Voltage-sensitive Ion Channels Research Articles

Analogous structural, electrical, mechanical, and optical features of blue phases and voltage-sensitive ion channels

Analogous structural, electrical, mechanical, and optical features of blue phases and voltage-sensitive ion channels

Preferential electrostatic interactions of phosphatidic acid with arginines.

Phosphatidic acid (PA) is an anionic lipid that preferentially interacts with proteins in a diverse set of cellular processes such as transport, apoptosis, and neurotransmission. One such interaction is that of the PA lipids with the proteins of voltage-sensitive ion channels. In comparison to several other similarly charged anionic lipids, PA lipids exhibit much stronger interactions. Intrigued and motivated by this finding, we sought out to gain deeper understanding into the electrostatic interactions of anionic lipids with charged proteins. Using the voltage sensor domain (VSD) of the KvAP channel as a model system, we performed long-timescale atomistic simulations to analyze the interactions of POPA, POPG, and POPI lipids with arginines (ARGs). Our simulations reveal two mechanisms. First, POPA is able to interact not only with surface ARGs but is able to snorkel and interact with a buried arginine. POPG and POPI lipids on the other hand show weak interactions even with both the surface and buried ARGs. Second, deprotonated POPA with -2 charge is able to break the salt-bridge connection between VSD protein segments and establish its own electrostatic bond with the ARG. Based on these findings, we propose a headgroup size hypothesis for preferential solvation of proteins by charged lipids. These findings may be valuable in understanding how PA lipids could be modulating kinematics of transmembrane proteins in cellular membranes.

On molecular steps that activate a voltage sensitive ion channel at critical depolarization

At high transmembrane electric field, a voltage sensitive ion channel is an insulator; when the field is critically reduced, it becomes a conductor of selected ions. The Channel Activation by Electrostatic Repulsion (CAbER) hypothesis proposes that an ordered polarization field of induced dipoles at the high electric field magnitude of the excitable state is overcome by thermal disorder at a critical depolarization. Increased repulsions between positive charges in the S4 segments cause an allosteric transition in which these segments expand and separate in a chiral proteinquake. The increased space allows the P segments to refold and the ion-semiconducting S5 and S6 segments to relax and expand outward in a breathing mode. Stripped permeant ions enter widened hydrogen bonds in the core helices of these segments. Driven by concentration differences and the electric field, the ions hop along transient pathways across the channel, appearing as fractal, stochastic bursts of single-channel currents. To support order amid thermal fluctuations, an object must be of a minimum size. The critical role of an ion channel's size suggests that the evolution of Metazoa became possible only after its DNA had grown enough to code for proteins larger than the correlation length.

Voltage sensitive ion channels, minimal size of ordered phases and the evolution of metazoa.

The complex electrical, mechanical and optical behavior of a voltage sensitive ion channel (VSIC) requires that the macromolecule possess at least one ordered phase. For an object to support order, it must be of a minimum size to overcome thermal fluctuations. The limiting size of a stable phase, the correlation length, depends on temperature. Converging lines of experimental evidence indicate that the VSIC is a ferroelectric liquid crystal of the blue phase type. Reaching beyond the analogy of a gated pore, the Channel Activation by Electrostatic Repulsion (CAbER) hypothesis (Leuchtag 2022 Biophys J 121(3):92a) postulates that voltage sensitivity arises from polarization due to the induction of dipoles in the branched sidechains of the numerous isoleucine, leucine and valine residues, producing a polar order in the excitable (closed) phase and making it an insulator by compressing and crowding the ion-conducting segments. On threshold depolarization the dipoles collapse into thermal chaos, reducing the macromolecule's dielectric permittivity and thereby increasing the long-range Coulomb repulsions between the conserved positive charges of the four S4 segments, pushing them apart. The consequent relaxation of the S5 and S6 segments allows their core hydrogen bonds to widen and allow permeant ions to enter and percolate stochastically through the membrane. The critical role of VSIC size in the CAbER model has implications for the beginning of multicellularity during the emergence of the Metazoa in the genomic revolution. At about 300 K, the size effect underlies VSIC activation as an order–disorder transition. This property of the size effect implies that the evolution of Metazoa became possible only after the organism's DNA had grown extensive enough to code for ion channels with dimensions larger than the correlation length to sustain an ordered polar, bioferroelectric, phase.

Using many different voltage protocols to characterise discrepancy in mathematical ion channel models.

