Electroporation can cause artefacts due to solubilization of cations from the electrode plates. Aluminum ions enhance conversion of inositol 1,3,4,5-tetrakisphosphate into inositol 1,4,5-trisphosphate in electroporated L1210 cells

Application of pulsed electric field technology to skin engineering

Tissue engineering encompasses a range of techniques that direct the growth of cells into a living tissue construct for regenerative medicine applications, disease models, drug discovery, and safety testing. These techniques have been implemented to alleviate the clinical burdens of impaired healing of skin, bone, and other tissues. Construct development requires the integration of tissue-specific cells and/or an extracellular matrix-mimicking biomaterial for structural support. Production of such constructs is generally expensive and environmentally costly, thus eco-sustainable approaches should be explored. Pulsed electric field (PEF) technology is a nonthermal physical processing method commonly used in food production and biomedical applications. In this review, the key principles of PEF and the application of PEF technology for skin engineering will be discussed, with an emphasis on how PEF can be applied to skin cells to modify their behaviour, and to biomaterials to assist in their isolation or sterilisation, or to modify their physical properties. The findings indicate that the success of PEF in tissue engineering will be reliant on systematic evaluation of key parameters, such as electric field strength, and their impact on different skin cell and biomaterial types. Linking tangible input parameters to biological responses critical to healing will assist with the development of PEF as a sustainable tool for skin repair and other tissue engineering applications.

Nanosecond electric pulses are equally effective in electrochemotherapy with cisplatin as microsecond pulses

BACKGROUND

Nanosecond electric pulses showed promising results in electrochemotherapy, but the underlying mechanisms of action are still unexplored. The aim of this work was to correlate cellular cisplatin amount with cell survival of cells electroporated with nanosecond or standardly used 8 × 100 μs pulses and to investigate the effects of electric pulses on cisplatin structure.

MATERIALS AND METHODS

Chinese hamster ovary CHO and mouse melanoma B16F1 cells were exposed to 1 × 200 ns pulse at 12.6 kV/cm or 25 × 400 ns pulses at 3.9 kV/cm, 10 Hz repetition rate or 8 × 100 μs pulses at 1.1 (CHO) or 0.9 (B16F1) kV/cm, 1 Hz repetition rate at three cisplatin concentrations. Cell survival was determined by the clonogenic assay, cellular platinum was measured by inductively coupled plasma mass spectrometry. Effects on the structure of cisplatin were investigated by nuclear magnetic resonance spectroscopy and high-resolution mass spectrometry.

RESULTS

Nanosecond pulses equivalent to 8 × 100 μs pulses were established in vitro based on membrane permeabilization and cell survival. Equivalent nanosecond pulses were equally efficient in decreasing the cell survival and accumulating cisplatin intracellularly as 8 × 100 μs pulses after electrochemotherapy. The number of intracellular cisplatin molecules strongly correlates with cell survival for B16F1 cells, but less for CHO cells, implying the possible involvement of other mechanisms in electrochemotherapy. The high-voltage electric pulses did not alter the structure of cisplatin.

CONCLUSIONS

Equivalent nanosecond pulses are equally effective in electrochemotherapy as standardly used 8 × 100 μs pulses.

Cytotoxicity of a Cell Culture Medium Treated with a High-Voltage Pulse Using Stainless Steel Electrodes and the Role of Iron Ions

High-voltage pulses applied to a cell suspension cause not only cell membrane permeabilization, but a variety of electrolysis reactions to also occur at the electrode–solution interfaces. Here, the cytotoxicity of a culture medium treated by a single electric pulse and the role of the iron ions in this cytotoxicity were studied in vitro. The experiments were carried out on mouse hepatoma MH-22A, rat glioma C6, and Chinese hamster ovary cells. The cell culture medium treated with a high-voltage pulse was highly cytotoxic. All cells died in the medium treated by a single electric pulse with a duration of 2 ms and an amplitude of just 0.2 kV/cm. The medium treated with a shorter pulse was less cytotoxic. The cell viability was inversely proportional to the amount of electric charge that flowed through the solution. The amount of iron ions released from the stainless steel anode (>0.5 mM) was enough to reduce cell viability. However, iron ions were not the sole reason of cell death. To kill all MH-22A and CHO cells, the concentration of Fe³⁺ ions in a medium of more than 2 mM was required.

Optimised Electroporation for Loading of Extracellular Vesicles with Doxorubicin

The clinical use of chemotherapeutics is limited by several factors, including low cellular uptake, short circulation time, and severe adverse effects. Extracellular vesicles (EVs) have been suggested as a drug delivery platform with the potential to overcome these limitations. EVs are cell-derived, lipid bilayer nanoparticles, important for intercellular communication. They can transport bioactive cargo throughout the body, surmount biological barriers, and target a variety of tissues. Several small molecule drugs have been successfully incorporated into the lumen of EVs, permitting efficient transport to tumour tissue, increasing therapeutic potency, and reducing adverse effects. However, the cargo loading is often inadequate and refined methods are a prerequisite for successful utilisation of the platform. By systematically evaluating the effect of altered loading parameters for electroporation, such as total number of EVs, drug to EV ratio, buffers, pulse capacitance, and field strength, we were able to distinguish tendencies and correlations. This allowed us to design an optimised electroporation protocol for loading EVs with the chemotherapeutic drug doxorubicin. The loading technique demonstrated improved cargo loading and EV recovery, as well as drug potency, with a 190-fold increased response compared to naked doxorubicin.

Aluminum particles generated during millisecond electric pulse application enhance adenovirus-mediated gene transfer in L929 cells

Gene electrotransfer is an attractive method of non-viral gene delivery. However, the mechanism of DNA penetration across the plasma membrane is widely discussed. To explore this process for even larger structures, like viruses, we applied various combinations of short/long and high/low-amplitude electric pulses to L929 cells, mixed with a human adenovirus vector expressing GFP. We observed a transgene expression increase, both in the number of GFP-converted cells and GFP levels, when we added a low-voltage/millisecond-pulse treatment to the adenovirus/cell mixture. This increase, reflecting enhanced virus penetration, was proportional to the applied electric field amplitude and pulse number, but was not associated with membrane permeabilization, nor to direct cell modifications. We demonstrated that this effect is mainly due to adenovirus particle interactions with aggregated aluminum particles released from energized electrodes. Indeed, after centrifugation of the pulsed viral suspension and later on addition to cells, the activity was found mainly associated with the aluminum aggregates concentrated in the lower fraction and was proportional to generated quantities. Overall, this work focused on the use of electrotransfer to facilitate the adenovirus entry into cell, demonstrating that modifications of the penetrating agent can be more important than modifications of the target cell for transfer efficacy.

