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Cells Aug 2022All living cells maintain a charge distribution across their cell membrane (membrane potential) by carefully controlled ion fluxes. These bioelectric signals regulate...
All living cells maintain a charge distribution across their cell membrane (membrane potential) by carefully controlled ion fluxes. These bioelectric signals regulate cell behavior (such as migration, proliferation, differentiation) as well as higher-level tissue and organ patterning. Thus, voltage gradients represent an important parameter for diagnostics as well as a promising target for therapeutic interventions in birth defects, injury, and cancer. However, despite much progress in cell and molecular biology, little is known about bioelectric states in human stem cells. Here, we present simple methods to simultaneously track ion dynamics, membrane voltage, cell morphology, and cell activity (pH and ROS), using fluorescent reporter dyes in living human neurons derived from induced neural stem cells (hiNSC). We developed and tested functional protocols for manipulating ion fluxes, membrane potential, and cell activity, and tracking neural responses to injury and reinnervation in vitro. Finally, using morphology sensor, we tested and quantified the ability of physiological actuators (neurotransmitters and pH) to manipulate nerve repair and reinnervation. These methods are not specific to a particular cell type and should be broadly applicable to the study of bioelectrical controls across a wide range of combinations of models and endpoints.
Topics: Humans; Induced Pluripotent Stem Cells; Membrane Potentials; Neural Stem Cells; Neuronal Outgrowth; Neurons
PubMed: 36010547
DOI: 10.3390/cells11162470 -
Experimental Brain Research Aug 2020I-waves represent high-frequency (~ 600 Hz) repetitive discharge of corticospinal fibers elicited by single-pulse stimulation of motor cortex. First detected and...
I-waves represent high-frequency (~ 600 Hz) repetitive discharge of corticospinal fibers elicited by single-pulse stimulation of motor cortex. First detected and examined in animal preparations, this multiple discharge can also be recorded in humans from the corticospinal tract with epidural spinal electrodes. The exact underpinning neurophysiology of I-waves is still unclear, but there is converging evidence that they originate at the cortical level through synaptic input from specific excitatory interneuronal circuitries onto corticomotoneuronal cells, controlled by GABAAergic interneurons. In contrast, there is at present no supportive evidence for the alternative hypothesis that I-waves are generated by high-frequency oscillations of the membrane potential of corticomotoneuronal cells upon initial strong depolarization. Understanding I-wave physiology is essential for understanding how TMS activates the motor cortex.
Topics: Animals; Evoked Potentials, Motor; Humans; Interneurons; Membrane Potentials; Motor Cortex; Pyramidal Tracts; Transcranial Magnetic Stimulation
PubMed: 32185405
DOI: 10.1007/s00221-020-05764-4 -
Pflugers Archiv : European Journal of... Jun 2024Neutrophil granulocytes play a crucial role in host defense against invading pathogens and in inflammatory diseases. The aim of this study was to elucidate membrane...
Neutrophil granulocytes play a crucial role in host defense against invading pathogens and in inflammatory diseases. The aim of this study was to elucidate membrane potential dynamics during the initial phase of neutrophil activation and its relation to migration and production of reactive oxygen species (ROS). We performed ROS production measurements of neutrophils from healthy C57BL/6J mice after TNFα-priming and/or C5a stimulation. The actin cytoskeleton was visualized with fluorescence microscopy. Furthermore, we combined migration assays and measurements of membrane potential dynamics after stimulating unprimed and/or TNFα-primed neutrophils with C5a. We show that C5a has a concentration-dependent effect on ROS production and chemokinetic migration. Chemokinetic migration and chemotaxis are impaired at C5a concentrations that induce ROS production. The actin cytoskeleton of unstimulated and of ROS-producing neutrophils is not distributed in a polarized way. Inhibition of the phagocytic NADPH oxidase NOX2 with diphenyleneiodonium (DPI) leads to a polarized distribution of the actin cytoskeleton and rescues chemokinetic migration of primed and C5a-stimulated neutrophils. Moreover, C5a evokes a pronounced depolarization of the cell membrane potential by 86.6 ± 4.2 mV starting from a resting membrane potential of -74.3 ± 0.7 mV. The C5a-induced depolarization occurs almost instantaneously (within less than one minute) in contrast to the more gradually developing depolarization induced by PMA (lag time of 3-4 min). This initial depolarization is accompanied by a decrease of the migration velocity. Collectively, our results show that stimulation with C5a evokes parallel changes in membrane potential dynamics, neutrophil ROS production and motility. Notably, the amplitude of membrane potential dynamics is comparable to that of excitable cells.
