Heat Injary and Changes in Electrical Resistance of Leaf Tissue

More effective means are needed for early diagnosis and quantitative evaluation of plant injury caused by various stresses. Measuring of tissue electrical resistance has been used in the research of SO2 injury recently and satisfactory results has been obtained. The present paper describes the change of tissue electrical resistance in connection with the response of plants to high temperature. Wheat and tobacco leaves were tranted with different high temperatures (30–60℃). Electrical resistance was measured during and after the treatment by means of Zhu’s newly improved method of the determination of the mid-region voltake drop on passing a stable electric current through the leaf tissue. Experimental results showed that electrical resistance changed regularly with the increase of temperature. At the range of nninjurious temperature, tissue electrical resistance kept the same level as control. Around the subinjurious temperature, electrical resistance increased remarkably and could be gradually restored after the cease of treatment. At injurious temperatures, tissue electrical resistance rised at first, and then declined. The higher the temperature, the earlier and quicker the decline, and finally it reached the lowest level showing the death of the tissue. If leaves were taken back to ordinary temperature at the rising stage or just the beginning of decrease, they could recover, in general, in their electrical resistance. They conld not recover after a substantial drop of electrical resistance, showing the oeeurence of irreversible injnry. Therefore the changes of tissue electrical resistance reflected to a certain degree the extent of heat injury. Ion leakage and ethane production were also measured parallelly. As for reflection of the extent of heat injury, changes of tissue electrical resistance is more sensitive than both ion leakage and ethane produetlon. The rise of tissue electrical resistance at thc earlier stage of heat treatment is discussed in connection with the changes of the two constituents of tissue electrical resistance-membrane resistance and apoplast resistance.     

Electrical stimulation of cultured lepidopteran dorsal vessel tissue: an experiment for development of bioactuators

An insect dorsal vessel (DV) is well suited for a bioactuator since it is capable of contracting autonomously, and its tissue and cells are more environmentally robust under culturing conditions compared with mammalian tissue. In this study, electrical pulse stimulation was examined so as to regulate a bioactuator using the DV tissue. The DV tissue of a larva of Ctenoplusia agnate was assembled on a micropillar array, which was stimulated after culturing for about 3 wk. The contraction of the DV tissue was evaluated by image analysis to measure lateral displacements at the micropillar top. As a result, suitable stimulation conditions in a 35-mm petri dish were determined as: applied voltage of 10 V with 20-ms duration. Next, the time lag between the onset of electrical stimulus and the onset of mechanical contraction (electromechanical delay (EMD)) was estimated. A light-emitting diode (LED) was connected serially with the petri dish, and the LED flashed when electrical pulses were given. Movie images were analyzed in which electrical pulses made the DV tissue contract and the LED flashed virtually simultaneously; from these, the EMD was estimated as approximately 50 ms. These results suggest that the electrical pulse stimulation is capable of regulating the DV tissue, and the micropillar array is a useful biological tool to investigate physiological properties of muscle tissue.     

Evaluation of the impedance technique for cryosurgery in a theoretical model of the head

Bioimpedance is a noninvasive technique that produces information on the electrical characteristics of tissue inside the body from currents injected and electrical potentials measured on the surface of the body. Because freezing causes a large increase in tissue electrical impedance we thought that it may also cause significant changes in the surface electrical potential making the bioimpedance technique suitable for noninvasive monitoring and imaging of cryosurgery. To evaluate the feasibility of the bioimpedance technique in cryosurgery we examined, as a case study, a theoretical model for the electrical potentials during brain cryosurgery. A three-dimensional spherical model was used to calculate the change in the electrical potential distribution in the head as a function of the current source location and the size of the frozen lesion in the brain. The numerical calculations were executed using the finite volume method and the iterative successive over relaxation method. The results demonstrate that, indeed, freezing inside the head produces measurable changes in the electrical potential on the outer surface-the scalp.     