Continuum analysis to assess field enhancements for tailoring electroporation driven by monopolar or bipolar pulsing based on nonuniformly distributed nanoparticles

Recent reports indicate that nanoparticle (NP) clusters near cell membranes could enhance local electric fields, leading to heightened electroporation. This aspect is quantitatively analyzed through numerical simulations whereby time dependent transmembrane potentials are first obtained on the basis of a distributed circuit mode, and the results then used to calculate pore distributions from continuum Smoluchowski theory. For completeness, both monopolar and bipolar nanosecond-range pulse responses are presented and discussed. Our results show strong increases in TMP with the presence of multiple NP clusters and demonstrate that enhanced poration could be possible even over sites far away from the poles at the short pulsing regime. Furthermore, our results demonstrate that nonuniform distributions would work to enable poration at regions far away from the poles. The NP clusters could thus act as distributed electrodes. Our results were roughly in line with recent experimental observations.

Electroporation with nanosecond pulses and bleomycin or cisplatin results in efficient cell kill and low metal release from electrodes

Nanosecond electric pulses have several potential advantages in electroporation-based procedures over the conventional micro- and millisecond pulses including low level of heating, reduced electrochemical reactions and reduced muscle contractions making them alluring for use in biomedicine and food industry. The aim of this study was to evaluate if nanosecond pulses can enhance the cytotoxicity of chemotherapeutics bleomycin and cisplatin in vitro and to quantify metal release from electrodes in comparison to 100 μs pulses commonly used in electrochemotherapy. The effects of nanosecond pulse parameters (voltage, pulse duration, number of pulses) on cell membrane permeabilization, resealing and on cell survival after electroporation only and after electrochemotherapy with bleomycin and cisplatin were evaluated on Chinese hamster ovary cells. Application of permeabilizing nanosecond pulses in combination with chemotherapeutics resulted in successful cell kill. Higher extracellular concentrations of bleomycin - but not cisplatin - were needed to achieve the same decrease in cell survival with nanosecond pulses as with eight 100 μs pulses, however, the tested bleomycin concentrations were still considerably lower compared to doses used in clinical practice. Decreasing the pulse duration from microseconds to nanoseconds and concomitantly increasing the amplitude to achieve the same biological effect resulted in reduced release of aluminum ions from electroporation cuvettes.

Efficiency and cell viability implications using tip type electroporation in zebrafish sperm cells

Sperm-mediated gene transfer (SMGT) has a potential use for zebrafish transgenesis. However, transfection into fish sperm cells still needs to be improved. The objective was to demonstrate the feasibility of tip type electroporation in zebrafish sperm, showing a protocol that provide high transfection efficiency, with minimal side-effects. Sperm was transfected with a Cy3-labelled DNA using tip type electroporation with voltages ranging from 500 to 1500 V. Sperm kinetics parameters were assessed using Computer Assisted Semen Analysis (CASA) and cell integrity, reactive oxygen species (ROS), mitochondrial functionality and transfection rate were evaluated by flow cytometry. The transfection rates were positively affected by tip type electroporation, reaching 64.9% ± 3.6 in the lowest voltage used (500 V) and 86.6% ± 1.9 in the highest (1500 V). The percentage of overall motile sperm in the electrotransfected samples was found to decrease with increasing field strength (P < 0.05). Increase in the sperm damaged plasma membrane was observed with increasing field strength (P < 0.05). ROS and sperm mitochondrial functionality did not present a negative response after the electroporation (P > 0.05). Overall results indicate that tip type electroporation enhances the internalization of exogenous DNA into zebrafish sperm cells with minimal harmful effects to sperm cells.

Electrofusion by a bipolar pulsed electric field: Increased cell fusion efficiency for monoclonal antibody production

The excessive cell death rate caused by electrofusion with unipolar pulses (UPs) has been a bottleneck to increasing cell fusion efficiency in monoclonal antibody technology. Several studies have confirmed that compared with UPs, bipolar pulses (BPs) with microsecond pulse widths can increase electropermeabilization while reducing cell death. Given these characteristics, BPs were used to increase cell fusion efficiency in this study. Cell staining and hybridoma culture experiments were performed using SP2/0 mouse myeloma cells and lymphocytes. Based on the equal energy principle, UPs and BPs were delivered to electrodes at a distance of 3.81 mm, with electric field intensities ranging from 2 kV/cm to 3 kV/cm and pulse duration of 40 μs for the UPs and 20-20 μs for the BPs. The results of cell staining experiments showed that cell fusion efficiency was 3-fold greater with BPs than with UPs. Similarly, the results of the hybridoma culture experiments showed that the hybridoma yields were 0.26‰ and 0.23‰ (2.5 kV/cm and 3 kV/cm, respectively) in the UP groups and increased to 0.46‰ and 0.35‰ in the BP groups. Taken together, the results show that the efficiency of heterologous cell fusion can be greatly increased if BPs are used instead of the commonly applied UPs. This study may provide a promising method for monoclonal antibody technology.

Intracellular Delivery by Membrane Disruption: Mechanisms, Strategies, and Concepts

Intracellular delivery is a key step in biological research and has enabled decades of biomedical discoveries. It is also becoming increasingly important in industrial and medical applications ranging from biomanufacture to cell-based therapies. Here, we review techniques for membrane disruption-based intracellular delivery from 1911 until the present. These methods achieve rapid, direct, and universal delivery of almost any cargo molecule or material that can be dispersed in solution. We start by covering the motivations for intracellular delivery and the challenges associated with the different cargo types-small molecules, proteins/peptides, nucleic acids, synthetic nanomaterials, and large cargo. The review then presents a broad comparison of delivery strategies followed by an analysis of membrane disruption mechanisms and the biology of the cell response. We cover mechanical, electrical, thermal, optical, and chemical strategies of membrane disruption with a particular emphasis on their applications and challenges to implementation. Throughout, we highlight specific mechanisms of membrane disruption and suggest areas in need of further experimentation. We hope the concepts discussed in our review inspire scientists and engineers with further ideas to improve intracellular delivery.

