Channel Recordings Research Articles

Eeg based smart emotion recognition using meta heuristic optimization and hybrid deep learning techniques

In the domain of passive brain-computer interface applications, the identification of emotions is both essential and formidable. Significant research has recently been undertaken on emotion identification with electroencephalogram (EEG) data. The aim of this project is to develop a system that can analyse an individual’s EEG and differentiate among positive, neutral, and negative emotional states. The suggested methodology use Independent Component Analysis (ICA) to remove artefacts from Electromyogram (EMG) and Electrooculogram (EOG) in EEG channel recordings. Filtering techniques are employed to improve the quality of EEG data by segmenting it into alpha, beta, gamma, and theta frequency bands. Feature extraction is performed with a hybrid meta-heuristic optimisation technique, such as ABC-GWO. The Hybrid Artificial Bee Colony and Grey Wolf Optimiser are employed to extract optimised features from the selected dataset. Finally, comprehensive evaluations are conducted utilising DEAP and SEED, two publically accessible datasets. The CNN model attains an accuracy of approximately 97% on the SEED dataset and 98% on the DEAP dataset. The hybrid CNN-ABC-GWO model achieves an accuracy of approximately 99% on both datasets, with ABC-GWO employed for hyperparameter tuning and classification. The proposed model demonstrates an accuracy of around 99% on the SEED dataset and 100% on the DEAP dataset. The experimental findings are contrasted utilising a singular technique, a widely employed hybrid learning method, or the cutting-edge method; the proposed method enhances recognition performance.

Characterization of a novel Ca2+-Activated potassium channel in rat brain rough endoplasmic reticulum

ObjectivesPotassium channels in the endoplasmic reticulum (ER) are crucial for maintaining calcium balance during calcium fluxes. Disruption in ER calcium balance leads to ER stress, implicated in diseases like diabetes and Alzheimer's disease (AD). However, limited data exists on ER potassium channels in excitable tissues such as the brain. To fill this gap, we aimed to evaluate potassium currents in rat brain rough endoplasmic reticulum (RER). MethodsRats were euthanized under deep anesthesia and their brains were immediately removed. The brains were then homogenized in ice-cold sucrose buffer, followed by the extraction of RER microsomes through a series of centrifugation processes. Purity of sample was evaluated using western blotting technique. Single channel recordings were done in voltage steps from +50 to −60 mV following incorporation of rat brain RER vesicles into planar bilayers. ResultsWe observed a voltage-dependent potassium channel with an approximate conductance of 188 pS. Channel open probability was low at negative voltages, increasing at positive voltages. The channel was blocked by Charybdotoxin but not by Iberiotoxin. Additionally, TRAM-34, a specific KCa3.1 channel blocker, suppressed channel current amplitude and open probability. Western blot analysis revealed specific bands for anti-KCa3.1 antibody, approximately 50 kDa in brain homogenate and RER fraction. ConclusionOur study provides strong evidence for the presence of an KCa3.1 channel on the RER membrane in rat brain, exhibiting distinct electro-pharmacological profile compared to plasma membrane and other organelles.

Biophysical essentials – A full stack open-source software framework for conserved and advanced analysis of patch-clamp recordings