The Kv11.1 protein encoded by the hERG gene forms the primary subunit of a voltage-sensitive ion channel responsible for IKr in cardiomyocytes. Mathematical models of the macroscopic current are fitted to data from patch-clamp experiments - in which the whole-cell current is recorded in response to an applied voltage protocol. These models are a valuable tool for understanding the proarrhythmic effects of drugs and mutations, as they can provide accurate, quantitative predictions of the macroscopic current. In recent years, information rich protocols (that do not rely on the channels returning to steady state between voltage pulses) were designed to calibrate mathematical IKr models using short, dense time series. These protocols have been adapted for use on high-throughput automated patch clamp machines in CHO cells overexpressing hERG at either room or physiological temperatures. There are many choices of such protocols to apply during a patch-clamp experiment. We designed twelve protocols under various criteria, all of which should provide enough information to fit simple models of IKr uniquely. However, the parameters in imperfect models are forced to make different compromises to fit data from different protocols. The results highlight the impact of model discrepancy (the difference between models and reality) on parameter estimation and prediction. In particular, we show that the parameter estimates obtained depend on the chosen protocol, and how parameters fitted to protocols which highlight a significant amount of model discrepancy can lead to poor predictions. These results motivate the need for new experimental design methods that account for model discrepancy and aid in model selection. Furthermore, we suggest cross-validation as a tool to help evaluate the trustworthiness of model predictions, which may help identify good models of IKr as well as other macroscopic currents.

TPC1-Type Channels in Physcomitrium patens: Interaction between EF-Hands and Ca2.

Two-pore channels (TPCs) are members of the superfamily of ligand-gated and voltage-sensitive ion channels in the membranes of intracellular organelles of eukaryotic cells. The evolution of ordinary plant TPC1 essentially followed a very conservative pattern, with no changes in the characteristic structural footprints of these channels, such as the cytosolic and luminal regions involved in Ca2+ sensing. In contrast, the genomes of mosses and liverworts encode also TPC1-like channels with larger variations at these sites (TPC1b channels). In the genome of the model plant Physcomitrium patens we identified nine non-redundant sequences belonging to the TPC1 channel family, two ordinary TPC1-type, and seven TPC1b-type channels. The latter show variations in critical amino acids in their EF-hands essential for Ca2+ sensing. To investigate the impact of these differences between TPC1 and TPC1b channels, we generated structural models of the EF-hands of PpTPC1 and PpTPC1b channels. These models were used in molecular dynamics simulations to determine the frequency with which calcium ions were present in a coordination site and also to estimate the average distance of the ions from the center of this site. Our analyses indicate that the EF-hand domains of PpTPC1b-type channels have a lower capacity to coordinate calcium ions compared with those of common TPC1-like channels.

Voltage sensitive ion channels: hardware or soft matter? Can we participate in a dialogue?

Standard models of voltage sensing in voltage-sensitive ion channels assume rigidity in gates and other everyday devices, but if rigidity requires the cooperation of numerous strong interatomic bonds, can it exist in a macromolecule at physiological temperature? Can an ion channel be pierced by a water-filled pore without suffering electrical breakdown? The Channel Activation by Electrostatic Repulsion (CAbER) hypothesis proposes that threshold reduction of the electric field magnitude across the excitable channel allows thermal disorder to overcome a partial order of electric dipoles induced by the high resting field.

Neural Stimulation In Vitro and In Vivo by Photoacoustic Nanotransducers

Summary Neuromodulation is an invaluable approach for the study of neural circuits and clinical treatment of neurological diseases. Here, we report semiconducting polymer nanoparticles based photoacoustic nanotransducers (PANs) for neural stimulation in vitro and in vivo. Our PANs strongly absorb the nanosecond pulsed laser in the near-infrared second window (NIR-II) and generate localized acoustic waves. PANs are shown to be surface modified and selectively bind onto neurons. PAN-mediated activation of primary neurons in vitro is achieved with ten 3-ns laser pulses at 1,030 nm over a 3-ms duration. In vivo neural modulation of mouse brain activities and motor activities is demonstrated by PANs directly injected into brain cortex. With submillimeter spatial resolution and negligible heat deposition, PAN stimulation is a new non-genetic method for precise control of neuronal activities, opening up potentials in non-invasive brain modulation.