Improvement in Electrotransfection of Cells Using Carbon-Based Electrodes

Electrotransfection has been widely used as a versatile, non-viral method for gene delivery. However, electrotransfection efficiency (eTE) is still low and unstable, compared to viral methods. To understand potential mechanisms of the unstable eTE, we investigated effects of electrode materials on eTE and viability of mammalian cells. Data from the study showed that commonly used metal electrodes generated a significant amount of particles during application of pulsed electric field, which could cause precipitation of plasmid DNA from solutions, thereby reducing eTE. For aluminum electrodes, the particles were composed of aluminum hydroxide and/or aluminum oxide, and their median sizes were 300 to 400 nm after the buffer being pulsed 4 to 8 times at 400 V cm^-1, 5 ms duration and 1 Hz frequency. The precipitation could be prevented by using carbon (graphite) electrodes in electrotransfection experiments. The use of carbon electrodes also increased cell viability. Taken together, the study suggested that electrodes made of inner materials were desirable for electrotransfection of cells in vitro.

Disinfection and toxicological assessments of pulsed UV and pulsed-plasma gas-discharge treated-water containing the waterborne protozoan enteroparasite Cryptosporidium parvum

We report for the first time on the comparative use of pulsed-plasma gas-discharge (PPGD) and pulsed UV light (PUV) for the novel destruction of the waterborne enteroparasite Cryptosporidium parvum. It also describes the first cyto-, geno- and ecotoxicological assays undertaken to assess the safety of water decontaminated using PPGD and PUV. During PPGD treatments, the application of high voltage pulses (16 kV, 10 pps) to gas-injected water (N2 or O2, flow rate 2.5L/min) resulted in the formation of a plasma that generated free radicals, ultraviolet light, acoustic shock waves and electric fields that killed ca. 4 log C. parvum oocysts in 32 min exposure. Findings showed that PPGD-treated water produced significant cytotoxic properties (as determined by MTT and neutral red assays), genotoxic properties (as determined by comet and Ames assays), and ecotoxic properties (as determined by Microtox™, Thamnotox™ and Daphnotox™ assays) that are representative of different trophic levels in aquatic environment (p<0.05). Depending in part on the type of injected gas used, PPGD-treated water became either alkaline (pH ≤ 8.58, using O2) or acidic (pH ≥ 3.21, using N2) and contained varying levels of reactive free radicals such as ozone (0.8 mg/L) and/or dissociated nitric and nitrous acid that contributed to the observed disinfection and toxicity. Chemical analysis of PPGD-treated water revealed increasing levels of electrode metals that were present at ≤ 30 times the tolerated respective values for EU drinking water. PUV-treated water did not exhibit any toxicity and was shown to be far superior to that of PPGD for killing C. parvum oocysts taking only 90 s of pulsing [UV dose of 6.29 μJ/cm(2)] to produce a 4-log reduction compared to a similar reduction level achieved after 32min PPGD treatment as determined by combined in vitro CaCo-2 cell culture-qPCR.

Micro-/nanofluidics based cell electroporation

Non-viral gene delivery has been extensively explored as the replacement for viral systems. Among various non-viral approaches, electroporation has gained increasing attention because of its easy operation and no restrictions on probe or cell type. Several effective systems are now available on the market with reasonably good gene delivery performance. To facilitate broader biological and medical applications, micro-/nanofluidics based technologies were introduced in cell electroporation during the past two decades and their advances are summarized in this perspective. Compared to the commercially available bulk electroporation systems, they offer several advantages, namely, (1) sufficiently high pulse strength generated by a very low potential difference, (2) conveniently concentrating, trapping, and regulating the position and concentration of cells and probes, (3) real-time monitoring the intracellular trafficking at single cell level, and (4) flexibility on cells to be transfected (from single cell to large scale cell population). Some of the micro-devices focus on cell lysis or fusion as well as the analysis of cellular properties or intracellular contents, while others are designed for gene transfection. The uptake of small molecules (e.g., dyes), DNA plasmids, interfering RNAs, and nanoparticles has been broadly examined on different types of mammalian cells, yeast, and bacteria. A great deal of progress has been made with a variety of new micro-/nanofluidic designs to address challenges such as electrochemical reactions including water electrolysis, gas bubble formation, waste of expensive reagents, poor cell viability, low transfection efficacy, higher throughput, and control of transfection dosage and uniformity. Future research needs required to advance micro-/nanofluidics based cell electroporation for broad life science and medical applications are discussed.

Single cell electroporation using microfluidic devices

Electroporation is a powerful technique to increase the permeability of cell membranes and subsequently introduce foreign materials into cells. Pores are created in the cell membrane upon application of an electric field (kV/cm). Most applications employ bulk electroporation, at the scale of 1 mL of cells (ca. one million cells). However, recent progresses have shown the interest to miniaturize the technique to a single cell. Single cell electroporation is achieved either using microelectrodes which are placed in close vicinity to one cell, or in a microfluidic format. We focus here on this second approach, where individual cells are trapped in micrometer-size structures within a microchip, exposed in situ to a high electric field and loaded with either a dye (proof-of-principle experiments) or a plasmid. Specifically, we present one device that includes an array of independent electroporation sites for customized and successive poration of nine cells. The different steps of the single cell electroporation protocol are detailed including cell sample preparation, cell trapping, actual cell poration and on-chip detection of pore formation. Electroporation is illustrated here with the transport of dyes through the plasma membrane, the transfection of cells with GFP-encoding plasmids, and the study of the ERK1 signaling pathway using a GFP-ERK1 protein construct expressed by the cells after their transfection with the corresponding plasmid. This last example highlights the power of microfluidics with the implementation of various steps of a process (cell poration, culture, imaging) performed at the single cell level, on a single device.

