scholarly journals The Nature of the Negative Resistance in Bimolecular Lipid Membranes Containing Excitability-Inducing Material

1970 ◽  
Vol 55 (1) ◽  
pp. 119-133 ◽  
Author(s):  
Gerald Ehrenstein ◽  
Harold Lecar ◽  
Ralph Nossal
Keyword(s):  
Membrane Potential ◽  
Lipid Membranes ◽  
Lipid Membrane ◽  
Negative Resistance ◽  
Voltage Dependent ◽  
The Difference ◽  
Ion Conducting ◽  
Opening And Closing

When sufficiently small amounts of excitability-inducing material (EIM) are added to a bimolecular lipid membrane, the conductance is limited to a few discrete levels and changes abruptly from one level to another. From our study of these fluctuations, we have concluded that the EIM-doped bilayer contains ion-conducting channels capable of undergoing transitions between two states of different conductance. The difference in current between the "open" and "closed" states is directly proportional to the applied membrane potential, and corresponds to a conductance of about 3 x 10-10 ohm-1. The fraction of the total number of channels that is open varies from unity to zero as a function of potential. The voltage-dependent opening and closing of channels explains the negative resistance observed for bimolecular lipid membranes treated with greater amounts of EIM.

scholarly journals Melittin Induces Local Order Changes in Artificial and Biological Membranes as Revealed by Spectral Analysis of Laurdan Fluorescence

Toxins ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 705
Author(s):  
Bogdan Zorilă ◽  
George Necula ◽  
Mihai Radu ◽  
Mihaela Bacalum
Keyword(s):  
Lipid Membranes ◽  
Lipid Membrane ◽  
Local Order ◽  
Generalized Polarization ◽  
Membrane Probe ◽  
Area Per Lipid ◽  
The Difference ◽  
Log Normal ◽  
Laurdan Fluorescence ◽  
Natural Lipid

Antimicrobial peptides (AMPs) are a class of molecules widely used in applications on eukaryotic and prokaryotic cells. Independent of the peptide target, all of them need to first pass or interact with the plasma membrane of the cells. In order to have a better image of the peptide action mechanism with respect to the particular features of the membrane it is necessary to better understand the changes induced by AMPs in the membranes. Laurdan, a lipid membrane probe sensitive to polarity changes in the environment, is used in this study for assessing changes induced by melittin, a well-known peptide, both in model and natural lipid membranes. More importantly, we showed that generalized polarization (GP) values are not always efficient or sufficient to properly characterize the changes in the membrane. We proved that a better method to investigate these changes is to use the previously described log-normal deconvolution allowing us to infer other parameters: the difference between the relative areas of elementary peak (ΔSr), and the ratio of elementary peaks areas (Rs). Melittin induced a slight decrease in local membrane fluidity in homogeneous lipid membranes. The addition of cholesterol stabilizes the membrane more in the presence of melittin. An opposite response was observed in the case of heterogeneous lipid membranes in cells, the local order of lipids being diminished. RS proved to be the most sensitive parameter characterizing the local membrane order, allowing us to distinguish among the responses to melittin of both classes of membrane we investigated (liposomes and cellular membranes). Molecular simulation of the melittin pore in homogeneous lipid bilayer suggests that lipids are more closely packed in the proximity of the melittin pore (a smaller area per lipid), supporting the experimental observation.

scholarly journals Kinetics of the Opening and Closing of Individual Excitability-Inducing Material Channels in a Lipid Bilayer

1974 ◽  
Vol 63 (6) ◽  
pp. 707-721 ◽  
Author(s):  
Gerald Ehrenstein ◽  
Robert Blumenthal ◽  
Ramon Latorre ◽  
Harold Lecar
Keyword(s):  
Lipid Bilayers ◽  
Ionic Current ◽  
Energy Difference ◽  
Excitable Membranes ◽  
Voltage Dependent ◽  
Ion Conducting ◽  
The Many ◽  
Approach To Steady State ◽  
Opening And Closing ◽  
Kinetics Of