Analysis of the dynamic permeation experiment with implication to cartilaginous tissue engineering

In the present study, a I-D dynamic permeation of a monovalent electrolyte solution through a negatively charged-hydrated cartilaginous tissue is analyzed using the mechano-electrochemical theory developed by Lai et al. (1991) as the constitutive model for the tissue. The spatial distributions of stress, strain, fluid pressure, ion concentrations, electrical potential, ion and fluid fluxes within and across the tissue have been calculated. The dependencies of these mechanical, electrical and physicochemical responses on the tissue fixed charge density, with specified modulus, permeability, diffusion coefficients, and frequency and magnitude of pressure differential are determined. The results demonstrate that these mechanical, electrical and physicochemical fields within the tissue are intrinsically and nonlinearly coupled, and they all vary with time and depth within the tissue.     

Magnetoacoustic imaging of electrical conductivity of biological tissues at a spatial resolution better than 2 mm

Magnetoacoustic tomography with magnetic induction (MAT-MI) is an emerging approach for noninvasively imaging electrical impedance properties of biological tissues. The MAT-MI imaging system measures ultrasound waves generated by the Lorentz force, having been induced by magnetic stimulation, which is related to the electrical conductivity distribution in tissue samples. MAT-MI promises to provide fine spatial resolution for biological tissue imaging as compared to ultrasound resolution. In the present study, we first estimated the imaging spatial resolution by calculating the full width at half maximum (FWHM) of the system point spread function (PSF). The actual spatial resolution of our MAT-MI system was experimentally determined to be 1.51 mm by a parallel-line-source phantom with Rayleigh criterion. Reconstructed images made from tissue-mimicking gel phantoms, as well as animal tissue samples, were consistent with the morphological structures of the samples. The electrical conductivity value of the samples was determined directly by a calibrated four-electrode system. It has been demonstrated that MAT-MI is able to image the electrical impedance properties of biological tissues with better than 2 mm spatial resolution. These results suggest the potential of MAT-MI for application to early detection of small-size diseased tissues (e.g. small breast cancer).     

Defects formation and spiral waves in a network of neurons in presence of electromagnetic induction

Complex anatomical and physiological structure of an excitable tissue (e.g., cardiac tissue) in the body can represent different electrical activities through normal or abnormal behavior. Abnormalities of the excitable tissue coming from different biological reasons can lead to formation of some defects. Such defects can cause some successive waves that may end up to some additional reorganizing beating behaviors like spiral waves or target waves. In this study, formation of defects and the resulting emitted waves in an excitable tissue are investigated. We have considered a square array network of neurons with nearest-neighbor connections to describe the excitable tissue. Fundamentally, electrophysiological properties of ion currents in the body are responsible for exhibition of electrical spatiotemporal patterns. More precisely, fluctuation of accumulated ions inside and outside of cell causes variable electrical and magnetic field. Considering undeniable mutual effects of electrical field and magnetic field, we have proposed the new Hindmarsh–Rose (HR) neuronal model for the local dynamics of each individual neuron in the network. In this new neuronal model, the influence of magnetic flow on membrane potential is defined. This improved model holds more bifurcation parameters. Moreover, the dynamical behavior of the tissue is investigated in different states of quiescent, spiking, bursting and even chaotic state. The resulting spatiotemporal patterns are represented and the time series of some sampled neurons are displayed, as well.     

Turnover of protein-bound serine phosphate in respiring slices of guinea-pig cerebral cortex. Effects of putative transmitters, tetrodotoxin and other agents

