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    Home > Biochemistry News > Biotechnology News > The mechanism of change of cell membrane potential and ion permeability during the occurrence of action potential was studied.

    The mechanism of change of cell membrane potential and ion permeability during the occurrence of action potential was studied.

    • Last Update: 2020-08-10
    • Source: Internet
    • Author: User
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    The action potential is a short, rapid change in membrane potential (100 mV), during which the polarity of the cell membrane and outside is reversed, that is, the cell membrane is negative from the resting state of the membrane, the outer membrane is positive, to the negative state inside the membrane.
    a single action potential includes only a fraction of the entire excitatory cell membrane.
    is different from the hierarchical action potential, the action potential is conducted from the starting point of the action potential along the entire cell membrane, and the intensity of conduction does not decay with the change of distance.
    this paper describes how a series of events occur during the occurrence of action potential and changes in cell membrane potential and ion permeability. rapid reversal of cell membrane potential during
    action potential If a small potential stimulation of the cell membrane does not cause it to produce an action potential, the cell membrane produces a graded potential (graded potential).
    increase in stimulus intensity, the magnitude of the graded potential is gradually increased, and the graded potential produces a depolarized local potential.
    when giving a threshold stimulation to the cell membrane that can produce an action potential, it is observed that a slow depolarization process occurs first, and when depolarization reaches a critical level of about -55 ——-50 mV, i.e. the threshold potential, an explosive depolarization process is immediately occurred.
    first recorded a sharp upward deflection of the potential waveform, reaching 0 mV rear membrane potential polarity flipping.
    compared to the cell membrane, at this time the potential in the cell membrane is positive, and then the membrane is rapidly repolarized back to the resting potential level.
    due to the generally large driving force of complex polarization, the recovery of the membrane potential exceeds the resting potential value, resulting in a potential that is negative than the resting potential (e.g. -80 mV), i.e. the positive and rear potential, before returning to the resting membrane potential level (Figure 1).
    a rapid change in potential from the threshold potential to the peak, and then back to the resting level, a rapid potential change called action potential. The membrane polarity flip portion of the
    action potential (between 0-30 mV) is called overshot.
    in a given cell, the waveform of the action potential is always the same. the action potential of
    nerve cells generally lasts only 1 ms.
    how the permeability of the cell membrane and the significant change seamount of ion movement lead to the occurrence of the action potential cell membrane change from a relatively balanced and stable resting state to an action potential? We know that K-plus is the most important ion to maintain the static membrane potential, and in the resting state, the cell membrane is much more permeable to K-plus than the Na-plus.
    however, during the action potential, the permeability of the cell membrane to K-plus and Na-plus changes greatly, and these ions flow rapidly across the membrane according to their electrochemical gradient, which, because these are charged ions, forms a transmembrane current. The flow of ions during the
    action potential is mainly related to the channels of two kinds of ions: the voltage-dependent Na-gate channel and the K-gate channel.
    can think of the channel as a door that selectively opens up the passage of filled ions, or closes to block the passage of ions.
    changes in the three-dimensional structure of the channel protein, it is determined whether the channel is open or closed.
    three types of gated channels are known to exist: (1) voltage gated channels, (2) chemical gated channels, and (3) mechanical gated channels.
    1 voltage gated sodium ion channel and potassium ion channel voltage gated channel consists of charged protein wrap. The electric field around the
    channel can apply force to the charged site in the cell membrane channel that alters its structure.
    generally speaking, many cell membrane proteins are quite stable and not subject to fluctuations in membrane voltage, however, channel proteins are highly sensitive to changes in membrane voltage, and a very small change in channel morphology will trigger potential changes, which in turn will cause the transformation of channel morphology. There are two gating states for the
    Na-channel: active state and inactivity state (Figure 2).
    active door is like a closed door, or is open, or closed.
    a gaffe-prone door consists of an amino acid residue, as if a ball were chained together.
    the door is open when the ball is freely suspended under the chain, and when the ball binds to the receptor at the mouth of the channel, the door is closed.
    the channel allows ions to pass through only when both the active state and the disactivity state are open.
    the two doors as long as either is closed, ions will not pass through the channel.
    according to this model, the voltage gated Na-channel door will be switched between three states: (1) although closed but capable of opening (activated state door closed, gaffe door open) ;(2) open or active state (2 doors are open) ;(3) closed state, no ability to open (active state door open, gaffe door closed).
    the voltage gateD K-channel door works in a similar way to the Na-channel door, but it has only one gating state, is open, or is closed (Figure 3).
    2 changes in ion permeability during the action potential in the resting state of the membrane, all the Na-channel and K-channel are closed, at this time, the activation of the Na-channel is closed, and the non-live door is open.
    this indicates that the gated Na-channel is closed at this time but is in a state of ability to open.
    in the resting state there is no Na-plus or K-plus flow through the voltage-gated channel, however, due to the presence of many leakage K-channels and a very small number of leakage Na-channel, the resting state of the K-through membrane penetration capacity than Na-50-75 times, there are still Na and K-plus permeable membrane leakage.
    as the cell membrane develops towards the threshold potential, the membrane depolarizes, and some of the activation doors of the Na-channel open, i.e. at this time the doors in the two states of the Na-channel are all open, the concentration gradient of Na plus (the membrane is higher than the membrane) and the voltage gradient (membrane) Externally positive, the membrane is negative) all drive the rapid flow of Na plus to the cell, the flow of Na plus with a positive charge further depolarizes the membrane, and more and more Na-channel opens, resulting in more and more Na-plus internal currents, forming a positive feedback process.
