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Heart Rhythm Jul 2021Although atrial fibrillation ablation is increasingly used for rhythm control therapy, antiarrhythmic drugs (AADs) are commonly used, either alone or in combination with...
BACKGROUND
Although atrial fibrillation ablation is increasingly used for rhythm control therapy, antiarrhythmic drugs (AADs) are commonly used, either alone or in combination with ablation. The effectiveness of AADs is highly variable. Previous work from our group suggests that alterations in atrial resting membrane potential (RMP) induced by low Pitx2 expression could explain the variable effect of flecainide.
OBJECTIVE
The purpose of this study was to assess whether alterations in atrial/cardiac RMP modify the effectiveness of multiple clinically used AADs.
METHODS
The sodium channel blocking effects of propafenone (300 nM, 1 μM), flecainide (1 μM), and dronedarone (5 μM, 10 μM) were measured in human stem cell-derived cardiac myocytes, HEK293 expressing human Na1.5, primary murine atrial cardiac myocytes, and murine hearts with reduced Pitx2c.
RESULTS
A more positive atrial RMP delayed I recovery, slowed channel inactivation, and decreased peak action potential (AP) upstroke velocity. All 3 AADs displayed enhanced sodium channel block at more positive atrial RMPs. Dronedarone was the most sensitive to changes in atrial RMP. Dronedarone caused greater reductions in AP amplitude and peak AP upstroke velocity at more positive RMPs. Dronedarone evoked greater prolongation of the atrial effective refractory period and postrepolarization refractoriness in murine Langendorff-perfused Pitx2c hearts, which have a more positive RMP compared to wild type.
CONCLUSION
Atrial RMP modifies the effectiveness of several clinically used AADs. Dronedarone is more sensitive to changes in atrial RMP than flecainide or propafenone. Identifying and modifying atrial RMP may offer a novel approach to enhancing the effectiveness of AADs or personalizing AAD selection.
Topics: Action Potentials; Animals; Anti-Arrhythmia Agents; Atrial Fibrillation; Disease Models, Animal; Dronedarone; Female; Flecainide; Heart Atria; Male; Membrane Potentials; Mice; Propafenone; Sodium; Voltage-Gated Sodium Channel Blockers
PubMed: 33737232
DOI: 10.1016/j.hrthm.2021.03.016 -
Methods in Enzymology 2020Voltage imaging in living cells offers the tantalizing possibility of combining the temporal resolution of electrode-based methods with the spatial resolution of imaging...
Voltage imaging in living cells offers the tantalizing possibility of combining the temporal resolution of electrode-based methods with the spatial resolution of imaging techniques. Our lab has been developing voltage-sensitive fluorophores, or VoltageFluors, that respond to changes in cellular and neuronal membrane potential via a photoinduced electron transfer (PeT)-based mechanism. This unique mechanism enables both the fast response kinetics and high sensitivity required to record action potentials in single trials, across multiple cells without the need for stimuli-triggered averaging. In this chapter, we present a methodology for imaging membrane potential dynamics from dozens of neurons simultaneously in vitro. Using simple, commercially available cameras, illumination sources, and microscope optics in combination with the far-red synthetic voltage-sensitive fluorophore BeRST-1 (Berkeley Red Sensor of Transmembrane potential) provides a readily applied method for monitoring neuronal activity in cultured neurons. We discuss different types of voltage-sensitive dyes, considerations for selecting imaging modalities, and outline procedures for the culture of rat hippocampal neurons and performing voltage imaging experiments with these samples. Finally, we provide an example of how changes to the metabolic input to cultured hippocampal neurons can alter their activity profile.
Topics: Action Potentials; Animals; Fluorescent Dyes; Hippocampus; Membrane Potentials; Neurons; Rats
PubMed: 32560798
DOI: 10.1016/bs.mie.2020.04.028 -
Food and Chemical Toxicology : An... Feb 2022A significant rise in the incidence of obesity and type 2 diabetes has occurred worldwide in the last two decades. Concurrently, a growing body of evidence suggests a... (Review)
Review
A significant rise in the incidence of obesity and type 2 diabetes has occurred worldwide in the last two decades. Concurrently, a growing body of evidence suggests a connection between exposure to environmental pollutants, particularly insecticides, and the development of obesity and type 2 diabetes. This review summarizes key evidence of (1) the presence of different types of neuronal receptors - target sites for neurotoxic insecticides - in non-neuronal cells, (2) the activation of these receptors in non-neuronal cells by membrane-depolarizing insecticides, and (3) changes in metabolic functions, including lipid and glucose accumulation, associated with changes in membrane potential. Based on these findings, we propose that changes in membrane potential (V) by certain insecticides serve as a novel regulator of lipid and glucose metabolism in non-excitable cells associated with obesity and type 2 diabetes.
