6.2 The Na+ gating current

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来自 Peking University 的课程

Advanced Neurobiology I

217 个评分

Peking University

Advanced Neurobiology I

217 个评分

Hello everyone! Welcome to advanced neurobiology! Neuroscience is a wonderful branch of science on how our brain perceives the external world, how our brain thinks, how our brain responds to the outside of the world, and how during disease or aging the neuronal connections deteriorate. We’re trying to understand the molecular, cellular nature and the circuitry arrangement of how nervous system works. Through this course, you'll have a comprehensive understanding of basic neuroanatomy, electral signal transduction, movement and several diseases in the nervous system. This advanced neurobiology course is composed of 2 parts (Advanced neurobiology I and Advanced neurobiology II, and the latter will be online later). They are related to each other on the content but separate on scoring and certification, so you can choose either or both. It’s recommended that you take them sequentially and it’s great if you’ve already acquired a basic understanding of biology. Thank you for joining us!

从本节课中

Ion channels, membrane potential and synaptic transmission

Let's continue with the ion channels, membrane potential and synaptic transmission.

6.1 Voltage sensing15:39

6.2 The Na+ gating current8:04

6.3 Inactivation gates17:37

6.4 Ion channel, membrane potential and synaptic transmission I15:12

6.5 Ion channel, membrane potential and synaptic transmission II7:30

6.6 Ion channel, membrane potential and synaptic transmission III12:53

6.7 Ion channel, membrane potential and synaptic transmission IV7:01

6.8 Ion channel, membrane potential and synaptic transmission V9:44

与讲师见面

Yan Zhang
Professor
School of Life Sciences, Peking University
Yulong Li
Research Fellow
School of Life Sciences, Peking University

Where you have a large abundance of sodium, potassium channels.

For example, if you want to measure the sodium gating currents, how do you do it?

First, you block all other ion channels because you only

want to measure the current mediated by the gating particle movements.

And so, you block potassium channels, blah, blah, blah, meaning other channels.

And then, actually, you also block the [INAUDIBLE] channels.

Because, your prediction will be, well, if you block this port,

If you are still in the right electrical field,

these skating particles in the electrical field, they are still going to move.

But because they block the sodium channels, then this will be good.

You have less background currents, so you are able to,

more precisely, measure the gating currents.

So, here is the result.

[COUGH] So, you can measure the gating of sodium

in the presence of TTX and blocking all the rest of other ion channels and

you'll see there's this Current changes.

Okay, this is a gating current.

And if you are not using the TTX, what you observe is

that you have this gating trapped current, but then,

the immediate opening of the sodium channel will

allow the sodium influx, so then you have this compound.

You have both of the gating current and

this water gated through the channel opened, mediated the current influx.

And this arrangement, actually, is not bad, because the direction of

the gating current is different than the direction of the sodium currents.

But the not blocking the sodium current.

And if we are starting the potassium channel changing current.

If we are in the same direction, then there is almost no way for

you to separate the current mediator by opening of those iron channel or

the current due to the movement of this charged particles.

And, so, these measurements, you actually can do mutagenesis from them.

More precisely, you can mutate those grating particles

that you can postulate the or and then,

you're prediction would be well, then that would be less current if they move.

And your prediction will also be that because of the, so

this is one of the example of the Shaker potassium channel.

You can block the potassium channel and you can measure the gating current.

And you can find that during the depolarization,

the gating current is from one direction.

And I'll tell you, going back to the resting condition,

the gating particle also move back.

So, the iron channel that has this confirmation that you will

move at certain wattage, and

then move back once you moving the wattage back to the original state.

But if you look here, as you can see that the moving speed might be different.

So, for example, moving towards this end tends to be faster

than moving back to the resting state.

And then if you are really the opening of the ion channel

which is shown g is in conductance under a different voltages.

You found that the wattage channels will open at different wattages so

you can measure to this conductance.

So this indicates that there is a sodium current or

potassium current going through this ion channel in the wattage dependent manner.

But if you superimpose the gating current measurement,

what he found is he also has the water dependency, but

it moved faster or the curve is left shifted.

What does that mean?

This indicates that the gated particle already moved

even before to the opening of the ion channel.

For example, this ion channel open can be described by this G.

About -50 millivolt this ion channel are start to open.

So you can see this is a certain current.

But what you found actually, the ion channel itself

are already start to undergo conformational changes.

Starting probably from minus 75 million volts,

it already starts to change its confirmation.

We sort of change a lot of confirmation.

Here, you have a large gating current.

Okay, gating current measurement indicates how

much the confirmation of change happening.

How much is the charged particle are moving in the electrical field?

If they move the largest distance, you will create the largest current.

So, in this case, you can understand well,

after this gating particle in this S4 region that are moving a lot.

You already created for example about 50% of the grating particle

movements you start to have the opening of this ion channel.

So this plot indicates that it is this voltage sensor that first moves.

They first move and then subsequently dragging the pore to open.

Because the voltage dependency is left shifted.

Any questions so far?

[COUGH] And this is the experiment that, again,

some of our students suggest that indeed, for

example, MacKeenen, mutate those sides,

and then they measured The [INAUDIBLE]

dependency art during the recording.

For example, certain reside is more important than

the because when you are moving it, mutating it,

you are actually significantly, shift locating particles changes.

And then the currently this people are still debated

that what is actually the gating particle looks like.

Previously before the crystal structure,

people postulate that it is gating particle might originate in

a confirmation that some of them have moved in this vertical directions.

But with more crystal structure studies,

many the studies from Rotmokines lab that when they

crystallize with the help of some antibodies,

they found that actually locating particles is

not in the but rather it's like a paddle.

And then you will sort of vertically move the paddle wheel so

the tilt slight to mediate the confirmation.

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