THE IONIC BASIS OF ELECTRICAL ACTIVITY IN NERVE AND MUSCLE

An afferent nerve-like electronic device with somatic mechanical perception and sensation management

Tactile and pain perception are essential for biological skin to interact with the external environment. This complex interplay of sensations allows for the detection of potential threats and appropriate responses to stimuli. However, the challenge is to enable flexible electronics to respond to mechanical stimuli such as biological skin, and researchers have not clearly reported the successful integration of somatic mechanical perception and sensation management functions into neuro-like electronics. In this work, an afferent nerve-like device with a pressure sensor and a perception management module is proposed. The pressure sensor comprises two conductive fabric layers and an ionic hydrogel, forming a capacitor structure that emulates the swift transition from tactile to pain perception under mechanical stimulation. Drawing inspiration from the neuronal "gate control" mechanism, the sensation management module adjusts signals in response to rubbing, accelerating the discharge process and reducing the perception duration, thereby replicating the inhibitory effect of biological neurons on pain following tactile interference. This integrated device, encompassing somatic mechanical perception and sensation management, holds promise for applications in soft robotics, prosthetics, and human-machine interaction.

Soft Memristor at a Microbubble Interface

Memristors show promising features for neuromorphic computing. Here we report a soft memristor based on the liquid-vapor surface of a microbubble. The thickness of the liquid film was modulated by electrostatic and interfacial forces, enabling resistance switches. We found a pinched current hysteresis at scanning periods between 1.6 and 51.2 s, while representing a resistor below 1.6 s and a diode-like behavior above 51.2 s. We approximate the thickening/thinning dynamics of liquid film by pressure-driven flow at the interface and derived the impacts of salt concentration and voltage amplitude on the memory effects. Our work opens a new approach to building nanofluidic memristors by a soft interface, which may be useful for new types of neuromorphic computing in the future.

Low sodium availability in hydroponically manipulated host plants promotes cannibalism in a lepidopteran herbivore

As an abundant element in the Earth's crust, sodium plays an unusual role in food webs. Its availability in terrestrial environments is highly variable, but it is nonessential for most plants, yet essential for animals and most decomposers. Accordingly, sodium requirements are important drivers of various animal behavioural patterns and performance levels. To specifically test whether sodium limitation increases cannibalism in a gregarious lepidopteran herbivore, we hydroponically manipulated Helianthus annuus host plants' tissue-sodium concentrations. Gregarious larvae of the bordered patch butterfly, Chlosyne lacinia, cannibalized siblings when plant-tissue sodium concentrations were low in two separate experiments. Although cannibalism was almost non-existent when sodium concentrations were high, individual mortality rates were also high. Sodium concentration in host plants can have pronounced effects on herbivore behaviour, individual-level performance, and population demographics, all of which are important for understanding the ecology and evolution of plant-animal interactions across a heterogeneous phytochemical landscape.

Artificial Action Potential and Ionic Power Device Inspired by Ion Channels and Excitable Cell

In vivo, the membrane potential of the excitable cell working by ion gradients plays a significant role in bioelectricity generation and nervous system operation. Conventional bioinspired power systems generally have adopted ion gradients, but overlook the functions of ion channels and Donnan effect to generate efficient ion flow in the cell. Here, cell-inspired ionic power device implementing the Donnan effect using multi-ions and monovalent ion exchange membranes as artificial ion channels is realized. Different ion-rich electrolytes on either side of the selective membrane generate the ion gradient potentials with high ionic currents and reduce the osmotic imbalance of the membrane. Based on this device, the artificial neuronal signaling is presented by the mechanical switching system of the ion selectivity like mechanosensitive ion channels in a sensory neuron. Compared with reverse electrodialysis, which requires a low concentration, a high-power device with ten times the current and 8.5 times the power density is fabricated. This device activates grown muscle cells by increasing power through serial connection like an electric eel, and shows the possibility of an ion-based artificial nervous system.

The significance of bioelectricity on all levels of organization of an organism. Part 1: From the subcellular level to cells

Bioelectricity plays an essential role in the structural and functional organization of biological organisms. In this first article of our three-part series, we summarize the importance of bioelectricity for the basic structural level of biological organization, i.e. from the subcellular level (charges, ion channels, molecules and cell organelles) to cells.

A color-coded graphical guide to the Hodgkin and Huxley papers

The five papers published by Hodgkin and Huxley in 1952 are seminal works in the field of physiology, earning their authors the Nobel Prize in 1963 and ushering in the era of membrane biophysics. The papers present a considerable challenge to the novice student, but this has been partly allayed by recent publications that have updated the reporting of current and voltage to reflect the modern convention and two books that describe the contents of the papers in detail. A disadvantage is that these guides contain hundreds of pages, requiring considerable time and energy on behalf of the reader. We present a concise guide to the Hodgkin and Huxley papers that includes only essential content, with the data presented in a linear and logical manner. We have color-coded figures for ease of understanding and included boxes that summarize key information for easy reference. It is our expectation that this article will act as an accessible introduction for students to the work of Hodgkin and Huxley and hopefully foster an appreciation for a fascinating story that repays in-depth study.NEW & NOTEWORTHY The Hodgkin and Huxley papers continue to inspire and intimidate, 70 years after their publication. The diverse subjects they cover include advanced experimental procedures, complex data analysis, calculus, and modeling, all of which ensure the papers can present a challenging read. We present a concise guide to the papers that includes only essential content depicted in color-coded graphs, allowing tracking of data from recordings to analysis and incorporation into the model to ease understanding.

Study of transmembrane ion transport under tonicity imbalance using a combination of low frequency-electrical impedance spectroscopy (LF-EIS) and improved ion transport model

Transmembrane ion transport under tonicity imbalance has been investigated using a combination of low frequency-electrical impedance spectroscopy (LF-EIS) and improved ion transport model, by considering the cell diameterd[m] and the initial intracellular ion concentrationc_in[mM] as a function of tonicity expressed by sucrose concentrationc_s[mM]. The transmembrane ion transport is influenced by extracellular tonicity conditions, leading to a facilitation/inhibition of ion passage through the cell membrane. The transmembrane transport coefficientP[m s^-1], which represents the ability of transmembrane ion transport, is calculated by the extracellular ion concentrations obtained by improved ion transport model and LF-EIS measurement.Pis calculated as 4.11 × 10^-6and 3.44 × 10^-6m s^-1atc_sof 10 and 30 mM representing hypotonic condition, 2.44 × 10^-6m s^-1atc_sof 50 mM representing isotonic condition, and 3.68 × 10^-6, 5.16 × 10^-6, 9.51 × 10^-6, and 14.89 × 10^-6m s^-1atc_sof 75, 100, 125 and 150 mM representing hypertonic condition. The LF-EIS results indicate that the transmembrane ion transport is promoted under hypertonic and hypotonic conditions compared to isotonic condition. To verify the LF-EIS results, fluorescence intensityF[-] of extracellular potassium ions is observed to obtain the temporal distribution of average potassium ion concentration within the region of 3.6μm from cell membrane interfacec_ROI[mM]. The slopes of ∆c_ROI/c_ROI1to timetare 0.0003, 0.0002, and 0.0006 under hypotonic, isotonic, and hypertonic conditions, wherec_ROI1denotes initialc_ROI, which shows the same tendency with LF-EIS result that is verified by the potassium ion fluorescence observation.

