Dipole Potential of Bilayer Membranes

Abstract

Membrane dipole potential (DP) manifests at the lipid–water interface. In contrast to a surface and a transmembrane potential, it is dependent neither on the charge of the lipid nor on the ionic strength of the surrounding solution. With respect to the considerable magnitude of 200–300 mV in bilayer membranes, DP has long been supposed to play an important role in a number of physiological processes. Meanwhile it is well established that DP is responsible for differences in the permeability of oppositely charged hydrophobic ions, charged carriers, some potential sensitive dyes, charged spin label probes and nonelectrogenic carriers. A novel exciting hypothesis is that the regulation of ion-transporting cell membrane proteins is possible via an effect of the local electric field of the lipid (DP) on the kinetics of charge-transporting steps of the proteins. This idea enhances de novo the interest in the DP. One of the main difficulties hindering the progress of DP investigation in cell membrane is the lack of methods that would enable its direct recording. The majority of DP research was carried out with vesicular and planar bilayers. At the moment, they represent the most convenient and reliable system to understand the origin and significance of DP. Recent investigations on model systems support the notion that the DP affects peptide channel insertion and conductivity. In the present chapter an overview concerning origin, modification and significance of the DP is given. Methods, which determine the DP of planar bilayers are reviewed. In the mean time, a number of substances have been investigated with regard to their ability to alter the membrane DP. The classification of the DP modifiers undertaken here indicates that their investigation has rather spontaneous character. Some examples demonstrate the biological importance of the DP.