I'm doing Na current recording on brain slice, and specifically in ventral lateral hypothalamus. I used CsSO3 and CsCl based internal solution to remove K+, and the cell was held at -70 mV, the voltage step I applied is from -90 mV to + 60 mV, each step is 10 mV. I espected to see Na current from around -50 or 60 mV, however, I didn't see any Na current until the voltage reached +10 mV. I used clampex for recording.
I tried looking it up online, and couldn't find any answer.
Can anyone help me with the issue?
Thank you so much!
It´s odd. I suggest to check if you introduce some offset on the amplifier (like trying to offset zero current after sealing or entering the pipette in the bath with a holding potential). If this is not the case, I suggest to unground everything to check for ground loops, which could be introducing some offset.
Hi,
I am not familiar with slice recordings, but did you check your Rseries resistance (inner pipette resistance)? This should be below 20MOhm. If this is not the case the +10 mV activation voltage could be not the true voltage. We have quite the same problem and tried to solve it with bigger pipettes.
Looks like you may have a high junctional potential which can be cancelled online by pipette offset or offline. Series resitance can definitely be another issue. At what potential do you ge the peak of the Na+ current? Usually it is around 0 mV (+/-10mV). A quick way of checking that would be switching to current clamp and observing the series resitance and in case you also try with a K+ based internal solution try to evoke spikes and analyse the spike threshold.
You should also try to record the same using typical K+ based internal solution just to negate out the effect of Cs+ on Na+ channels (although I dont know of any so far).
Good Luck!
Check that your bath and pipette silver-chloride electrodes are clean and have enough silver-chloride on the silver wire; or just put them in bleach solution for 30 min.
Use a model electronic cell and verify that your Clampex values of the current and voltage in your protocol are the same as the values that you can read on the meter of your amplifier. If not, you need to recalibrate your Clampex/Digidata.
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