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 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)