Vagus nerve bundle stimulation using 1505-nm laser irradiation in an in-vivo rat model

Laser nerve stimulation using near-infrared laser irradiation has recently been studied in the peripheral nervous system as an alternative method to conventional electrical nerve stimulation. Bringing this method to the vagus nerve model could leverage this emerging stimulation approach to be tested in broader preclinical applications. Here, we report the capability of the laser nerve stimulation method on the rat vagus nerve bundle with a 1505-nm diode laser operated in continuous-wave mode. Studies of the stimulation threshold and laser-induced acute thermal injury to the nerve bundle were also performed to determine a temperature window for safe, reliable and reproducible laser stimulation of the rat vagus nerve bundle. The results show that laser stimulation of the vagus nerve bundle provides reliable and reproducible nerve stimulation in a rat model. These results also confirm a threshold temperature of >42°C with acute nerve damage observed above 46°C. A strong correlation was obtained between the laser time required to raise the nerve temperature above the stimulation threshold and the mean arterial pressure response. Advantages of the method such as non-contact delivery of external stimulus signals at mm scaled distance in air, enhanced spatial selectivity and electrical artefact-free measurements may indicate its potential to counteract the side effects of conventional electrical vagus nerve stimulation.

Circuits and Synapses: Hypothesis, Observation, Controversy and Serendipity - An Opinion Piece

More than a century of dedicated research has resulted in what we now know, and what we think we know, about synapses and neural circuits. This piece asks to what extent some of the major advances - both theoretical and practical - have resulted from carefully considered theory, or experimental design: endeavors that aim to address a question, or to refute an existing hypothesis. It also, however, addresses the important part that serendipity and chance have played. There are cases where hypothesis driven research has resulted in important progress. There are also examples where a hypothesis, a model, or even an experimental approach - particularly one that seems to provide welcome simplification - has become so popular that it becomes dogma and stifles advance in other directions. The nervous system rejoices in complexity, which should neither be ignored, nor run from. The emergence of testable "rules" that can simplify our understanding of neuronal circuits has required the collection of large amounts of data that were difficult to obtain. And although those collecting these data have been criticized for not advancing hypotheses while they were "collecting butterflies," the beauty of the butterflies always enticed us toward further exploration.

Flexible Electrodes for In Vivo and In Vitro Electrophysiological Signal Recording

A variety of electrophysiological signals (electrocardiography, electromyography, electroencephalography, etc.) are generated during the physiological activities of human bodies, which can be collected by electrodes and thus provide critical insights into health status or facilitate fundamental scientific research. The long-term stable and high-quality recording of electrophysiological signals is the premise for their further applications, leading to demands for flexible electrodes with similar mechanical modulus and minimized irritation to human bodies. This review summarizes the latest advances in flexible electrodes for the acquisition of various electrophysiological signals. First, the concept of electrophysiological signals and the characteristics of different subcategory signals are introduced. Second, the invasive and noninvasive methods are reviewed for electrophysiological signal recording with a highlight on the design of flexible electrodes, followed by a discussion on their material selection. Subsequently, the applications of the electrophysiological signal acquisition in pathological diagnosis and restoration of body functions are discussed, showing the advantages of flexible electrodes. Finally, the main challenges and opportunities in this field are discussed. It is believed that the further exploration of materials for flexible electrodes and the combination of multidisciplinary technologies will boost the applications of flexible electrodes for medical diagnosis and human-machine interface.

Monarch caterpillars are robust to combined exposure to the roadside micronutrients sodium and zinc

Human activities are increasing the environmental availability of micronutrients, including sodium and some essential metals. Micronutrients are often limiting in animal diets but may have negative effects when consumed in excess. Though prior research has documented how elevated exposure to individual micronutrients can impact organismal development and fitness, we know less about combined effects of multiple micronutrients. In the wild, monarch butterfly larvae (Danaus plexippus) commonly consume plants in roadside habitats that contain elevated levels of sodium (from road salt) and zinc (from vehicle wear-and-tear). We reared monarch caterpillars to adulthood to test individual and combined effects of dietary sodium and zinc on components of fitness, sodium-linked phenotypes (proxies for neural and flight muscle development) and concentrations of sodium and zinc in adult butterflies. Monarch survival was not impacted by elevated sodium or zinc individually or in combination. Yet, monarchs feeding on sodium-treated milkweed developed relatively larger eyes, consistent with a positive effect of sodium on neural development. Measurements of element concentrations in butterfly and plant tissue indicated that monarchs had higher zinc levels than those present in zinc-treated milkweed but lower sodium levels than those present in sodium-treated milkweed. Monarchs developing on sodium-treated milkweed also had prolonged development time, which might be a cost associated with developing extra neural tissue or investing in mechanisms to excrete excess dietary sodium during the larval stage. Our results indicate that sodium, more than zinc, is likely influencing phenotypic development and performance of insect pollinators in roadside habitats. Yet, in contrast to previous work, our experiment suggests that the highest levels of sodium found along roads are not always harmful for developing monarchs. Future work could consider how potentially stressful effects of micronutrients could be mitigated by increased macronutrient availability or how developmental factors such as migratory status might increase micronutrient requirements.

Epilepsy as a dynamical system, a most needed paradigm shift in epileptology

The idea of the epileptic brain being highly excitable and facilitated to synchronic activity has guided pharmacological treatment since the early twentieth century. Although tackling epilepsy's seizure-prone feature, by tonically modifying overall circuit excitability and/or connectivity, the last 50 years of drug development has not seen a substantial improvement in seizure suppression of refractory epilepsies. This review presents a new conceptual framework for epilepsy in which the temporal dynamics of the disease plays a more critical role in both its understanding and therapeutic strategies. The repetitive epileptiform pattern (characteristic during ictal activity) and other well-defined electrographic signatures (i.e., present during the interictal period) are discussed in terms of the sequential activation of the circuit motifs. Lessons learned from the physiological activation of neural circuitry are used to further corroborate the argument and explore the transition from proper function to a state of instability. Furthermore, the review explores how interfering in the temporally dependent abnormal connectivity between circuits may work as a therapeutic approach. We also review the use of probing stimulation to access network connectivity and evaluate its power to determine transitional states of the dynamical system as it moves towards regions of instability, especially when conventional electrographic monitoring is proven inefficient. Unorthodox cases, with little or no scalp electrographic correlate, in which ictogenic circuitry and/or seizure spread is temporally restricted to neurovegetative, cognitive, and motivational areas are shown as possible explanations for sudden death in epilepsy (SUDEP) and other psychiatric comorbidities. In short, this review presents a paradigm shift in the way that we address the disease and is aimed to encourage debate rather than narrow the rationale epilepsy is currently engaged in. This article is part of the Special Issue "NEWroscience 2018".