1. The effect of various agents on the turnover of protein-bound phosphorus in respiring slices of cerebral cortex was studied. 2. Confirming previous work turnover was increased by the application of electrical pulses for 10s to the tissue. 3. Turnover was also increased by exposure of the slices for 10min to noradrenaline (0.5mm), 5-hydroxytryptamine (1mum) and histamine (0.1mm). 4. When slices were stimulated by electrical pulses in the presence of histamine the increase in turnover was the sum of the responses given by each agent above, suggesting that different phosphorylating systems were involved. 5. Tetrodotoxin (0.5mum) blocked the increased turnover due to electrical pulses, but not that due to histamine. Tetrodotoxin also prevented the increase in tissue cyclic AMP content caused by the application of electrical pulses. 6. Phosphoprotein turnover was not affected by adenosine, despite the increase in tissue cyclic AMP content given by this agent. 7. Adenosine blocked the phosphoprotein response to histamine, but did not affect the response to electrical pulses. 8. The results are discussed in relation to the hypothesis that the stimulation of protein phosphorus turnover by electrical pulses is secondary to the release of cyclic AMP in the tissue.     

Dielectric spectroscopy for noninvasive examination of corneal tissue]

Dielectric spectroscopy is a non-invasive contact technique that permits the in vivo measurement of the specific electrical properties of biological tissue induced by an external electrical field. Permittivity, relaxation time and specific conductivity as a function of corneal hydration (wet weight/dry weight) and temperature were measured in 10 porcine corneas. Variation of tissue hydration has a minor influence on the signal, with a significant variation of the signal being detectable only for relatively dry tissue. A much greater influence was found for temperature, in particular on relaxation times. Dielectric spectroscopy provides us with an opportunity to detect structural, in particular temperature-induced, changes in living tissue. In the frequency range investigated, hydration has only a small influence on the dielectric properties of the tissue.     

Intracranial Nonthermal Irreversible Electroporation: In Vivo Analysis

Nonthermal irreversible electroporation (NTIRE) is a new minimally invasive technique to treat cancer. It is unique because of its nonthermal mechanism of tumor ablation. Intracranial NTIRE procedures involve placing electrodes into the targeted area of the brain and delivering a series of short but intense electric pulses. The electric pulses induce irreversible structural changes in cell membranes, leading to cell death. We correlated NTIRE lesion volumes in normal brain tissue with electric field distributions from comprehensive numerical models. The electrical conductivity of brain tissue was extrapolated from the measured in vivo data and the numerical models. Using this, we present results on the electric field threshold necessary to induce NTIRE lesions (495–510 V/cm) in canine brain tissue using 90 50-μs pulses at 4 Hz. Furthermore, this preliminary study provides some of the necessary numerical tools for using NTIRE as a brain cancer treatment. We also computed the electrical conductivity of brain tissue from the in vivo data (0.12–0.30 S/m) and provide guidelines for treatment planning and execution. Knowledge of the dynamic electrical conductivity of the tissue and electric field that correlates to lesion volume is crucial to ensure predictable complete NTIRE treatment while minimizing damage to surrounding healthy tissue.     

Electrosensitive polyacrylic acid/fibrin hydrogel facilitates cell seeding and alignment

Three-dimensional cell culture and conditioning is an effective means to guide cell distribution and patterning for tissue engineered constructs such as vascular grafts. Polyacrylic acid is known as an electroresponsive polymer, capable of transforming environmental stimuli like electrical energy to mechanical forces. In this study, we developed an electrosensitive and biocompatible hydrogel-based smart device composed of acrylic acid and fibrin as a tissue engineered construct to mechanically stimulate cells. Structural properties of the hydrogel were assessed by FTIR-ATR, scanning electron microscopy, prosimetry, and swelling measurement. Distribution and alignment of porcine smooth muscle cells (pSMCs) seeded on the surface of lyophilized hydrogels were evaluated and quantified by two-photon laser scanning microscopy. Smooth muscle cell tissue constructs exposed to 2 h of pulsatile electrical stimulation showed significantly enhanced cell penetration and alignment due to dynamic changes produced by alternative swelling and deswelling, in comparison with static samples. On the basis of the results, this hydrogel under electrical stimulation works as a mechanical pump, which can direct SMC alignment and facilitate infiltration and distribution of cells throughout the structure.     

