters of the equation (1) were calculated. The influence of the polarization potential amplitude, the membrane and the electrolyte composition on the electrocompressibility was studied. Phosphatidylcholine, phosphatidylserine and cholesterol were used for formation of the membranes. The additions of a-tocopherol and bolaamphiphilic sterol dimer were also used. It was found that the membrane composition and the amount of the solvent residued inside the bilayer had the main influence on the membrane elasticity. The presence of the bolaamphiphilic lipids significantly decreases the membrane electrocompressibility. The increase of the polarization potential amplitude causes increasing of this parameter.

 The measurements of the membrane electrocompressibility can be applied for studies of the phenomena inside the bilayer, eg. membrane strukture, transport through membranes, polymerization of lipids.