Topics: Animals; Cell Membrane; Diabetes Mellitus, Type 2; Environmental Exposure; Environmental Pollutants; Humans; Insecticides; Membrane Potentials; Obesity
PubMed: 34990786
DOI: 10.1016/j.fct.2021.112804 -
Microbiology (Reading, England) Sep 2022Transmembrane potential is one of the main bioenergetic parameters of bacterial cells, and is directly involved in energizing key cellular processes such as transport,...
Transmembrane potential is one of the main bioenergetic parameters of bacterial cells, and is directly involved in energizing key cellular processes such as transport, ATP synthesis and motility. The most common approach to measure membrane potential levels is through use of voltage-sensitive fluorescent dyes. Such dyes either accumulate or are excluded from the cell in a voltage-dependent manner, which can be followed by means of fluorescence microscopy, flow cytometry, or fluorometry. Since the cell's ability to maintain transmembrane potential relies upon low and selective membrane ion conductivity, voltage-sensitive dyes are also highly sensitive reporters for the activity of membrane-targeting antibacterials. However, the presence of an additional membrane layer in Gram-negative (diderm) bacteria complicates their use significantly. In this paper, we provide guidance on how membrane potential and its changes can be monitored reliably in Gram-negatives using the voltage-sensitive dye 3,3'-dipropylthiadicarbocyanine iodide [DiSC(5)]. We also discuss the confounding effects caused by the presence of the outer membrane, or by measurements performed in buffers rather than growth medium. We hope that the discussed methods and protocols provide an easily accessible basis for the use of voltage-sensitive dyes in Gram-negative organisms, and raise awareness of potential experimental pitfalls associated with their use.
Topics: Adenosine Triphosphate; Fluorescent Dyes; Gram-Negative Bacteria; Iodides; Membrane Potentials
PubMed: 36165741
DOI: 10.1099/mic.0.001227 -
Biologia Futura Dec 2022Membrane theory makes it possible to compute the membrane potential of living cells accurately. The principle is that the plasma membrane is selectively permeable to...
Membrane theory makes it possible to compute the membrane potential of living cells accurately. The principle is that the plasma membrane is selectively permeable to ions and that its permeability to mobile ions determines the characteristics of the membrane potential. However, an artificial experimental cell system with an impermeable membrane can exhibit a nonzero membrane potential, and its characteristics are consistent with the prediction of the Goldman-Hodgkin-Katz eq., which is a noteworthy concept of membrane theory, despite the membrane's impermeability to mobile ions. We noticed this troublesome facet of the membrane theory. We measured the potentials through permeable and impermeable membranes where we used the broad varieties of membranes. Then we concluded that the membrane potential must be primarily, although not wholly, governed by the ion adsorption-desorption process rather than by the passage of ions across the cell membrane. A theory based on the Association-Induction Hypothesis seems to be a more plausible mechanism for the generation of the membrane potential and to explain this unexpected physiological fact. The Association-Induction Hypothesis states that selective ion permeability of the membrane is not a condition for the generation of the membrane potential in living cells, which contradicts the prediction of the membrane theory. Therefore, the Association-Induction Hypothesis is the actual cause of membrane potential. We continued the theoretical analysis by taking into account the Association-Induction Hypothesis and saw that its universality as a cause of potential generation mechanism. We then concluded that the interfacial charge distribution is one of the fundamental causes of the membrane potential.
Topics: Membrane Potentials; Adsorption; Ions
PubMed: 36463564
DOI: 10.1007/s42977-022-00139-y -
Environmental Microbiology Aug 2020The Plasma Membrane Proteolipid 3 (PMP3, UPF0057 family in Uniprot) family consists of abundant small hydrophobic polypeptides with two predicted transmembrane helices....
