Cell Electrical Response Research Articles

A Self-Powered Hydrogel/Nanogenerator System Accelerates Wound Healing by Electricity-Triggered On-Demand Phosphatase and Tensin Homologue (PTEN) Inhibition.

Electrical stimulation therapy (EST) has been established as an effective strategy to accelerate wound healing by stimulating cell proliferation and migration, ultimately promoting re-epithelialization and vascularization, two key processes that significantly influence the rate of wound healing. Phosphatase and tensin homologue (PTEN), a widely expressed protein in somatic cells, works as a "brake" regulating cell differentiation, proliferation, and migration. Given that this "brake" also works in cell electrical responses, there is a hypothesis that PTEN inhibition may amplify the efficacy of EST in wound treatment. However, long-term inhibition of PTEN may result in DNA damage and reduce DNA repair, which poses a significant challenge to the safe use of PTEN inhibitors. To address this issue, we developed a system that combines PTEN inhibitor loaded electro-responsive hydrogel (BPV@PCP) with a wearable direct current pulse piezoelectric nanogenerator (PENG). The PENG converts the rat's motions into electric fields that synchronously charge the wound edge tissue and BPV@PCP. Electric field intensity was lower when the rat was quiet or anesthetized, which is insufficient to trigger an effective PTEN inhibitor release. However, when the rat was in action, the electric field intensity exceeded 625 mV/mm, resulting in a rapid drug release. This on-demand PTEN inhibition accelerated wound healing by amplifying cell electric responsiveness while avoiding negative effects associated with continuous overinhibition of PTEN. Notably, this system improves vascularization not only by improving endothelial cell electric responsiveness but also through the paracrine pathway, in which electrical stimulation and PTEN inhibition synergically promote VEGF secretion.

Maximum power estimation through injection dependent electroluminescence imaging

AbstractThe mathematical models applied to photovoltaic (PV) modules are typically oversimplified. In general, the models applied to individual PV cells are modified to obtain the “cell” voltage by dividing the module voltage by number of cells in the module. Due to the complexity of the current–voltage (IV) relation and the presence of bypass diodes in commercial PV modules this approach is inappropriate and can lead to incorrect conclusions about the electrical response of a module. This paper provides a method of determining each cell's electrical response using a combination of the Dark IV response of the entire module and injection dependent electroluminescence (EL) imaging. This combination of characterization techniques makes use of equipment that is readily available in commercial facilities as well as regular PV characterization laboratories. This method can be used as an alternative to lock‐in thermography (LIT) based methods, as the equipment required is not always present in standard PV characterization laboratories. In this study, Evolutionary Algorithms are used to optimize the individual cells' electrical parameters. This advanced characterization method can be utilized in commercial facilities, to investigate atypical module electrical response and in research laboratories to investigate the degradation in individual cells within a module.

A Biological-Based Photovoltaic Electrochemical Cell: Modelling the Impedance Spectra

The impedance response of an electrochemical cell able to convert sunlight into electrical power is analyzed and discussed. Light conversion is due to a photosynthetic system known as reaction center, which is the core of photosynthesis in several living beings. Under illumination, an abrupt transformation drives the cell electrical response from insulator to conductor and a photocurrent is observed. The impedance spectrum shows a peculiar shape which significantly modifies after the protein activation. It has been analyzed by means of a graphical/analytical/numerical procedure. Some impedance graphical representations are indicated as the most appropriate to suggest the design of an equivalent electrical circuit. Then, the analytical expression of this circuit is formulated and used to set-up a custom Phyton code useful for fitting experimental data. Finally, an appropriate normalization procedure is proposed, which validates data in dark and light and can be useful as a fast screening of measurements.

Hair Cell Transduction, Tuning, and Synaptic Transmission in the Mammalian Cochlea.

Sound pressure fluctuations striking the ear are conveyed to the cochlea, where they vibrate the basilar membrane on which sit hair cells, the mechanoreceptors of the inner ear. Recordings of hair cell electrical responses have shown that they transduce sound via submicrometer deflections of their hair bundles, which are arrays of interconnected stereocilia containing the mechanoelectrical transducer (MET) channels. MET channels are activated by tension in extracellular tip links bridging adjacent stereocilia, and they can respond within microseconds to nanometer displacements of the bundle, facilitated by multiple processes of Ca2+-dependent adaptation. Studies of mouse mutants have produced much detail about the molecular organization of the stereocilia, the tip links and their attachment sites, and the MET channels localized to the lower end of each tip link. The mammalian cochlea contains two categories of hair cells. Inner hair cells relay acoustic information via multiple ribbon synapses that transmit rapidly without rundown. Outer hair cells are important for amplifying sound-evoked vibrations. The amplification mechanism primarily involves contractions of the outer hair cells, which are driven by changes in membrane potential and mediated by prestin, a motor protein in the outer hair cell lateral membrane. Different sound frequencies are separated along the cochlea, with each hair cell being tuned to a narrow frequency range; amplification sharpens the frequency resolution and augments sensitivity 100-fold around the cell's characteristic frequency. Genetic mutations and environmental factors such as acoustic overstimulation cause hearing loss through irreversible damage to the hair cells or degeneration of inner hair cell synapses. © 2017 American Physiological Society. Compr Physiol 7:1197-1227, 2017.