Topics: Animals; Neutrophils; Complement C5a; Reactive Oxygen Species; Mice, Inbred C57BL; Mice; Membrane Potentials; NADPH Oxidases; Actin Cytoskeleton; Tumor Necrosis Factor-alpha; Cell Movement; Neutrophil Activation; NADPH Oxidase 2
PubMed: 38613695
DOI: 10.1007/s00424-024-02947-8 -
ACS Nano Jan 2024We present super-resolution microscopy of isolated functional mitochondria, enabling real-time studies of structure and function (voltages) in response to...
We present super-resolution microscopy of isolated functional mitochondria, enabling real-time studies of structure and function (voltages) in response to pharmacological manipulation. Changes in mitochondrial membrane potential as a function of time and position can be imaged in different metabolic states (not possible in whole cells), created by the addition of substrates and inhibitors of the electron transport chain, enabled by the isolation of vital mitochondria. By careful analysis of structure dyes and voltage dyes (lipophilic cations), we demonstrate that most of the fluorescent signal seen from voltage dyes is due to membrane bound dyes, and develop a model for the membrane potential dependence of the fluorescence contrast for the case of super-resolution imaging, and how it relates to membrane potential. This permits direct analysis of mitochondrial structure and function (voltage) of isolated, individual mitochondria as well as submitochondrial structures in the functional, intact state, a major advance in super-resolution studies of living organelles.
Topics: Mitochondria; Organelles; Microscopy; Membrane Potentials; Coloring Agents; Fluorescent Dyes
PubMed: 37289571
DOI: 10.1021/acsnano.3c02768 -
ENeuro 2021Excitatory synaptic transmission in many neurons is mediated by two coexpressed ionotropic glutamate receptor subtypes, AMPA and NMDA receptors, that differ in kinetics,...
Excitatory synaptic transmission in many neurons is mediated by two coexpressed ionotropic glutamate receptor subtypes, AMPA and NMDA receptors, that differ in kinetics, ion selectivity, and voltage-sensitivity. AMPA receptors have fast kinetics and are voltage-insensitive, while NMDA receptors have slower kinetics and increased conductance at depolarized membrane potentials. Here, we report that the voltage dependency and kinetics of NMDA receptors act synergistically to stabilize synaptic integration of EPSPs across spatial and voltage domains. Simulations of synaptic integration in simplified and morphologically realistic dendritic trees revealed that the combined presence of AMPA and NMDA conductances reduce the variability of somatic responses to spatiotemporal patterns of excitatory synaptic input presented at different initial membrane potentials and/or in different dendritic domains. This moderating effect of the NMDA conductance on synaptic integration was robust across a wide range of AMPA-to-NMDA ratios, and results from synergistic interaction of NMDA kinetics (which reduces variability across membrane potential) and voltage dependence (which favors stabilization across dendritic location). When combined with AMPA conductance, the NMDA conductance compensates for voltage-dependent and impedance-dependent changes in synaptic driving force, and distance-dependent attenuation of synaptic potentials arriving at the axon, to increase the fidelity of synaptic integration and EPSP-spike coupling across both neuron state (i.e., initial membrane potential) and dendritic location of synaptic input. Thus, synaptic NMDA receptors convey advantages for synaptic integration that are independent of, but fully compatible with, their importance for coincidence detection and synaptic plasticity.
Topics: Excitatory Postsynaptic Potentials; Neurons; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Synapses; Synaptic Transmission
PubMed: 33468538
DOI: 10.1523/ENEURO.0396-20.2020 -
Biochemical and Biophysical Research... Sep 2020Historically, the field of tissue engineering has been adept at modulating the chemical and physical microenvironment. This approach has yielded significant progress,...
