Common action of certain viruses, toxins, and activated complement: pore formation and its prevention by extracellular Ca2+

1984 ◽  
Vol 4 (9) ◽  
pp. 797-805 ◽  
Author(s):  
C. L. Bashford ◽  
G. M. Alder ◽  
K. Patel ◽  
C. A. Pasternak
Keyword(s):  
Membrane Potential ◽  
Pore Formation ◽  
Divalent Cations ◽  
Surface Membrane ◽  
Daudi Cells ◽  
High Concentrations ◽  
Common Action

Haemolysis by Sendal virus, α-toxin, and activated complement is inhibited by high concentrations of divalent cations. In Daudi cells, sublytic amounts of these agents induce the following changes: collapse of surface membrane potential, uptake of Na+ and loss of K+ from cells, and leakage of phosphorylated metabo-tites from cells. The changes induced by Sendal virus and complement are sensitive to physiological concentrations of extracellular Ca2+. It is concluded that fluctuations in plasma Ca2+ concentration may affect the damaging action of certain pore-forming agents on susceptible cells.

Effects of hydrogen peroxide and hypochlorite on membrane potential of mitochondria in situ in rat heart cells

1991 ◽  
Vol 69 (11) ◽  
pp. 1705-1712 ◽  
Author(s):  
Noburu Konno ◽  
K. J. Kako
Keyword(s):  
Hydrogen Peroxide ◽  
Membrane Potential ◽  
Mitochondrial Membrane Potential ◽  
Rat Heart ◽  
Mitochondrial Membrane ◽  
Isolated Rat Heart ◽  
Heart Mitochondria ◽  
High Concentrations ◽  
Isolated Rat

Hydrogen peroxide (H2O2) and hypochlorite (HOCl) cause a variety of cellular dysfunctions. In this study we examined the effects of these agents on the electrical potential gradient across the inner membrane of mitochondria in situ in isolated rat heart myocytes. Myocytes were prepared by collagenase digestion and incubated in the presence of H2O2 or HOCl. Transmembrane electrical gradients were measured by distribution of [3H]triphenylmethylphosphonium+, a lipophilic cation. The particulate fraction was separated from the cytosolic compartment first by permeabilization using digitonin, followed by rapid centrifugal sedimentation through a bromododecane layer. We found that the mitochondrial membrane potential (161 ± 7 mV, negative inside) was relatively well maintained under oxidant stress, i.e., the potential was decreased only at high concentrations of HOCl and H2O2 and gradually with time. The membrane potential of isolated rat heart mitochondria was affected similarly by H2O2 and HOCl in a concentration- and time-dependent manner. High concentrations of oxidants also reduced the cellular ATP level but did not significantly change the matrix volume. When the extra-mitochondrial free calcium concentration was increased in permeabilized myocytes, the transmembrane potential was decreased proportionally, and this decrease was potentiated further by H2O2. These results support the view that heart mitochondria are equipped with well-developed defense mechanisms against oxidants, but the action of H2O2 on the transmembrane electrical gradient is exacerbated by an increase in cytosolic calcium. Keywords: ATP, calcium, cardiomyocyte, cell defense, mitochondrial membrane potential, oxidant, triphenylmethylphosphonium.

Membrane potential of single asymmetric nanopores: Divalent cations and salt mixtures

2019 ◽  
Vol 573 ◽  
pp. 579-587 ◽  
Author(s):  
Patricio Ramirez ◽  
Javier Cervera ◽  
Vicente Gomez ◽  
Mubarak Ali ◽  
Saima Nasir ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Divalent Cations ◽  
Salt Mixtures

Effects of some divalent cations on motoneurones in cats

1979 ◽  
Vol 57 (9) ◽  
pp. 944-956 ◽  
Author(s):  
K. Krnjević ◽  
Y. Lamour ◽  
J. F. MacDonald ◽  
A. Nistri
Keyword(s):  
Membrane Potential ◽  
Action Potential ◽  
Intracellular Recording ◽  
Dorsal Root ◽  
Divalent Cations ◽  
The Other ◽  
Depressant Effect ◽  
Na Inactivation ◽  
Conductance Increase ◽  
Root Stimulation