Electrospun hyaluronic acid-carbon nanotube nanofibers for neural engineering

Electroactive biomaterials enable the delivery of an electrical stimulus to modulate neuronal activity in neural engineering treatments spanning neurological disorders, pain management, and regenerative medicine. Our research focused on developing a biocompatible conductive material composite consisting of an ultra-low concentration of carbon nanotubes (CNT) within hyaluronic acid (HA) nanofibers. We hypothesized that electrical stimulation through composite nanofibers would improve neurite outgrowth by providing a substrate that is both permissive to neuron growth and to electronic to ionic conduction that could activate voltage sensitive regenerative pathways. We evaluated the electrical properties of the composite material through impedance spectroscopy and cyclic voltammetry. Mechanics and surface characteristics were evaluated through atomic force microscopy using quantitative nanomechanical mapping. A custom stimulation chamber was fabricated and electrical stimulus parameters, using a charge-balanced biphasic square wave, required to elicit increased neurite outgrowth were determined. Neurons cultured on stimulated substrates of HA-CNT nanofibers exhibited significantly longer growth than unstimulated HA-CNT and HA control substrates. The HA-CNT material could be translated to other regenerative medicine applications including skin and cardiac tissue. Statement of significanceThis article describes a unique conductive biomaterial consisting of hyaluronic acid, combined with multi-walled carbon nanotubes, electrospun into a nanofiber composite. We have shown that the biomaterial's electrical properties can be improved (decreased impedance and increased charge capacity) by adding less than 0.01% carbon nanotubes. By using this ultra-low concentration, our material is biocompatible and mechanically appropriate for nerve regeneration. While electrical stimulation has been previously shown to increase neurite outgrowth, electrically conductive materials are typically non-degradable, brittle and/or mechanically stiff. We have optimized stimulation voltage and duration to activate voltage sensitive ion channels and increase nerve growth and provided robust mechanical characterization to show the synergistic effect of material properties and electrical stimulation on neuron behavior.

Four Ways to Fit an Ion Channel Model

Mathematical models of ionic currents are used to study the electrophysiology of the heart, brain, gut, and several other organs. Increasingly, these models are being used predictively in the clinic, for example, to predict the risks and results of genetic mutations, pharmacological treatments, or surgical procedures. These safety-critical applications depend on accurate characterization of the underlying ionic currents. Four different methods can be found in the literature to fit voltage-sensitive ion channel models to whole-cell current measurements: method 1, fitting model equations directly to time-constant, steady-state, and I-V summary curves; method 2, fitting by comparing simulated versions of these summary curves to their experimental counterparts; method 3, fitting to the current traces themselves from a range of protocols; and method 4, fitting to a single current trace from a short and rapidly fluctuating voltage-clamp protocol. We compare these methods using a set of experiments in which hERG1a current was measured in nine Chinese hamster ovary cells. In each cell, the same sequence of fitting protocols was applied, as well as an independent validation protocol. We show that methods 3 and 4 provide the best predictions on the independent validation set and that short, rapidly fluctuating protocols like that used in method 4 can replace much longer conventional protocols without loss of predictive ability. Although data for method 2 are most readily available from the literature, we find it performs poorly compared to methods 3 and 4 both in accuracy of predictions and computational efficiency. Our results demonstrate how novel experimental and computational approaches can improve the quality of model predictions in safety-critical applications.

Using Light to Endow Stem-Cell-Derived Cardiomyocytes With Virtual IK1 Conductances

Using Light to Endow Stem-Cell-Derived Cardiomyocytes With Virtual IK1 Conductances

Eliminating Warrantless Assumptions Facilitates Consideration of an Electrostatic Model of Ion-Channel Activation

Models of voltage-sensitive ion channels (VSICs) that don’t specify the way reduction in electric field at threshold activation leads to observed outward S4 motions don’t provide satisfactory explanations of voltage sensing [Bezanilla F (2008) Neuron50:456-468]. Current models depend on unrealistic assumptions: screening of charges by a putative water-filled pore, and simple mechanical devices. A gate, screw, paddle or other everyday device cannot physically explain activation of the highly energetic resting channel, a far-from-equilibrium macromolecular system: The α-helix's hydrogen bonds are too weak to support such rigid structures. The energy required to lengthen the H-bonds is provided when the capacitive energy lost in the voltage reduction to threshold does mechanical work on the channel. Similarities exist between excitable membranes and ferroelectrics [Leuchtag HR (1987) J Theor Biol 127:321-340; 127:341-359; (2008) Voltage-Sensitive Ion Channels, Springer]. The ferroelectricity of excitable membranes must originate in the channels, since VSICs are their active components. In ferroelectrics, the dielectric coefficient ε is a function of the electric field. Electrostatic forces are inversely proportional to ε. Evidence from molecules with the sidechains of the branched-chain amino acids isoleucine, leucine and valine shows that their ε becomes remarkably large in a high electric field [Yoshino K, Sakurai T (1991) in: Goodby JW et al. Ferroelectric Liquid Crystals:317-363], comparable to that in a resting channel. According to the Channel Activation by Electrostatic Repulsion (CAbER) model, ε is high at rest potential and drops on depolarization. The consequently increased electrostatic repulsion between positively charged arginine and lysine residues at activation expands the S4 segments. This outward motion reconfigures the VSIC into an “open” structure with pore-domain sites wide enough to accommodate unhydrated permeant ions that hop stochastically across the channel [Leuchtag HR (2016) Biophys. J. 112(3):544a; 112(3):543a-544a].

