PRINCIPLES OF OPERATION
•
83
Chapter 8
Absolute Value
The absolute value of the membrane capacitance shows on the WHOLE CELL
CAP. dial after the whole-cell current transient has been eliminated. This value
may be used for estimating the surface area of the cell assuming that the
capacitance of 1 cm
2
membrane is 1 µF. The setting of this control is available for
computer acquisition on the CELL CAPACITANCE output telegraph on the rear
panel of the Axopatch 200B.
Limitations
The measurement of series resistance (R
s
) and cell capacitance (C
m
) is accurate
only if the membrane resistance (R
m
) is significantly greater than R
s
.
Series Resistance
In patch clamping, the term refers to the pipette resistance plus any other access resistances
to the patch or cell.
The SERIES RESISTANCE and WHOLE CELL CAP. controls, along with %
PREDICTION and % CORRECTION, are active in WHOLE CELL mode. In PATCH
mode, only SERIES RESISTANCE and % CORRECTION are functional.
Absolute Value
The absolute range of the series resistance shows on the SERIES RESISTANCE
dial after the whole-cell current transient has been eliminated. The range of the
SERIES RESISTANCE values is 0 - 100 MΩ.
Correction, Prediction, and Lag
As discussed in the previous section (Capacitance Compensation), eliminating the current
transient by setting the SERIES RESISTANCE and WHOLE CELL CAP. controls does not
improve the speed of clamping the cell.
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