Background and ObjectivesPatch-Clamp recordings allow for in depth electrophysiological characterization of single cells, their general biophysical properties as well as characteristics of voltage- and ligand-gated ionic currents. Different acquisition modes, such as whole-cell patch-clamp recordings in the current or voltage clamp configuration, capacitance measurements or single channel recordings from cultured cells as well as acute brain slices are routinely performed for these purposes. Nevertheless, multipurpose transparent and adaptable software tools to perform reproducible state-of-the-art analysis of multiple experiment types and to manage larger sets of experimental data are currently unavailable. MethodsBiophysical Essentials (BPE) was developed as an open-source full stack python software for transparent and reproducible analysis of electrophysiological recordings. For validation, BPE results were compared with manually analyzed single-cell patch-clamp data acquired from a human in vitro nociceptor-model and mouse dorsal root ganglia neurons. ResultsWhile initially designed to improve time consuming and repetitive analysis steps, BPE was further optimized as a technical software solution for entire workflow processing including data acquisition, data preprocessing, normalization and visualization and of single recordings up to stacked calculations and statistics of multiple experiments. BPE can operate with different file formats from different amplifier systems and producers. An in-process database logs all analysis steps reproducible review and serves as a central storage point for recordings. Statistical testing as well as advanced analysis functions like Boltzmann-fitting and dimensional reduction methods further support the researchers' needs in projects involving electrophysiology techniques. ConclusionsBPE extends beyond available patch-clamp specific, open source – and commercial analysis tools in particular because of reproducible and sharable analysis workflows. BPE enables full analysis from raw data acquisition to publication ready result visualizations – all within one single program. Thereby, BPE significantly enhances transparency in the analytical process of patch-clamp data analysis. BPEs function scope is completely accessible through an easy-to-use graphical user interface eliminating the need for programing language proficiency as required by many community patch-clamp analysis frameworks and algorithms.

Угроза социальной инженерии и фишинга в современной информационной безопасности

Information is the most important resource of any company in our time, so ensuring its protection is one of the priority business tasks of each organization. Over the years, technical security systems have been increasingly improved through technological developments, the recording of multiple channels of information leakage and the growing need for information security in general. Well-designed technical protection systems will always perform the tasks assigned to them, but one single factor can make them useless – a person. People will remain human, with their weaknesses, prejudices, stereotypes and mistakes, being the weakest link in the security chain. So attacks started to gain popularity, targeting not the system itself, but its users, the so-called social engineering attacks. In this article the issues of threats of social engineering and phishing in modern information security are considered. During the work the history and principle of social engineering were analyzed. As a result, an example of a real phishing attack (penteste) was presented, the analysis of statistical data was made. Conclusions about the phishing threat were presented.

A Cell-Type Selective Stimulation and Recording System for Retinal Ganglion Cells.

Future retinal implants will require a stimulation selectivity between different sub-types of Retinal Ganglion Cells (RGCs) to evoke natural perceptions rather than phosphenes in patients. To achieve this, a cell-type specific stimulation pipeline is required that identifies target RGC sub-types from recorded input images and extracts the specific stimulation parameters to activate this cell-type selectively. Promising biological experiments showed that ON-/OFF- sustained/transient RGCs could be selectively activated by modulating repetition rate and amplitude of an electrical stimulation current in the kilohertz range. This research presents a 42 channel current controlled stimulation and recording system on chip (SoC) with parameter input from a real time target RGC selection algorithm. The SoC is able to stimulate retinal tissue with sinusoidal frequencies higher than 1 kHz at amplitudes of up to 200 μA at a supply voltage of 1.8 V. It also includes tunable recording units with an integrated action potential detection pipeline that are able to amplify signals between 1 Hz and 50 kHz. The required area of one stimulator is 0.0071 mm2, while one recording unit consumes an area of 0.0092 mm2. The application of sinusoidal stimulation currents in the kilohertz range towards retinal tissue leads to a suppressive response of only certain RGC sub-types that has not been oberved before, using electrical stimulation. Because this response is very similar to the natural light response of RGCs, this stimulation approach can lead to a more genuine visual perception for patients using retinal implants.

Activation of BKα channel provented uremic cardiomyopathy by attenuating oxidative stress

