Voltage Clamp Explained (Tetrodotoxin And Tetraethylammonium) | Clip
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- Опубликовано: 13 июл 2024
- Welcome to Science With Tal!
In this clip of the Signal Propagation in the Neuron video, we will go over the voltage clamp apparatus and the different results we can get from it to better understand the underlying mechanisms of the action potential. You will see here and in the comment section the time stamps associated with each topic that I’ve covered.
Note that the graphs are not up to scale but the general shapes of the curves reflect the true behaviours of the variables in question.
To improve the quality of my content, I highly value the feedback from the viewer so do not hesitate to give any feedback in the comment section.
Timestamps
0:00 Introduction
0:22 Historical perspective on the action potential recordings
1:13 Voltage clamp apparatus explained
3:15 What happens with the capacitive current
4:20 Trial 1: Small hyperpolarization (Vc = -70 mV)
5:23 Trial 2: Small depolarization (Vc = -50 mV)
5:42 Voltage clamp convention (inward/outward)
7:10 Trial 3: Big depolarization (Vc = 0 mV)
8:10 Voltage clamp experiment at different Vc values
8:50 Voltage clamp with no external Na
9:38 Voltage clamp with tetrodotoxin
10:07 Voltage clamp with tetraethylammonium
10:29 Final word on the ions responsible for the action potential
10:40 Current and conductance (K & Na) measurements from voltage clamp recordings
13:34 Similarities and differences of K & Na currents and conductances
14:55 Conclusion & references
Resources used
Here is a list of the resources that I’ve used to produce this video. (Author: title resource)
Dale Purves: Neuroscience (6th edition)
Eric Kandel: Principles of neural science (6th edition)
Alan Hodgkin & Andrew Huxley: A quantitative description of membrane current and its application to conduction and excitation in nerve
Alan Hodgkin & William Albert Hugh Rushton: The electrical constants of a crustacean nerve fibre.
To have more information on these resources, you can refer to the conclusion section where a more formal citation is provided.
Video credits
Writing: Tal Klimenko
Voice: Tal Klimenko
Animations: Tal Klimenko
Drawings: Tal Klimenko
Editing: Tal Klimenko
Introductory jingle: Thierry Du Sablond
Conclusion music: lukrembo - jay ( • lukrembo - jay (royalt... )
excellent video for a complex topic, clear with beautiful diagrams and graphics !!!
you deserve much more recognition for the work you produce...
you have my subscription and my like !!
Thank you very much for the kind words! I am glad you enjoyed it and found it helpful!
I have been learning this all semester, and never quite fully understood it. I watched your video and I understand the difference between the clamp current and ionic current. Thank you so much!
Wonderful, glad it helped! Thank you!
Great video!
Thanks!
great video!! Only a couple of things, why at minuti 1:20 at -50mV we have no current but at -20mV we have, what exactly happens between that two values? what is the factor that triggers the channels to open? and what happens at 0mV to have such a high inward current respect to -20mv and +20mv? Sorry, I'm bit confused. Thanks a bunch!!!
Hi, good question! This is something that I look into a bit deeper in this video about the Hodgkin-Huxley model (Hodgkin-Huxley Model of Voltage-Gated Channels Explained). At 11:39 to 13:34, what I try to illustrate with the sequential steps is that the current and conductance of sodium and potassium (which can be isolated from voltage clamp experiments) are drastically different.
The reason why the sodium current happens first and closes quickly whereas the potassium current opens later and is sustained has everything to do with the kinetics of the voltage gated channels (which can be explained by the Hodgkin-Huxley Model).
To answer your question more directly, the main factor that makes the current increase between -50, -20 and 0 mV for sodium is that since they are voltage-gated (VG) channels, the channels open a bigger pore with higher voltage and let more sodium ions enter, thus, leading to a higher current.
For the +20 mV condition, recall that the equilibrium potential of sodium is about +60 mV so as the command voltage approaches that value, the sodium current diminishes since there is less net movement into the cell (let me know if you need clarifications on the equilibrium potential). On the other hand for potassium, its equilibrium potential is at about -80 mV so its current keeps rising.
Let me know if this helps, thanks for the feedback!
@@sciencewithtal thanks a bunch!! all clear now, I will also give a look at the video you’ve mentioned
I didn't fully understand why there is an inward current during hyperpolarization, such as when Vcommand is set to -70 mV. Because typically, inward current indicates depolarization. Could you explain this?"
Good question, that was something confusing for me as well!
Basically, if I reword what I mention in the video: we have a cell at rest at -60 mV, and now we clamp it to -70 mV. To do so, the voltage clamp will send negative charges to push the membrane potential towards -70 mV. Given that the neuron wants to stay at -60 mV, the neuron will open leak channels (IL) that will send positive charges inside to get back to rest and this is what you see on the readout as the inward/depolarizing current.
In other words, with voltage clamp you are measuring the current response of the neuron and since it gets hyperpolarized, its response will be to open channels and depolarize to come back to the resting potential.
Hope that clarifies your question, let me know if I can help further!
Thank you very much! Crystal clear now.
I don't understand. I thought that in an operation amplifier, the potential between the (+) and (-) ends must be 0. But in that case, the potential between extracellular and intracellular space AKA membrane potential, should be 0
From the way I understand, the offset between the (+) and the (-) terminals has to be set to 0 to give the corresponding difference in voltage between the two. Basically, it sets the ground/reference electrode to 0 mV and makes it so that the voltage picked up by the electrode inside the neuron is the membrane potential (e.g. -70 mV). If the (+) and (-) terminals are offset by -10 mV then the reading will give -80 or -60 mV depending on the arrangement of the apparatus. Let me know if that makes sense!