Excitable Membrane, Ion Channel, Electrostatics: A Historical Sketch

The roughly one-tenth of a volt across an excitable membrane may not seem large, but across a membrane two lipid molecules thick it yields an electric field comparable to one causing atmospheric lightning. Early attempts to explain the physical basis of the nerve impulse modeled its ion currents as stemming from two processes: the movement of ionic charges by the electric field and the ion diffusion due to ion-concentration differences across the membrane. Hampered by its assumptions of constant properties, this classical electrodiffusion model couldn’t explain axonal membrane data. An eclectic approach combining an equation from electrodiffusion theory with elements of cable theory, wave theory and circuit theory—capacitor, batteries, variable conductors—transformed biophysical science with its successful fitting of the action potential's time course. The development of glass pipette electrodes that restrict ion flow to microscopic membrane patches led to the isolation of ion channels, glycoprotein macromolecules that selectively conduct ion currents. Because it's easy to visualize water-filled pores across these macromolecules, fitted with gates that block or allow ion currents across the membrane, they were named voltage-gated ion channels. This approach is challenged because of its: simplistic models of everyday devices, including screws and paddles; assumption of constant channel capacitance; and disregard of electrostatic repulsions between same-charge residues. Genetic engineering techniques brought the discovery of structural features of many such ion channels. One universal feature is a membrane-spanning segment with a regular array of positively charged amino-acid residues. All also contain multiple amino acids whose sidechains fork into two branches. An electrostatic model based on the ion channel's strong similarities to ferroelectric liquid crystals containing branched chains helps explain the depolarization-driven activation of voltage-sensitive ion channels. [See Leuchtag H R (2008) Voltage-Sensitive Ion Channels, Springer; (2017) Biophys. J. 112(3):544a; 112(3):543a-544a; 112(3):464a.]

Determining the Target of Membrane Sterols on the Gating of Voltage-Gated Potassium Channels using Voltage-Clamp Fluorometry

Membrane lipids can affect the gating of voltage sensitive ion channels through different non-specific and specific mechanisms. It has been shown that cholesterol and 7-dehydrocholesterol (7DHC) have remarkable effects on the gating of Kv1.3 (shift in voltage-dependency of activation and a slower rate of activation) but it is not clear whether these effects are mediated by the actions through the voltage sensor domain (VSD) or the pore domain (PD). Our aim was to investigate whether the major target of the action of these membrane sterols is the VSD, PD or the coupling between these two domains. To test the specificity of the effect we carried out our measurements on channels with differing structures and gating mechanisms: Kv1.3 and the non-domain-swapped Kv10.1. Current recordings were performed with VCF technique using a Xenopus laevis oocyte expression system. To monitor the movement of the VSDs of the channels the specific cysteine residues on the S3-S4 extracellular linker were labeled with MTS-TAMRA. By electrophysiological measurements we determined typical current parameters of the channels and F-V curves from the fluorescent signal in control and sterol-loaded cells. In the oocyte expression system we were able to successfully reproduce the shift in voltage-dependency of activation and a slower rate of activation in the case of Kv1.3 and as a novel finding we obtained similar results with Kv10.1. We found no voltage shifts in the F-V curves paralleling the G-V shift in either ion channel, only the slopes of these curves were decreased in both cases. These results suggest that cholesterol and 7-DHC exert their effects by acting directly on the PD and/or the coupling mechanism, instead of influencing the VSD. Support: KTIA_NAP_13-2-2015-0009

Spontaneous, local diastolic subsarcolemmal calcium releases in single, isolated guinea-pig sinoatrial nodal cells.