Numerical simulation of deformations and electrical potentials in a cartilage substitute

Cartilage exhibits a swelling and shrinking behaviour that influences the function of the cells inside the tissue. This behaviour is caused by mechanical, chemical and electrical loads. It is described by the electrochemomechanical mixture theory, in which the tissue is represented by four components: a charged porous solid, a fluid, cations and anions. By distinguishing between the cations and anions, electrical phenomena can be modelled. This mixture theory is verified by fitting the deformations and the electrical potentials in a uniaxial confined swelling and compression experiment to a mixed finite element simulation. The fitted stiffness, permeability, diffusion coefficients, and osmotic coefficients are in the same range as reported in literature.     

Signaling and transport processes related to the carnivorous lifestyle of plants living on nutrient-poor soil

In Eukaryotes, long-distance and rapid signal transmission is required in order to be able to react fast and flexibly to external stimuli. This long-distance signal transmission cannot take place by diffusion of signal molecules from the site of perception to the target tissue, as their speed is insufficient. Therefore, for adequate stimulus transmission, plants as well as animals make use of electrical signal transmission, as this can quickly cover long distances. This update summarises the most important advances in plant electrical signal transduction with a focus on the carnivorous Venus flytrap. It highlights the different types of electrical signals, examines their underlying ion fluxes and summarises the carnivorous processes downstream of the electrical signals.     

The feasibility of computational modelling technique to detect the bladder cancer

A numerical technique, finite element analysis (FEA) was used to model the electrical properties, the bio impedance of the bladder tissue in order to predict the bladder cancer. This model results showed that the normal bladder tissue have significantly higher impedance than the malignant tissue that was in opposite with the impedance measurements or the experimental results. Therefore, this difference can be explained using the effects of inflammation, oedema on the urothelium and the property of the bladder as a distensible organ. Furthermore, the different current distributions inside the bladder tissue (in histological layers) in normal and malignant cases and finally different applied pressures over the bladder tissue can cause different impedances for the bladder tissue. Finally, it is believed that further studies have to be carried out to characterise the human bladder tissue using the electrical impedance measurement and modelling techniques.     

Electrical stimulation of cultured myocardial cells

This paper reports on the use of a cardiac tissue monolayer model in the investigation of some of the fundamental electrical properties of cardiac muscle. The response of cardiac tissue to increasing levels of electrical stimulus is investigated and the strength-duration curve for rectangular waveform stimulation is measured. An experimental protocol is established which provides for uniform field stimulation of the cells, and allows the cellular response (contraction) to be recorded.     

THE RELATIONSHIP BETWEEN AMINO ACID INCORPORATION INTO PROTEIN IN ISOLATED NEOCORTEX SLICES AND THE TISSUE CONTENT OF FREE AMINO ACID

Abstract— The uptake of radioactive leucine by incubated neocortex slices was found to be increased by electrical stimulation, yielding a higher content of radioactive amino acid per g fresh weight of tissue which was maintained for prolonged periods of stimulation. The increased tissue content may be associated with tissue swelling found on electrical stimulation, but the additional amino acid uptake was by an active process rather than by passive diffusion. Additions of valine (2.5–10 m m ) or tryptophan (1 m m ) to the incubation medium was found to depress the tissue leucine content. Decreasing the tissue free leucine content by incubating slices in medium containing 5 m m -valine was found to decrease the incorporation of leucine and lysine into tissue protein, indicating that under these conditions tissue free amino acid becomes rate limiting for amino acid incorporation into protein. By analogy with the properties of cerebral tissue in oitro it is suggested that electrical activity in vivo may cause localized increases in free amino acid concentration which may serve to regulate protein synthesis in conditions where the concentration of free amino acids are rate limiting.     

Interstitial potentials and their change with depth into cardiac tissue.