The Effect of Electroporation Type Pulsed Electric Fields on DNA in Aqueous Solution

Electroporation is a physical phenomenon in which pulsed electric fields applied across a cell produce transient (reversible) or permanent (irreversible) permeabilization of the cell membrane. Irreversible electroporation is an important method of sterilization in the food industry and it is becoming an important minimally invasive tissue ablation technique in medicine. Motivated by recent observations of apoptosis like marker stains in irreversibly electroporated cells we performed a study on the effects of electroporation type electric pulses on the integrity of naked DNA in solution. Using gel electrophoresis analyses we show that pulses of the irreversible electroporation type have the ability to affect the naked DNA in solution. It is found that some electric parameters that lead to cell death by irreversible electroporation also cause changes in the naked DNA exposed to the same procedure. Our analysis tentatively suggests that some electroporation type electric pulses cause nicks in the DNA molecule. Therefore, it is possible that the mechanisms of cell death in irreversible electroporation also include damages to the DNA. However, this work did not investigate the possible effects of electroporation induced electrode corrosion byproducts, such as Al3+ ions on DNA integrity; which should be also studied in the future. In general, since electroporation phenomena based applications are widely used in medicine and biotechnology, the current study suggests that further research into the effects of electroporation type electric pulses on the DNA are warranted.

Spectral alteration and degradation of cyanidin-3-glucoside exposed to pulsed electric field

Anthocyanins are polyphenol antioxidants that have been shown to prevent many chronic diseases. The compounds are not stable, so they tend to be decolorized or degraded during processing and storage. In this study, the spectral characteristics alteration and degradation products of cyanidin-3-glucoside (Cyd-3-glc) exposed to pulsed electric field (PEF) were investigated, and the reaction kinetics was discussed. The intensity of the UV-vis spectra decreased noticeably upon PEF treatment without modification of the spectral pattern. Protocatechuic acid and 2,4,6-trihydroxybenzoic acid were identified as degradation products of both PEF and thermally treated Cyd-3-glc, but cyanidin present in thermally treated Cyd-3-glc was absent in PEF-treated Cyd-3-glc, indicating that the first step of Cyd-3-glc degradation induced by PEF was not the hydrolysis of glycosidic bonds, which was different from that of thermal degradation. With increased electric field intensity or treatment time, the degradation of Cyd-3-glc and the formation of protocatechuic acid were enhanced; their kinetics (except 7 kV/cm for protocatechuic acid formation) were well fitted to a first-order reaction. Meanwhile, a good correlation was present between Cyd-3-glc degradation and protocatechuic acid formation.

Increase of the roughness of the stainless-steel anode surface due to the exposure to high-voltage electric pulses as revealed by atomic force microscopy

The changes of the stainless-steel electrode surface morphology occurring due to dissolution of the anode under the action of electric pulses which are commonly utilized in cell electromanipulation procedures, have been studied by using atomic force microscopy. The surface of the polished electrode was rather smooth--the average roughness was 13-17 nm and the total roughness 140-180 nm. After the treatment of the chamber filled with 154 mM NaCl solution to a series of short (about 20 mus), high-voltage (4 kV) pulses, the roughness of the surface of the anode has increased, depending on the total amount of the electric charge that has passed through the unit area of the electrode, and exceeded 400 nm for the dissolution charge of 0.24 A s/cm(2). No changes of the cathode surface were detected. Well-defined peaks with the width of 1-2 mum and the height of over 400 nm have appeared. These peaks create local enhancements of the electric field at the interface between the solution and the electrode surface which can lead to the non-homogeneity treatment of cells by electric pulses and can facilitate the occurrence of the electrical breakdown of the liquid samples.

Nanosecond pulsed electric field generators for the study of subcellular effects

Modeling and experimental studies have shown that pulsed electric fields of nanosecond duration and megavolt per meter amplitude affect subcellular structures but do not lead to the formation of large pores in the outer membrane. This "intracellular electromanipulation" requires the use of pulse generators which provide extremely high power but low energy pulses. In this study, we describe the concept of the required pulsed power sources, their design, operation, and the necessary diagnostics. Two types of pulse generators based on the Blumlein line principle have been developed and are described here. One system is designed to treat a large number of cells in cuvettes holding volumes from 0.1 to 0.8 ml. Pulses of up to 40 kV amplitude, with a duration of 10 ns and a rise time close to 1 ns can be applied to the cuvette. For an electrode gap of 1 mm this voltage corresponds to an average electric field of 40 MV/m. The second system allows for real time observation of individual cells under a microscope. It generates pulses of 10-300 ns duration with a rise time of 3.5 ns and voltage amplitudes up to 1 kV. Connected to a microreactor with an electrode gap of 100 microm, electric fields up to 10 MV/m are applied.

Electroporation of cells in microfluidic devices: a review

In recent years, several publications on microfluidic devices have focused on the process of electroporation, which results in the poration of the biological cell membrane. The devices involved are designed for cell analysis, transfection or pasteurization. The high electric field strengths needed are induced by placing the electrodes in close proximity or by creating a constriction between the electrodes, which focuses the electric field. Detection is usually achieved through fluorescent labeling or by measuring impedance. So far, most of these devices have only concerned themselves solely with the electroporation process, but integration with separation and detection processes is expected in the near future. In particular, single-cell content analysis is expected to add further value to the concept of the microfluidic chip. Furthermore, if advanced pulse schemes are employed, such microdevices can also enhance research into intracellular electroporation.

Plasma membrane voltage changes during nanosecond pulsed electric field exposure

The change in the membrane potential of Jurkat cells in response to nanosecond pulsed electric fields was studied for pulses with a duration of 60 ns and maximum field strengths of approximately 100 kV/cm (100 V/cell diameter). Membranes of Jurkat cells were stained with a fast voltage-sensitive dye, ANNINE-6, which has a subnanosecond voltage response time. A temporal resolution of 5 ns was achieved by the excitation of this dye with a tunable laser pulse. The laser pulse was synchronized with the applied electric field to record images at times before, during, and after exposure. When exposing the Jurkat cells to a pulse, the voltage across the membrane at the anodic pole of the cell reached values of 1.6 V after 15 ns, almost twice the voltage level generally required for electroporation. Voltages across the membrane on the side facing the cathode reached values of only 0.6 V in the same time period, indicating a strong asymmetry in conduction mechanisms in the membranes of the two opposite cell hemispheres. This small voltage drop of 0.6-1.6 V across the plasma membrane demonstrates that nearly the entire imposed electric field of 10 V/mum penetrates into the interior of the cell and every organelle.

