Liquid Junction Potential
What Liquid Junction Potential (LJP) is and how it can be corrected for in patch-clamp experiments

What is LJP?

  • When two different ionic solutions meet, a small voltage can form at the junction. In patch-clamp experiments, this occurs at the tip of the pipette where the internal solution meets the bath solution.

  • This voltage difference occurs because smaller ions (like Cl-) move faster than large ions (like gluconate), so a small standing voltage is present across the liquid junction.

  • When patch-clamping cells the amplifier offset voltage is adjusted to zero when the pipette is in open-tip configuration with the bath, but this reading is not really zero because LJP is present. This is the cause of LJP error in patch-clamp experiments.

  • When a patch-clamp recording shows a voltage of -70 mV, the voltage isn’t actually -70 mV because it is off by the size of the LJP.

  • Scientists can measure or calculate the LJP, then use its known value to correct patch-clamp recordings.

  • Changing the extracellular solution or intracellular solution will change LJP.

How to Correct for LJP in Electrophysiology Experiments

Consider the case when you zero your meter as the pipette is in the bath:

Vmeasured = Vactual + LJP

Rearranging this formula, the actual voltage of the cell is what the meter says minus the LJP:

Vactual = Vmeasured - LJP

How to Calculate LJP

How to Measure LJP Experimentally

  • Zero the amplifier with intracellular solution in the bath and in your pipette

  • Replace the bath with extracellular solution

  • The measured voltage is the negative LJP (invert its sign to get LJP)