Transendothelial Electrical Resistance Measurement across the Blood-Brain Barrier: A Critical Review of Methods

The blood–brain barrier (BBB) represents the tightest endothelial barrier within the cardiovascular system characterized by very low ionic permeability. Our aim was to describe the setups, electrodes, and instruments to measure electrical resistance across brain microvessels and culture models of the BBB, as well as critically assess the influence of often neglected physical and technical parameters such as temperature, viscosity, current density generated by different electrode types, surface size, circumference, and porosity of the culture insert membrane. We demonstrate that these physical and technical parameters greatly influence the measurement of transendothelial electrical resistance/resistivity (TEER) across BBB culture models resulting in severalfold differences in TEER values of the same biological model, especially in the low-TEER range. We show that elevated culture medium viscosity significantly increases, while higher membrane porosity decreases TEER values. TEER data measured by chopstick electrodes can be threefold higher than values measured by chamber electrodes due to different electrode size and geometry, resulting in current distribution inhomogeneity. An additional shunt resistance at the circumference of culture inserts results in lower TEER values. A detailed description of setups and technical parameters is crucial for the correct interpretation and comparison of TEER values of BBB models.

Synergism and unintended effects of the association between imidacloprid and sodium chloride (NaCl) on the management of Euschistus heros

BACKGROUND

The use of insecticidal solutions containing sodium chloride (NaCl) has been proposed as a more environmentally friendly alternative to managing stink bug infestations of Neotropical soybean fields. The potential sublethal and undesirable effects of this practice have, however, been overlooked, especially with novel insecticides. Here, we have evaluated experimentally whether the addition of NaCl (0.5% w/v) to imidacloprid-containing solutions could alter insecticide toxicity and modify the reproductive responses of the Neotropical brown stink bug Euschistus heros.

RESULTS

Adding NaCl to imidacloprid solutions significantly increased imidacloprid toxicity against E. heros. The exposure to E. heros to sublethal concentrations of imidacloprid affected the insect's mating abilities in a concentration-dependent manner. The addition of NaCl to solutions containing imidacloprid at concentrations as low as 0.126 μg a.i. cm^-2 (i.e. the equivalent to 3% of field rate recommendation) also impacted the sexual behavior of E. heros, reducing mating duration. NaCl-exposed stink bugs, however, exhibited higher fecundity and fertility rates than those insects that were unexposed to NaCl or those that were exposed to sublethal levels of imidacloprid only.

CONCLUSIONS

The addition of low amounts of NaCl resulted in a higher toxicity of imidacloprid. This practice, however, can also lead to undesirable effects as increasing reproductive output of E. heros that can potentially compromise the management of these insect pests.

Feeling the heat: source–sink mismatch as a mechanism underlying the failure of thermal tolerance

A mechanistic explanation for the tolerance limits of animals at high temperatures is still missing, but one potential target for thermal failure is the electrical signaling off cells and tissues. With this in mind, here I review the effects of high temperature on the electrical excitability of heart, muscle and nerves, and refine a hypothesis regarding high temperature-induced failure of electrical excitation and signal transfer [the temperature-dependent deterioration of electrical excitability (TDEE) hypothesis]. A central tenet of the hypothesis is temperature-dependent mismatch between the depolarizing ion current (i.e. source) of the signaling cell and the repolarizing ion current (i.e. sink) of the receiving cell, which prevents the generation of action potentials (APs) in the latter. A source–sink mismatch can develop in heart, muscles and nerves at high temperatures owing to opposite effects of temperature on source and sink currents. AP propagation is more likely to fail at the sites of structural discontinuities, including electrically coupled cells, synapses and branching points of nerves and muscle, which impose an increased demand of inward current. At these sites, temperature-induced source–sink mismatch can reduce AP frequency, resulting in low-pass filtering or a complete block of signal transmission. In principle, this hypothesis can explain a number of heat-induced effects, including reduced heart rate, reduced synaptic transmission between neurons and reduced impulse transfer from neurons to muscles. The hypothesis is equally valid for ectothermic and endothermic animals, and for both aquatic and terrestrial species. Importantly, the hypothesis is strictly mechanistic and lends itself to experimental falsification.

N-benzhydryl quinuclidine compounds are a potent and Src kinase-independent inhibitor of NALCN channels

BACKGROUND AND PURPOSE

NALCN is a Na⁺ leak, GPCR-activated channel that regulates the resting membrane potential and neuronal excitability. Despite numerous possible roles for NALCN in both normal physiology and disease processes, lack of specific blockers hampers further investigation.

EXPERIMENTAL APPROACH

The effect of N-benzhydryl quinuclidine compounds on NALCN channels was demonstrated using whole-cell patch-clamp recordings in HEK293T cells overexpressing NALCN and acutely isolated nigral dopaminergic neurons that express NALCN endogenously. Src kinase activity was measured using a Src kinase assay kit, and voltage and current-clamp recordings from nigral dopaminergic neurons were used to measure NALCN currents and membrane potentials.

KEY RESULTS

N-benzhydryl quinuclidine compounds inhibited NALCN channels without affecting TRPC channels, another important route for Na⁺ leak. In HEK293T cells overexpressing NALCN, N-benzhydryl quinuclidine compounds potently suppressed muscarinic M₃ receptor-activated NALCN currents. Structure-function relationship studies suggest that the quinuclidine ring with a benzhydryl group imparts the ability to inhibit NALCN currents regardless of Src family kinases. Moreover, N-benzhydryl quinuclidine compounds inhibited not only GPCR-activated NALCN currents but also background Na⁺ leak currents and hyperpolarized the membrane potential in native midbrain dopaminergic neurons that express NALCN endogenously.

CONCLUSION AND IMPLICATIONS

These findings suggest that N-benzhydryl quinuclidine compounds have a pharmacological potential to directly inhibit NALCN channels and could be a useful tool to investigate functions of NALCN channels.

