No bubble?

Experimental procedures often have lots of superstitions.
Even in electrophysiological techniques there are plenty of those.
Superstitions often make one comfortable while doing stressful experiments; however, it looks silly when you see someone following a superstition that you don't believe in.

Here's an example: the bubbles in a glass capillary microelectrode.
I know some people seriously worry about those bubbles. They let the electrode sit in a tube filled with 3M KCl solution for a few minutes. It looks as if some sort of Buddhist ceremony with an insence standing up in front of an altar.

I don't believe that religion and here's why.
Here is a microelectrodes with ugly bubbles.

I let the silver wire not to penetrate through these bubbles.

And the resistance was...

The voltage drop was -38mV with no bridge when -1nA was passed. 

So the electrode resistance was 38 MΩ.

Then, I let the bubble go out. 

Yes it took me a few minutes to get rid of all tiny bubbles.

And the resistance was...

It was reduced by 1 MΩ. 
So, those ugly stupid bubbles costed me 1 MΩ!

1 MΩ, Oh well...
Tell you what, when you play with 6 electrodes simultaneously poking around neurons looking for Si2 or Si3 or whatever cells, 1 MΩ drift is nothing.  The electrode resistance will change anyway by tens of MΩ when you poke around the brain looking for cells. It is no worth spending a good few minutes just to get rid of those stupid 1 MΩ bubbles. Just go for a poke with it and replace it when clogged. Think about the efficiency of your labor. Don't worry about the bubbles. 

Fixing a power hub for micromanipulators

   There was overnight leakage of the cooling water for the chilling stage under dissection microscope in one of our student's electrophysiology rig. The dripped water soaked the the entire power hub for micromanipulators under the anti-vibration table. It stopped working, of course. It is Siskiyou MC1000e. It would cost $$$ if you buy a new one.

   By checking around with an electrical tester, I found a disconnected path on the printed circuit board. I had to create a new path with a hook-up wire (red arrow).

    There was another bad news. One of the pins in the male D-SUB connector was also broken. I don't know how it could happen but it was one of the critical one that feeds current to the manipulator. I created a fake pin from a piece of hook-up wire and attached into the connector. It worked well.

    Now the manipulator is moving fine.
    You know, I can be the author of "Zen and the art of electrophyiology rig maintenance" some day.

Patch-clamp amplifier vs. intracellular amplifier

People often ask me what the differences are between Axopatch and Axoclamp (both are made by Axon Instruments).

The answer is simple: Axopatch is a highly-sensitive I-V converter (ammeter). Axoclamp is a highly-stable voltmeter.


Axopatch or so-called patch-clamp amplifiers are designed for recording the membrane current, but it can also measure the membrane potential under the "current clamp mode".
On the other hand, Axoclamp is an amplifier designed for recording voltage with high-resistance microelectrodes. You can also measure membrane current by using "voltage-clamp mode." One may think that the continuous single-electrode voltage clamp mode in Axoclamp sounds very similar or almost identical to the whole-cell patch clamp by Axopatch.

Having either one being able do both voltage and current recordings, why do we need both?



The headstage of Axopatch contains a highly sensitive I-V converter, so that it can measure current with better s/n ratio. It can indirectly measure the voltage by calculating from the current being passed and membrane input resistance, but very susceptible to errors due to changes in the electrode resistance. This is why the patch pipette has to be big, with a resistance as low as possible.

Ironically, the large electrode tip makes he recorded potential less accurate, because of the junctional current. Junctional current is produced by the difference between the electrode solution and the cytoplasmic fluid. This current can be minimized by adjusting the ionic content of the electrode solution and reducing the size of the electrode tip (but this will increase the electrode resistance).


The headstage of Axoclamp contains the "voltage follower" circuit. This voltage follower circuit is the "magic" that makes it possible to record voltage with a sharp mega-ohm electrode. A voltage follower produce virtually infinite input resistance, which makes the electrode resistance almost negligible. Thus, the voltage recorded by Axoclamp is more accurate and relieble than Axopatch.
The current measured under voltage clamp mode in Axoclamp is actually the current generated artificially in the feedback circuit. Such indirect measurement is bad in s/n ratio and slower than Axopatch.