<p>In a <a href="https://en.wikipedia.org/wiki/Patch_clamp" rel="nofollow noreferrer">current-clamp (or voltage-clamp, for that matter)</a> experiment, you have a pair of electrodes; one is in the bath somewhere acting as a ground, the other is suspended in a glass pipette full of some salt solution, usually one that roughly mimics the intracellular ion composition, with some adjustments for convenience or experimental reasons. In a whole-cell configuration that is typical of a current-clamp experiment, the experimenter presses this glass pipette against the cell and sucks the membrane in, such that the inside of the cell and the inside of the pipette are all one electrically-connected space.</p>
<p>When you &quot;clamp&quot; current to some level, that means that the amplifier is making sure a certain current runs between those two wires; you then measure the voltage required to maintain this current as a read out of the cell's function in some way.</p>
<p>&quot;Injecting electrons&quot; is really not too far off from the truth. It pretty much acts like a battery in that circuit, except that the voltage of the battery is adjusted dynamically to fix the current (rather than the voltage being constant as in a typical household battery). The rest is really a matter of electrochemistry rather than any neuroscience: the ground wires used are typically <a href="https://en.wikipedia.org/wiki/Silver_chloride_electrode" rel="nofollow noreferrer">silver chloride-coated</a>, so the actual electrochemistry that occurs is the redox reaction between solid atomic silver and silver chloride.</p>
<p>None of the silver interacts with the tissue, though; spatially the electrodes are far from the cell itself. Electricity is conducted through the liquid ionic medium like it always does: other positive charges are attracted to negativity/repulsed by positivity, and vice-versa.</p>

CC BY-SA 4.0
2021-07-15T12:19:05.953Z
Oh so nothing is actually injected inside the cell soma? I was under the impression that the pipette was introduced inside the cell, effectively piercing the membrane.
Johncowk
CC BY-SA 4.0
2021-07-15T14:13:41.940Z
@Johncowk Nothing is injected, but the contents of the cell and pipette mix, and since the pipette volume is massive compared to the cell you can just assume it's the same as the pipette solution. That doesn't relate to "injecting current" though.
Bryan Krause
CC BY-SA 4.0
2021-07-16T08:39:30.763Z
Yeah but effectively you end up with some saline solution of the pipette inside the cell soma?
Johncowk
CC BY-SA 4.0
2021-07-16T13:19:23.900Z
@Johncowk You can assume all the inside is saline solution once you patch. But that has nothing to do with "injecting current".
Bryan Krause
CC BY-SA 4.0
2021-07-16T15:12:52.753Z
Ok, I understand now. Thanks!
Johncowk
CC BY-SA 4.0
2021-07-14T17:20:52.633Z
2021-07-14T17:20:52.633Z
Bryan Krause
<p>I am news to the field of computational neuroscience, and I constantly see equations involving an &quot;input current&quot;, which can be tested experimentally by injecting &quot;currents&quot; into neurons and simultaneously recording the membrane potential.</p>
<p>Now, this &quot;current&quot; is not an actual flow of electrons (I'm assuming ?) from a metal electrode so my question is the following: what is actually injected inside the cell in such measurements? How does it works?</p>

<electrophysiology>
What do current-clamp pipettes inject in neuronal recordings?
Johncowk
# What do current-clamp pipettes inject in neuronal recordings?

(Asked by: username_0 on 2021-07-14)

I am news to the field of computational neuroscience, and I constantly see equations involving an "input current", which can be tested experimentally by injecting "currents" into neurons and simultaneously recording the membrane potential.

Now, this "current" is not an actual flow of electrons (I'm assuming ?) from a metal electrode so my question is the following: what is actually injected inside the cell in such measurements? How does it works?

**Tags:** electrophysiology


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## 1 answers

### Answer by username_1 on 2021-07-14. Score: 2 | Accepted answer

In a [current-clamp (or voltage-clamp, for that matter)](https://en.wikipedia.org/wiki/Patch_clamp) experiment, you have a pair of electrodes; one is in the bath somewhere acting as a ground, the other is suspended in a glass pipette full of some salt solution, usually one that roughly mimics the intracellular ion composition, with some adjustments for convenience or experimental reasons. In a whole-cell configuration that is typical of a current-clamp experiment, the experimenter presses this glass pipette against the cell and sucks the membrane in, such that the inside of the cell and the inside of the pipette are all one electrically-connected space.

When you "clamp" current to some level, that means that the amplifier is making sure a certain current runs between those two wires; you then measure the voltage required to maintain this current as a read out of the cell's function in some way.

"Injecting electrons" is really not too far off from the truth. It pretty much acts like a battery in that circuit, except that the voltage of the battery is adjusted dynamically to fix the current (rather than the voltage being constant as in a typical household battery). The rest is really a matter of electrochemistry rather than any neuroscience: the ground wires used are typically [silver chloride-coated](https://en.wikipedia.org/wiki/Silver_chloride_electrode), so the actual electrochemistry that occurs is the redox reaction between solid atomic silver and silver chloride.

None of the silver interacts with the tissue, though; spatially the electrodes are far from the cell itself. Electricity is conducted through the liquid ionic medium like it always does: other positive charges are attracted to negativity/repulsed by positivity, and vice-versa.

> **Comments:**
> **username_0**: Oh so nothing is actually injected inside the cell soma? I was under the impression that the pipette was introduced inside the cell, effectively piercing the membrane.  
> **username_1**: @username_0 Nothing is injected, but the contents of the cell and pipette mix, and since the pipette volume is massive compared to the cell you can just assume it's the same as the pipette solution. That doesn't relate to "injecting current" though.  
> **username_0**: Yeah but effectively you end up with some saline solution of the pipette inside the cell soma?  
> **username_1**: @username_0 You can assume all the inside is saline solution once you patch. But that has nothing to do with "injecting current".  
> **username_0**: Ok, I understand now. Thanks!  

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