A redox-based electrogenetic CRISPR system to connect with and control biological information networks

Electronic information can be transmitted to cells directly from microelectronics via electrode-activated redox mediators. These transmissions are decoded by redox-responsive promoters which enable user-specified control over biological function. Here, we build on this redox communication modality by establishing an electronic eCRISPR conduit of information exchange. This system acts as a biological signal processor, amplifying signal reception and filtering biological noise. We electronically amplify bacterial quorum sensing (QS) signaling by activating LasI, the autoinducer-1 synthase. Similarly, we filter out unintended noise by inhibiting the native SoxRS-mediated oxidative stress response regulon. We then construct an eCRISPR based redox conduit in both E. coli and Salmonella enterica. Finally, we display eCRISPR based information processing that allows transmission of spatiotemporal redox commands which are then decoded by gelatin-encapsulated E. coli. We anticipate that redox communication channels will enable biohybrid microelectronic devices that could transform our abilities to electronically interpret and control biological function.

Erythrocyte plasma membrane potential: past and current methods for its measurement

The plasma membrane functions both as a natural insulator and a diffusion barrier to the movement of ions. A wide variety of proteins transport and pump ions to generate concentration gradients that result in voltage differences, while ion channels allow ions to move across the membrane down those gradients. Plasma membrane potential is the difference in voltage between the inside and the outside of a biological cell, and it ranges from ~- 3 to ~- 90 mV. Most of the most significant discoveries in this field have been made in excitable cells, such as nerve and muscle cells. Nevertheless, special attention has been paid to some events controlled by changes in membrane potential in non-excitable cells. The origins of several blood disorders, for instance, are related to disturbances at the level of plasma membrane in erythrocytes, the structurally simplest red blood cells. The high simplicity of erythrocytes, in particular, made them perfect candidates for the electrophysiological studies that laid the foundations for understanding the generation, maintenance, and roles of membrane potential. This article summarizes the methodologies that have been used during the past decades to determine Δψ in red blood cells, from seminal microelectrodes, through the use of nuclear magnetic resonance or lipophilic radioactive ions to quantify intra and extracellular ions, to continuously renewed fluorescent potentiometric dyes. We have attempted to highlight the advantages and disadvantages of each methodology, as well as to provide a description of the technical aspects involved.

Pioneers in CNS inhibition: 2. Charles Sherrington and John Eccles on inhibition in spinal and supraspinal structures

This article reviews the contributions of the English neurophysiologist, Charles Scott Sherrington [1857-1952], and his Australian PhD trainee and collaborator, John Carew Eccles [1903-1997], to the concept of central inhibition in the spinal cord and brain. Both were awarded Nobel Prizes; Sherrington in 1932 for "discoveries regarding the function of neurons," and Eccles in 1963 for "discoveries concerning the ionic mechanisms involved in excitation and inhibition in central portions of the nerve cell membrane." Both spoke about central inhibition at their Nobel Prize Award Ceremonies. The subsequent publications of their talks were entitled "Inhibition as a coordinative factor" and "The ionic mechanism of postsynaptic inhibition", respectively. Sherrington's work on central inhibition spanned 41 years (1893-1934), and for Eccles 49 years (1928-1977). Sherrington first studied central inhibition by observing hind limb muscle responses to electrical (peripheral nerve) and mechanical (muscle) stimulation. He used muscle length and force measurements until the early 1900s and electromyography in the late 1920s. Eccles used these techniques while working with Sherrington, but later employed extracellular microelectrode recording in the spinal cord followed in 1951 by intracellular recording from spinal motoneurons. This considerably advanced our understanding of central inhibition. Sherrington's health was poor during his retirement years but he nonetheless made a small number of largely humanities contributions up to 1951, one year before his death at the age of 94. In contrast, Eccles retained his health and vigor until 3 years before his death and published prolifically on many subjects during his 22 years of official retirement. His last neuroscience article appeared in 1994 when he was 91. Despite poor health he continued thinking about his life-long interest, the mind-brain problem, and was attempting to complete his autobiography in the last years of his life.

Relationship between inorganic ion distribution, resting membrane potential, and the ΔG' of ATP hydrolysis: a new paradigm

Cell membrane potential and inorganic ion distributions are currently viewed from a kinetic electric paradigm, which ignores thermodynamics. The resting membrane potential is viewed as a diffusion potential. The 9 major inorganic ions found in blood plasma (Ca²⁺, Na⁺, Mg²⁺, K⁺, H⁺, Cl^-, HCO₃^-, H₂PO₄^-, and HPO₄^2-) are distributed unequally across the plasma membrane. This unequal distribution requires the energy of ATP hydrolysis through the action of the Na⁺-K⁺ ATPase. The cell resting membrane potential in each of 3 different tissues with widely different resting membrane potentials has been shown to be equal to the Nernst equilibrium potential of the most permeant inorganic ion. The energy of the measured distribution of the 9 major inorganic ions between extra- and intracellular phases was essentially equal to the independently measured energy of ATP hydrolysis, showing that the distribution of these 9 major ions was in near-equilibrium with the ΔG' of ATP. Therefore, thermodynamics does appear to play an essential role in the determination of the cell resting membrane potential and the inorganic ion distribution across the plasma membrane.-Veech, R. L., King, M. T., Pawlosky, R., Bradshaw, P. C., Curtis, W. Relationship between inorganic ion distribution, resting membrane potential, and the ΔG' of ATP hydrolysis: a new paradigm.

Bio-instructive materials for musculoskeletal regeneration

The prevalence and cost of disorders affecting the musculoskeletal system are predicted to rise significantly in the coming years due to the aging global population and the increase of associated risk factors. Despite being the second largest cause of disability, the clinical options for therapeutic intervention remain limited. The clinical translation of cell-based therapies for the treatment of musculoskeletal disorders faces many challenges including maintenance of cell survival in the harsh in vivo environment and the lack of control over regulating cell phenotype upon implantation. In order to address these challenges, the development of bio-instructive materials to modulate cell behavior has taken center stage as a strategy to increase the therapeutic potential of various cell populations. However, the determination of the necessary cues for a specific application and how these signals should be presented from a biomaterial remains elusive. This review highlights recent biochemical and physical strategies used to engineer bio-instructive materials for the repair of musculoskeletal tissues. There is a particular emphasis on emerging efforts such as the engineering of immunomodulatory and antibacterial materials, as well as the incorporation of these strategies into biofabrication and organ-on-a-chip approaches. STATEMENT OF SIGNIFICANCE: Disorders affecting the musculoskeletal system affect individuals across the lifespan and have a profound effect on mobility and quality of life. While small defects in many tissues can heal successfully, larger defects are often unable to heal or instead heal with inferior quality fibrous tissue and require clinical intervention. Cell-based therapies are a promising option for clinical translation, yet challenges related to maintaining cell survival and instructing cell phenotype upon implantation have limited the success of this approach. Bio-instructive materials provide an exciting opportunity to modulate cell behavior and enhance the efficacy of cell-based approaches for musculoskeletal repair. However, the identification of critical instructive cues and how to present these stimuli is a focus of intense investigation. This review highlights recent biochemical and physical strategies used to engineer bio-instructive materials for the repair of musculoskeletal tissues, while also considering exciting progress in the engineering of immunomodulatory and antibacterial materials.