Background: Uremic cardiomyopathy and renal fibrosis contribute to chronic kidney disease (CKD)-induced morbidity and mortality. Our previous study found that activation of the large conductance calcium-activated potassium channels (BK channels) attenuated renal fibrosis in mice (Wang et al, Kid Int, 2021). We hypothesized that upregulation of BK channels would suppress cardiac fibrosis in CKD. Methods: CKD mice were induced by 5/6 nephrectomy. To upregulation of BKa channels, BMS-191011 (10 mg/kg BW) was given by IP injection every day for 6-8 weeks. Single channel recordings were used to analyze the activation of BKa channel. Blood pressure was measured by non-invasive photoplethysmography using the tail-cuff method. Echocardiogram was used to assess cardiac function. Cultured H9C2 cardiac myoblasts were used to detect the impact of BK opener (NS1916 20mM) on fibrosis markers and oxidative stress. The mRNA expression of BKa in heart was assayed by qPCR. The Hydrogen peroxide (H2O2) was tested by Amplex Red Hydrogen Peroxide Kit. DHE (Dihydroethidium) was assayed to detect superoxide. Superoxide Dismutase (SOD), a defense of oxidative enzyme, was measured using colorimetric activity kit. Results: The expression of BKa mRNA and protein were decreased and cardiac fibrosis was increased in the heart of CKD mice. Single channel recordings showed that human uremic serum (User) attenuated the activation of BKa channel. Upregulation of BKa channel by BSM-191011 decreased the CKD-induced increase in systolic and diastolic blood pressure. Echocardiogram showed that LV end-diastolic dimension increased in 5/6Nx mice, but back to normal after BK opener treatment. Ejection fraction also improved by this treatment. Fibronectin and vimentin were also significantly increased in CKD heart, whereas BMS treatment attenuated the amount of both proteins. In cultured cardiac myoblasts, User and TGFβ increased fibronectin and collagen I, which were in a dose-dependent manner. BKa openers (NS1916) limited the User and TGF-induced upregulation of both proteins in H9C2 cells. User also significantly increased H2O2 and superoxide production in cultured H9C2 cells. Activation of BKa significantly abolished this upregulation. In addition, User and TGFβ decrease SOD production, NS1916 blocked this decline in a dose dependent manner. Conclusions: Activation of BK channel in CKD animals attenuates cardiac fibrosis likely through reduction of uremia-induced oxidative stress. This study could provide new approaches for developing therapeutic strategies for treating uremic cardiomyopathy in chronic kidney diseases. the Department of Veteran Affairs MERIT Award 5I01BX000994 to HC. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Exploiting passive acoustic recordings of seismic survey datasets

Marine seismic reflection surveys provide a dense and abundant dataset covering a large region of geological interest in the ocean. These data provide an opportunity for acoustic analysis with varying environmental characteristics, both in the water column and the seabed. In a typical survey, an airgun array is fired tens to hundreds of thousands of times, and hundreds of receiver channels record the acoustic signal reflected from the seabed after each shot. Additionally, the high amplitude signal broadcast from airgun arrays used in these surveys may be measured passively by hydrophones located close to the survey. In this work, we consider the data measured by Ocean Observatories Initiative (OOI) hydrophones adjacent to two seismic surveys, MGL1905, and MGL2104. In each case, a 6600 in3 airgun array is fired ∼every 37.5 m along multiple survey lines extending 10s to 100s of kilometers. Each survey generates multiple terabytes of acoustic data, and many of the shots are also captured by OOI hydrophones. This work aims to combine these two datasets to evaluate the acoustic behavior of airgun shots over a variety of conditions and examine the relationship between various environmental factors and acoustic propagation behavior. [Work supported by ONR.]

All optical neural interfaces

Brain/computer interfaces (BCIs) rely on the concurrent recording of many channels of electrical activity from excitable tissue. Traditionally such neural interfacing has been performed using cumbersome, channel-limited multielectrode arrays. We believe that BCIs can greatly benefit from using an optical approach based on simple yet powerful liquid-crystal based transducer technology. This approach potentially offers a technology platform that can sustain the necessary bandwidth, density of channels, responsivity, and conformability that are required for the long-term viability of such interfaces. In this paper we review the overall architecture of this approach, the challenges it faces, and the solutions that are being developed at UNSW Sydney.

Role of paraoxonase 3 in regulating ENaC-mediated Na+ transport in the distal nephron.