The kinetics of the opening and closing of individual ion-conducting channels in lipid bilayers doped with small amounts of excitability-inducing material (EIM) are determined from discrete fluctuations in ionic current. The kinetics for the approach to steady-state conductance during voltage clamp are determined for lipid bilayers containing many EIM channels. The two sets of measurements are found to be consistent, verifying that the voltage-dependent conductance of the many-channel EIM system arises from the opening and closing of individual EIM channels. The opening and closing of the channels are Poisson processes. Transition rates for these processes vary exponentially with applied potential, implying that the energy difference between the open and closed states of an EIM channel is linearly proportional to the transmembrane electric field. A model incorporating the above properties of the EIM channels predicts the observed voltage dependence of ionic conductance and conductance relaxation time, which are also characteristic of natural electrically excitable membranes.

scholarly journals Conductive Properties and Gating of Channels Formed by Syringopeptin 25A, a Bioactive Lipodepsipeptide from Pseudomonas syringae pv. syringae, in Planar Lipid Membranes

1999 ◽  
Vol 12 (5) ◽  
pp. 401-409 ◽  
Author(s):  
Mauro Dalla Serra ◽  
Ivonne Bernhart ◽  
Paola Nordera ◽  
Domenico Di Giorgio ◽  
Alessandro Ballio ◽  
...  
Keyword(s):  
Pseudomonas Syringae ◽  
Lipid Membranes ◽  
Pore Radius ◽  
Maximal Conductance ◽  
Channel Opening ◽  
Current Voltage ◽  
Voltage Dependent ◽  
Planar Lipid Membranes ◽  
Opening And Closing ◽  
Conductive Properties

Syringopeptin 25A, a pseudomonad lipodepsipeptide, can form ion channels in planar lipid membranes. Pore conductance is around 40 pS in 0.1 M NaCl. Channel opening is strongly voltage dependent and requires a negative potential on the same side of the membrane where the toxin was added. These pores open and close with a lifetime of several seconds. At negative voltages, an additional pore state of around 10 pS and a lifetime of around 30 ms is also present. The voltage dependence of the rates of opening and closing of the stable pores is exponential. This allows estimation of the equivalent charge that is moved across the membrane during the process of opening at about 2.6 elementary charges. When NaCl is present, the pore is roughly 3 times more permeant for anions than for cations. The current voltage characteristic of the pore is nonlinear, i.e., pore conductance is larger at negative than at positive voltages. The maximal conductance of the pore depends on the concentration of the salt present, in a way that varies almost linearly with the conductivity of the solution. From this, an estimate of a minimal pore radius of 0.4 nm was derived.

scholarly journals Ion channels and ion selectivity

2017 ◽  
Vol 61 (2) ◽  
pp. 201-209 ◽  
Author(s):  
Benoît Roux
Keyword(s):  
Ion Channels ◽  
Lipid Membrane ◽  
Ion Selectivity ◽  
Transport Systems ◽  
K Channel ◽  
Diffusion Limit ◽  
Macromolecular Transport ◽  
Loosely Coupled ◽  
Voltage Dependent ◽  
Opening And Closing

Specific macromolecular transport systems, ion channels and pumps, provide the pathways to facilitate and control the passage of ions across the lipid membrane. Ion channels provide energetically favourable passage for ions to diffuse rapidly and passively according to their electrochemical potential. Selective ion channels are essential for the excitability of biological membranes: the action potential is a transient phenomenon that reflects the rapid opening and closing of voltage-dependent Na+-selective and K+-selective channels. One of the most critical functional aspects of K+ channels is their ability to remain highly selective for K+ over Na+ while allowing high-throughput ion conduction at a rate close to the diffusion limit. Permeation through the K+ channel selectivity filter is believed to proceed as a ‘knockon’ mechanism, in which 2–3 K+ ions interspersed by water molecules move in a single file. Permeation through the comparatively wider and less selective Na+ channels also proceeds via a loosely coupled knockon mechanism, although the ions do not need to be fully dehydrated. While simple structural concepts are often invoked to rationalize the mechanism of ion selectivity, a deeper analysis shows that subtle effects play an important role in these flexible dynamical structures.

scholarly journals QCM SENSOR SENSITIVITY ANALYSIS OF SILVER ELECTRODES COATED WITH LIPID MEMBRANE OLEYL ALCOHOL TOWARD NaCl AND HCl