Voltage-Dependent Profile Structures of a Kv-Channel via Time-Resolved Neutron Interferometry

Available experimental techniques cannot determine high-resolution three-dimensional structures of membrane proteins under a transmembrane voltage. Hence, the mechanism by which voltage-gated cation channels couple conformational changes within the four voltage sensor domains, in response to either depolarizing or polarizing transmembrane voltages, to opening or closing of the pore domain's ion channel remains unresolved. Single-membrane specimens, composed of a phospholipid bilayer containing a vectorially oriented voltage-gated K+ channel protein at high in-plane density tethered to the surface of an inorganic multilayer substrate, were developed to allow the application of transmembrane voltages in an electrochemical cell. Time-resolved neutron reflectivity experiments, enhanced by interferometry enabled by the multilayer substrate, were employed to provide directly the low-resolution profile structures of the membrane containing the vectorially oriented voltage-gated K+ channel for the activated, open and deactivated, closed states of the channel under depolarizing and hyperpolarizing transmembrane voltages applied cyclically. The profile structures of these single membranes were dominated by the voltage-gated K+ channel protein because of the high in-plane density. Importantly, the use of neutrons allowed the determination of the voltage-dependent changes in both the profile structure of the membrane and the distribution of water within the profile structure. These two key experimental results were then compared to those predicted by three computational modeling approaches for the activated, open and deactivated, closed states of three different voltage-gated K+ channels in hydrated phospholipid bilayer membrane environments. Of the three modeling approaches investigated, only one state-of-the-art molecular dynamics simulation that directly predicted the response of a voltage-gated K+ channel within a phospholipid bilayer membrane to applied transmembrane voltages by utilizing very long trajectories was found to be in agreement with the two key experimental results provided by the time-resolved neutron interferometry experiments.

Chemical synapses without synaptic vesicles: Purinergic neurotransmission through a CALHM1 channel-mitochondrial signaling complex

Conventional chemical synapses in the nervous system involve a presynaptic accumulation of neurotransmitter-containing vesicles, which fuse with the plasma membrane to release neurotransmitters that activate postsynaptic receptors. In taste buds, type II receptor cells do not have conventional synaptic features but nonetheless show regulated release of their afferent neurotransmitter, ATP, through a large-pore, voltage-gated channel, CALHM1. Immunohistochemistry revealed that CALHM1 was localized to points of contact between the receptor cells and sensory nerve fibers. Ultrastructural and super-resolution light microscopy showed that the CALHM1 channels were consistently associated with distinctive, large (1- to 2-μm) mitochondria spaced 20 to 40 nm from the presynaptic membrane. Pharmacological disruption of the mitochondrial respiratory chain limited the ability of taste cells to release ATP, suggesting that the immediate source of released ATP was the mitochondrion rather than a cytoplasmic pool of ATP. These large mitochondria may serve as both a reservoir of releasable ATP and the site of synthesis. The juxtaposition of the large mitochondria to areas of membrane displaying CALHM1 also defines a restricted compartment that limits the influx of Ca²⁺ upon opening of the nonselective CALHM1 channels. These findings reveal a distinctive organelle signature and functional organization for regulated, focal release of purinergic signals in the absence of synaptic vesicles.

Time-Resolved Neutron Interferometry and the Mechanism of Electromechanical Coupling in Voltage-Gated Ion Channels

The mechanism of electromechanical coupling for voltage-gated ion channels (VGICs) involved in neurological signal transmission, primarily Nav- and Kv-channels, remains unresolved. Anesthetics have been shown to directly impact this mechanism, at least for Kv-channels. Molecular dynamics computer simulations can now predict the structures of VGICs embedded within a hydrated phospholipid bilayer membrane as a function of the applied transmembrane voltage, but significant assumptions are still necessary. Nevertheless, these simulations are providing new insights into the mechanism of electromechanical coupling at the atomic level in 3-D. We show that time-resolved neutron interferometry can be used to investigate directly the profile structure of a VGIC, vectorially oriented within a single hydrated phospholipid bilayer membrane at the solid-liquid interface, as a function of the applied transmembrane voltage in the absence of any assumptions or potentially perturbing modifications of the VGIC protein and/or the host membrane. The profile structure is a projection of the membrane's 3-D structure onto the membrane normal and, in the absence of site-directed deuterium labeling, is provided at substantially lower spatial resolution than the atomic level. Nevertheless, this novel approach can be used to directly test the validity of the predictions from molecular dynamics simulations. We describe the key elements of our novel experimental approach, including why each is necessary and important to providing the essential information required for this critical comparison of "simulation" vs "experiment." In principle, the approach could be extended to higher spatial resolution and to include the effects of anesthetics on the electromechanical coupling mechanism in VGICs.

Microbial nanowires - Electron transport and the role of synthetic analogues

Electron transfer is central to cellular life, from photosynthesis to respiration. In the case of anaerobic respiration, some microbes have extracellular appendages that can be utilised to transport electrons over great distances. Two model organisms heavily studied in this arena are Shewanella oneidensis and Geobacter sulfurreducens. There is some debate over how, in particular, the Geobacter sulfurreducens nanowires (formed from pilin nanofilaments) are capable of achieving the impressive feats of natural conductivity that they display. In this article, we outline the mechanisms of electron transfer through delocalised electron transport, quantum tunnelling, and hopping as they pertain to biomaterials. These are described along with existing examples of the different types of conductivity observed in natural systems such as DNA and proteins in order to provide context for understanding the complexities involved in studying the electron transport properties of these unique nanowires. We then introduce some synthetic analogues, made using peptides, which may assist in resolving this debate. Microbial nanowires and the synthetic analogues thereof are of particular interest, not just for biogeochemistry, but also for the exciting potential bioelectronic and clinical applications as covered in the final section of the review.

STATEMENT OF SIGNIFICANCE

Some microbes have extracellular appendages that transport electrons over vast distances in order to respire, such as the dissimilatory metal-reducing bacteria Geobacter sulfurreducens. There is significant debate over how G. sulfurreducens nanowires are capable of achieving the impressive feats of natural conductivity that they display: This mechanism is a fundamental scientific challenge, with important environmental and technological implications. Through outlining the techniques and outcomes of investigations into the mechanisms of such protein-based nanofibrils, we provide a platform for the general study of the electronic properties of biomaterials. The implications are broad-reaching, with fundamental investigations into electron transfer processes in natural and biomimetic materials underway. From these studies, applications in the medical, energy, and IT industries can be developed utilising bioelectronics.

