USE OF THE PATCH CLAMP – A TUTORIAL
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Chapter 3
cell contents) and the cell capacitance can be read on the SERIES RESISTANCE and
WHOLE CELL CAP. controls, respectively. Usually, the access resistance will be about
three times that of the pipette alone. The whole-cell capacitance value can be used to
estimate the total surface area of the cell assuming that 1 cm
2
of membrane has 1 µF
capacitance.
If your currents are large, you will want to use series resistance compensation to increase
the frequency response of the whole-cell clamp and to minimize the command voltage error
due to the IR drop across the access resistance. The proper adjustment of these controls is
discussed in the Whole-Cell Recording (Model Cell) section above.
The Axopatch 200B contains a 4-pole internal Bessel filter with five frequencies for
filtering the current output. For many experiments, the 1, 2, 5, 10 and 100 kHz settings
available will be sufficient. If other frequency cutoffs are required, they must be provided
from an external filter. Again, be sure that you take into account that the final bandwidth is
that of the cascaded internal and external filters.
We do not recommend the use of LEAK SUBTRACTION in the whole-cell configuration
since with whole-cell recordings it is exceedingly difficult to determine the fraction of the
leak current due to the seal vs. the fraction due to background currents which might have
some dependence on voltage. Software packages like pCLAMP allow a user-specified
after-the-fact leakage correction, which is a much safer procedure.
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