Paraoxonase 3 (PON3) is expressed in the aldosterone-sensitive distal nephron, where filtered Na+ is reabsorbed mainly via the epithelial Na+ channel (ENaC) and Na+ -coupled co-transporters. We previously showed that PON3 negatively regulates ENaC through a chaperone mechanism. The present study aimed to determine the physiological role of PON3 in renal Na+ and K+ homeostasis. Pon3 knockout (KO) mice had higher amiloride-induced natriuresis and lower plasma [K+ ] at baseline. Single channel recordings in split-open tubules showed that the number of active channels per patch was significantly higher in KO mice, resulting in a higher channel activity in the absence of PON3. Although whole kidney abundance of ENaC subunits was not altered in Pon3 KOs, ENaC gamma subunit was more apically distributed within the connecting tubules and cortical collecting ducts of Pon3 KO kidneys. Additionally, small interfering RNA-mediated knockdown of PON3 in cultured mouse cortical collecting duct cells led to an increased surface abundance of ENaC gamma subunit. As a result of lower plasma [K+ ], sodium chloride co-transporter phosphorylation was enhanced in the KO kidneys, a phenotype that was corrected by a high K+ diet. Finally, PON3 expression was upregulated in mouse kidneys under dietary K+ restriction, potentially providing a mechanism to dampen ENaC activity and associated K+ secretion. Taken together, our results show that PON3has a role in renal Na+ and K+ homeostasis through regulating ENaC functional expression in the distal nephron. KEY POINTS: Paraoxonase 3 (PON3) is expressed in the distal nephron of mouse kidneys and functions as a molecular chaperone to reduce epithelial Na+ channel (ENaC) expression and activity in heterologous expression systems. We examined the physiological role of PON3 in renal Na+ and K+ handling using a Pon3 knockout (KO) mouse model. At baseline, Pon3 KO mice had lower blood [K+ ], more functional ENaC in connecting tubules/cortical collecting ducts, higher amiloride-induced natriuresis, and enhanced sodium chloride co-transporter (NCC) phosphorylation. Upon challenge with a high K+ diet, Pon3 KO mice had normalized blood [K+ ] and -NCC phosphorylation but lower circulating aldosterone levels compared to their littermate controls. Kidney PON3 abundance was altered in mice under dietary K+ loading or K+ restriction, providing a potential mechanism for regulating ENaC functional expression and renal Na+ and K+ homeostasis in the distal nephron.

Protein nanopore-based sensors for public health analyte detection.

High-throughput and label-free protein nanopore-based sensors are extensively used in DNA sequencing, single-protein analysis, molecular sensing and chemical catalysis with single channel recording. These technologies show great potential for identifying various harmful substances linked to public health by addressing the limitations of current portability and the speed of existing techniques. In this review, we provide an overview of the fundamental principles of nanopore sensing, with a focus on chemical modification and genetic engineering strategies aimed at enhancing the detection sensitivity and identification accuracy of protein nanopores. The engineered protein nanopores enable direct sensing, while the introduction of aptamers and substrates enables indirect sensing, translating the physical structure and chemical properties of analytes into readable signals. These scientific discoveries and engineering efforts have provided new prospects for detecting and monitoring trace hazardous substances.

Calcium chelation independent effects of BAPTA on endogenous ANO6 channels in HEK293T cells

Selective calcium chelator 1,2-Bis(2-aminophenoxy) ethane-N,N,N′,N′-tetraacetic acid (BAPTA) is a common tool to investigate calcium signaling. However, BAPTA express various effects on intracellular calcium signaling, which are not related to its ability to bind Ca2+. In patch clamp experiments, we investigated calcium chelation independent effects of BAPTA on endogenous calcium-activated chloride channels ANO6 (TMEM16F) in HEK293T cells. We have found that application of BAPTA to intracellular solution led to two distinct effects on channels properties. On the one hand, application of BAPTA acutely reduced amplitude of endogenous ANO6 channels induced by 10 μM Ca2+ in single channel recordings. On the other hand, BAPTA application by itself induced ANO6 channel activity in the absence of the intracellular calcium elevation. Open channel probability was enhanced by increasing the intracellular BAPTA concentration from 0.1 to 1 and 10 mM. Another calcium chelator EGTA did not demonstrate chelation independent effects on the ANO6 activity in the same conditions. Due to off target effects BAPTA should be used with caution when studying calcium-activated ANO6 channels.