Changes of the solution pH due to exposure by high-voltage electric pulses

The change of the pH of a NaCl solution (139-149 mM NaCl) buffered with 5-15 mM sodium phosphates (pH 7.4) during electromanipulation was studied. It has been determined that an increase in the pH value of electroporation solution of a whole chamber volume, caused by the application of electric field pulses, commonly used in cell electromanipulation procedures, can exceed 1-2 pH units. Several materials for the cathode were tested. In all cases a stainless steel anode was utilized. The aluminum cathode gave a two-fold greater DeltapH in comparison with platinum, copper or stainless steel cathodes. In addition, a substantial release of aluminum (up to 1 mg/l) from the cathode was observed. It has also been found that the shift in pH depended on the medium conductivity: DeltapH of the solution, in which sucrose was substituted for NaCl, was about 5 times less. On the basis of the results obtained here, to avoid the plausible undesirable consequences of the cathodic electrolysis processes, in particular under the conditions of strong electric treatment, it could be recommended that chambers with aluminum electrodes not be utilized and one should use strongly buffered solutions of low conductivity and alternating current (sine or square wave) bipolar electric pulses.

Cell membrane electropermeabilization by symmetrical bipolar rectangular pulses. Part II. Reduced electrolytic contamination

The paper presents a comparative study of the contamination of a cell suspension by ions released from aluminum cuvettes (Al(3+)) and stainless steel electrodes (Fe(2+)/Fe(3+)) during cell membrane electropermeabilization by unipolar and by symmetrical bipolar rectangular electric pulses. A single pulse and a train of eight pulses were delivered to electrodes at a 2-mm distance, with 100-micros and 1-ms pulse durations, and amplitudes ranging from 0 to 400 V for unipolar, and from 0 to 280 V for bipolar pulses. We found that the released concentrations of Al(3+) and Fe(2+)/Fe(3+) were always more than one order of magnitude lower with bipolar pulses than with unipolar pulses of the same amplitude and duration. We then investigated the viability of DC-3F cells after 1 h of incubation in the medium containing different concentrations of Al(3+) or Fe(2+)/Fe(3+) within the range of measured released concentrations (up to 2.5 mM for both ions), thus separating the effects of electrolytic contamination from the effects of electropermeabilization itself. For Fe(2+)/Fe(3+), loss of cell viability became significant at concentrations above 1.5 mM, while for Al(3+), no effect on cell survival was detected within the investigated range. Still, reports on the biochemical effects of released Al(3+) also suggest that with aluminum cuvettes, electrolytic contamination can be detrimental. Our study shows that electrolytic contamination and its detrimental effects can be largely reduced with no loss in efficiency of electropermeabilization, if bipolar rectangular pulses of the same amplitude and duration are used instead of the commonly applied unipolar pulses.

Electric pulse-induced precipitation of biological macromolecules in electroporation

We found that electric discharge through solution of biological macromolecules (DNA, RNA and proteins) causes precipitation of significant portions of these macromolecules. This precipitation is a consequence of the interaction of biological macromolecules with the metal ions solubilized from the anode plate by the electric pulse, and occurs in both absence and presence of the cells in poration medium. Precipitated fractions of macromolecules sediments at the centrifugation speed used to pellet eukaryotic cells and does not dissolve when washed with buffer. Our data indicate a complication of the direct evaluation of electroporation efficiency based on the assumption that electroporated biological macromolecules which remain associated with the cells after several washes, are successfully electroinjected into the cytoplasm of cells.

Modulation of Ins(2,4,5)P3-stimulated Ca2+ mobilization by ins(1,3,4, 5)P4: enhancement by activated G-proteins, and evidence for the involvement of a GAP1 protein, a putative Ins(1,3,4,5)P4 receptor

We have previously shown that addition of Ins(1,3,4,5)P4 to permeabilized L1210 cells increases the amount of Ca2+ mobilized by a submaximal concentration of Ins(2,4,5)P3, and we suggested that, in doing this, Ins(1,3,4,5)P4 is not working via an InsP3 receptor but indirectly via an InsP4 receptor [Loomis-Husselbee, Cullen, Dreikhausen, Irvine and Dawson (1996) Biochem. J. 314, 811-816]. Here we have investigated whether this effect might be mediated by GAP1(IP4BP), recently identified as a putative receptor for Ins(1,3, 4,5)P4. GAP1(IP4BP) is a protein that interacts with one or more monomeric G-proteins, so we sought evidence for involvement of monomeric G-proteins in the effects of Ins(1,3,4,5)P4 in permeabilized L1210 cells. Guanosine 5'-[gamma-thio]triphosphate (GTP[S]) enhanced the effect of Ins(1,3,4,5)P4 on Ins(2,4, 5)P3-stimulated Ca2+ mobilization, but had no effect on the action of Ins(2,4,5)P3 alone. A specific enhancement of only the action of Ins(1,3,4,5)P4 was also seen with GTP[S]-loaded R-Ras or Rap1a (two G-proteins known to interact with GAP1(IP4BP)), whereas H-Ras was inactive at similar concentrations. Guanosine 5'-[beta-thio]diphosphate (GDP[S]) did not alter the action of either Ins(2,4,5)P3 or Ins(1,3,4,5)P4. Finally, the addition of exogenous GAP1(IP4BP), purified from platelets, markedly enhanced the effect of Ins(1,3,4,5)P4, and again, the amount of Ca2+ mobilized by Ins(2,4,5)P3 alone was unaltered. We conclude that the increase in Ins(2,4,5)P3-stimulated Ca2+ mobilization by Ins(1,3,4, 5)P4 may be mediated by GAP1(IP4BP) or a closely related protein (such as GAP1(m)), and if so, the action of the GAP1 is not solely to regulate GTP loading of a G-protein, but rather it acts with a G-protein to cause its effect.

Breaking the barrier: methods for reversible permeabilization of cellular membranes

Plasma membrane constitutes a major barrier for the entry of hydrophilic molecules into the cell interior. Selective and reversible permeabilization of this barrier is a prerequisite for many biotechnological applications. This article reviews general principles of membrane permeabilization based on biological, chemical, and physical methods and mechanisms of the delivery of extrinsic substances to cell interior. The emphasis is given on the methods that have significantly contributed to our understanding of biological phenomena on membrane level or have been widely used in current biotechnology, such as delivery by membrane vehicles, electropermeabilization, microinjection, and biolistics. The mechanisms of the internalization of extrinsic substances and the advantages and drawbacks of individual techniques are discussed with respect to specific applications in biotechnology.

