Concentration Gradient Effect on the Capturing Ratio of Nanopore for DNA

2015 ◽  
Vol 656-657 ◽  
pp. 554-560
Author(s):  
Jing Jie Sha ◽  
Wei Si ◽  
Yin Zhang ◽  
Yun Fei Chen
Keyword(s):  
Concentration Gradient ◽  
Electrical Potential ◽  
Ionic Currents ◽  
Fixed Time ◽  
Controlled Delivery ◽  
Glass Capillary ◽  
Ion Conductance ◽  
Duration Time ◽  
In Trans ◽  
Pass Through

As the single molecules detection tool, nanopore is applied in more and more fields, such as medicine controlled delivery, ion conductance microscopes, nanosensors and DNA sequencing. When molecules pass through a nanopore, they will physically block the pore and produce measurable changes in ionic currents under an external electrical potential. Based on analyzing the resultant electrical signals, it is possible to detect various bio-molecules.Generally, the capturing ratio of nanopre for molecules is dependent on the intensity of electrical potential, to which the duration time of event is inversely proportional. It is difficult to analyze the too short duration time. Therefore, we investigate the study on concentration gradient of ionic solution effect on the capturing ratio of nanopore for DNA, which is in order to get the higher capturing ratio with the invariant duration time.In the experiments, we add different concentration solution in trans and cis parts of naopore separately to form the concentration gradient. We use three different types nanopore (α-hemolysin nanopore, Si3N4 membrane nanopore, glass capillary nanopore) to compare and get the similar results. The events of DNA translocating through nanopore are observed more compressed during the fixed time under the higher concentration gradient and there is no change to the duration time of DNA passing through the nanopore. It is demonstrated that concentration gradient could increase the capturing ratio of nanopore for DNA.

Understanding the electrical behavior of the action potential in terms of elementary electrical sources

2015 ◽  
Vol 39 (1) ◽  
pp. 15-26 ◽  
Author(s):  
Javier Rodriguez-Falces
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Present Report ◽  
Electrical Potential ◽  
Ionic Currents ◽  
New Approach ◽  
Electrical Potentials ◽  
Proposed Model ◽  
Ionic Mechanisms ◽  
Human Electrophysiology

A concept of major importance in human electrophysiology studies is the process by which activation of an excitable cell results in a rapid rise and fall of the electrical membrane potential, the so-called action potential. Hodgkin and Huxley proposed a model to explain the ionic mechanisms underlying the formation of action potentials. However, this model is unsuitably complex for teaching purposes. In addition, the Hodgkin and Huxley approach describes the shape of the action potential only in terms of ionic currents, i.e., it is unable to explain the electrical significance of the action potential or describe the electrical field arising from this source using basic concepts of electromagnetic theory. The goal of the present report was to propose a new model to describe the electrical behaviour of the action potential in terms of elementary electrical sources (in particular, dipoles). The efficacy of this model was tested through a closed-book written exam. The proposed model increased the ability of students to appreciate the distributed character of the action potential and also to recognize that this source spreads out along the fiber as function of space. In addition, the new approach allowed students to realize that the amplitude and sign of the extracellular electrical potential arising from the action potential are determined by the spatial derivative of this intracellular source. The proposed model, which incorporates intuitive graphical representations, has improved students' understanding of the electrical potentials generated by bioelectrical sources and has heightened their interest in bioelectricity.

Detection of DNA in a Nanopore Fabricated From Glass Tube

2013 ◽  
Author(s):  
Jingjie Sha ◽  
Yunfei Chen
Keyword(s):  
Single Molecule ◽  
Glass Tube ◽  
Electrical Current ◽  
Ionic Currents ◽  
Dna Molecules ◽  
Dna Translocation ◽  
Glass Capillary ◽  
Minimum Diameter ◽  
Osmotic Flow ◽  
Electro Osmotic Flow

Nanopores are increasingly utilized as tools for single molecule detection in biotechnology. Here, we report an improved fabrication process to make solid-state nanopores from glass tubes with the help of paraffin. Based on the physical footprint of the phase change of the paraffin, nanocavity is formed in the broken terminal after thermally compressing and pulling the glass capillary. Nanopores with the minimum diameter of 20 nm are fabricated. The key step is to control the thickness of paraffin layer attached in the inner wall, which could affect the diameter of the nanopore. We investigate 48Kb λ-DNA molecules translocate through the fabricated glass nanopore. Because DNA molecules with the negative charges could be driven by the electrical force to pass through the nanopore and could physically block the pore to produce measurable changes in ionic currents. A transient electrical current changing is used to detect the DNA molecules in the solution. In the experiments, many events of DNA translocation were observed under the positive potential. We demonstrate that DNA molecules could be detected by the nanopore fabricated from glass tube. However, we also find the events of DNA translocation under the negative potential, which is because of the electro-osmotic flow (EOF) effects. It is found that the electro-osmotic flow inside the nanopore plays an important role in the DNA translocation process, and thus depends on the size of the pore. We shows that the effective driving force on DNA in a nanopore is the co-effects of the force of the electric field and the drag force of the electro-osmotic flow.