2019 ◽  
Vol 11 (2) ◽  
pp. 65
Author(s):  
Auliya Rahmatul Ummah ◽  
Imam Tazi ◽  
Muthmainnah Muthmainnah
Keyword(s):  
Lipid Membranes ◽  
Oleyl Alcohol ◽  
Lipid Membrane ◽  
Electronic Tongue ◽  
Test Substance ◽  
Frequency Change ◽  
Sensor Sensitivity ◽  
Before And After ◽  
Silver Electrodes ◽  
The Difference

<p>One of the sensors, which is currently being developed is the QCM sensor. The QCM sensor is a sensor that utilizes the frequency change to detect a change in mass due to a test substance. The use of a QCM sensor includes other forms of electronic tongue sensor that can distinguish five basic flavours on the tongue. QCM sensor can also be varied electrodes using various lipid membranes such as electronic tongues to increase sensor sensitivity. This research aims to determine the sensitivity of the QCM sensor before and after coated with the lipid membrane to NaCl and HCl. The sensitivity of the QCM sensor to NaCl is 1.47 Hz/M for uncoated sensor and 0.63 Hz/M for coated sensor, while the sensitivity of HCl is 4.55 Hz/M for uncoated sensor and 4.93 Hz/M for coated sensor. The difference of the results is caused by the nature of ionization of the compound and the amount of concentration used. The result of the sensitivity research shows that the QCM sensor with Oleyl Alcohol lipid membrane is more sensitive to HCl than NaCl.</p>

scholarly journals The kinetics of monazomycin-induced voltage-dependent conductance. I. Proof of the validity of an empirical rate equation.

1981 ◽  
Vol 78 (2) ◽  
pp. 171-200 ◽  
Author(s):  
R U Muller ◽  
G Orin ◽  
C S Peskin
Keyword(s):  
Differential Equation ◽  
Membrane Potential ◽  
Rate Constant ◽  
Lipid Membranes ◽  
Molecular Model ◽  
Induced Voltage ◽  
Power Functions ◽  
Voltage Dependent ◽  
Conductance Changes ◽  
Kinetics Of

Monazomycin (a positively-charged, polyene-like antibiotic) induces a strongly voltage-dependent conductance in thin lipid membranes when added to one of the bathing solutions. We show here that the kinetics of conductance changes after a step of membrane potential are only superficially similar to the kinetics of the potassium gating system of squid giant axons, in that the beginning of conductance increases are growth functions of the time, as opposed to power functions of the time. We find that the rate constant (reciprocal of the time constant) of the growth varies with the approximately 2.6 power of the monazomycin concentration. The rate constant also varies exponentially with membrane potential such that an e-fold change is associated with a 10-11 mV change of membrane potential. We show that solutions of a simple differential equation are able to reproduce the actual conductance changes almost exactly. In the accompanying paper (Muller and Peskin. 1981. J. Gen. Physiol. 78:201-229), we derive the differential equation from a molecular model and use the theoretical equation so obtained to investigate the gating current of this system and to predict an interesting form of memory.

scholarly journals Electrochemical Properties of Lipid Membranes Self-Assembled from Bicelles

Membranes ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 11
Author(s):  
Damian Dziubak ◽  
Kamil Strzelak ◽  
Slawomir Sek
Keyword(s):  
Electrochemical Properties ◽  
Self Assembly ◽  
Lipid Membranes ◽  
Lipid Membrane ◽  
Membrane Resistance ◽  
Electrochemical Characteristics ◽  
Freeze Thaw ◽  
Lipid Films ◽  
Supported Lipid Membranes

Supported lipid membranes are widely used platforms which serve as simplified models of cell membranes. Among numerous methods used for preparation of planar lipid films, self-assembly of bicelles appears to be promising strategy. Therefore, in this paper we have examined the mechanism of formation and the electrochemical properties of lipid films deposited onto thioglucose-modified gold electrodes from bicellar mixtures. It was found that adsorption of the bicelles occurs by replacement of interfacial water and it leads to formation of a double bilayer structure on the electrode surface. The resulting lipid assembly contains numerous defects and pinholes which affect the permeability of the membrane for ions and water. Significant improvement in morphology and electrochemical characteristics is achieved upon freeze–thaw treatment of the deposited membrane. The lipid assembly is rearranged to single bilayer configuration with locally occurring patches of the second bilayer, and the number of pinholes is substantially decreased. Electrochemical characterization of the lipid membrane after freeze–thaw treatment demonstrated that its permeability for ions and water is significantly reduced, which was manifested by the relatively high value of the membrane resistance.