Synergistic effects of inositol 1,3,4,5-tetrakisphosphate on inositol 2,4,5-triphosphate-stimulated Ca2+ release do not involve direct interaction of inositol 1,3,4,5-tetrakisphosphate with inositol triphosphate-binding sites

We have previously found that for permeabilized L1210 cells, low micromolar concentrations of Ins(1,3,4,5)P4 added prior to Ins(2,4,5)P3 enhance the effects of suboptimal concentrations of Ins(2,4,5)P3 in causing Ca2+ release from InsP3-sensitive Ca2+ stores [Cullen, Irvine and Dawson (1990) Biochem J. 271, 549-553]. If this was due either to some conversion of added Ins(1,3,4,5)P4 into Ins(1,4,5)P3 by the 3-phosphatase, or to Ins(1,3,4,5)P4 acting as a weak (or partial) agonist on the InsP3 receptor it would be expected that,in the presence of thimerosal to sensitize the InsP3 receptor, the dose-response curve to Ins(1,3,4,5)P4 would be left-shifted by the same extent as that of Ins(1,4,5)P3. This was found not to be the case; the dose-response curve to Ins(1,3,4,5)P4 was not shifted at all by thimerosal. Furthermore, L-Ins(1,3,4,5)P4, which can displace radiolabelled D-Ins(1,3,4,5)P4 but not D-Ins(1,4,5)P3 from their respective high-affinity binding sites, mimicked the effects of D-Ins(1,3,4,5)P4 in enhancing the slow phase of Ins(2,4,5)P3-stimulated Ca2+ release. Ins(1,3,4,5)P4 caused an increase in magnitude of the slow phase of InsP3-stimulated Ca2+ release leaving the magnitude of the fast phase unaltered, in contrast to increasing Ins(2,4,5)P3 concentrations which increased the size of both phases. In addition, Ins(1,3,4,5)P4 decreased the rate constant for the slow phase of Ca2+ release. These findings point strongly to the conclusion that InsP4 is not working directly via the InsP3 receptor but indirectly via an InsP4 receptor.

Spatial compartmentation and time resolution of photooxidation of a cell membrane probe in electropermeabilized Chinese hamster ovary cells

When electropulsed by short strong electric field pulses, cells can be permeabilized transiently (electropermeabilization). The transient electroinduced membrane restructuration which supports enhanced membrane permeability is topologically well defined on the surface of the cell. Exchange of polar species only takes place on the part of the cell surface which is controlled by the field intensity. Electropermeabilization is a stress for the cell and metabolic responses associated with this stress must be studied. A key point is to discover whether this stress affects the whole cell surface or especially the permeabilized part. This was investigated by photochemical time-dependent methodology. Analysis of the photooxidation reaction of 5-(N-hexadecanoyl)-aminofluorescein, an interfacial light-sensitive fluorescent probe, inserted into the Chinese hamster ovary cell membrane showed that the rate of reaction was accelerated when the cell population was electropermeabilized. This increase in the rate constant depended on the field strength. A theoretical approach suggested that modulation of the photooxidation reaction was restricted to the electropermeabilized part of the cell surface. The difference of reactivity could be correlated with an activator effect of oxygen-reactive species generated by an electro-induced oxidative jump and suggested that these species were localized in the permeabilized part of the plasma membrane. Using fluorescence digitized videomicroscopy imaging on a single cell, such spatial heterogeneity of the photooxidation reaction was indeed directly observed when the cell was electropermeabilized. There was heterogeneous compartmentation of the membrane reaction into two independent domains with specific reactivity. The direct observation is that long-lived electropermeabilization only affects a restricted part of the pulsed cell surface, from both a structural and a metabolic point of view.

Effects of aluminium on the hepatic inositol polyphosphate phosphatase

There is speculation that some of the toxic effects of Al3+ may originate from it perturbing inositol phosphate/Ca2+ signalling. For example, in permeabilized L1210 mouse lymphoma cells, 10-50 microM Al3+ activated Ins(1,3,4,5)P4-dependent Ca2+ mobilization and Ins(1,3,4,5)P4 3-phosphatase activity [Loomis-Husselbee, Cullen, Irvine and Dawson (1991) Biochem. J. 277, 883-885]. Ins(1,3,4,5)P4 3-phosphatase activity is performed by a multiple inositol polyphosphate phosphatase (MIPP) that also attacks Ins(1,3,4,5,6)P5 and InsP6 [Craxton, Ali and Shears (1995) Biochem. J. 305, 491-498]: 5-50 microM Al3+ increased MIPP activity towards both Ins(1,3,4,5)P4 (by 30%) and Ins(1,3,4,5,6)P5 (by up to 500%), without affecting metabolism of InsP6. Higher concentrations of Al3+ inhibited metabolism of all three substrates, and in the case of InsP6, Al3+ altered the pattern of accumulating products. When 1-50 microM Al3+ was present, InsP6 became a less effective inhibitor of Ins(1,3,4,5)P4 3-phosphatase activity; this effect did not depend on the presence of cellular membranes, contrary to a previous proposal. The latter phenomenon largely explains how, in a cell-free system where Ins(1,3,4,5)P4 3-phosphatase is inhibited by endogenous InsP6, the addition of Al3+ can apparently increase the enzyme activity. However, there was no effect of either 10 or 25 microM Al3+ (in either the presence or absence of apotransferrin) on inositol phosphate profiles in either Jurkat E6-1 lymphoma cells or AR4-2J pancreatoma cells.