Thermal/electrical modeling for abuse-tolerant design of lithium ion modules

Proper understanding of heat generation and design of heat dissipation paths are critical for ensuring the safety of lithium ion modules during abuse events such as external shorts. Additionally, the behavior of positive thermal coefficient (PTC) current limiting devices—generally effective at the single-cell level—can be difficult to predict for a multi-cell module. To help guide battery pack design, a coupled thermal/electrical model of a commercial 18 650-size cell and a module with 16 cells in parallel (16P) are developed. Cell electrical response is modeled using an equivalent circuit, including the temperature-dependent behavior of the PTC. Cell thermal response is modeled with a high-resolution thermal model from which a simpler 5-node thermal circuit model is extracted. Cell models are integrated into a module-level model considering cell-to-cell electrical and thermal interactions via conduction, convection, and radiation. The module-level model is validated with a 16P external short experiment and applied in a parametric study to assess thermal safety margin. Copyright © 2009 John Wiley & Sons, Ltd.

Numerical analysis of start-up operation of a tubular solid oxide fuel cell

The purpose of the current study is to numerically predict the start up behavior of a tubular solid oxide fuel cell (SOFC) using a 2-D transient model. The developed model provides the transient response of the start-up mode as well as the steady state operation of the SOFC. A code based on finite volume method is utilized to solve the transient nonlinear transport equations of the cell (momentum, species and energy equations). To account for the Ohmic losses and Joule heating of the current that passes through the cell body, a discretized network circuit is adopted. The local electrochemical parameters are calculated based on the local pressure, temperature, and concentrations of the species. At each time step an iterative procedure is used to solve the electrochemical, electrical and transport equations simultaneously. The model predicts the cell output voltage, the local EMF and the state variables (pressure, temperature and species concentration) during the start up. It also predicts the cell heat-up rate for hot input gases as well as the start up time of the SOFC. The results show that the gases mass flow rate and temperature affect the heat-up rate. Also during the start-up, the cell electrical response is about 2.5 times quicker than the cell temperature response. The start-up time for the cell output voltage is about 50 min.

Neurite‐specific Ca2+ dynamics underlying sound processing in an auditory interneurone

Concepts on neuronal signal processing and integration at a cellular and subcellular level are driven by recording techniques and model systems available. The cricket CNS with the omega-1-neurone (ON1) provides a model system for auditory pattern recognition and directional processing. Exploiting ON1's planar structure we simultaneously imaged free intracellular Ca(2+) at both input and output neurites and recorded the membrane potential in vivo during acoustic stimulation. In response to a single sound pulse the rate of Ca(2+) rise followed the onset spike rate of ON1, while the final Ca(2+) level depended on the mean spike rate. Ca(2+) rapidly increased in both dendritic and axonal arborizations and only gradually in the axon and the cell body. Ca(2+) levels were particularly high at the spike-generating zone. Through the activation of a Ca(2+)-sensitive K(+) current this may exhibit a specific control over the cell's electrical response properties. In all cellular compartments presentation of species-specific calling song caused distinct oscillations of the Ca(2+) level in the chirp rhythm, but not the faster syllable rhythm. The Ca(2+)-mediated hyperpolarization of ON1 suppressed background spike activity between chirps, acting as a noise filter. During directional auditory processing, the functional interaction of Ca(2+)-mediated inhibition and contralateral synaptic inhibition was demonstrated. Upon stimulation with different sound frequencies, the dendrites, but not the axonal arborizations, demonstrated a tonotopic response profile. This mirrored the dominance of the species-specific carrier frequency and resulted in spatial filtering of high frequency auditory inputs.

Modelling the early steps of transduction in insect olfactory receptor neurons

Olfactory transduction is a multistep process whose basic function is to convert a low energy reaction, the odorant-receptor interaction that may involve a single odorant molecule, into a whole cell electrical response, the receptor potential, which triggers the firing of one or more action potentials. Although much effort has been devoted to the experimental analysis of transduction in olfactory receptor neurons (ORNS), especially in the favorable moth sex-pheromone receptor neuron, its modelling is less advanced. The model we investigated, which takes into account the translocation of pheromone molecules from air to the extracellular space, their deactivation and their interaction with receptors, focuses on the membrane cascade. It involves the interaction of receptors, G-proteins and effector enzymes, whose reaction rates are limited by lateral diffusion in the membrane. The evolutions in time of these species in response to single pulse stimulation of various intensities were compared to one another and to the experimentally measured electrical response. The results obtained suggest that the receptor-to-effector conversion is fast with respect to the receptor response, that it presents a small amplification factor, contrary to the photoreceptor, and that most of the amplification is achieved in the post-effector processes involving the second messenger and ionic channels.