Historically, the field of tissue engineering has been adept at modulating the chemical and physical microenvironment. This approach has yielded significant progress, but it is imperative to further integrate our understanding of other fundamental cell signaling paradigms into tissue engineering methods. Bioelectric signaling has been demonstrated to be a vital part of tissue development, regeneration, and function across organ systems and the extracellular matrix is known to alter the bioelectric properties of cells. Thus, there is a need to bolster our understanding of how matrix and bioelectric signals interact to drive cell phenotype. We examine how cardiac progenitor cell differentiation is altered by simultaneous changes in both resting membrane potential and extracellular matrix composition. Pediatric c-kit cardiac progenitor cells were differentiated on fetal or adult cardiac extracellular matrix while being treated with drugs that alter resting membrane potential. Smooth muscle gene expression was increased with depolarization and decreased with hyperpolarization while endothelial and cardiac expression were unchanged. Early smooth muscle protein expression is modified by matrix developmental age, with fetal ECM appearing to amplify the effects of resting membrane potential. Thus, combining matrix composition and bioelectric signaling represents a potential alternative for guiding cell behavior in tissue engineering and regenerative medicine.
Topics: Animals; Cell Differentiation; Cells, Cultured; Extracellular Matrix; Humans; Membrane Potentials; Myocytes, Cardiac; Myocytes, Smooth Muscle; Stem Cells; Swine; Tissue Engineering; Tissue Scaffolds
PubMed: 32828293
DOI: 10.1016/j.bbrc.2020.06.149 -
Bioelectromagnetics Jan 2021To explore cellular responses to high magnetic fields (HMF), we present a model of the interactions of cells with a homogeneous HMF that accounts for the magnetic force...
To explore cellular responses to high magnetic fields (HMF), we present a model of the interactions of cells with a homogeneous HMF that accounts for the magnetic force exerted on paramagnetic/diamagnetic species. There are various chemical species inside a living cell, many of which may have large concentration gradients. Thus, when an HMF is applied to a cell, the concentration-gradient magnetic forces act on paramagnetic or diamagnetic species and can either assist or oppose large particle movement through the cytoplasm. We demonstrate possibilities for changing the machinery in living cells with HMFs and predict two new mechanisms for modulating cellular functions with HMFs via (i) changes in the membrane potential and (ii) magnetically assisted intracellular diffusiophoresis of large proteins. By deriving a generalized form for the Nernst equation, we find that an HMF can change the membrane potential of the cell and thus have a significant impact on the properties and biological functionality of cells. The elaborated model provides a universal framework encompassing current studies on controlling cell functions by high static magnetic fields. Bioelectromagnetics. 2021;42:27-36. © 2020 Bioelectromagnetics Society.
Topics: Biological Transport; Magnetic Fields; Membrane Potentials; Protein Transport; Proteins
PubMed: 33179821
DOI: 10.1002/bem.22309 -
Journal of Neurophysiology Oct 2021Predominant expression of leak-type K channels provides astrocytes a high membrane permeability to K ions and a hyperpolarized membrane potential that are crucial for... (Review)
Review
Predominant expression of leak-type K channels provides astrocytes a high membrane permeability to K ions and a hyperpolarized membrane potential that are crucial for astrocyte function in brain homeostasis. In functionally mature astrocytes, the expression of leak K channels creates a unique membrane K conductance that lacks voltage-dependent rectification. Accordingly, the conductance is named ohmic or passive K conductance. Several inwardly rectifying and two-pore domain K channels have been investigated for their contributions to passive conductance. Meanwhile, gap junctional coupling has been postulated to underlie the passive behavior of membrane conductance. It is now clear that the intrinsic properties of K channels and gap junctional coupling can each act alone or together to bring about a passive behavior of astrocyte conductance. Additionally, while the passive conductance can generally be viewed as a K conductance, the actual representation of this conductance is a combined expression of multiple known and unknown K channels, which has been further modified by the intricate morphology of individual astrocytes and syncytial gap junctional coupling. The expression of the inwardly rectifying K channels explains the inward-going component of passive conductance disobeying Goldman-Hodgkin-Katz constant field outward rectification. However, the K channels encoding the outward-going passive currents remain to be determined in the future. Here, we review our current understanding of ion channels and biophysical mechanisms engaged in the passive astrocyte K conductance, propose new studies to resolve this long-standing puzzle in astrocyte physiology, and discuss the functional implication(s) of passive behavior of K conductance on astrocyte physiology.
Topics: Animals; Astrocytes; Biophysical Phenomena; Gap Junctions; Humans; Membrane Potentials; Potassium; Potassium Channels
PubMed: 34525325
DOI: 10.1152/jn.00330.2021 -
Chaos (Woodbury, N.Y.) Nov 2023The membrane potential of a neuron is mainly controlled by the gradient distribution of electromagnetic field and concentration diversity between intracellular and...