The intracellular distribution of inositol polyphosphates in HL60 promyeloid cells

1. HL60 promyeloid cells contain high intracellular concentrations of inositol polyphosphates, notably inositol 1,3,4,5,6-pentakisphosphate (InsP5) and inositol hexakisphosphate (InsP6). To determine their intracellular location(s), we studied the release of inositol (poly)phosphates, of ATP, and of cytosolic and granule-enclosed enzymes from cells permeabilized by four different methods. 2. When cells were treated with digitonin, all of the inositol phosphates were released in parallel with the cytosolic constituents. Most of the InsP5 and InsP6 was released before significant permeabilization of azurophil granules. 3. Similar results were obtained from cells preloaded with ethylene glycol and permeabilized by osmotic lysis. 4. Electroporation at approximately 500 V/cm caused rapid release of free inositol. Higher field strengths provoked release of most of the ATP, InsP5 and InsP6, but only slight release of the intracellular enzymes. Multiple discharges released approximately 80-90% of total InsP5 and InsP6. In the absence of bivalent-cation chelators, InsP5 and InsP6 were released less readily than ATP. 5. Treatment of cells with Staphylococcus aureus alpha-toxin caused quantitative release of inositol and ATP, without release of intracellular enzymes. However, inositol phosphates were released much less readily than inositol or ATP. Even after prolonged incubation with a high concentration of alpha-toxin, only approximately 50-70% of InsP2, InsP3 and InsP4 and < or = 20% of InsP5 and InsP6 were released, indicating that the high charge or large hydrated radius of InsP5 and InsP6 might limit their release through small toxin-induced pores. 6. These results indicate that most intracellular inositol metabolites are either in, or in rapid exchange with, the cytosolic compartment of HL60 cells. However, they leave open the possibility that a small proportion of cellular InsP5 and InsP6 (< or = 10-20%) might be in some intracellular bound form.

Generation of reactive-oxygen species induced by electropermeabilization of Chinese hamster ovary cells and their consequence on cell viability

Cells can be permeabilized transiently when pulsed by a brief intense external electric field. The molecular and cellular bases of cell electropermeabilization are still unclear. This process can be described by a local transient membrane organisation in which high permeability exists. In this study, using the chemiluminescent probe lucigenin, we showed that electropulsation of Chinese hamster ovary cells induced generation of reactive oxygen species at the electropermeabilized cell level. This generation was directly associated with the part of the membrane surface which is electrically restructured, as shown by its dependence on electric parameters. The electroinduced cell process was activated by Ca2+ and Mg2+ ions, and by exogenous adenosine 5'-triphosphate. A metal-ion-catalyzed Haber-Weiss reaction was thought to occur in the process, as shown by the action of effector molecules of Haber-Weiss reaction such as the chelating agent EDTA, and the hydroxyl radical scavenger dimethylsulfoxide. The modulation of the oxygen species electroinduction and the use of antioxidant products (dimethylsulfoxide, sodium L-ascorbate) showed that cell survival after electric treatment was directly correlated to the oxidative jump intensity. This observation had to be associated with the cell-damaging action of oxygen-reactive species.

Aluminium inhibits muscarinic agonist-induced inositol 1,4,5-trisphosphate production and calcium mobilization in permeabilized SH-SY5Y human neuroblastoma cells

The effects of aluminium (as Al3+) on carbachol-induced inositol 1,4,5-trisphosphate (InsP3) production and Ca2+ mobilisation were assessed in electropermeabilised human SH-SY5Y neuroblastoma cells. Al3+ had no effect on InsP3-induced Ca2+ release but appreciably reduced carbachol-induced Ca2+ release (IC50 of approximately 90 microM). Al3+ also inhibited InsP3 production (IC50 of approximately 15 microM). Dimethyl hydroxypyridin-4-one, a potent Al3+ chelator (Ks = 31), at 100 microM was able to abort and reverse the effects of Al3+ on both Ca2+ release and InsP3 production. These data suggest that, in permeabilised cells, the effect of Al3+ on the phosphoinositide-mediated signalling pathway is at the level of phosphatidylinositol 4,5-bisphosphate hydrolysis. This may reflect interference with receptor-G protein-phospholipase C coupling or an interaction with phosphatidylinositol 4,5-bisphosphate.

Myo-inositol 1,3,4,5-tetrakisphosphate can independently mobilise intracellular calcium, via the inositol 1,4,5-trisphosphate receptor: studies with myo-inositol 1,4,5-trisphosphate-3-phosphorothioate and myo-inositol hexakisphosphate

Myo-inositol 1,3,4,5-tetrakisphosphate [Ins(1,3,4,5)P4] acts as a full agonist for Ca2+ release in saponin-permeabilised SH-SY5Y neuroblastoma cells. Studies were conducted in the presence of myo-inositol hexakisphosphate (InsP6, 10 microM), to inhibit the Ins(1,3,4,5)P(4)-3-phosphatase catalysed back conversion of Ins(1,3,4,5)P4 to Ins(1,4,5)P3. HPLC analysis confirmed that Ins(1,3,4,5)P4 releases the entire content of Ins(1,4,5)P3-sensitive intracellular Ca2+ stores, independent of 3-phosphatase activity. Further we utilised racemic myo-inositol 1,4,5-trisphosphate-3-phosphorothioate [DL-Ins(1,3,4,5)P(4)-3S], a novel intrinsically Ins(1,3,4,5)P(4)-3-phosphatase resistant Ins(1,3,4,5)P4 analogue. DL-Ins(1,3,4,5)P(4)-3S specifically displaced [3H]Ins(1,4,5)P3 from bovine adrenal cortex Ins(1,4,5)P3 binding sites (IC50 = 889 nM, compared to Ins(1,4,5)P3, IC50 = 4.4 nM and Ins(1,3,4,5)P4, IC50 = 152 nM). DL-Ins(1,3,4,5)P(4)-3S was a full agonist for Ca2+ release (EC50 = 4.7 microM), being 90- and 2-fold less potent than Ins(1,4,5)P3 and Ins(1,3,4,5)P4 (with InsP6), respectively. DL-Ins(1,3,4,5)P(4)-3S will be an important tool for identification of potentially exclusive Ins(1,3,4,5)P4 second messenger functions, since its resistance to 3-phosphatase action precludes the inconvenient artefact of steady state Ins(1,4,5)P3 generation.