scholarly journals Interactions of Linear Analogues of Battacin with Negatively Charged Lipid Membranes

Membranes ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 192
Author(s):  
Kinga Burdach ◽  
Dagmara Tymecka ◽  
Aneta Urban ◽  
Robert Lasek ◽  
Dariusz Bartosik ◽  
...  
Keyword(s):  
Lipid Membranes ◽  
Liquid Crystalline ◽  
Lipid Membrane ◽  
Attenuated Total Reflection ◽  
Gram Positive ◽  
Insertion Depth ◽  
Force Microscopy ◽  
Acyl Chains ◽  
Hydrophobic Portion ◽  
Membrane Fluidization

The increasing resistance of bacteria to available antibiotics has stimulated the search for new antimicrobial compounds with less specific mechanisms of action. These include the ability to disrupt the structure of the cell membrane, which in turn leads to its damage. In this context, amphiphilic lipopeptides belong to the class of the compounds which may fulfill this requirement. In this paper, we describe two linear analogues of battacin with modified acyl chains to tune the balance between the hydrophilic and hydrophobic portion of lipopeptides. We demonstrate that both compounds display antimicrobial activity with the lowest values of minimum inhibitory concentrations found for Gram-positive pathogens. Therefore, their mechanism of action was evaluated on a molecular level using model lipid films mimicking the membrane of Gram-positive bacteria. The surface pressure measurements revealed that both lipopeptides show ability to bind and incorporate into the lipid monolayers, resulting in decreased ordering of lipids and membrane fluidization. Atomic force microscopy (AFM) imaging demonstrated that the exposure of the model bilayers to lipopeptides leads to a transition from the ordered gel phase to disordered liquid crystalline phase. This observation was confirmed by attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) results, which revealed that lipopeptide action causes a substantial increase in the average tilt angle of lipid acyl chains with respect to the surface normal to compensate for lipopeptide insertion into the membrane. Moreover, the peptide moieties in both molecules do not adopt any well-defined secondary structure upon binding with the lipid membrane. It was also observed that a small difference in the structure of a lipophilic chain, altering the balance between hydrophobic and hydrophilic portion of the molecules, results in different insertion depth of the active compounds.

Effects of ouabain on background and voltage-dependent currents in canine colonic myocytes

1990 ◽  
Vol 259 (3) ◽  
pp. C402-C408 ◽  
Author(s):  
E. P. Burke ◽  
K. M. Sanders
Keyword(s):  
Membrane Potential ◽  
Potential Gradient ◽  
Circular Muscle ◽  
Input Resistance ◽  
Pump Current ◽  
Muscle Layer ◽  
Membrane Properties ◽  
Resting Potential ◽  
Voltage Dependent ◽  
In Cells

Previous studies have suggested that the membrane potential gradient across the circular muscle layer of the canine proximal colon is due to a gradient in the contribution of the Na(+)-K(+)-ATPase. Cells at the submucosal border generate approximately 35 mV of pump potential, whereas at the myenteric border the pump contributes very little to resting potential. Results from experiments in intact muscles in which the pump is blocked are somewhat difficult to interpret because of possible effects of pump inhibitors on membrane conductances. Therefore, we studied isolated colonic myocytes to test the effects of ouabain on passive membrane properties and voltage-dependent currents. Ouabain (10(-5) M) depolarized cells and decreased input resistance from 0.487 +/- 0.060 to 0.292 +/- 0.040 G omega. The decrease in resistance was attributed to an increase in K+ conductance. Studies were also performed to measure the ouabain-dependent current. At 37 degrees C, in cells dialyzed with 19 mM intracellular Na+ concentration [( Na+]i), ouabain caused an inward current averaging 71.06 +/- 7.49 pA, which was attributed to blockade of pump current. At 24 degrees C or in cells dialyzed with low [Na+]i (11 mM), ouabain caused little change in holding current. With the input resistance of colonic cells, pump current appears capable of generating at least 35 mV. Thus an electrogenic Na+ pump could contribute significantly to membrane potential.

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