Uptake and release calcium from the sarcoplasmic reticulum (SR) (dubbed “calcium clock”), in the form of spontaneous, rhythmic, local diastolic calcium releases (LCRs), together with voltage-sensitive ion channels (membrane clock) form a coupled system that regulates the action potential (AP) firing rate. LCRs activate Sodium/Calcium exchanger (NCX) that accelerates diastolic depolarization and thus participating in regulation of the time at which the next AP will occur. Previous studies in rabbit SA node cells (SANC) demonstrated that the basal AP cycle length (APCL) is tightly coupled to the basal LCR period (time from the prior AP-induced Ca2+ transient to the diastolic LCR occurrence), and that this coupling is further modulated by autonomic receptor stimulation. Although spontaneous LCRs during diastolic depolarization have been reported in SANC of various species (rabbit, cat, mouse, toad), prior studies have failed to detect LCRs in spontaneously beating SANC of guinea-pig, a species that has been traditionally used in studies of cardiac pacemaker cell function. We performed a detailed investigation of whether guinea-pig SANC generate LCRs and whether they play a similar key role in regulation of the AP firing rate. We used two different approaches, 2D high-speed camera and classical line-scan confocal imaging. Positioning the scan-line beneath sarcolemma, parallel to the long axis of the cell, we found that rhythmically beating guinea-pig SANC do, indeed, generate spontaneous, diastolic LCRs beneath the surface membrane. The average key LCR characteristics measured in confocal images in guinea-pig SANC were comparable to rabbit SANC, both in the basal state and in the presence of β-adrenergic receptor stimulation. Moreover, the relationship between the LCR period and APCL was subtended by the same linear function. Thus, LCRs in guinea-pig SANC contribute to the diastolic depolarization and APCL regulation. Our findings indicate that coupled-clock system regulation of APCL is a general, species-independent, mechanism of pacemaker cell normal automaticity. Lack of LCRs in prior studies is likely explained by technical issues, as individual LCRs are small stochastic events occurring mainly near the cell border.

Novel roles for voltage sensitive ion channels in retinal pigment epithelium and phagocytosis

SummaryPhotoreceptors of the retina undergo a daily renewal process where they shed 10% of their outer segment disks that are then digested by the retinal pigment epithelium (RPE). Recent work demonstrated that L‐type calcium channels in RPE are important for the diurnal regulation of this process. We investigated the regulatory role of several ion channels of the RPE in phagocytosis using human embryonic stem cell (hESC)‐derived RPE and freshly isolated mouse tissue. The ion channels were first characterized by patch clamp recordings. The localization of photoreceptor outer segments (POS) and different ion channels during phagocytosis were studied by incubating hESC‐derived RPE with purified POS particles or by dissecting mouse RPE during the physiological peak of POS shedding. Our phagocytosis assays and subsequent immunolabeling showed a promising co‐localization between certain voltage sensitive ion channels, opsin and proteins involved in the phagocytosis pathway. Moreover, blocking the activity of these channels significantly reduced the efficiency of the process. Overall, several types of ion channels appear to be involved in the phagocytosis pathway. Yet, more work is required to assess their specific role.

Nanosecond pulsed electric fields depolarize transmembrane potential via voltage-gated K+, Ca2+ and TRPM8 channels in U87 glioblastoma cells

Nanosecond pulsed electric fields (nsPEFs) have a variety of applications in the biomedical and biotechnology industries. Cancer treatment has been at the forefront of investigations thus far as nsPEFs permeabilize cellular and intracellular membranes leading to apoptosis and necrosis. nsPEFs may also influence ion channel gating and have the potential to modulate cell physiology without poration of the membrane. This phenomenon was explored using live cell imaging and a sensitive fluorescent probe of transmembrane voltage in the human glioblastoma cell line, U87 MG, known to express a number of voltage-gated ion channels. The specific ion channels involved in the nsPEF response were screened using a membrane potential imaging approach and a combination of pharmacological antagonists and ion substitutions. It was found that a single 10ns pulsed electric field of 34kV/cm depolarizes the transmembrane potential of cells by acting on specific voltage-sensitive ion channels; namely the voltage and Ca2+ gated BK potassium channel, L- and T-type calcium channels, and the TRPM8 transient receptor potential channel.