In cats under Dial, Co, Mn, La, and Sr were injected extracellularly near lumbosacral motoneurones. All tended to improve intracellular recording, but when the membrane potential was initially stable, Mn, and especially Co, had a moderate and reproducible depolarizing action. Both Mn and Co depressed excitatory postsynaptic potentials evoked by dorsal root stimulation. The prominent after-hyperpolarization (a.h.p.), which normally follows the motoneuronal action potential, was consistently and reversibly depressed by Mn and Co (as well as La), the underlying conductance increase being also diminished, but there was no significant reduction in the after-depolarization. By contrast, Sr tended to potentiate the a.h.p., especially when this was depressed by a previous injection of Co or Mn. Unlike the other cations, Co had a marked depressant effect on the action potential, particularly its rate of rise. Since the action potential could be immediately restored by hyperpolarization or by an injection of Sr (in the absence of depolarization), Co may enhance Na inactivation.

scholarly journals Daptomycin Pore Formation and Stoichiometry Depend on Membrane Potential of Target Membrane

2018 ◽  
Vol 63 (1) ◽  
Author(s):  
Gabriela Seydlová ◽  
Albert Sokol ◽  
Petra Lišková ◽  
Ivo Konopásek ◽  
Radovan Fišer
Keyword(s):  
Membrane Potential ◽  
Lipid Bilayers ◽  
Pore Formation ◽  
Content Type ◽  
Calcium Dependent ◽  
Screening Experiment ◽  
Serious Infections ◽  
Fluorescence Methods ◽  
Initial Membrane ◽  
Target Membrane

ABSTRACT Daptomycin is a calcium-dependent lipodepsipeptide antibiotic clinically used to treat serious infections caused by Gram-positive pathogens. Its precise mode of action is somewhat controversial; the biggest issue is daptomycin pore formation, which we directly investigated here. We first performed a screening experiment using propidium iodide (PI) entry to Bacillus subtilis cells and chose the optimum and therapeutically relevant conditions (10 µg/ml daptomycin and 1.25 mM CaCl2) for the subsequent analyses. Using conductance measurements on planar lipid bilayers, we show that daptomycin forms nonuniform oligomeric pores with conductance ranging from 120 pS to 14 nS. The smallest conductance unit is probably a dimer; however, tetramers and pentamers occur in the membrane most frequently. Moreover, daptomycin pore-forming activity is exponentially dependent on the applied membrane voltage. We further analyzed the membrane-permeabilizing activity in B. subtilis cells using fluorescence methods [PI and DiSC3(5)]. Daptomycin most rapidly permeabilizes cells with high initial membrane potential and dissipates it within a few minutes. Low initial membrane potential hinders daptomycin pore formation.

Cellular and subcellular mechanisms of cardiac pacemaker oscillations

1979 ◽  
Vol 81 (1) ◽  
pp. 205-215
Author(s):  
R. W. Tsien ◽  
R. S. Kass ◽  
R. Weingart
Keyword(s):  
Membrane Potential ◽  
Voltage Clamp ◽  
Surface Membrane ◽  
Cardiac Pacemaker ◽  
Oscillatory Activity ◽  
Purkinje Fibre ◽  
Pacemaker Activity ◽  
Heart Cells ◽  
Control Loop ◽  
Internal Oscillation

Rhythmic oscillations in the membrane potential of heart cells are important in normal cardiac pacemaker activity as well as cardiac arrhythmias. Two fundamentally different mechanisms of oscillatory activity can be distinguished at the cellular and subcellular level. The first mechanism, referred to as a surface membrane oscillator, can be represented by a control loop in which membrane potential changes evoke delayed conductance changes and vice versa. Since the surface membrane potential is a key variable within the control loop, the oscillation can be interrupted at any time by holding the membrane potential constant with a voltage clamp. This mode of oscillation seems to describe spontaneous pacemaker activity in the primary cardiac pacemaker (sinoatrial node) as well as other regions (Purkinje fibre, atrial or ventricular muscle). In all tissues studied so far, the pacemaker depolarization is dominated by the slow shutting-off of an outward current, largely carried by potassium ions. The second mechanism can be called an internal oscillator since it depends upon a subcellular rhythm generator which is largely independent from the surface membrane. Under voltage clamp, the existence of the internal oscillation is revealed by the presence of oscillations in membrane conductance or contractile force which occur even though the membrane potential is held fixed. The two oscillatory mechanisms are not mutually exclusive; the subcellular mechanism can be preferentially enhanced in any given cardiac cell by conditions which elevate intracellular calcium. Such conditions include digitalis intoxication, high Cao, low Nao, low or high Ko, cooling, or rapid stimulation. Several lines of evidence suggest that the subcellular mechanism involves oscillatory variations in myoplasmic calcium, probably due to cycles of Ca uptake and release by the sarcoplasmic reticulum. The detailed nature of the Cai oscillator and its interaction with the surface membrane await further investigation.

