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American Journal of Physiology. Cell... Jun 2022We endeavored to understand the factors determining the peak force-resting membrane potential () relationships of isolated slow-twitch soleus and fast-twitch extensor...
We endeavored to understand the factors determining the peak force-resting membrane potential () relationships of isolated slow-twitch soleus and fast-twitch extensor digitorum longus (EDL) muscles from mice (25°C), especially in relation to fatigue. Interrelationships between intracellular K activity ([Formula: see text]), extracellular K concentration ([K]), resting , action potentials, and force were studied. The large resting variation was mainly due to the variability of [Formula: see text]. Action potential overshoot-resting relationships determined at 4 and 8-10 mM [K] after short (<5 min) and prolonged (>50 min) depolarization periods revealed a constant overshoot from -90 to -70 mV providing a safety margin. Overshoot decline with depolarization beyond -70 mV was less after short than prolonged depolarization. Inexcitable fibers occurred only with prolonged depolarization. The overshoot decline during action potential trains (2 s) exceeded that during short depolarizations. Concomitant lower extracellular [Na] and raised [K] depressed the overshoot in an additive manner and peak force in a synergistic manner. Raised [K]-induced force loss was exacerbated with transverse wire versus parallel plate stimulation in soleus, implicating action potential propagation failure in the surface membrane. Increasing stimulus pulse parameters restored tetanic force at 9-10 mM [K] in soleus but not EDL, indicative of action potential failure within trains. The peak tetanic force-resting relationships (determined with resting from deeper rather than surface fibers) were dynamic and showed pronounced force depression over -69 to -60 mV in both muscle types, implicating that such depolarization contributes to fatigue. The K-Na interaction shifted this relationship toward less depolarized potentials, suggesting that the combined ionic effect is physiologically important during fatigue.
Topics: Animals; Fatigue; Membrane Potentials; Mice; Muscle Contraction; Muscle Fatigue; Muscle Fibers, Slow-Twitch; Muscle, Skeletal; Potassium; Sodium
PubMed: 35385328
DOI: 10.1152/ajpcell.00401.2021 -
International Journal of Molecular... Mar 2023Voltage-gated ion channels are integral membrane proteins that respond to changes in membrane potential with rapid variations in membrane permeability to ions [...].
Voltage-gated ion channels are integral membrane proteins that respond to changes in membrane potential with rapid variations in membrane permeability to ions [...].
Topics: Ion Channels; Membrane Potentials; Cell Membrane Permeability; Ions; Drug Design
PubMed: 37047455
DOI: 10.3390/ijms24076484 -
Bioelectrochemistry (Amsterdam,... Dec 2020Conventional electric stimuli of micro- and millisecond duration excite or activate cells at voltages 10-100 times below the electroporation threshold. This ratio is... (Review)
Review
Conventional electric stimuli of micro- and millisecond duration excite or activate cells at voltages 10-100 times below the electroporation threshold. This ratio is remarkably different for nanosecond electric pulses (nsEP), which caused excitation and activation only at or above the electroporation threshold in diverse cell lines, primary cardiomyocytes, neurons, and chromaffin cells. Depolarization to the excitation threshold often results from (or is assisted by) the loss of the resting membrane potential due to ion leaks across the membrane permeabilized by nsEP. Slow membrane resealing and the build-up of electroporation damages prevent repetitive excitation by nsEP. However, peripheral nerves and muscles are exempt from this rule and withstand multiple cycles of excitation by nsEP without the loss of function or signs of electroporation. We show that the damage-free excitation by nsEP may be enabled by the membrane charging time constant sufficiently large to (1) cap the peak transmembrane voltage during nsEP below the electroporation threshold, and (2) extend the post-nsEP depolarization long enough to activate voltage-gated ion channels. The low excitatory efficacy of nsEP compared to longer pulses makes them advantageous for medical applications where the neuromuscular excitation is an unwanted side effect, such as electroporation-based cancer and tissue ablation.
