Junction Potential Calculator (JPCalcWin)
JPCalc (Barry, 1994; J. Neurosci. Method., 51: 107-116) is a research/teaching program designed
- to show graphically how junction potentials arise in a variety of different patch-clamp configurations and other electrophysiological situations;
- to then enable the ready calculation of junction potential corrections, given the solution data, and
- to show clearly how those junction potential corrections need to be applied to the appropriate physiological measurements [see review on junction potentials, J. Membrane Biol., 121, 101-117 (1991)].
JPCalc for Windows, or JPCalcW, was produced from JPCalc by Axon Instruments, Inc (now part of Molecular Devices Corp.). It is either available with their pClamp package, or as a stand-alone program from Professor Peter H Barry. The cost of the JPCalcWsoftware package on a CD, printed graphical Users' Manual and a laboratory license for multiple computers in the one lab/research group and cost of international express courier is A$175 (ex GST).
Alternatively, an electronic version of the above package may be purchased for A$95 (ex GST). Purchase is normally by credit card (VISA or MasterCard) to SDR Clinical Technology, Sydney. So far JPCalc or JPCalcW has been purchased by far more than 100 laboratories in at least 17 different countries. This program should also run with Apple Macintosh computers provided they have a fully compatible Windows/DOS emulation package. Further details can be obtained by e-mailing firstname.lastname@example.org.
While JPCalc for Windows (JPCalcW) will run under 32-bit Vista, Windows 7 and earlier Windows, it will NOT DIRECTLY run under 64-bit Windows, but it will run in Windows XP-mode.
JPCalcWin is a new 64-bit compatible stand-alone liquid junction potential program
A typical screen uses this program to calculate the liquid junction potential corrections for an inside-out patch, in which the bath solution has just been changed, is shown in the figure below. The original (control) bath solution was Csol and the new bath solution is Csol2 . Note that the salt composition of the reference agar-salt-bridge pipette was chosen to be very similar to that of the original (control) bath solution, to minimise history-dependent effects at that liquid junction of the agar-salt-bridge reference electrode.
VL represents the amplifier offset required to balance the liquid junction potential between the original bath solution and the pipette solution (Cpip), when the patch-clamp amplifier was zeroed prior to patching the cell; VL21 is the change in liquid junction potential at the reference salt-bridge electrode; VP is the pipette potential and Vm is the potential across the inside-out membrane patch in the orientation shown by the arrow. The ions are all included in the 42 Predefined Ion Values already stored in the program and additional ions may be included in User Ion Values in the program if the valency (z) and relative mobility (u) of an ion is known.
In this example, the liquid junction potential, VL, between original solution and pipette solution is +8.7 mV and the shift in liquid junction potential at the reference salt-bridge pipette, VL21 is -13.3 mV, since as indicated Vm = -VP + (VL + VL21), this means that Vm = -VP - 4.6 mV, as indicated.
As in the case of JPCalcW and JPCalc, JPCalcWin will both calculate the liquid junction potentials and show how they must be applied to correct the measured membrane potentials.