Internal configuration and electric potential in planar negatively charged lipid head group region in contact with ionic solution.

The lipid bilayer composed of negatively charged lipid 1-palmitoyl-3-oleoyl-sn-glycero-3-phosphatidylserine (POPS) in contact with an aqueous solution of monovalent salt ions was studied theoretically by using the mean-field modified Langevin-Poisson-Boltzmann (MLPB) model. The MLPB results were tested by using molecular dynamic (MD) simulations. In the MLPB model the charge distribution of POPS head groups is theoretically described by the negatively charged surface which accounts for negatively charged phosphate groups, while the positively charged amino groups and negatively charged carboxylate groups are assumed to be fixed on the rod-like structures with rotational degree of freedom. The spatial variation of relative permittivity, which is not considered in the well-known Gouy-Chapman (GC) model or in MD simulations, is thoroughly derived within a strict statistical mechanical approach. Therefore, the spatial dependence and magnitude of electric potential within the lipid head group region and its close vicinity are considerably different in the MLPB model from the GC model. The influence of the bulk salt concentration and temperature on the number density profiles of counter-ions and co-ions in the lipid head group region and aqueous solution along with the probability density function for the lipid head group orientation angle was compared and found to be in qualitative agreement in the MLPB and MD models.

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.

Feasibility of employing model-based optimization of pulse amplitude and electrode distance for effective tumor electropermeabilization.

In electrochemotherapy (ECT) electropermeabilization, parameters (pulse amplitude, electrode setup) need to be customized in order to expose the whole tumor to electric field intensities above permeabilizing threshold to achieve effective ECT. In this paper, we present a model-based optimization approach toward determination of optimal electropermeabilization parameters for effective ECT. The optimization is carried out by minimizing the difference between the permeabilization threshold and electric field intensities computed by finite element model in selected points of tumor. We examined the feasibility of model-based optimization of electropermeabilization parameters on a model geometry generated from computer tomography images, representing brain tissue with tumor. Continuous parameter subject to optimization was pulse amplitude. The distance between electrode pairs was optimized as a discrete parameter. Optimization also considered the pulse generator constraints on voltage and current. During optimization the two constraints were reached preventing the exposure of the entire volume of the tumor to electric field intensities above permeabilizing threshold. However, despite the fact that with the particular needle array holder and pulse generator the entire volume of the tumor was not permeabilized, the maximal extent of permeabilization for the particular case (electrodes, tissue) was determined with the proposed approach. Model-based optimization approach could also be used for electro-gene transfer, where electric field intensities should be distributed between permeabilizing threshold and irreversible threshold-the latter causing tissue necrosis. This can be obtained by adding constraints on maximum electric field intensity in optimization procedure.

Optimisation of pulse parameters in vitro for in vivo electrochemotherapy.

The aim of our study was to optimise electric pulse parameters for electrochemotherapy by sampling the space of pulse parameter variables using systematic in vitro experiments. For this purpose we defined parameters that describe the effectiveness of different sets of electric pulse parameters in vitro and combined them into an objective function that characterises requirements for successful electrochemotherapy. The objective function values were calculated for all the sets of electric pulse parameters included in in vitro experiments. Similar values were grouped together by hierarchical clustering. The 'electrochemotherapeutic' effectiveness of two sets of pulse parameters (8 pulses, 100 micros, 1 Hz and 1 pulse, 1000 micros, 1 Hz), which belong to the most efficient cluster, and one set of pulse parameters (16 pulses, 20 ms, 1 Hz), which belongs to the least efficient cluster, was tested in vivo on a murine tumor model. The sets of pulse parameters from the most efficient cluster had comparable effects in vivo, while the electrochemotherapy with the set of pulse parameters from the least efficient cluster was less effective. Our results demonstrated that electric pulse parameters for effective in vivo application can be determined from in vitro experiments considering application specifications.

Inter-pulse interval between rectangular voltage pulses affects electroporation threshold of artificial lipid bilayers.

This paper describes experiments that determine how the inter-pulse interval between rectangular pulses in a train of pulses alters the threshold of electroporation of 1-pamitoyl 2-oleoyl phosphatidycholine bilayer lipid membranes. The bilayers were exposed to a train of sixteen 100-micros duration pulses. Threshold voltage and the sequence number of the pulse in the train, where onset of the electroporation occurred, were recorded for six inter-pulse intervals (infinity, 1000 micros, 100 micros, 10 micros, 1 micros, 0 micros). The threshold voltage of the pulse train decreased linearly with the logarithm of the inter-pulse interval. When the inter-pulse interval was 1 microm, electroporation threshold dropped to that of a single pulse with duration 1600 micros (equal to the sum of all pulse durations in the train). In this case, the occurrence of bilayer rupture was almost equally frequent for all pulses in the train. When the inter-pulse interval between the pulses exceeded 1 micros, the influence of the previous pulse on the response to the following pulse declined. It became more likely that the bilayer ruptured during the first half of the train. These experimental observations suggest that a train of pulses applied with short inter-pulse interval (less than 1 ms) can lower the electroporation threshold of bilayer lipid membranes.