Pressure Pulsatility Links Cardio-Respiratory and Brain Rhythmicity.

This article presents evidence indicating that intracranial pressure (ICP) pulsatility, associated with the heartbeat and breathing, is not just a source of mechanical artefact in electrical recordings, but is "sensed" and plays a role in the brain's information processing. Patch-clamp recording of pressure-activated channels, and detection of Piezo2-protein channel expression in brain neurons, suggest that these channels provide neurons with an intrinsic resonance to ICP pulsatility, which acts to synchronize remote neural networks. Direct measurements in human patients indicate that heartbeat and breathing rhythms generate intracranial forces of tens of millinewtons, exceeding by orders of magnitude the localized forces shown by atomic force microscopy and optical tweezers to activate Piezo channels in isolated neocortical and hippocampal neurons. Additionally, many human touch and proprioceptors, which are also transduced by Piezo channels, show spiking that is phase-locked to heartbeat- and breathing-induced extracranial pressure pulsations. Finally, based on the observation that low-frequency oscillations modulate the phase and amplitude of high-frequency oscillations, body and brain oscillations are proposed to form a single hierarchical system in which the heartbeat is the basic frequency and scaling factor for all other oscillations. Together, these results support the idea that ICP pulsatility may be elemental in modulating the brain's electrical rhythmicity.

Deep learning and beamforming comparison of source ranging in a laboratory tank

Deep learning has been shown to be useful for ocean acoustics applications, such as source ranging. The variable nature of the ocean causes difficulty when attempting to apply trained models to new datasets. To explore ways to train supervised deep learning models that are robust to environmental variability, laboratory tank measurements can be used. A laboratory tank presents a system where uncertainty in the acoustic environment can be adjusted in a more controlled manner. In this work, recordings of ultrasonic chirps (50–200 kHz) are obtained at different source-receiver positions. Time-averaged spectral density levels are used to train one-dimensional convolutional neural networks that predict source-receiver range. The trained networks are tested on data obtained under different conditions. Data augmentation techniques are applied to increase the models’ robustness in the presence of limited uncertainty. Metrics such as root mean-squared error and mean absolute percent error are used to quantify the model’s performance. The results from deep learning with single channel recordings and multi-channel recordings are compared with traditional beamforming methods on the multi-channel data. [Work supported by the Office of Naval Research.]

Broadly applicable methods for the detection of artefacts in electroencephalography acquired simultaneously with hemodynamic recordings

Electroencephalography (EEG) data, acquired simultaneously with magnetic resonance imaging (MRI), must be corrected for artefacts related to MR gradient switches (GS) and the cardioballistic (CB) effect. Canonical approaches require additional signal acquisition for artefact detection (e.g., MR volume onsets, ECG), without which the EEG data would be rendered uncleanable from these artefacts.•We present two broadly applicable methods for artefact detection based on peak detection combined with temporal constraints with respect to periodicity directly from the EEG data itself; no additional signals are required.We validated the performance of our methods versus the two canonical approaches for detection of GS/CB artefact, respectively, on 26 healthy human EEG-functional MRI resting-state datasets. Utilising various performance metrics, we found our methods to perform as well as – and sometimes better than - the canonical standard approaches. With as little as one EEG channel recording, our methods can be applied to detect GS/CB artefacts in EEG data acquired simultaneously with MRI in the absence of MR volume onsets and/or an ECG recording. The detected artefact onsets can then be fed into the standard artefact correction software.

Adenosine stimulates the basolateral 50pS K+ channel in renal proximal tubule via adenosine-A1 receptor.