The electrical source strength for an isolated, active, excitable fiber can be taken to be its transmembrane current as an excellent approximation. The transmembrane current can be determined from intracellular potentials only. But for multicellular preparations, particularly cardiac ventricular muscle, the electrical source strength may be changed significantly by the presence of the interstitial potential field. This report examines the size of the interstitial potential field as a function of depth into a semi-infinite tissue structure of cardiac muscle regarded as syncytial. A uniform propagating plane wave of excitation is assumed and the interstitial potential field is found based on consideration of the medium as a continuum (bidomain model). As a whole, the results are inconsistent with any of the limiting cases normally used to represent the volume conductor, and suggest that in only the thinnest of tissue (less than 200 micron) can the interstitial potentials be ignored.     

Electric and magnetic fields from two-dimensional anisotropic bisyncytia.

Cardiac tissue can be considered macroscopically as a bidomain, anisotropic conductor in which simple depolarization wavefronts produce complex current distributions. Since such distributions may be difficult to measure using electrical techniques, we have developed a mathematical model to determine the feasibility of magnetic localization of these currents. By applying the finite element method to an idealized two-dimensional bisyncytium with anisotropic conductivities, we have calculated the intracellular and extracellular potentials, the current distributions, and the magnetic fields for a circular depolarization wavefront. The calculated magnetic field 1 mm from the tissue is well within the sensitivity of a SQUID magnetometer. Our results show that complex bisyncytial current patterns can be studied magnetically, and these studies should provide valuable insight regarding the electrical anisotropy of cardiac tissue.     

Tumor ablation with irreversible electroporation

We report the first successful use of irreversible electroporation for the minimally invasive treatment of aggressive cutaneous tumors implanted in mice. Irreversible electroporation is a newly developed non-thermal tissue ablation technique in which certain short duration electrical fields are used to permanently permeabilize the cell membrane, presumably through the formation of nanoscale defects in the cell membrane. Mathematical models of the electrical and thermal fields that develop during the application of the pulses were used to design an efficient treatment protocol with minimal heating of the tissue. Tumor regression was confirmed by histological studies which also revealed that it occurred as a direct result of irreversible cell membrane permeabilization. Parametric studies show that the successful outcome of the procedure is related to the applied electric field strength, the total pulse duration as well as the temporal mode of delivery of the pulses. Our best results were obtained using plate electrodes to deliver across the tumor 80 pulses of 100 micros at 0.3 Hz with an electrical field magnitude of 2500 V/cm. These conditions induced complete regression in 12 out of 13 treated tumors, (92%), in the absence of tissue heating. Irreversible electroporation is thus a new effective modality for non-thermal tumor ablation.     

Electrical injury mechanisms: electrical breakdown of cell membranes

Electric fields are capable of damaging cells through both thermal and nonthermal mechanisms. While joule heating is generally recognized to mediate tissue injury in electrical trauma, the possible role of electrical breakdown of cell membranes has not been thoroughly considered. Evidence is presented suggestive that in many instances of electrical trauma the local electrical field is of sufficient magnitude to cause electrical breakdown of cell membranes and cell lysis. In theory, large cells such as muscle and nerve cells are more vulnerable to electrical breakdown. To illustrate the significance of cell size and orientation, a geometrically simple model of an elongated cell is analyzed.     

Water potential increase in sliced leaf tissue as a cause of error in vapor phase determinations of water potential

Earlier reports that the water potential of sliced leaf tissue is higher than that of unsliced control tissue are confirmed. The effect is shown to increase as damage to the tissue due to slicing is increased. However, there is some evidence that increase in damage beyond a certain point causes water potentials to fall again towards the control value. The electrical resistance of washings from sliced leaf tissue increases with increase in the time interval between slicing and washing. Both the rise in water potential of sliced tissue and the rise in electrical resistance of washings are partially and reversibly inhibited by low temperature. These results suggest that the remaining intact cells actively accumulate solutes released from the cells cut open on slicing. The sap from the sliced cells is thereby diluted and flows passively into the intact cells. Since pressure potential changes more rapidly with cell volume than does osmotic potential, the net result is a rise in the total water potential of sliced tissue. It is concluded that this effect may cause spuriously high water potential values to be measured if excessively small pieces of leaf tissue are used. This is demonstrated with stacks of annuli cut from leaves.