The Plasma Membrane Proteolipid 3 (PMP3, UPF0057 family in Uniprot) family consists of abundant small hydrophobic polypeptides with two predicted transmembrane helices. Plant homologues were upregulated in response to drought/salt-stresses and yeast deletion mutants exhibited conditional growth defects. We report here abundant expression of Group I PMP3 homologues (PMP3(i)hs) during normal vegetative growth in both prokaryotic and eukaryotic cells, at a level comparable to housekeeping genes, implicating the regular cellular functions. Expression of eukaryotic PMP3(i)hs was dramatically upregulated in response to membrane potential (Vm) variability (Vm ), whereas PMP3(i)hs deletion-knockdown led to Vm changes with conditional growth defects. Bacterial PMP3(i)h yqaE deletion led to a shift of salt sensitivity; Vm alternations with exogenous K addition downregulated prokaryotic PMP3(i)hs, suggesting [K ]-Vm axis being a significant feedback element in prokaryotic ionic homeostasis. Remarkably, the eukaryotic homologues functionally suppressed the conditional growth defects in bacterial deletion mutant, demonstrating the conserved cross-kingdom membrane functions by PMP3(i)hs. These data demonstrated a direct reciprocal relationship between PMP3(i)hs expression and Vm differentials in both prokaryotic and eukaryotic cells. Cumulative with PMP3(i)hs ubiquitous abundance, their lipid-binding selectivity and membrane protein colocalization, we propose [PMP3(i)hs]-Vm axis as a key element in membrane homeostasis.
Topics: Archaea; Bacteria; Droughts; Ion Channels; Membrane Potentials; Membrane Proteins; Osmolar Concentration; Proteolipids; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins; Sodium Chloride; Stress, Physiological
PubMed: 32307863
DOI: 10.1111/1462-2920.15027 -
Advances in Physiology Education Dec 2022Since its discovery in the mid-20th century, the Hodgkin-Huxley biophysical model of the squid giant axon's (SGA's) neurophysiology has traditionally served as the basis... (Review)
Review
Since its discovery in the mid-20th century, the Hodgkin-Huxley biophysical model of the squid giant axon's (SGA's) neurophysiology has traditionally served as the basis for the teaching of action potential (AP) dynamics in the physiology classroom. This model teaches that leak conductances set membrane resting potential; that fast, inactivating, voltage-gated sodium channels effect the SGA AP upstroke; and that delayed, rectifying, noninactivating voltage-gated potassium channels carry AP repolarization and the early part of the afterhyperpolarization (AHP). This model serves well to introduce students to the fundamental ideas of resting potential establishment and maintenance, as well as basic principles of AP generation and propagation. Furthermore, the Hodgkin-Huxley SGA model represents an excellent and accessible starting point for discussion of the concept of AP threshold and the role of passive electrical properties of the neuron. Additionally, the introduction of the Hodgkin-Huxley model of the SGA AP permits the integration of physiological principles, as instructors ask students to apply previously studied principles of transporter and channel biophysics to the essential physiological phenomenon of electrical signal conduction. However, both some early observations as well as more recent evidence strongly suggest that this seminal invertebrate model of AP dynamics does not appropriately capture the full story for mammalian axons. We review recent evidence that mammalian axonal nodes of Ranvier repolarize largely (though not exclusively) through the activity of leak potassium-ion (K) conductances carried through two-pore domain (K) channels. We call for changes to physiology textbooks and curricula to highlight this remarkable difference in invertebrate and mammalian AP repolarization mechanisms. Historically, physiology courses have typically taught that action potential repolarization occurs exclusively due to the activation of delayed-rectifier voltage-gated potassium channels. Here, we review and highlight recent evidence that leak potassium channels of the two-pore domain (K) class may largely serve this repolarization role at mammalian nodes of Ranvier. We call for the inclusion of these ideas in physiology curricula at all levels, from high school to graduate school.
Topics: Animals; Humans; Action Potentials; Potassium Channels, Tandem Pore Domain; Membrane Potentials; Potassium Channels, Voltage-Gated; Axons; Potassium; Mammals
PubMed: 36173340
DOI: 10.1152/advan.00171.2021 -
Acta Biotheoretica May 2023It is common to say that the origin of the membrane potential is attributed to transmembrane ion transport, but it is theoretically possible to explain its generation by...