Coupling mechanisms in airway smooth muscle

1990 ◽  
Vol 258 (4) ◽  
pp. L119-L133 ◽  
Author(s):  
R. F. Coburn ◽  
C. B. Baron
Keyword(s):  
Smooth Muscle ◽  
Membrane Potential ◽  
Airway Smooth Muscle ◽  
Electromechanical Coupling ◽  
Cell Function ◽  
Surface Membrane ◽  
Smooth Muscles ◽  
Membrane Receptors ◽  
Airway Smooth Muscle Cells ◽  
Coupling Mechanisms

This review documents available information about coupling mechanisms involved in airway smooth muscle force development and maintenance and relaxation of force. Basic concepts, obtained from experiments performed on many different mammalian cell types, are in place regarding coupling between surface membrane receptors and cell function; these concepts are considered as a framework for understanding coupling between receptors and contractile proteins in smooth muscles and in airway smooth muscles. We have divided various components of coupling mechanisms into those dependent on changes in the surface membrane potential (electromechanical coupling) and those independent of the surface membrane potential (pharmacomechanical coupling). We have, to some degree, emphasized modulation of coupling mechanisms by intrasurface membrane microprocessing or by second messengers. A challenge for the future is to obtain a better understanding of how coupling mechanisms are altered or modulated during different phases of contractions evoked by a single agonist and under conditions of multiple agonist exposure to airway smooth muscle cells.

Mechanisms of vasodilation induced by vasoactive intestinal polypeptide in rabbit mesenteric artery

1985 ◽  
Vol 249 (2) ◽  
pp. H231-H240 ◽  
Author(s):  
T. Itoh ◽  
T. Sasaguri ◽  
Y. Makita ◽  
Y. Kanmura ◽  
H. Kuriyama
Keyword(s):  
Membrane Potential ◽  
Vasoactive Intestinal Polypeptide ◽  
Mesenteric Artery ◽  
Muscle Cells ◽  
Free Solution ◽  
Cyclic Monophosphate ◽  
Rabbit Mesenteric Artery ◽  
High Concentrations ◽  
Intestinal Polypeptide

Vasoactive intestinal polypeptide (VIP; over 10(-13) M) inhibited the norepinephrine (NE)-induced contraction evoked from the rabbit mesenteric artery. Increased concentrations of VIP (over 10(-9) M) inhibited the contractions induced by caffeine and 39 mM [K]o. However, VIP (below 10(-7) M) had no effect on the membrane potential and resistance of muscle cells. In Ca-free solution, VIP (10(-10) M) inhibited the NE-induced contraction, but the second application of NE after removal of VIP enlarged the amplitude of contraction over that in the control. Yet when 10(-9) M VIP was applied, both the first and second contractions were consistently smaller than those observed by application of 10(-10) M VIP. In Na- and Ca-free solution, repetitive applications of NE generated contractions longer than those observed in Ca-free solution. When VIP (10(-10) M) was applied once (3 min), the contraction was inhibited only once during repetitive applications of NE. VIP (over 10(-9) M) dose dependently inhibited the NE-induced contraction and had a long-lasting inhibition after washout of the tissue. In saponin-treated skinned muscles, VIP (10(-7) M) had no effect on the Ca-induced contraction or on the Ca store sites. VIP (over 10(-8) M) was about 10 times more potent than equimolar concentrations of isoproterenol in increasing the content of adenosine 3', 5'-cyclic monophosphate (cAMP). These results indicate that VIP (10(-10) M) selectively inhibits the Ca release activated by NE, and high concentrations (over 10(-9) M) would expectedly increase the Ca extrusion from cells following increase in the levels of cAMP.

scholarly journals Prebiotic amino acids bind to and stabilize prebiotic fatty acid membranes