Background: The basolateral potassium channels play an important role in maintaining the membrane transport in the renal proximal tubules (PT) and adenosine receptors have been shown to regulate the trans-epithelial Na+ absorption in the PT. The aim of the present study is to explore whether adenosine also regulates the basolateral K+ channel of the PT and to determine the adenosine receptor type and the signaling pathway which mediates the effect of adenosine on the K+ channel. Methods: We have used the single channel recording to examine the basolateral K+ channel activity in the proximal tubules of the mouse kidney. All experiments were performed in cell-attached patches. Results: Single channel recording has detected a 50pS inwardly-rectifying K+ channel with high channel open probability and this 50 pS K+ channel is a predominant type K+ channel in the basolateral membrane of the mouse PT. Adding adenosine increased 50pS K+ channel activity in cell-attached patches, defined by NPo (a product of channel Numbers and Open Probability). The adenosine-induced stimulation of the 50pS K+ channel was absent in the PT pretreated with DPCPX, a selective inhibitor of adenosine A1 receptor. In contrast, adenosine was still able to stimulate the 50pS K+ channel in the PT pretreated with CP-66713, a selective adenosine A2 receptor antagonist. This suggests that the stimulatory effect of adenosine on the 50pS K+ channel of the PT was mediated by adenosine-A1 receptor. Moreover, the effect of adenosine on the 50 pS K+ channel was blocked in the PT pretreated with U-73122 or Calphostin C, suggesting that adenosine-induced stimulation of the 50pS K+ channels of the PT was due to the activation of phospholipase C (PLC) and protein kinase C (PKC) pathway. In contrast, the inhibition of phospholipase A2 (PLA2) with AACOCF3 or inhibition of protein kinase A (PKA) with H8 failed to block the adenosine-induced stimulation of the 50pS K+ channel of the PT. Conclusion: We conclude that adenosine activates the 50pS K+ channels in the basolateral membrane of PT via adenosine-A1 receptor. Furthermore, the effect of adenosine on the 50pS K+ channel is mediated by PLC-PKC signaling pathway.

Real-time quantitative characterization of ion channel activities for automated control of a lipid bilayer system

This paper describes a novel signal processing method to characterize the activity of ion channels on a lipid bilayer system in a real-time and quantitative manner. Lipid bilayer systems, which enable single-channel level recordings of ion channel activities against physiological stimuli in vitro, are gaining attention in various research fields. However, the characterization of ion channel activities has heavily relied on time-consuming analyses after recording, and the inability to return the quantitative results in real time has long been a bottleneck to incorporating the system into practical products. Herein, we report a lipid bilayer system that integrates real-time characterization of ion channel activities and real-time response based on the characterization result. Unlike conventional batch processing, an ion channel signal is divided into short segments and processed during the recording. After optimizing the system to maintain the same characterization accuracy as conventional operation, we demonstrated the usability of the system with two applications. One is quantitative control of a robot based on ion channel signals. The velocity of the robot was controlled every second, which was around tens of times faster than the conventional operation, in proportion to the stimulus intensity estimated from changes in ion channel activities. The other is the automation of data collection and characterization of ion channels. By constantly monitoring and maintaining the functionality of a lipid bilayer, our system enabled continuous recording of ion channels over 2 h without human intervention, and the time of manual labor has been reduced from conventional 3 h to 1 min at a minimum. We believe the accelerated characterization and response in the lipid bilayer systems presented in this work will facilitate the transformation of lipid bilayer technology toward a practical level, finally leading to its industrialization.

Revealing the single-channel characteristics of OprD (OccAB1) porins from hospital strains of Acinetobacter baumannii.

Nowadays, reports of antimicrobial resistance (AMR) against many antibiotics are increasing because of their misapplication. With this rise, there is a serious decrease in the discovery and development of new types of antibiotics amid an increase in multi-drug resistance. Unfermented Acinetobacter baumannii from gram-negative bacteria, which is one of the main causes of nosocomial infections and multi-drug resistance, has 4 main kinds of antibiotic resistance mechanism: inactivating antibiotics by enzymes, reduced numbers of porins and changing of their target or cellular functions due to mutations, and efflux pumps. In this study, characterization of the possible mutations in OprD (OccAB1) porins from hospital strains of A. baumannii were investigated using single channel electrophysiology and compared with the standard OprD isolated from wild type ATCC 19,606. For this aim, 5 A. baumannii bacteria samples were obtained from patients infected with A. baumannii, after which OprD porins were isolated from these A. baumannii strains. OprD porins were then inserted in an artificial lipid bilayer and the current-voltage curves were obtained using electrical recordings through a pair of Ag/AgCl electrodes. We observed that each porin has a characteristic conductance and single channel recording, which then leads to differences in channel diameter. Finally, the single channel data have been compared with the gene sequences of each porin. It was interesting to find out that each porin isolated has a unique porin diameter and decreased anion selectivity compared to the wild type.