Topics: Animals; Cell Line; Cell Membrane Permeability; Electric Stimulation; Electroporation; Humans; Membrane Potentials
PubMed: 32711366
DOI: 10.1016/j.bioelechem.2020.107598 -
Accounts of Chemical Research Jan 2020Membrane potential is a fundamental biophysical property maintained by every cell on earth. In specialized cells like neurons, rapid changes in membrane potential drive... (Review)
Review
Membrane potential is a fundamental biophysical property maintained by every cell on earth. In specialized cells like neurons, rapid changes in membrane potential drive the release of chemical neurotransmitters. Coordinated, rapid changes in neuronal membrane potential across large numbers of interconnected neurons form the basis for all of human cognition, sensory perception, and memory. Despite the importance of this highly orchestrated and distributed activity, the traditional method for recording membrane potential is through the use of highly invasive single-cell electrodes that offer only a small glimpse of the total activity within a system. Fluorescent dyes that change their optical properties in response to changes in biological voltage have the potential to provide a powerful complement to traditional electrode-based methods of inquiry. Voltage-sensitive fluorescent indicators would allow the direct observation of membrane potential changes, significantly expanding our ability to monitor membrane potential dynamics in living systems. Toward this end, we have initiated a program to design, synthesize, and apply voltage-sensitive fluorophores that report on membrane potential dynamics with high sensitivity and speed. The basis for this optical voltage sensing is membrane potential-dependent photoinduced electron transfer (PeT). Voltage-sensitive fluorophores, or VoltageFluors, possess a fluorophore, a conjugated molecular wire, and an aniline donor. At resting potentials, in which the cell has a hyperpolarized or negative potential relative to the outside of the cell, PeT from the aniline donor is enhanced and fluorescence is diminished. At depolarized potentials, the membrane potential decreases the rate of PeT, allowing an increase in fluorescence. We show that a number of different fluorophores, molecular wires, and aniline donors can be employed to generate fast and sensitive VoltageFluor dyes. Multiple lines of evidence point to a PeT-based mechanism for voltage sensing, delivering fast response kinetics (∼25 ns), good sensitivity (>60% Δ/), compatibility with two-photon illumination, excellent signal-to-noise, and the ability to detect neuronal and cardiac action potentials in single trials. In this Account, we provide an overview of the challenges facing the design of fluorescent voltage indicators. We trace the development of molecular wire-based fluorescent voltage indicators within our group, beginning from fluorescein-based VoltageFluor to long-wavelength indicators that use modern fluorophores like silicon rhodamine and carbofluorescein. We examine design principles for PeT-based voltage indicators, showcase the use of our recent indicators for two-photon voltage imaging in intact brains, and explore the development of hybrid indicators that can localize to genetically defined cells. Finally, we highlight outstanding challenges to and opportunities for voltage imaging.
Topics: Animals; Fluorescent Dyes; Humans; Membrane Potentials; Molecular Structure
PubMed: 31834772
DOI: 10.1021/acs.accounts.9b00514 -
Sensors (Basel, Switzerland) Oct 2015Beta cells in the pancreatic islets of Langerhans are precise biological sensors for glucose and play a central role in balancing the organism between catabolic and... (Review)
Review
Beta cells in the pancreatic islets of Langerhans are precise biological sensors for glucose and play a central role in balancing the organism between catabolic and anabolic needs. A hallmark of the beta cell response to glucose are oscillatory changes of membrane potential that are tightly coupled with oscillatory changes in intracellular calcium concentration which, in turn, elicit oscillations of insulin secretion. Both membrane potential and calcium changes spread from one beta cell to the other in a wave-like manner. In order to assess the properties of the abovementioned responses to physiological and pathological stimuli, the main challenge remains how to effectively measure membrane potential and calcium changes at the same time with high spatial and temporal resolution, and also in as many cells as possible. To date, the most wide-spread approach has employed the electrophysiological patch-clamp method to monitor membrane potential changes. Inherently, this technique has many advantages, such as a direct contact with the cell and a high temporal resolution. However, it allows one to assess information from a single cell only. In some instances, this technique has been used in conjunction with CCD camera-based imaging, offering the opportunity to simultaneously monitor membrane potential and calcium changes, but not in the same cells and not with a reliable cellular or subcellular spatial resolution. Recently, a novel family of highly-sensitive membrane potential reporter dyes in combination with high temporal and spatial confocal calcium imaging allows for simultaneously detecting membrane potential and calcium changes in many cells at a time. Since the signals yielded from both types of reporter dyes are inherently noisy, we have developed complex methods of data denoising that permit for visualization and pixel-wise analysis of signals. Combining the experimental approach of high-resolution imaging with the advanced analysis of noisy data enables novel physiological insights and reassessment of current concepts in unprecedented detail.