2019 ◽  
Vol 116 (35) ◽  
pp. 17239-17244 ◽  
Author(s):  
Caitlin E. Cornell ◽  
Roy A. Black ◽  
Mengjun Xue ◽  
Helen E. Litz ◽  
Andrew Ramsay ◽  
...  
Keyword(s):  
Amino Acids ◽  
Fatty Acid ◽  
Divalent Cations ◽  
Building Blocks ◽  
Rna Catalysis ◽  
Membrane Stabilization ◽  
Molecular Building Blocks ◽  
Prebiotic Amino Acids ◽  
Self Assembled ◽  
High Concentrations

The membranes of the first protocells on the early Earth were likely self-assembled from fatty acids. A major challenge in understanding how protocells could have arisen and withstood changes in their environment is that fatty acid membranes are unstable in solutions containing high concentrations of salt (such as would have been prevalent in early oceans) or divalent cations (which would have been required for RNA catalysis). To test whether the inclusion of amino acids addresses this problem, we coupled direct techniques of cryoelectron microscopy and fluorescence microscopy with techniques of NMR spectroscopy, centrifuge filtration assays, and turbidity measurements. We find that a set of unmodified, prebiotic amino acids binds to prebiotic fatty acid membranes and that a subset stabilizes membranes in the presence of salt and Mg2+. Furthermore, we find that final concentrations of the amino acids need not be high to cause these effects; membrane stabilization persists after dilution as would have occurred during the rehydration of dried or partially dried pools. In addition to providing a means to stabilize protocell membranes, our results address the challenge of explaining how proteins could have become colocalized with membranes. Amino acids are the building blocks of proteins, and our results are consistent with a positive feedback loop in which amino acids bound to self-assembled fatty acid membranes, resulting in membrane stabilization and leading to more binding in turn. High local concentrations of molecular building blocks at the surface of fatty acid membranes may have aided the eventual formation of proteins.

scholarly journals External Nickel Inhibits Epithelial Sodium Channel by Binding to Histidine Residues within the Extracellular Domains of α and γ Subunits and Reducing Channel Open Probability

2002 ◽  
Vol 277 (51) ◽  
pp. 50098-50111 ◽  
Author(s):  
Shaohu Sheng ◽  
Clint J. Perry ◽  
Thomas R. Kleyman
Keyword(s):  
Divalent Cations ◽  
Wild Type Mouse ◽  
Inhibitory Effect ◽  
Inward Rectification ◽  
Dependent Manner ◽  
Open Probability ◽  
Histidine Residues ◽  
Low Concentrations ◽  
High Concentrations ◽  
A Site

Epithelial sodium channels (ENaC) are regulated by various intracellular and extracellular factors including divalent cations. We studied the inhibitory effect and mechanism of external Ni2+on cloned mouse α-β-γ ENaC expressed inXenopusoocytes. Ni2+reduced amiloride-sensitive Na+currents of the wild type mouse ENaC in a dose-dependent manner. The Ni2+block was fast and partially reversible at low concentrations and irreversible at high concentrations. ENaC inhibition by Ni2+was accompanied by moderate inward rectification at concentrations higher than 0.1 mm. ENaC currents were also blocked by the histidine-reactive reagent diethyl pyrocarbonate. Pretreatment of the oocytes with the reagent reduced Ni2+inhibition of the remaining current. Mutations at αHis282and γHis239located within the extracellular loops significantly decreased Ni2+inhibition of ENaC currents. The mutation αH282D or double mutations αH282R/γH239R eliminated Ni2+block. All mutations at γHis239eliminated Ni2+-induced inward current rectification. Ni2+block was significantly enhanced by introduction of a histidine at αArg280. Lowering extracellular pH to 5.5 and 4.4 decreased or eliminated Ni2+block. Although αH282C-β-γ channels were partially inhibited by the sulfhydryl-reactive reagent [2-(trimethylammonium)ethyl] methanethiosulfonate bromide (MTSET), α-β-γ H239C channels were insensitive to MTSET. From patch clamp studies, Ni2+did not affect unitary current but decreased open probability when perfused into the recording pipette. Our results suggest that external Ni2+reduces ENaC open probability by binding to a site consisting of αHis282and γHis239and that these histidine residues may participate in ENaC gating.

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