    depolarization reaches the threshold potential, the permeability of the membrane to Na plus suddenly increases significantly, more than 600 times the permeability of K-plus.
    at this point, channels that are open or closed are no longer open.
    in the early phase of depolarization, with more and more Ofa-levelopenings, the membrane potential begins to decrease, and when the threshold potential is reached, the number of Na-channel openings is sufficient to initiate a positive feedback process generated by an action potential, so that a large number of remaining Na-channels are also opened one after another.
    compared with the permeability of K-plus, at this time the cell membrane to The permeability of Na plus occupies an absolute advantage, a large number of Na-plus into the cell, the membrane potential quickly changed from negative positive, and close to the equilibrium potential of the Na plus (approximately 60 mV).
    at this point the potential has reached the level of the equilibrium potential of the Na-plus, but not really the equilibrium potential level of the Na-plus, which is due to the fact that the Na-channel starts to close and enters the inactivated state and the permeability of the Na-plus drops to the resting state level. what event
    caused the Na-channel to go down? When the membrane reaches the threshold potential value, each Na-channel gating change is related to the existence of 2 closely related events, first activate the rapid opening of the state door to cause the membrane depolarization, so that the channel into an open configuration (Figure 4).
    However, it is amazing that the channel is open at the same time also started the channel closure process, the channel configuration changes open the channel, but also the gaffe gate ball and the open-state door receptor combination, blocking the ion channel hole.
    is slower to close than a fast-opening channel.
    after the activation door is opened, the gaffe door closes for a period of time, there is a delay time of about 0.5 ms, the door of 2 states is open, and the Na-plus rapidly flows into the cell, causing the action potential to peak. After
    , the gaffe door begins to close and the permeability of the membrane to the Na plus drops vertically to the level of the resting film potential.
    the Na-channel maintains this inactivated configuration until the membrane returns to its resting value.
    the voltage-gated K-channel opens at the same time that the action potential reaches a peak, i.e. the Na-channel is inactive.
    the threshold stimulation of the K-channel door to depolarization produces a delayed voltage reaction.
    in the threshold stimulation, there are three interconnected events: (1) the rapid opening of the Na-active state door, which allows the Na-plus to enter the cell, and the membrane rises rapidly from the threshold potential level to the peak of the action potential;
    when the Na-channel is closed and K-plus continues to leak from the inner membrane, the membrane potential will gradually slowly return to the resting potential level because there is no Na-plus that continues to enter the cell.
    However, when the action potential reaches peak, due to the opening of the K-channel at this time, accelerates the speed of membrane potential to the resting potential level recovery, the opening of the voltage-gated K-channel greatly increases the penetration of K-plus, is the resting state of The Na-permeability of 300 times, a large number of positive charge of K-plus flow from the cell, resulting in the K-concentration gradient and the dwelling gradient in the membrane.
    it is worth noting that at the peak of the action potential, due to the positive potential of the cell to the in-cell K-plus rejection effect, at this time k-plus potential gradient is pointed from the membrane to the membrane, and the static potential potential gradient of the membrane is the opposite direction.
    as the action potential returns to its resting state, the changed membrane voltage causes the Na-channel to close completely, at which point the activation door of the Na-channel is closed and the missing door is open.
    this is a configuration that has the ability to reopen, ready to react to another new stimulus that comes.
    the open voltage gated K-channel door during the action potential is also closed, only a small number of leakage K-channel open, full ya small amount of K-plus leakage from the cell.
    due to the slow shutdown of the voltage-gated K-channel, it continuously increases the penetration of the cell membrane to K-plus, and the slightly excessive outflow of K-plus makes the intercellular potential more negative than in a resting state, forming a superpolarized potential (Figure 4g).
    the special effect of potassium ion channels on the static membrane potential: regulating electroexcation and terminating the action potential K-channel is the most widely distributed and largest family of voltage-controlled ion channels known to date.
    vertebrates have at least 17 different genetically coded, With S1-S6 different forms of K-plus channels.
    ions passing through the K-channel are generally very selective, and the permeability is quite different, among them, the K-gt; Rb-GT4-plus Cs-gt-Li-, Na-Plus,Ca2-plus."
    in normal physiological conditions, the permeability ratio of Pk/PNa (the ratio of K-plus and Na-pass-through) is greater than 100, and the Na-plus can block the K-plus channel.
    some K-plus channels allow Na-plus to pass in the absence of a K-plus completely, a feature similar to the Ca2-plus channel.
    the Ca2 plus channel can also pass through the Na-plus current and the K-plus current when the Ca2 plus is completely missing.
    according to the high specific selectivity of the K-channel and the characteristics of the equilibrium potential approach to -90 mV, the most basic function of the K-channel should be to inhibit the excited cells.
    the excitatory activity of the K-plus channels against the Na-plus and Ca2-channels, which acts as a stabilizing static potential, keeping the cells non-excited.
    although some K-channels play a decisive role in the static potential, the voltage dependence and kinetic properties of the K-channels in excitable cells make them have other special functions, such as regulating the complex polarization process, modifying the action potential time, controlling the frequency of impulse release, and determining the characteristics of rhythmic pulse release. These characteristics of the
    K-channel make it play a very broad and important role in regulating the strength and frequency of all types of muscle contractions, in the release of nerve end-termination neurotransmitters, and in the event of weakening the strength of synaptic connections.
    Source: Zuo Mingxue (School of Life Sciences, Beijing Normal University)
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