Relative dielectric constants and selectivity ratios in open ionic channels

We investigate the effects of the relative dielectric coefficient on ionic flows in open ion channels, using mathematical analysis of reasonably general Poisson-Nernst-Planck type models that can include the finite sizes of ions. The value of the relative dielectric coefficient is of course a crucial parameter for ionic behavior in general. Using the powerful theory of singularly perturbed problems in applied mathematics, we show that some properties of open channels are quite insensitive to variation in the relative dielectric coefficient, thereby explaining such effects seen unexpectedly in simulations. The ratio between the total number of one ion species and that of another ion species, and the ratio between the flux of one ion species and that of another ion species do not depend significantly on the relative dielectric coefficient.

Probing Lipid Bilayers under Ionic Imbalance

Biological membranes are normally under a resting transmembrane potential (TMP), which originates from the ionic imbalance between extracellular fluids and cytosols, and serves as electric power storage for cells. In cell electroporation, the ionic imbalance builds up a high TMP, resulting in the poration of cell membranes. However, the relationship between ionic imbalance and TMP is not clearly understood, and little is known about the effect of ionic imbalance on the structure and dynamics of biological membranes. In this study, we used coarse-grained molecular dynamics to characterize a dipalmitoylphosphatidylcholine bilayer system under ionic imbalances ranging from 0 to ∼0.06 e charges per lipid (e/Lip). We found that the TMP displayed three distinct regimes: 1) a linear regime between 0 and 0.045 e/Lip, where the TMP increased linearly with ionic imbalance; 2) a yielding regime between ∼0.045 and 0.060 e/Lip, where the TMP displayed a plateau; and 3) a poration regime above ∼0.060 e/Lip, where we observed pore formation within the sampling time (80 ns). We found no structural changes in the linear regime, apart from a nonlinear increase in the area per lipid, whereas in the yielding regime the bilayer exhibited substantial thinning, leading to an excess of water and Na⁺ within the bilayer, as well as significant misalignment of the lipid tails. In the poration regime, lipid molecules diffused slightly faster. We also found that the fluid-to-gel phase transition temperature of the bilayer dropped below the normal value with increased ionic imbalances. Our results show that a high ionic imbalance can substantially alter the essential properties of the bilayer, making the bilayer more fluid like, or conversely, depolarization of a cell could in principle lead to membrane stiffening.

Dynamical study of Νaν channel excitability under mechanical stress

Alteration of [Formula: see text] channel functions (channelopathies) has been encountered in various hereditary muscle diseases. [Formula: see text] channel mutations lead to aberrant excitability in skeletal muscle myotonia and paralysis. In general, these mutations disable inactivation of the [Formula: see text] channel, producing either repetitive action potential firing (myotonia) or electrical dormancy (flaccid paralysis) in skeletal muscles. These "sick-excitable" cell conditions were shown to correlate with a mechanical stretch-driven left shift of the conductance factors of the two gating mechanisms of a fraction of [Formula: see text] channels, which make them firing at inappropriate hyperpolarised (left-shifted) voltages. Here we elaborate on a variant of the Hodgkin-Huxley model that includes a stretch elasticity energy component in the activation and inactivation gate kinetic rates. We show that this model reproduces fairly well sick-excitable cell behaviour and can be used to predict the parameter domains where aberrant excitability or paralysis may occur. By allowing us to separate the incidences of activation and inactivation gate impairments in [Formula: see text] channel excitability, this model could be a strong asset for diagnosing the origin of excitable cell disorders.

Experimental Insight into the Thermodynamics of the Dissolution of Electrolytes in Room-Temperature Ionic Liquids: From the Mass Action Law to the Absolute Standard Chemical Potential of a Proton

Room-temperature ionic liquids (ILs) are a class of nonaqueous solvents that have expanded the realm of modern chemistry, drawing increasing interest over the last few decades, not only in terms of their own unique physical chemistry but also in many applications including organic synthesis, electrochemistry, and biological systems, wherein charged solutes (i.e., electrolytes) often play vital roles. However, our fundamental understanding of the dissolution of an electrolyte in an IL is still rather limited. For example, the activity of a charged species has frequently been assumed to be unity without a clear experimental basis. In this study, we have discussed a standard component-based scheme for the dissolution of an electrolyte in an IL, supported by our observation of ideal Nernstian responses for the reduction of silver and ferrocenium salts in a representative IL, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([emim⁺][NTf₂ ^-] or [emim⁺][TFSI^-]). Using this scheme, which was also supported by temperature-dependent measurements with ILs having longer alkyl chains in the imidazolium ring, and the solubility of the IL in water, we established the concept of Gibbs transfer energies of "pseudo-single ions" from the IL to conventional neutral molecular solvents (water, acetonitrile, and methanol). This concept, which bridges component- and constituent-based energetics, utilizes an extrathermodynamic assumption, which itself was justified by experimental observations. These energies enable us to eliminate inner potential differences between the IL and molecular solvents (solvent-solvent interactions), that is, on a practical level, conditional liquid junction potential differences, so that we can discuss ion-solvent interactions independently. Specifically, we have examined the standard electrode potential of the ferrocenium/ferrocene redox couple, Fc⁺/Fc, and the absolute intrinsic standard chemical potential of a proton in [emim⁺][NTf₂ ^-], finding that the proton is more acidic in the IL than in water by 6.5 ± 0.6 units on the unified pH scale. These results strengthen the progress on the physical chemistry of ions in IL solvent systems on the basis of their activities, providing a rigorous thermodynamic framework.

Evidence for the functional involvement of members of the TRP channel family in the uptake of Na(+) and NH4 (+) by the ruminal epithelium

Large quantities of protein are degraded in the fermentative parts of the gut to ammonia, which is absorbed, detoxified to urea, and excreted, leading to formation of nitrogenous compounds such as N2O that are associated with global warming. In ruminants, channel-mediated uptake of NH4 (+) from the rumen predominates. The molecular identity of these channels remains to be clarified. Ruminal cells and epithelia from cows and sheep were investigated using patch clamp, Ussing chamber, microelectrode techniques, and qPCR. In patch clamp experiments, bovine ruminal epithelial cells expressed a conductance for NH4 (+) that could be blocked in a voltage-dependent manner by divalent cations. In the native epithelium, NH4 (+) depolarized the apical potential, acidified the cytosol and induced a rise in short-circuit current (I sc) that persisted after the removal of Na(+), was blocked by verapamil, enhanced by the removal of divalent cations, and was sensitive to certain transient receptor potential (TRP) channel modulators. Menthol or thymol stimulated the I sc in Na(+) or NH4 (+) containing solutions in a dose-dependent manner and modulated transepithelial Ca(2+) fluxes. On the level of messenger RNA (mRNA), ovine and bovine ruminal epithelium expressed TRPA1, TRPV3, TRPV4, TRPM6, and TRPM7, with any expression of TRPV6 marginal. No bands were detected for TRPV1, TRPV5, or TRPM8. Functional and molecular biological data suggest that the transport of NH4 (+), Na(+), and Ca(2+) across the rumen involves TRP channels, with TRPV3 and TRPA1 emerging as prime candidate genes. TRP channels may also contribute to the transport of NH4 (+) across other epithelia.