Topics: Animals; Calcium; Islets of Langerhans; Membrane Potentials; Mice; Models, Biological; Optical Imaging
PubMed: 26516866
DOI: 10.3390/s151127393 -
Channels (Austin, Tex.) Dec 2023Inward rectifier potassium channels (Kir channels) exist in a variety of cells and are involved in maintaining resting membrane potential and signal transduction in most... (Review)
Review
Inward rectifier potassium channels (Kir channels) exist in a variety of cells and are involved in maintaining resting membrane potential and signal transduction in most cells, as well as connecting metabolism and membrane excitability of body cells. It is closely related to normal physiological functions of body and the occurrence and development of some diseases. Although the functional expression of Kir channels and their role in disease have been studied, they have not been fully elucidated. In this paper, the functional expression of Kir channels in vascular endothelial cells and smooth muscle cells and their changes in disease states were reviewed, especially the recent research progress of Kir channels in stem cells was introduced, in order to have a deeper understanding of Kir channels in vascular tissues and provide new ideas and directions for the treatment of related ion channel diseases.
Topics: Endothelial Cells; Potassium Channels, Inwardly Rectifying; Membrane Potentials; Cell Membrane; Myocytes, Smooth Muscle; Potassium
PubMed: 37463317
DOI: 10.1080/19336950.2023.2237303 -
Current Neuropharmacology 2018Several tumor entities including brain tumors aberrantly overexpress intermediate conductance Ca2+ activated KCa3.1 K+ channels. These channels contribute significantly... (Review)
Review
BACKGROUND
Several tumor entities including brain tumors aberrantly overexpress intermediate conductance Ca2+ activated KCa3.1 K+ channels. These channels contribute significantly to the transformed phenotype of the tumor cells.
METHOD
PubMed was searched in order to summarize our current knowledge on the molecular signaling upstream and downstream and the effector functions of KCa3.1 channel activity in tumor cells in general and in glioblastoma cells in particular. In addition, KCa3.1 expression and function for repair of DNA double strand breaks was determined experimentally in primary glioblastoma cultures in dependence on the abundance of proneural and mesenchymal stem cell markers.
RESULTS
By modulating membrane potential, cell volume, Ca2+ signals and the respiratory chain, KCa3.1 channels in both, plasma and inner mitochondrial membrane, have been demonstrated to regulate many cellular processes such as migration and tissue invasion, metastasis, cell cycle progression, oxygen consumption and metabolism, DNA damage response and cell death of cancer cells. Moreover, KCa3.1 channels have been shown to crucially contribute to resistance against radiotherapy. Futhermore, the original in vitro data on KCa3.1 channel expression in subtypes of glioblastoma stem(-like) cells propose KCa3.1 as marker for the mesenchymal subgroup of cancer stem cells and suggest that KCa3.1 contributes to the therapy resistance of mesenchymal glioblastoma stem cells.
