A new system for bilayer lipid membrane capacitance measurements: method, apparatus and applications

Bilayer Lipid Membrane as Memcapacitance: Capacitance-Voltage Pinched Hysteresis and Negative Insertion Conductance

Inelastic (dissipative) effects of different natures in lipid bilayer membranes can lead to hysteresis phenomena. Early, it was shown that lipid bilayer membranes, under the action of a periodic sinusoidal voltage, demonstrate pinched-hysteresis loops in the experimental capacitance-voltage dependences and are almost the only example of the physical implementation of memcapacitance. Here, we propose an equivalent circuit and mathematical framework for analyzing the dynamic nonlinear current response of a lipid bilayer membrane as an externally controlled memcapacitance. Solving a nonlinear differential equation for the equivalent circuit of a membrane in the form of a parallel connection of a nonlinear viscoelastic capacitor and an active resistance using the small parameter method, we obtain explicit analytical dependences for the current response of the membrane and pinched-hysteresis loops. The explicit solutions and their comparison with experimental data allow us to identify the lumped equivalent circuit parameters that govern the memcapacitor behavior of the membrane and hence the magnitude of the hysteresis. We quantify the memcapacitance hysteresis in terms of negative work done by the control signal. An analysis of the formulas leads to the conclusion that the determining factor for the appearance of pinched hysteresis is the type of nonlinear dependence of the device capacitance on voltage.

Chronopotentiometric technique as a method for electrical characterization of bilayer lipid membranes

The basic electrical parameters of bilayer lipid membranes are capacitance and resistance. This article describes the application of chronopotentiometry to the research of lipid bilayers. Membranes were made from egg yolk phosphatidylcholine. The chronopotentiometric characteristic of the membranes depends on the current value. For low current values, no electroporation takes place and the voltage rises exponentially to a constant value. Based on these kinds of chronopotentiometric curves, a method of the membrane capacitance and the membrane resistance calculations are presented.

Planar lipid bilayers: observing pore creation and extinction

From an electrical point of view a planar lipid bilayer can be considered as a non-perfect capacitor; it can be presented as an ideal capacitor in parallel with resistor. In this study the whole measuring system including planar lipid bilayer was modeled by an equivalent electric circuit in Spiceopus software. Such a model gives additional information of experimentally obtained results. In this way we analyze measurements of transmembrane voltage that appears on planar lipid bilayer as consequence of linear rising current. Small voltage drops were obtained before the planar lipid bilayer breakdown. The model showed that effective current on planar lipid bilayer is actually much smaller than the current applied with current generator and should be used in calculations of a conductance related to voltage drops.

A system for the determination of planar lipid bilayer breakdown voltage and its applications

In this paper, we focus on measurement principles used in electroporation studies on planar lipid bilayers. In particular, we point out the voltage-clamp measurement principle that has great importance when the breakdown voltage of a planar lipid bilayer is under consideration; however, it is also appropriate for the determination of other planar lipid bilayer electrical properties such as resistance and capacitance. A new experimental system that is based on the voltage-clamp measurement principle is described. With the use of a generator that can generate arbitrary-type signals, many specific shapes of a voltage signal could be generated, and therefore, the experimental system is appropriate for a broad spectrum of measurements.

Mitochondrial porin incorporation into black lipid membranes: ionic and gating contribution to the total current

We present a new ac device useful for simultaneous measurements of ionic charge movement (conductance) and gating charge displacement (capacitance) in mitochondrial porin channels incorporated in two kinds of black lipid membranes (BLMs), made up of phosphatidylinositol (charged surface) and oxidized cholesterol (neutral surface). In particular, we investigated the conductance/capacitance variations during the process of porin incorporation (VDAC) at different porin concentrations. While conductance variations are present throughout the porin concentration range investigated, a threshold value seems to be necessary in order to detect a significant capacitance variation. A clear steady state in both conductance and capacitance is reached for the phosphatidylinositol bilayer, while for the oxidized cholesterol membranes, the steady state is reached only for the conductance. The dependence of capacitance characteristics on the membrane applied voltage V(m) is investigated before porin incorporation and at the ionic current steady state. The results obtained confirm that before porin incorporation, there is a small dependence on V(m)(2), while afterwards we find evidence of a dual exponential voltage dependence (a result similar to that found for conductance). Finally, we investigated the capacitance dependence on the radius of the hole separating the two compartments of the cell used in the measurements. In this study, performed only with oxidized cholesterol, the radius was varied from 200 to 1050 microm. We observed a significant variation in the specific capacitance in particular for smaller radii. The results were interpreted by a simple geometrical model taking into account the influence of the torus.

Changes of structural and dynamic properties of model lipid membranes induced by alpha-tocopherol: implication to the membrane stabilization under external electric field

The effects of alpha-tocopherol on electric properties of bilayer lipid membranes were investigated. Planar bilayer membranes formed by the Mueller-Rudin method were used. Voltammetric and chronopotentiometric measurements were performed using a four-electrode potentiostat-galvanostat. It was demonstrated that registration of membrane capacitance, resistance, and voltammetric characteristics provided information about the change in the structure and permeability of bilayer lipid membranes. The results suggested that incorporation of alpha-tocopherol into lipid membrane destabilized its structure and facilitated the electrogeneration of pores. The possible role of observed changes in physiological functions of alpha-tocopherol was discussed.

Chronopotentiometric studies of electroporation of bilayer lipid membranes

The constant-intensity current chronopotentiometric measurements of egg yolk phosphatidylcholine bilayer membranes (BLM) are presented. It is demonstrated that a constant-intensity current flowing through the bilayer membranes generates the pores in their structures. For the current intensity from 0.1 to 2.0 nA, the generated pores open and close cyclically. The frequency of oscillations depends on the current intensity: the higher current intensity, the higher frequency of pore oscillations. It is suggested that the presented method may allow to create one pore in BLM and to observe its dynamical behaviour. Based on chronopotentiometric curves, a method of pore conductance calculations is presented. It is demonstrated that the value of obtained conductance can be applied for pore diameter estimation. The hypothetical application of constant-current method as a biotechnological tool for selective and controlled incorporation of molecules into microorganisms is discussed.