Active Transport of Sulphate Ions by the Malpighian Tubules of Larvae of the Mosquito Aedes Campestris

1975 ◽  
Vol 62 (2) ◽  
pp. 367-378
Author(s):  
S. H. P. MADDRELL ◽  
J. E. PHILLIPS
Keyword(s):  
Active Transport ◽  
Concentration Gradient ◽  
Electrical Potential ◽  
Malpighian Tubules ◽  
Potential Difference ◽  
Electrical Potential Difference ◽  
Sulphate Content ◽  
Anal Papillae ◽  
Tracer Experiments

1. Larvae of Aedes campestris ingest and absorb into their haemolymph large quantities of the sulphate-rich water in which they live, yet they are able to maintain the sulphate content of the haemolymph well below that of the environment. 2. Tracer experiments showed that sulphate regulation was not achieved by deposition of precipitates in the tissues. 3. In vitro preparations of Malpighian tubules secrete sulphate ions actively against both a three times concentration gradient and an electrical potential difference of 20 mV. This transport is half saturated at about 10 mM. 4. The rate of sulphate secretion by the Malpighian tubules is sufficient to remove all of the sulphate ingested by larvae living in waters which contain less than 100 mM of this anion. At higher concentrations, sulphate ions are probably also excreted elsewhere, perhaps by the rectum or anal papillae.

scholarly journals Structural basis for activation of voltage sensor domains in an ion channel TPC1

2018 ◽  
Vol 115 (39) ◽  
pp. E9095-E9104 ◽  
Author(s):  
Alexander F. Kintzer ◽  
Evan M. Green ◽  
Pawel K. Dominik ◽  
Michael Bridges ◽  
Jean-Paul Armache ◽  
...  
Keyword(s):  
Ion Channel ◽  
Conformational Changes ◽  
Electrical Potential ◽  
Structural Basis ◽  
Ion Conductance ◽  
Activated State ◽  
Voltage Dependent ◽  
Internal Side ◽  
Transmembrane Electrical Potential ◽  
Gating Charges

Voltage-sensing domains (VSDs) couple changes in transmembrane electrical potential to conformational changes that regulate ion conductance through a central channel. Positively charged amino acids inside each sensor cooperatively respond to changes in voltage. Our previous structure of a TPC1 channel captured an example of a resting-state VSD in an intact ion channel. To generate an activated-state VSD in the same channel we removed the luminal inhibitory Ca2+-binding site (Cai2+), which shifts voltage-dependent opening to more negative voltage and activation at 0 mV. Cryo-EM reveals two coexisting structures of the VSD, an intermediate state 1 that partially closes access to the cytoplasmic side but remains occluded on the luminal side and an intermediate activated state 2 in which the cytoplasmic solvent access to the gating charges closes, while luminal access partially opens. Activation can be thought of as moving a hydrophobic insulating region of the VSD from the external side to an alternate grouping on the internal side. This effectively moves the gating charges from the inside potential to that of the outside. Activation also requires binding of Ca2+ to a cytoplasmic site (Caa2+). An X-ray structure with Caa2+ removed and a near-atomic resolution cryo-EM structure with Cai2+ removed define how dramatic conformational changes in the cytoplasmic domains may communicate with the VSD during activation. Together four structures provide a basis for understanding the voltage-dependent transition from resting to activated state, the tuning of VSD by thermodynamic stability, and this channel’s requirement of cytoplasmic Ca2+ ions for activation.

scholarly journals Identification of a lipid scrambling domain in ANO6/TMEM16F

eLife ◽  
2015 ◽  
Vol 4 ◽  
Author(s):  
Kuai Yu ◽  
Jarred M Whitlock ◽  
Kyleen Lee ◽  
Eric A Ortlund ◽  
Yuan Yuan Cui ◽  
...  
Keyword(s):  
Patch Clamp ◽  
Homology Modeling ◽  
Concentration Gradient ◽  
Ionic Currents ◽  
Cellular Mechanism ◽  
Chimeric Proteins ◽  
Patch Clamp Recording ◽  
Phospholipid Scramblase ◽  
Bidirectional Transport ◽  
Phospholipid Scrambling