Unpicking DNA translocation in nanopores with simultaneous single-molecule fluorescence and optical single channel recording.

Nanopore-based DNA sequencing offers high throughput and long reads by measuring blockades in current as a strand is translocated through the pore, providing a single-molecule readout with high time resolution. However, electrical measurements alone offer only information regarding the current block itself; to improve nanopore sensing, a molecular picture of the steps of analyte binding, capture and translocation is required. Optical single channel recording of calcium flux through the nanopore enables parallel single-molecule capture events to be distinguished. We combine optical single channel recording with a single molecule fluorescence readout of DNA unzipping to correlate the steps of individual translocations and image the location of the system components. By annealing short oligomers bearing fluorophore-quencher pairs to the translocating DNA strand, we map the process of nanopore capture, threading and unzipping.

Channel-lipid interactions drive the emergence of ion channel clustering, channel-channel cooperativity, and activation hysteresis.

The activation of voltage gated ion channels has been intensely investigated for decades and it is now so well characterized that we have an atomically-detailed description of the major conformational changes taking place at the level of the single molecule. However, this accurate picture cannot accommodate recent experimental observations that highlight a dramatic and so far unsuspected collective behavior: voltage gated ion channels in physiological membranes form clusters and gate cooperatively. Here we present a quantitative theory that bridges these two vastly different length scales and reconciles these seemingly conflicting views. This novel conceptual framework, which is rooted in the statistical physics of immiscible fluids, accounts for the formation of lipid rafts and for the bias they entail on the conformation of the residing ion channels. First, we use tens-of-microseconds MARTINI simulations to show that annular lipids have a distinct compositional bias, which is different for the resting and the activated states. We then use these simulations to estimate channel-lipid interactions and thus parametrize a mesoscopic model. This allows us to explore the spatial organization of ion channels and their response (in the time domain) to changes in the transmembrane potential. We find that channels embedded in membranes close to a miscibility transition develop attractive long-range interactions that give rise to clustering effects. Strikingly, the lipid phase behavior is itself affected by the activation state of the ion channels. Finally, we observed strong activation cooperativity and long time-scales hysteresis effects which can potentially explain the modal gating phenomena observed in many single channel recordings.

Elementary mechanisms underlying activation of leak sodium channels.

The sodium-leak channel (NALCN) are weakly voltage-dependent ion channels responsible for background Na+ permeability that controls resting membrane potential in neurons and other excitable cells. Although homologous to voltage-gated Na+ and Ca2+ channels, NALCN is distinct in associating with auxiliary subunits FAM155A, UNC-79, and UNC-80 which augment its function. Precise regulation of this channel's activity is physiologically crucial, as gain of function mutations in humans lead to severe congenital neurodevelopmental disorders in humans, including infantile hypotonia with psychomotor retardation and characteristic facies 1 (IHPRF1) and congenital contractures of limbs and face, hypotonia and developmental delay (CLIFAHDD). Here we performed cell-attached low noise single-channel recordings to dissect elementary properties of NALCN gating. Expression of NALCN with its canonical subunits revealed a largely non-selective channel with ∼27 pS conductance and a reversal potential of ∼5.7 mV. Scrutiny of single channel recordings showed distinct gating modes and low open probabilities. As extracellular Ca2+ block of NALCN is fundamental to its physiological function, we further probed underlying single channel mechanisms. In all, these results provide a framework to establish regulatory mechanisms in physiology and to contextualize altered channel function in pathophysiology.