Compensation Procedures EPC9 Manual 66
Example 2: An outside-out or whole-cell measurement with KCl-based internal
solution in the pipette. LJ should be set to 3 mV (see table) in order to correct for the
disappearance of a liquid junction potential between the KCl containing pipette and
the NaCl-based bath solution.
Example 3: An episode with low-chloride bath solution during the experiment of
example 2. It is assumed that the reference electrode in the bath includes a salt bridge
such that the change in Cl
-
concentration is not “seen” by the Ag-AgCl
-
-wire.
Nevertheless, a liquid junction potential will develop at the bath/salt-bridge
interface, unless a “bleeding” KCl-bridge is used (see Neher, 1992). Similarly, a
liquid junction potential will develop during local microperfusion. Thus, the
correction during the episode in low-chloride medium will be the sum of this liquid
junction potential and the correction of Example 2 (3 mV). Taking the value for a low
Cl
-
solution (e.g., sulfate Ringer; see table), we arrive at a value of LJ = 3 + (-6) = -3
mV, which should be set during that part of the experiment.
Note: The sulfate Ringer in this case is -6 mV (the inverse of the value in the table),
because this potential “appears” during the measurement with inverted polarity to the
convention of Barry & Lynch.
Example 4: An outside-out or whole-cell measurement with Cs-citrate-based
internal solution. In this case, LJ should be set to 12 mV (see table above).
Example 5: A cell-attached measurement with sulfate-Ringer in the pipette. Two
corrections apply: 1. the correction for the liquid junction potential during the
reference measurement (6 mV, see table above) and 2. the resting potential of the cell.
We assume the latter to be -60 mV and therefore set LJ to -54 mV. In the cell-attached
mode polarities of the amplifier readout are inverted, thus the amplifier will display
the “physiological” patch potential.
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