Detection of DNA molecules in a lipid nanotube channel in the low ion strength conditions

Investigation of the transport phenomena in the nanoscopic channels/pores with the diameter smaller than 100 nm is of utmost importance for various biological, medical, and technical applications. Presently, the main line of development of nanofluidics is creation of biosensors capable of detecting single molecules and manipulating them. Detection of molecules is based on the measurement of electric current through a channel of appropriate size: when the molecule enters the channel, which diameter is comparable with the molecule size, the ion current reduces. In order to improve transport properties of such channels, their walls are often coated with a lipid bilayer, which behaves as two-dimensional liquid and thus is capable of supporting transport phenomena. In the present work, we utilized this property of lipid membranes for the development of a method for detecting and controlling transport of single-stranded DNA through channels formed by membrane cylinders with the luminal radii of 5–7 nm. We have demonstrated that in the conditions of small ion strength, the appearance of a DNA molecule inside such channel is accompanied by an increase of its ion conductivity and can be controlled by the polarity of the applied voltage. The amplitude of the ion current increase allows evaluating the amount of DNA molecules inside the channels. It was also demonstrated that upon adsorption of DNA molecules on the lipid bilayer surface, the membrane cylinder behaves as a voltage-sensitive selective ion channel.

Motor Neurons.

Motor neurons translate synaptic input from widely distributed premotor networks into patterns of action potentials that orchestrate motor unit force and motor behavior. Intercalated between the CNS and muscles, motor neurons add to and adjust the final motor command. The identity and functional properties of this facility in the path from synaptic sites to the motor axon is reviewed with emphasis on voltage sensitive ion channels and regulatory metabotropic transmitter pathways. The catalog of the intrinsic response properties, their underlying mechanisms, and regulation obtained from motoneurons in in vitro preparations is far from complete. Nevertheless, a foundation has been provided for pursuing functional significance of intrinsic response properties in motoneurons in vivo during motor behavior at levels from molecules to systems. © 2017 American Physiological Society. Compr Physiol 7:463-484, 2017.

Findings from Condensed-State Physics on Branched-Chain Amino Acids Apply to Voltage-Sensitive Ion Channels

Dramatic effects on channel function by mutations of branched to unbranched residues demonstrate the importance of branched-chain amino acids (BCAAs)—I, L and V—in voltage-sensitive ion channels (VSICs): L to A mutations in Shaker K channel S4 segments shift conductance-voltage curves.1 Substitution of unbranched for branched residues in fragments of Nav channels alters their voltage response.2 Mutations of L to A in S4 segments of Nav1.4 channels alters steady-state activation curves and slows inactivation.3 Voltage-sensor motion in Ci-VSP channels is tuned over two orders of magnitude or shifted 120 mV by I126 of S1.4 In a Kv channel, I237 controls the voltage dependence of charge movement, shifting the Q-V curve toward more positive voltages; I287 controls the energy barrier underlying activation.5 In 1986, Yoshino et al. investigated whether sidechains of amino acids engender ferroelectric properties in molecules with aromatic rings and chiral centers. Three of them did, dramatically: the BCAA sidechains. One compound with an isoleucine sidechain, 4'-3M2CPOOB, exhibited a ferroelectric phase with extremely large spontaneous polarization and dielectric permittivity ε over 3000.6, 7 Applying these condensed-state-physics findings to VSICs suggests that the high-electric-field resting channel is ferroelectric, with a high ε, so that the electrostatic repulsions between the positively charged arginine and lysine residues of S4 are weak. Threshold depolarization, according to the Channel Activation by Electrostatic Repulsion (CAbER) hypothesis,8 converts the channel to a nonpolar phase with much lower ε, causing these repulsions to greatly increase, which expands the S4 segments. CAbER proposes that this observed outward S4 motion drives the channel into a stochastically ion-conducting, active, conformation. 1. Lopez GA et al. (1991) Neuron 7:327-336. 2. Helluin O et al. (2001) IEEE Trans Diel Elect Insul 8:637-643. 3. Bendahhou S et al. (2007) BBA 1768:1440-1447. 4. Lacroix JJ, Bezanilla F (2012) Biophys J 103: L23-L25. 5. Lacroix JJ et al. (2014) PNAS 111(19):E1950-E1959. 6. Yoshino K et al. (1986) Japan J App Phys 25:L416-L418. 7. Yoshino K, Sakurai T (1991) In: Goodby JW et al., Ferroelectric Liquid Crystals, Gordon and Breach. 8. Leuchtag HR (2008) Voltage-Sensitive Ion Channels, Springer; (2016) Biophys J 110(3) 277a; http://doi.org/10.13140/RG.2.1.3360.2328.