KV1 channels identified in rodent myelinated axons, linked to Cx29 in innermost myelin: support for electrically active myelin in mammalian saltatory conduction

Saltatory conduction in mammalian myelinated axons was thought to be well understood before recent discoveries revealed unexpected subcellular distributions and molecular identities of the K(+)-conductance pathways that provide for rapid axonal repolarization. In this study, we visualize, identify, localize, quantify, and ultrastructurally characterize axonal KV1.1/KV1.2 channels in sciatic nerves of rodents. With the use of light microscopic immunocytochemistry and freeze-fracture replica immunogold labeling electron microscopy, KV1.1/KV1.2 channels are localized to three anatomically and compositionally distinct domains in the internodal axolemmas of large myelinated axons, where they form densely packed "rosettes" of 9-nm intramembrane particles. These axolemmal KV1.1/KV1.2 rosettes are precisely aligned with and ultrastructurally coupled to connexin29 (Cx29) channels, also in matching rosettes, in the surrounding juxtaparanodal myelin collars and along the inner mesaxon. As >98% of transmembrane proteins large enough to represent ion channels in these specialized domains, ∼500,000 KV1.1/KV1.2 channels define the paired juxtaparanodal regions as exclusive membrane domains for the voltage-gated K(+)conductance that underlies rapid axonal repolarization in mammals. The 1:1 molecular linkage of KV1 channels to Cx29 channels in the apposed juxtaparanodal collars, plus their linkage to an additional 250,000-400,000 Cx29 channels along each inner mesaxon in every large-diameter myelinated axon examined, supports previously proposed K(+)conductance directly from juxtaparanodal axoplasm into juxtaparanodal myeloplasm in mammalian axons. With neither Cx29 protein nor myelin rosettes detectable in frog myelinated axons, these data showing axon-to-myelin linkage by abundant KV1/Cx29 channels in rodent axons support renewed consideration of an electrically active role for myelin in increasing both saltatory conduction velocity and maximum propagation frequency in mammalian myelinated axons.

Non-linear leak currents affect mammalian neuron physiology

In their seminal works on squid giant axons, Hodgkin, and Huxley approximated the membrane leak current as Ohmic, i.e., linear, since in their preparation, sub-threshold current rectification due to the influence of ionic concentration is negligible. Most studies on mammalian neurons have made the same, largely untested, assumption. Here we show that the membrane time constant and input resistance of mammalian neurons (when other major voltage-sensitive and ligand-gated ionic currents are discounted) varies non-linearly with membrane voltage, following the prediction of a Goldman-Hodgkin-Katz-based passive membrane model. The model predicts that under such conditions, the time constant/input resistance-voltage relationship will linearize if the concentration differences across the cell membrane are reduced. These properties were observed in patch-clamp recordings of cerebellar Purkinje neurons (in the presence of pharmacological blockers of other background ionic currents) and were more prominent in the sub-threshold region of the membrane potential. Model simulations showed that the non-linear leak affects voltage-clamp recordings and reduces temporal summation of excitatory synaptic input. Together, our results demonstrate the importance of trans-membrane ionic concentration in defining the functional properties of the passive membrane in mammalian neurons as well as other excitable cells.

Computational and Pharmacological Target of Neurovascular Unit for Drug Design and Delivery

The blood-brain barrier (BBB) is a dynamic and highly selective permeable interface between central nervous system (CNS) and periphery that regulates the brain homeostasis. Increasing evidences of neurological disorders and restricted drug delivery process in brain make BBB as special target for further study. At present, neurovascular unit (NVU) is a great interest and highlighted topic of pharmaceutical companies for CNS drug design and delivery approaches. Some recent advancement of pharmacology and computational biology makes it convenient to develop drugs within limited time and affordable cost. In this review, we briefly introduce current understanding of the NVU, including molecular and cellular composition, physiology, and regulatory function. We also discuss the recent technology and interaction of pharmacogenomics and bioinformatics for drug design and step towards personalized medicine. Additionally, we develop gene network due to understand NVU associated transporter proteins interactions that might be effective for understanding aetiology of neurological disorders and new target base protective therapies development and delivery.

The Effect of the Nonlinearity of the Response of Lipid Membranes to Voltage Perturbations on the Interpretation of Their Electrical Properties. A New Theoretical Description

Our understanding of the electrical properties of cell membranes is derived from experiments where the membrane is exposed to a perturbation (in the form of a time-dependent voltage or current change) and information is extracted from the measured output. The interpretation of such electrical recordings consists in finding an electronic equivalent that would show the same or similar response as the biological system. In general, however, there is no unique circuit configuration, which can explain a single electrical recording and the choice of an electric model for a biological system is based on complementary information (most commonly structural information) of the system investigated. Most of the electrophysiological data on cell membranes address the functional role of protein channels while assuming that the lipid matrix is an insulator with constant capacitance. However, close to their melting transition the lipid bilayers are no inert insulators. Their conductivity and their capacitance are nonlinear functions of both voltage, area and volume density. This has to be considered when interpreting electrical data. Here we show how electric data commonly interpreted as gating currents of proteins and inductance can be explained by the nonlinear dynamics of the lipid matrix itself.

Cell dialysis by sharp electrodes can cause nonphysiological changes in neuron properties

We recorded from lobster and leech neurons with two sharp electrodes filled with solutions often used with these preparations (lobster: 0.6 M K2SO4 or 2.5 M KAc; leech: 4 M KAc), with solutions approximately matching neuron cytoplasm ion concentrations, and with 6.5 M KAc (lobster, leech) and 0.6 M KAc (lobster). We measured membrane potential, input resistance, and transient and sustained depolarization-activated outward current amplitudes in leech and these neuron properties and hyperpolarization-activated current time constant in lobster, every 10 min for 60 min after electrode penetration. Neuron properties varied with electrode fill. For fills with molarities ≥2.5 M, neuron properties also varied strongly with time after electrode penetration. Depending on the property being examined, these variations could be large. In leech, cell size also increased with noncytoplasmic fills. The changes in neuron properties could be due to the ions being injected from the electrodes during current injection. We tested this possibility in lobster with the 2.5 M KAc electrode fill by making measurements only 10 and 60 min after penetration. Neuron properties still changed, although the changes were less extreme. Making measurements every 2 min showed that the time-dependent variations in neuron properties occurred in concert with each other. Neuron property changes with high molarity electrode-fill solutions were great enough to decrease neuron firing strongly. An experiment with (14)C-glucose electrode fill confirmed earlier work showing substantial leak from sharp electrodes. Sharp electrode work should thus be performed with cytoplasm-matched electrode fills.

