How to Calculate Conductance | Sciencing
Depolarization of the conductance-voltage relationship in the NaV mutant, EK, is due to altered fast inactivation. Colin H. Peters. Large-conductance chloride channels (maxi-Cl channels) were studied in cultured The bell-shaped steady state channel conductance-voltage relationship is. Now, I want to get the GV Curve (Conductance-Voltage Curve). .. So,could you show me more detailed steps on how to plot I-V relationship curve with Origin.
Altered sodium channel gating underlies diseases involving neurons, skeletal muscle, and the heart. Mutants in the cardiac sodium channel, NaV1. LQT3 is caused by gain-of-function channel defects causing incomplete inactivation and persistent inward current, prolonging the cardiac action potential [ 1012 ].
Electrical resistance and conductance - Wikipedia
Action potential prolongation puts the patient at risk for cardiac arrhythmia [ 1314 ]. In contrast, multiple loss-of-function mechanisms have been proposed for BrS1, and there is no clear consensus on the extent to which each mechanism contributes to arrhythmia [ 1516 ].
The depolarization hypothesis for BrS1 suggests that decreased sodium current slows conduction of electrical signals in the heart, which may be exacerbated by fibrosis and drugs. The decreases in conduction velocity lead to a heterogeneity of depolarization, responsible for the characteristic ST-segment elevation and inverted T-wave in BrS [ 1718 ].
In contrast, the repolarization hypothesis suggests that the decreases in sodium current lead to a less positive phase 0 depolarization in the ventricular action potential. The decrease in phase 0 sodium current may allow for the phase 1 transient outward potassium current IK,topresent in epicardial myocardium, to fully repolarize the outer heart wall prior to the action potential plateau. Early repolarization of the epicardium creates a transmural dispersion of repolarization across the heart wall, which causes the BrS ECG sign [ 19 ].
The EK mutant in the NaV1. EK does not alter channel expression, but rather alters channel gating to increase persistent sodium currents and decrease peak transient sodium currents [ 22 ].
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EK decreases the amount of peak sodium current in NaV1. Additionally, EK increases the amount of non-inactivating persistent current [ 2223 ]. Our lab recently added studies on the temperature and pH sensitivity of the EK mutant heterologously expressed in Chinese Hamster Ovary cells [ 1626 ]. In wildtype WT channels, lowered extracellular pH decreases peak sodium currents and increases the fraction of non-inactivating sodium channels [ 2728 ].
Furthermore, cardiac events are known to occur during ischemic heart disease and exercise and are associated with SIDS and cocaine use [ 29 — 33 ]. In particular, ischemia and cocaine use are associated with greater than 1 pH unit decreases in extracellular pH [ 34 — 37 ].
As lowered extracellular, but not intracellular, pH is known to decrease peak sodium currents and increase the fraction of persistent current in WT channels, the effects of low extracellular pH on mutant channels, which already may have decreased peak and increased persistent currents, are important [ 272838 ].
We previously showed EK has preferential sensitivity to changes in extracellular pH, with an increased depolarizing shift of the conductance curve, increased proton block of peak current, and an increase in the fraction of persistent current at pH 6.
It is not known, however, if EK affects gating currents or whether the preferential effects of lowered extracellular pH on ionic currents in the mutant are due to preferential effects on gating currents. In this paper, we report the results of experiments using the cut-open oocyte voltage-clamp procedure. We recorded ionic and gating currents to investigate how NaV1.
We also measured intracellular pH during some recordings to test whether the changes to the biophysical properties of the channels are due to changes in extracellular pH or concurrent changes to intracellular pH. We originally hypothesized that the depolarizing shift in the channel conductance curve in EK, and the greater depolarizing shift of conductance at low pH, are a direct result ofgating charge movement occurring at more depolarized membrane potentials.
Our results show that this is not the case; the depolarization of conductance in EK occurs in the presence of a hyperpolarized gating charge movement. Using a tetrameric model of the sodium channel, fluorescence recordings of labelled S4 voltage-sensors, and experiments on fast-inactivation deficient channels, we show that the depolarizing shift in the conductance curve is likely due to the mutant-dependent hyperpolarization and acceleration of fast inactivation. Mohamed Chahine Laval University [ 40 ].
Breeding was not performed at either facility. All animal surgery and animal care procedures were performed in accordance with the policies of the Canadian Council of Animal Care. All efforts were made to minimize suffering. At Simon Fraser University, euthanasia was confirmed by cervical dislocation and pithing of the brain. At Washington University, both terminal and survival surgeries were performed.
Conductance-voltage relations in large-conductance chloride channels in proliferating L6 myoblasts.
We injected oocytes with 55nL of purified NaV1. Ionic current experiments were performed within h after injection. The resistance and conductance of a wire, resistor, or other element is mostly determined by two properties: In the same way, a long, thin copper wire has higher resistance lower conductance than a short, thick copper wire.
Materials are important as well. A pipe filled with hair restricts the flow of water more than a clean pipe of the same shape and size. Similarly, electrons can flow freely and easily through a copper wire, but cannot flow as easily through a steel wire of the same shape and size, and they essentially cannot flow at all through an insulator like rubberregardless of its shape.
The difference between copper, steel, and rubber is related to their microscopic structure and electron configurationand is quantified by a property called resistivity. In addition to geometry and material, there are various other factors that influence resistance and conductance, such as temperature; see below.
Conductors and resistors[ edit ] A 6. An ohmmeter could be used to verify this value. Substances in which electricity can flow are called conductors. A piece of conducting material of a particular resistance meant for use in a circuit is called a resistor. Conductors are made of high- conductivity materials such as metals, in particular copper and aluminium. Resistors, on the other hand, are made of a wide variety of materials depending on factors such as the desired resistance, amount of energy that it needs to dissipate, precision, and costs.
Ohm's law The current-voltage characteristics of four devices: Two resistorsa diodeand a battery. The horizontal axis is voltage dropthe vertical axis is current. Ohm's law is satisfied when the graph is a straight line through the origin. Therefore, the two resistors are ohmic, but the diode and battery are not. For many materials, the current I through the material is proportional to the voltage V applied across it: Therefore, the resistance and conductance of objects or electronic components made of these materials is constant.
This relationship is called Ohm's lawand materials which obey it are called ohmic materials. Examples of ohmic components are wires and resistors. The current-voltage IV graph of an ohmic device consists of a straight line through the origin with positive slope. Other components and materials used in electronics do not obey Ohm's law; the current is not proportional to the voltage, so the resistance varies with the voltage and current through them.