The membrane potential of a neuron is mainly controlled by the gradient distribution of electromagnetic field and concentration diversity between intracellular and extracellular ions. Without considering the thickness and material property, the electric characteristic of cell membrane is described by a capacitive variable and output voltage in an equivalent neural circuit. The flexible property of cell membrane enables controllability of endomembrane and outer membrane, and the capacitive properties and gradient field can be approached by double membranes connected by a memristor in an equivalent neural circuit. In this work, two capacitors connected by a memristor are used to mimic the physical property of two-layer membranes, and an inductive channel is added to the neural circuit. A biophysical neuron is obtained and the energy characteristic, dynamics, self-adaption is discussed, respectively. Coherence resonance and mode selection in adaptive way are detected under noisy excitation. The distribution of average energy function is effective to predict the appearance of coherence resonance. An adaptive law is proposed to control the capacitive parameters, and the controllability of cell membrane under external stimulus can be explained in theoretical way. The neuron with memristive membranes explains the self-adaptive mechanism of parameter changes and mode transition from energy viewpoint.
Topics: Neurons; Cell Membrane; Electricity; Electromagnetic Fields; Membrane Potentials
PubMed: 37909904
DOI: 10.1063/5.0170121 -
The Journal of Physiology Jun 2022The K 1/D-type potassium current (I ) is an important determinant of neuronal excitability. This study explored whether and how I channels regulate the activation of...
The K 1/D-type potassium current (I ) is an important determinant of neuronal excitability. This study explored whether and how I channels regulate the activation of bronchopulmonary vagal afferent nerves. The single-neuron RT-PCR assay revealed that nearly all mouse bronchopulmonary nodose neurons expressed the transcripts of α-dendrotoxin (α-DTX)-sensitive, I channel-forming K 1.1, K 1.2 and/or K 1.6 α-subunits, with the expression of K 1.6 being most prevalent. Patch-clamp recordings showed that I , defined as the α-DTX-sensitive K current, activated at voltages slightly more negative than the resting membrane potential in lung-specific nodose neurons and displayed little inactivation at subthreshold voltages. Inhibition of I channels by α-DTX depolarized the lung-specific nodose neurons and caused an increase in input resistance, decrease in rheobase, as well as increase in action potential number and firing frequency in response to suprathreshold current steps. Application of α-DTX to the lungs via trachea in the mouse ex vivo vagally innervated trachea-lungs preparation led to action potential discharges in nearly half of bronchopulmonary nodose afferent nerve fibres, including nodose C-fibres, as detected by the two-photon microscopic Ca imaging technique and extracellular electrophysiological recordings. In conclusion, I channels act as a critical brake on the activation of bronchopulmonary vagal afferent nerves by stabilizing the membrane potential, counterbalancing the subthreshold depolarization and promoting the adaptation of action potential firings. Down-regulation of I channels, as occurs in various inflammatory diseases, may contribute to the enhanced C-fibre activity in airway diseases that are associated with excessive coughing, dyspnoea, and reflex bronchospasm and secretions. KEY POINTS: The α-dendrotoxin (α-DTX)-sensitive D-type K current (I ) is an important determinant of neuronal excitability. Nearly all bronchopulmonary nodose afferent neurons in the mouse express I and the transcripts of α-DTX-sensitive, I channel-forming K 1.1, K 1.2 and/or K 1.6 α-subunits. Inhibition of I channels by α-DTX depolarizes the bronchopulmonary nodose neurons, reduces the minimal depolarizing current needed to evoke an action potential (AP) and increases AP number and AP firing frequency in response to suprathreshold stimulations. Application of α-DTX to the lungs ex vivo elicits AP discharges in about half of bronchopulmonary nodose C-fibre terminals. Our novel finding that I channels act as a critical brake on the activation of bronchopulmonary vagal afferent nerves suggests that their down-regulation, as occurs in various inflammatory diseases, may contribute to the enhanced C-fibre activity in airway inflammation associated with excessive respiratory symptoms.
Topics: Action Potentials; Animals; Membrane Potentials; Mice; Neurons, Afferent; Nodose Ganglion; Patch-Clamp Techniques; Potassium Channels; Vagus Nerve
PubMed: 35430729
DOI: 10.1113/JP282803