Anthropogenic changes in sodium affect neural and muscle development in butterflies

The development of organisms is changing drastically because of anthropogenic changes in once-limited nutrients. Although the importance of changing macronutrients, such as nitrogen and phosphorus, is well-established, it is less clear how anthropogenic changes in micronutrients will affect organismal development, potentially changing dynamics of selection. We use butterflies as a study system to test whether changes in sodium availability due to road salt runoff have significant effects on the development of sodium-limited traits, such as neural and muscle tissue. We first document how road salt runoff can elevate sodium concentrations in the tissue of some plant groups by 1.5-30 times. Using monarch butterflies reared on roadside- and prairie-collected milkweed, we then show that road salt runoff can result in increased muscle mass (in males) and neural investment (in females). Finally, we use an artificial diet manipulation in cabbage white butterflies to show that variation in sodium chloride per se positively affects male flight muscle and female brain size. Variation in sodium not only has different effects depending on sex, but also can have opposing effects on the same tissue: across both species, males increase investment in flight muscle with increasing sodium, whereas females show the opposite pattern. Taken together, our results show that anthropogenic changes in sodium availability can affect the development of traits in roadside-feeding herbivores. This research suggests that changing micronutrient availability could alter selection on foraging behavior for some roadside-developing invertebrates.

Interacting ions in biophysics: real is not ideal

Ions in water are important throughout biology, from molecules to organs. Classically, ions in water were treated as ideal noninteracting particles in a perfect gas. Excess free energy of each ion was zero. Mathematics was not available to deal consistently with flows, or interactions with other ions or boundaries. Nonclassical approaches are needed because ions in biological conditions flow and interact. The concentration gradient of one ion can drive the flow of another, even in a bulk solution. A variational multiscale approach is needed to deal with interactions and flow. The recently developed energetic variational approach to dissipative systems allows mathematically consistent treatment of the bio-ions Na(+), K(+), Ca(2+), and Cl(-) as they interact and flow. Interactions produce large excess free energy that dominate the properties of the high concentration of ions in and near protein active sites, ion channels, and nucleic acids: the number density of ions is often >10 M. Ions in such crowded quarters interact strongly with each other as well as with the surrounding protein. Nonideal behavior found in many experiments has classically been ascribed to allosteric interactions mediated by the protein and its conformation changes. The ion-ion interactions present in crowded solutions-independent of conformation changes of the protein-are likely to change the interpretation of many allosteric phenomena. Computation of all atoms is a popular alternative to the multiscale approach. Such computations involve formidable challenges. Biological systems exist on very different scales from atomic motion. Biological systems exist in ionic mixtures (like extracellular and intracellular solutions), and usually involve flow and trace concentrations of messenger ions (e.g., 10(-7) M Ca(2+)). Energetic variational methods can deal with these characteristic properties of biological systems as we await the maturation and calibration of all-atom simulations of ionic mixtures and divalents.

Microtransplantation of cellular membranes from squid stellate ganglion reveals ionotropic GABA receptors

The squid has been the most studied cephalopod, and it has served as a very useful model for investigating the events associated with nerve impulse generation and synaptic transmission. While the physiology of squid giant axons has been extensively studied, very little is known about the distribution and function of the neurotransmitters and receptors that mediate inhibitory transmission at the synapses. In this study we investigated whether γ-aminobutyric acid (GABA) activates neurotransmitter receptors in stellate ganglia membranes. To overcome the low abundance of GABA-like mRNAs in invertebrates and the low expression of GABA in cephalopods, we used a two-electrode voltage clamp technique to determine if Xenopus laevis oocytes injected with cell membranes from squid stellate ganglia responded to GABA. Using this method, membrane patches containing proteins and ion channels from the squid's stellate ganglion were incorporated into the surface of oocytes. We demonstrated that GABA activates membrane receptors in cellular membranes isolated from squid stellate ganglia. Using the same approach, we were able to record native glutamate-evoked currents. The squid's GABA receptors showed an EC(50) of 98 μmol l(-1) to GABA and were inhibited by zinc (IC(50) = 356 μmol l(-1)). Interestingly, GABA receptors from the squid were only partially blocked by bicuculline. These results indicate that the microtransplantation of native cell membranes is useful to identify and characterize scarce membrane proteins. Moreover, our data also support the role of GABA as an ionotropic neurotransmitter in cephalopods, acting through chloride-permeable membrane receptors.

Ionic Interactions Are Everywhere

Ionic solutions are dominated by interactions because they must be electrically neutral, but classical theory assumes no interactions. Biological solutions are rather like seawater, concentrated enough so that the diameter of ions also produces important interactions. In my view, the theory of complex fluids is needed to deal with the interacting reality of biological solutions.

Proton exclusion by an aquaglyceroprotein: a voltage clamp study

BACKGROUND INFORMATION

In silico both orthodox aquaporins and aquaglyceroporins are shown to exclude protons. Supporting experimental evidence is available only for orthodox aquaporins. In contrast, the subset of the aquaporin water channel family that is permeable to glycerol and certain small, uncharged solutes has not yet been shown to exclude protons. Moreover, different aquaglyceroporins have been reported to conduct ions when reconstituted in planar bilayers.

RESULTS

To clarify these discrepancies, we have measured proton permeability through the purified Escherichia coli glycerol facilitator (GlpF). Functional reconstitution into planar lipid bilayers was demonstrated by imposing an osmotic gradient across the membrane and detecting the resulting small changes in ionic concentration close to the membrane surface. The osmotic water flow corresponds to a GlpF single channel water permeability of 0.7x10(-14) cm(3).subunit(-1).s(-1). Proton conductivity measurements carried out in the presence of a pH gradient (1 unit) revealed an upper limit of the H(+) (OH(-)) to H(2)O molecules transport stoichiometry of 2x10(-9). A significant GlpF-mediated ion conductivity was also not detectable.

CONCLUSIONS

The lack of a physiologically relevant GlpF-mediated proton conductivity agrees well with predictions made by molecular dynamics simulations.