liquid junction potential

8 posts / 0 new
lazy
liquid junction potential

Although there are some nice tools to calculate the lilquid junction potential, I 'd like to know how to obtain the value on the oscilloscope.
I think when I dip the electrode into the external solution, the current base line does not stay on zero line (0). I add the voltage to bring back the current line to the zero line. I think the voltage that I added is the liquid junction potential. Please let me know if my understanidng is OK or not.
Thanks.

Fraser Moss
You need to dip your pipette

You need to dip your pipette loaded with internal solution into some more internal solution that you have put in your chamber.

Zero the baseline offset

lift out your pipette and replace the solution in the chamber with your extracellular solution and dip the pipette back in.

jaga_ch
hi,

hi,
I was wondering which software do you use fo patch clamp? I work with Tida (Heka) and I am also trying to find out how to corect junction potential, however as far as I read and understood, the idea of adding the junction potential to the holding potential is right.
:)

lazy
I use Pulse software.

I use Pulse software.

Calculated by Kenyon's method, I obtained appx +10 mV of LJP.

(1) I simply input +10 to the LJP field, and then I do patch as the standard way. I am not sure this is correct or not. Note that I do not change the bath solution.

(2) First, I understood that the pipette has this value when dipped into the bath solution. So, if I set the HP to -70 mV in whole cell without LJP cancellation, then the real HP must be -60 mV (-70+10=-60).

(3) But, when the whole cell is achieved, the LJP should be disappaired! (I think most people agree with this). Then, for what we have to cancel the LJP? The real HP can be -80mV with LJP cancellation, while I believe it -70mV???

(4) But the manual says how to cancel the LJP, meaning that it is required for the process to achieve the whole cell configuration.

(5) Currently, I am thinking that the reason why we have to cancel the LJP is because Auto Vo reset includes the LJP value, indicating that the offset line (I believed 0 mV) is not 0 mV, but +10 mV. I need to cancel this value with the way that the manual says. I need not care about LJP disapprearance in whole cell configuration.

But I am not sure what I am doing is good or not. How about your case, dear patch clampers?

Fraser Moss
For those of you have

For those of you have problems understanfing the LJP this is a must read.

Correction for liquid junction potentials in patch clamp experiments.
Methods Enzymol. 1992;207:123-31.

Neher E.

This chapter describes corrections that have to be applied to measured membrane potentials in patch clamp experiments. Some of them [Eqs. (1)-(3)] are required regardless of the nature of the reference electrode (in the Ringer's solution bath) whenever the pipette-filling solution is different from the bath solution. They represent the liquid junction potentials that are present at the pipette tip before patch formation. In addition, corrections have to be applied when the bath solution is being changed during a measurement (i.e., after seal formation). In that case the following rules apply. (1) The new solution should never get into contact with the bare silver/silver chloride wire of the reference electrode. This requirement is best met by using a salt bridge. (2) The "best" salt bridge is a 3 M KCl bridge with an abrupt KCl-bath fluid boundary at its tip (see above). This bridge does not require any additional potential corrections, but it may lead to KCl poisoning of the bath or become contaminated by solutions used previously. (3) Local solution changes (microperfusion by puffer pipette, U tool or sewer pipe arrangements) as well as recessed KCl bridges require additional corrections, which (together with the simple liquid junction potential correction) are approximately given by Eqs. (6)-(8). It should be stressed that all equations given here represent approximate corrections, since liquid junction potentials are thermodynamically ill-defined. This is particularly relevant for Eqs. (6) and (7) where the sum of two liquid junction potentials appears.

PMID: 1528115

Order it from your library today!

Fraser Moss
Furthermore, if you use

Furthermore, if you use pClamp, it has a built in piece of software "JPCalc" that will give a best estimate of your LJP in your experiment if you give it all the parameters you will be using.

For a reference see J Neurosci Methods (1994) 51: 107-16.

Pubmed reference page

For the stand alone JPCalc program go here
http://web.med.unsw.edu.au/phbsoft/research_jpcalc.htm

lazy
I am considering 3 junction

I am considering 3 junction potentials:

(1) Junction potential between reference electrode and bath solution
(2) Ag/AgCl wire in the pipette and pipette solution
(3) liquid junction potential between pipette and bath solutions

In whole cell configuration, LJP will be disappeared.

Prior to patch process, I offset the potentials of (1) and (2), but not LJP (3), since it will disappear. For that, I give the value of the LJP calculated to the software.

Fraser Moss
Personally I always apply the

Personally I always apply the correction before. But I am 100% a voltage rather than current clamper.

Most amplifiers have separate controls for the offset and Vhold, so you can adjust the offset for zero current during the reference set up while Vhold is active and set to -Vlj (negative liquid junction potential).

this will anticipate the potential that will be seen by the patch after seal formation.

Vhold readings are then interpreted as -Vm for inside-out and Cell-attached patches or as +Vm for outside-out or whole-cell.