It is common to say that the origin of the membrane potential is attributed to transmembrane ion transport, but it is theoretically possible to explain its generation by the mechanism of ion adsorption. It has been previously suggested that the ion adsorption mechanism even leads to potential formulae identical to the famous Nernst equation or the Goldman-Hodgkin-Katz equation. Our further analysis, presented in this paper, indicates that the potential formula based on the ion adsorption mechanism leads to an equation that is a function of the surface charge density of the material and the surface potential of the material. Furthermore, we have confirmed that the equation holds in all the different experimental systems that we have studied. This equation appears to be a key equation that governs the characteristics of the membrane potential in all systems.
Topics: Animals; Membrane Potentials; Ion Transport; Adsorption
PubMed: 37148457
DOI: 10.1007/s10441-023-09467-5 -
Proceedings of the National Academy of... Apr 2024Biological membrane potentials, or voltages, are a central facet of cellular life. Optical methods to visualize cellular membrane voltages with fluorescent indicators...
Biological membrane potentials, or voltages, are a central facet of cellular life. Optical methods to visualize cellular membrane voltages with fluorescent indicators are an attractive complement to traditional electrode-based approaches, since imaging methods can be high throughput, less invasive, and provide more spatial resolution than electrodes. Recently developed fluorescent indicators for voltage largely report changes in membrane voltage by monitoring voltage-dependent fluctuations in fluorescence intensity. However, it would be useful to be able to not only monitor changes but also measure values of membrane potentials. This study discloses a fluorescent indicator which can address both. We describe the synthesis of a sulfonated tetramethyl carborhodamine fluorophore. When this carborhodamine is conjugated with an electron-rich, methoxy (-OMe) containing phenylenevinylene molecular wire, the resulting molecule, CRhOMe, is a voltage-sensitive fluorophore with red/far-red fluorescence. Using CRhOMe, changes in cellular membrane potential can be read out using fluorescence intensity or lifetime. In fluorescence intensity mode, CRhOMe tracks fast-spiking neuronal action potentials (APs) with greater signal-to-noise than state-of-the-art BeRST 1 (another voltage-sensitive fluorophore). CRhOMe can also measure values of membrane potential. The fluorescence lifetime of CRhOMe follows a single exponential decay, substantially improving the quantification of membrane potential values using fluorescence lifetime imaging microscopy (FLIM). The combination of red-shifted excitation and emission, mono-exponential decay, and high voltage sensitivity enable fast FLIM recording of APs in cardiomyocytes. The ability to both monitor and measure membrane potentials with red light using CRhOMe makes it an important approach for studying biological voltages.
Topics: Membrane Potentials; Fluorescent Dyes; Action Potentials; Cell Membrane; Microscopy, Fluorescence
PubMed: 38551837
DOI: 10.1073/pnas.2315264121 -
Physiology (Bethesda, Md.) Nov 2023The array of ion channels and transporters expressed in cell membranes, collectively referred to as the transportome, is a complex and multifunctional molecular... (Review)
Review
The array of ion channels and transporters expressed in cell membranes, collectively referred to as the transportome, is a complex and multifunctional molecular machinery; in particular, at the plasma membrane level it finely tunes the exchange of biomolecules and ions, acting as a functionally adaptive interface that accounts for dynamic plasticity in the response to environmental fluctuations and stressors. The transportome is responsible for the definition of membrane potential and its variations, participates in the transduction of extracellular signals, and acts as a filter for most of the substances entering and leaving the cell, thus enabling the homeostasis of many cellular parameters. For all these reasons, physiologists have long been interested in the expression and functionality of ion channels and transporters, in both physiological and pathological settings and across the different domains of life. Today, thanks to the high-throughput technologies of the postgenomic era, the omics approach to the study of the transportome is becoming increasingly popular in different areas of biomedical research, allowing for a more comprehensive, integrated, and functional perspective of this complex cellular apparatus. This article represents a first effort for a systematic review of the scientific literature on this topic. Here we provide a brief overview of all those studies, both primary and meta-analyses, that looked at the transportome as a whole, regardless of the biological problem or the models they used. A subsequent section is devoted to the methodological aspect by reviewing the most important public databases annotating ion channels and transporters, along with the tools they provide to retrieve such information. Before conclusions, limitations and future perspectives are also discussed.
Topics: Humans; Biomedical Research; Homeostasis; Membrane Potentials
PubMed: 37668550
DOI: 10.1152/physiol.00010.2023