High electrical field effects on cell membranes

Electrical charging of lipid membranes causes electroporation with sharp membrane conductance increases. Several recent observations, especially at very high field strength, are not compatible with the simple electroporation picture. Here we present several relevant experiments on cell electrical responses to very high external voltages. We hypothesize that, not only are aqueous pores created within the lipid membranes, but that nanoscale membrane fragmentation occurs, possibly with micelle formation. This effect would produce conductivity increases beyond simple electroporation and display a relatively fast turn-off with external voltage. In addition, material loss can be expected at the anode side of cells, in agreement with published experimental reports at high fields. Our hypothesis is qualitatively supported by molecular dynamics simulations. Finally, such cellular responses might temporarily inactivate voltage-gated and ion-pump activity, while not necessarily causing cell death. This hypothesis also supports observations on electrofusion.

Voltage-gated outward K currents in frog saccular hair cells.

A biophysical analysis of the voltage-gated K (Kv) currents of frog saccular hair cells enzymatically isolated with bacterial protease VIII was carried out, and their contribution to the cell electrical response was addressed by a modeling approach. Based on steady-state and kinetic properties of inactivation, two distinct Kv currents were found: a fast inactivating IA and a delayed rectifier IDRK. IA exhibited a strongly hyperpolarized inactivation V(1/2) (-83 mV), a relatively rapid single exponential recovery from inactivation (taurec of approximately 100 ms at -100 mV), and fast activation and deactivation kinetics. IDRK showed instead a less-hyperpolarized inactivation V(1/2) (-48 mV), a slower, double-exponential recovery from inactivation (taurec1 approximately 490 ms and taurec2 approximately 4,960 ms at -100 mV), and slower activation and deactivation kinetics. Steady-state activation gave a V(1/2) and a k of -46.2 and 8.2 mV for IA and -48.3 and 4.2 mV for IDRK. Both currents were not appreciably blocked by bath application of 10 mM TEA, but were inhibited by 4-AP, with IDRK displaying a higher sensitivity. IDRK also showed a relatively low affinity to linopirdine, being half blocked at approximately 50 microM. Steady-state and kinetic properties of IDRK and IA were described by 2nd- and 3rd-order Hodgkin-Huxley models, respectively. The goodness of our quantitative description of the Kv currents was validated by including IA and IDRK in a theoretical model of saccular hair cell electrical activity and by comparing the simulated responses with those obtained experimentally. This thorough description of the IDRK and IA will contribute toward understanding the role of these currents in the electrical response on this preparation.

The role of the medial olfactory pathways in olfaction: Behavioral and electrophysiological data

The role of the olfactory inputs transmitted by the medial olfactory pathways — i.e. anterior limb of the anterior commissure and medial forebrain bundle — was studied in rats submitted either to a bilateral lesion of the anterior commissure (bAC group) or to a bilateral transection of the lateral olfactory tract followed by an anterior commissure bilateral lesion (bCL group). In the bCL group, the characteristic emotional reactions usually observed in sham-operated rats to biologically meaningful odorants (odor of a predator or of conspecifics) were no longer observed; in this group, the modulation of mitral cell electrical responses according to the biological meaning of the stimuli disappeared and no habituation was noted when the stimulations were repeated: few responses appeared at random; lastly, all the stimuli tested, the odor of conspecifics excepted, did not exert an awaking influence on the sleeping rats (slow wave sleep). On the contrary, emotional reactions were always observed in the bAC group, a slight increase of reactivity to the odorants was even noted. In this group of animals, the anterior commissure bilateral lesion induced a large increase of the bulbar responses to all the odorants; the habituation of the electrical responses disappeared, a large percentage of responses being always noted even for the tenth series of stimulation; these results point out the great inhibitory influence that the anterior commissure exerts on the olfactory bulb activity. In these bAC rats almost usual awaking influences were noted, however, the odor of conspecifics became as efficient as fox odor to awake the animals. Results are discussed in relation to the functional role of the medial and lateral olfactory pathways, the integrity of both the pathways being necessary for an accurate olfactory process.

Transmission and integration of biologically meaningful olfactory information after bilateral transection of the lateral olfactory tract in the rat

The contribution of the olfactory inputs conveyed by the lateral olfactory tract (LOT) to the central olfactory areas in the onset of behavioral and electrophysiological responses i.e. multiunit activity of mitral cells was studied in rats which were submitted to a bilateral transection of LOT. The characteristic emotional reactions elicited in sham-operated rats by biologically meaningful odorants — odors of predator or of conspecific — were no longer observed after such lesion. At the olfactory bulb level, the differential habituation of mitral cell electrical responses according to the biological meaning of the stimuli disappeared in the rats with a bilateral section of LOT. However the awaking influence of the odorants when stimulations occurred during slow wave sleep remained unchanged: all the rats were more often awakened by the odor of predator than by the other stimuli. On the other hand, an inhibitory centrifugal influence of LOT on mitral cell electrical responses was noted in rats with a unilateral transection of LOT. The results are discussed in relation to the two olfactory pathways (lateral and medial). During wakefulness, LOT seems essential to the olfactory information processing; in slow wave sleep, the medial olfactory pathways appear to mediate olfactory discrimination and to elicit adapted arousal.