CONCLUSION
The data suggest KCa3.1 channel targeting in combination with radiotherapy as promising new tool to eradicate therapy-resistant mesenchymal glioblastoma stem cells.
Topics: Animals; Brain Neoplasms; Calcium Signaling; Cell Cycle; Glioblastoma; Humans; In Vitro Techniques; Intermediate-Conductance Calcium-Activated Potassium Channels; Membrane Potentials; PubMed; Tumor Cells, Cultured; Up-Regulation
PubMed: 28786347
DOI: 10.2174/1570159X15666170808115821 -
Journal of the Royal Society, Interface Apr 2018Voltage-gated proton channels are unique ion channels, membrane proteins that allow protons but no other ions to cross cell membranes. They are found in diverse species,... (Review)
Review
Voltage-gated proton channels are unique ion channels, membrane proteins that allow protons but no other ions to cross cell membranes. They are found in diverse species, from unicellular marine life to humans. In all cells, their function requires that they open and conduct current only under certain conditions, typically when the electrochemical gradient for protons is outwards. Consequently, these proteins behave like rectifiers, conducting protons out of cells. Their activity has electrical consequences and also changes the pH on both sides of the membrane. Here we summarize what is known about the way these proteins sense the membrane potential and the pH inside and outside the cell. Currently, it is hypothesized that membrane potential is sensed by permanently charged arginines (with very high p) within the protein, which results in parts of the protein moving to produce a conduction pathway. The mechanism of pH sensing appears to involve titratable side chains of particular amino acids. For this purpose their p needs to be within the operational pH range. We propose a 'counter-charge' model for pH sensing in which electrostatic interactions within the protein are selectively disrupted by protonation of internally or externally accessible groups.
Topics: Hydrogen-Ion Concentration; Ion Channels; Membrane Potentials; Models, Molecular; Patch-Clamp Techniques; Signal Transduction
PubMed: 29643227
DOI: 10.1098/rsif.2018.0108 -
Trends in Neurosciences May 2016Genetically encoded optical sensors of cell activity are powerful tools that can be targeted to specific cell types. This is especially important in neuroscience because... (Review)
Review
Genetically encoded optical sensors of cell activity are powerful tools that can be targeted to specific cell types. This is especially important in neuroscience because individual brain regions can include a multitude of different cell types. Optical imaging allows for simultaneous recording from numerous neurons or brain regions. Optical signals of membrane potential are useful because membrane potential changes are a direct sign of both synaptic and action potentials. Here we describe recent improvements in the in vitro and in vivo signal size and kinetics of genetically encoded voltage indicators (GEVIs) and discuss their relationship to alternative sensors of neural activity.
Topics: Animals; Brain; Membrane Potentials; Neurons; Voltage-Sensitive Dye Imaging
PubMed: 27130905
DOI: 10.1016/j.tins.2016.02.005 -
Current Opinion in Pharmacology Oct 2016G-protein coupled receptors (GPCRs) form the largest class of membrane proteins in humans and the targets of most present drugs. Membrane potential is one of the... (Review)
Review
G-protein coupled receptors (GPCRs) form the largest class of membrane proteins in humans and the targets of most present drugs. Membrane potential is one of the defining characteristics of living cells. Recent work has shown that the membrane voltage, and changes thereof, modulates signal transduction and ligand binding in GPCRs. As it may allow differential signalling patterns depending on tissue, cell type, and the excitation status of excitable cells, GPCR voltage sensitivity could have important implications for their pharmacology. This review summarises recent experimental insights on GPCR voltage regulation and the role of molecular dynamics simulations in identifying the structural basis of GPCR voltage-sensing. We discuss the potential significance for drug design on GPCR targets from excitable and non-excitable cells.
Topics: Drug Design; Humans; Ligands; Membrane Potentials; Molecular Dynamics Simulation; Receptors, G-Protein-Coupled; Signal Transduction
PubMed: 27474871
DOI: 10.1016/j.coph.2016.06.011