I mostly do voltage clamp recording using caesium methanesulfonate based low Cl- internal solution. I use a Narishige vertical puller to pull my electrodes. I constantly get a pipette resistance of 4.5-5 MOhm with my settings. Recently, another member of my lab started doing current clamp experiments and he is using K-gluconate internal, and he told me he found the resistance of his electrodes with my setting to be very high, around 11-12 MOhm. I was curious and I tried the potassium internal in my setup and it seemed to be correct, I found the resistance to be around 11. However, when I used caesium internal the resistance was still around 5 MOhm. I am wondering why this is the case. It is possible that maybe conductance varies between internals so there can be slight differences, but this is more than two-fold. I am wondering why this is the case? What should I consider my actual electrode resistance to be? When I patch, I have found the tip to be of perfect size for patching a striatal MSN, however I am unsure of the tip diameter.
The internal solution inside the pipette is likely to contain either debris or precipitates. One might use KCl or CsCl as internal solution to measure the pipette resistance. Usually, the resistance is better to range between 2-4 MOhm. “11 MOhm” is indeed too high. S.N.
I' d suggest increasing your voltage step to up 30 mV. The reason is that if the tip of your electrode too small, your amplifier cannot measure resistance correctly.
Sheng-Nan Wu thanks for your reply. However, this is not due to clogged tip, I have checked this.
Hello Priyabrata,
gluconate has a lower mobility, and therefore a lower conductivity, than other ions. I read someplace that gluconate can precipitate inside the electrode (tip) and gradually increase the resistance. Also, check that the osmolarity of the solutions are comparable. A lower osmolarity will also increase the resistance of the pipette.
Oh dear! Electrode resistance cannot be considered a measure of tip size BECAUSE it depends on the ionic composition of both external and electrode solutions. As pointed out to you, electrical resistance is a measure of ion mobility and it would not be surprising that methansulfonate and gluconate differ.
Hi!
It seems to me that the Cl- concentration in your K-gluconate-based solution may be too low. I once had the same problem when I tried to make the pipette solution with a chloride ion concentration of less than 1.5 mM. So check that the chloride ion concentration in your two solutions is close. In our lab we use both Cs-methanesulphonate-based and K-gluconate-based solutions with a Cl- concentration of 10-15 mM. The pipettes have the same resistance when filled with different solutions as long as the chloride ion concentration is close.
Thanks Dmitry for adding your experience. Remember Priyabrata that you have a chlorided wire and bath electrode to complete the circuit. If you change the [Cl-] in either solution, you will generate a voltage difference and that offset you can measure and account for, but is there even when you zero your trace before touching a cell.
I hoped that the answer Dmitry and Neil provided was the correct one, but after crosschecking it seems that my low Cl Cs based internal solution has 3.3 mM Cl and K-gluconate has 4 mM Cl. I am not sure if this small difference would give rise such a big difference in resistance.
Most papers frequently state the resistance of their electrode with their internal, but I am guessing there is no direct way to measure this considering internal and perfusion solution differs between experiments and experimenters. Unless someone takes time to measure the tip diameter of the electrode separately, that is.
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