Stereoselectivity of Ins(1,3,4,5)P4 recognition sites: implications for the mechanism of the Ins(1,3,4,5)P4-induced Ca2+ mobilization

Ins(1,3,4,5)P4 was able to mobilize the entire Ins(1,4,5)P3-sensitive intracellular Ca2+ store in saponin-permeabilized SH-SY5Y human neuroblastoma cells in a concentration-dependent manner, yielding an EC50 value of 2.05 +/- 0.45 microM, compared with 0.14 +/- 0.03 microM for Ins(1,4,5)P3. However, L-Ins(1,3,4,5)P4 [= D-Ins(1,3,5,6)P4] failed to cause mobilization of intracellular Ca2+ at concentrations up to 100 microM. Binding studies using pig cerebellar membranes as a source of both Ins(1,4,5)P3/Ins(1,3,4,5)P4-specific binding sites have revealed a marked contrast in their stereospecificity requirements. Ins(1,4,5)P3-receptors from pig cerebella exhibited stringent stereospecificity, L-Ins(1,4,5)P3 and L-Ins(1,3,4,5)P4 were > 1000-fold weaker, whereas Ins(1,3,4,5)P4 (IC50 762 +/- 15 nM) was only about 40-fold weaker than D-Ins(1,4,5)P3 (IC50 20.7 +/- 9.7 nM) at displacing specific [3H]Ins(1,4,5)P3 binding from an apparently homogeneous Ins(1,4,5)P3 receptor population. In contrast, the Ins(1,3,4,5)P4-binding site exhibited poor stereoselectivity. Ins(1,3,4,5)P4 produced a biphasic displacement of specific [32P]Ins(1,3,4,5)P4 binding, with two-site analysis revealing KD values for high- and low-affinity sites of 2.1 +/- 0.5 nM and 918 +/- 161 nM respectively. L-Ins(1,3,4,5)P4 also produced a biphasic displacement of specific [32P]Ins(1,3,4,5)P4 binding which was less than 10-fold weaker than with D-Ins(1,3,4,5)P4 (IC50 values for the high- and low-affinity sites of 17.2 +/- 3.7 nM and 3010 +/- 542 nM respectively). Therefore, although L-Ins(1,3,4,5)P4 appears to be a high-affinity Ins(1,3,4,5)P4-binding-site ligand in pig cerebellum, it is a very weak agonist at the Ca(2+)-mobilizing receptors of permeabilized SH-SY5Y cells. We suggest that the ability of D-Ins(1,3,4,5)P4 to access intracellular Ca2+ stores may derive from specific interaction with the Ins(1,4,5)P3- and not the Ins(1,3,4,5)P4-receptor population.

Sub-second oscillations of inositol 1,4,5-trisphosphate and inositol 1,3,4,5-tetrakisphosphate during platelet activation by ADP and thrombin: lack of correlation with calcium kinetics

The hypothesis that ADP and thrombin liberate Ins(1,4,5)P3 in blood platelets, with kinetics consistent for releasing Ca2+ within 2s, was tested by quenched-flow techniques. Both agonists stimulated transient and equal synthesis of Ins(1,4,5)P3 and Ins(1,3,4,5)P4 near 200 ms and later short-lived peaks, which were not correlated with the slower steady increase in intracellular [Ca2+] between 0.5 to 2 s detected by Indo-1. Shear forces alone caused transient liberation of these inositol phosphates within 0.5 s and up to 4 s, yet failed to increase intracellular [Ca2+].

Cell electropermeabilization: a new tool for biochemical and pharmacological studies

Cell electropermeabilization is the transient permeabilization of the plasma membrane by means of short and intense electric pulses. Under optimized conditions, electropermeabilization is compatible with cell survival. It provides a direct access into the cytosol to ions, small molecules, exogenous drugs and macromolecules. As cells remain functional, a large variety of cell biology questions can be addressed. Such 'in situ biochemistry' opens new possibilities beside the more classical studies dealing with unpermeabilized cells or subcellular extracts. Electropermeabilization also allows pharmacological studies with cells, cultured monolayers and in vivo tissues as well as the design of drug controlled-release systems.

Modulation of expression of endogenous collagenase and collagen genes by electroporation: possible involvement of Ca2+ and protein kinase C

We have investigated the effect of electroporation on the expression of collagen alpha 1(I), collagenase, c-fos and c-jun genes in human dermal fibroblasts (HDF), human smooth muscle cells (HSMC) and HeLa cells. Collagenase and collagen mRNA levels were respectively increased and decreased in a voltage-dependent manner in HDF harvested 2 days after a sham electroporation. These effects were still observed 10 days after electroporation. Similar effects occurred in electroporated HSMC. Neither collagen nor collagenase mRNAs were detected in control or electroporated HeLa cells. c-fos and c-jun mRNA levels were also increased in electroporated HDF, HSMC and HeLa cells harvested 1 h after plating. This suggests that factor AP1 (fos/jun) could mediate the up-regulation of collagenase expression in electroporated HDF and HSMC. When electroporation of HDF was performed in the presence of H7, an inhibitor of protein kinase C, no increase in collagenase mRNA level was observed, suggesting that protein kinase C might be involved in the transduction of the effect. All the effects reported were also suppressed when cells were electroporated in a medium containing EGTA, suggesting that Ca2+ might mediate the transduction of this effect.

A steady-state mechanism can account for the properties of inositol 2,4,5-trisphosphate-stimulated Ca2+ release from permeabilized L1210 cells

We have investigated the effects of sub-maximal Ins(2,4,5)P3 concentrations on the Ca2+ permeability of the residual undischarged Ca2+ stores in electroporated or digitonin-permeabilized L1210 cells by measuring Ca(2+)-efflux rate after addition of the ATPase inhibitor thapsigargin. Low concentrations of Ins(2,4,5)P3, causing rapid discharge of a small proportion of the releasable Ca2+, result in a substantial stimulation of Ca2+ efflux after thapsigargin addition. This indicates firstly that in the absence of thapsigargin there must have been a substantial, counterbalancing, increase in rate of Ca2+ pumping, and secondly that the increased Ca2+ permeability is more consistent with a steady state than with a quantal model of Ca2+ release. Similar increases in passive Ca2+ permeability are produced by addition of concentrations of ionomycin which produce equivalent changes in Ca2+ loading to those produced by Ins(2,4,5)P3, although the time course and initial rate of Ca2+ release are very much slower. In the presence of a Ca(2+)-buffering system, the time course of Ca2+ release by Ins(2,4,5)P3 becomes superimposable on that of ionomycin, indicating that the initial rapid phase of Ins(2,4,5)P3-stimulated Ca2+ is at least partially due to positive feedback from extravesicular Ca2+.