Current, voltage and bridge balance problems

Biophysics
1

Hello,

I’m setting up my first rig for intracellular electrophysiology.

I’m using an Axoclamp 2B amplifier and pClamp 9 software, and I have calibrated the software to the Axoclamp. I haven’t tried to impale anything yet. This problem starts when I simply place my electrode into the extracellular solution.

My problem is when I inject current down my electrode, the change in voltage occurs in the wrong direction. For example, if I inject a hyperpolarising step to remove series resistance the trace recording current moves in a negative direction but voltage appears to depolarise. Additionally, I cant use bridge balance to remove/calculate series resistance. Rather than reducing the step, it adds to it making it bigger! Now I’ve checked my calibration for voltage, which I have done by changing the input offset. Voltage appears to have been calibrated properly as the values that appear on the axoclamp match those on the comptuer. When I use input offset to make the values more negative on the Axoclamp, they move in a negative direction on the trace too. Besides, the problems I’m having with bridge balance suggest it’s something else.

I’ve remade my tip solution (1M KCl). I’ve used multiple tips. I don’t have an oscilloscope or a model cell.

Any ideas please?

2

Hi Nishan

It looks like you’re encountering a fundamental issue related to the electrode setup or the measurement configuration of your Axoclamp 2B. Based on the information you’ve described, the problem might involve either the polarity of your current injection, a misconfiguration in your amplifier setup, or the incorrect usage of your bridge balance function. Check the following:

  • Pipette and Solution: Confirm electrode resistance and solution quality (1M KCl should typically work).
  • Connections & Grounding: Ensure all ground connections are properly set up.
  • Try Smaller Current Steps: Start with a low current step to reduce any overcompensation in bridge balance.

Let us know if that helped