Phospholipid scrambling (PLS) is a ubiquitous cellular mechanism involving the regulated bidirectional transport of phospholipids down their concentration gradient between membrane leaflets. ANO6/TMEM16F has been shown to be essential for Ca2+-dependent PLS, but controversy surrounds whether ANO6 is a phospholipid scramblase or an ion channel like other ANO/TMEM16 family members. Combining patch clamp recording with measurement of PLS, we show that ANO6 elicits robust Ca2+-dependent PLS coinciding with ionic currents that are explained by ionic leak during phospholipid translocation. By analyzing ANO1-ANO6 chimeric proteins, we identify a domain in ANO6 necessary for PLS and sufficient to confer this function on ANO1, which normally does not scramble. Homology modeling shows that the scramblase domain forms an unusual hydrophilic cleft that faces the lipid bilayer and may function to facilitate translocation of phospholipid between membrane leaflets. These findings provide a mechanistic framework for understanding PLS and how ANO6 functions in this process.

scholarly journals The Permeability of the Sodium Channel to Organic Cations in Myelinated Nerve

1971 ◽  
Vol 58 (6) ◽  
pp. 599-619 ◽  
Author(s):  
Bertil Hille
Keyword(s):  
Hydrogen Bonds ◽  
Sodium Channel ◽  
Reversal Potential ◽  
Ionic Currents ◽  
Nerve Fibers ◽  
Organic Cations ◽  
Amino Groups ◽  
Myelinated Nerve ◽  
Methylene Groups ◽  
Pass Through

The relative permeability of sodium channels to 21 organic cations was studied in myelinated nerve fibers. Ionic currents under voltage-clamp conditions were measured in sodium-free solutions containing the test cation. The measured reversal potential and the Goldman equation were used to calculate relative permeabilities. The permeability sequence was: sodium ≈ hydroxylamine > hydrazine > ammonium ≈ formamidine ≈ guanidine ≈ hydroxyguanidine > aminoguanididine >> methylamine. The cations of the following compounds were not measurably permeant: N-methylhydroxylamine, methylhydrazine, methylamine, methylguanidine, acetamidine, dimethylamine, tetramethylammonium, tetraethylammonium, ethanolamine, choline, tris(hydroxymethyl)amino methane, imidazole, biguanide, and triaminoguanidine. Thus methyl and methylene groups render cations impermeant. The results can be explained on geometrical grounds by assuming that the sodium channel is an oxygen-lined pore about 3 A by 5 A in cross-section. One pair of oxygens is assumed to be an ionized carboxylic acid. Methyl and amino groups are wider than the 3 A width of the channel. Nevertheless, cations containing amino groups can slide through the channel by making hydrogen bonds to the oxygens. However, methyl groups, being unable to form hydrogen bonds, are too wide to pass through.

Recovery Course of Excitability in A Single Neurone of Onchidium Verruculatum

1971 ◽  
Vol 54 (2) ◽  
pp. 471-484
Author(s):  
YOSHIFUMI KATAYAMA
Keyword(s):  
Nerve Cell ◽  
Resting State ◽  
Time Course ◽  
Current Strength ◽  
Time Interval ◽  
Electrical Excitability ◽  
Glass Capillary ◽  
Time Duration ◽  
Minimum Quantity ◽  
Pass Through

The electrical excitability of a nerve cell of Onchidium verruculatum was measured by transmembrane depolarizing current pulses through a glass-capillary microelectrode inserted into the soma of the nerve cell. 1. The strength-duration and the strength-latency relations were measured during the resting state of a silent-type nerve cell, and both were represented by hyperbolic curves. This shows that the minimum quantity of electricity (that is, current strength multiplied by time duration required to produce a spike) must pass through the membrane to discharge impulses in the resting state of the nerve cell. 2. The strength-latency relations were obtained after a spontaneous spike. The stimulus began during the falling phase of a preceding firing and lasted for 300 ms. These relations were represented by two exponential terms. 3. The strength-duration relations were measured at various times after a preceding discharge and these were also represented approximately by hyperbolic curves in regularly firing or frequently firing neurones. These results suggested that a minimum quantity of electricity must be required to elicit a second spike at a given time interval after a preceding spike; and that the reciprocal of this value might represent the excitability after that time interval. 4. The time course of the reciprocal of the quantity referred to above expresses the process of the recovery of excitability in the nerve cell after a spike. This process can be expressed mathematically by two exponential terms.

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