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USE OF THE PATCH CLAMP – A TUTORIAL

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Chapter 3

Series Resistance Compensation

The Axopatch 200B is capable of series-resistance compensation equal to that of the

Axopatch 200A and substantially better than has been possible with any other commercial

patch clamp to date. In order to achieve the outstanding performance of the Axopatch

200B it is critical to set its controls properly. Because of the importance of this issue we go

to great lengths here to describe in detail the methods for properly setting the instrument.

We present both a brief method for experienced users and a more detailed method for those

not yet skilled in patch clamping. (See

REFERENCE

SECTION: PRINCIPLES OF

OPERATION

for a discussion of the theory of whole-cell and series-resistance

compensation).

Brief Method For Setting Series Resistance Compensation

At this point you have eliminated all capacitive current from the measured output.

However, the cell membrane response to a step voltage command will still proceed with the

time constant R

of about 330 µs for the model cell (where R

is the series resistance and

is the membrane capacitance). The Axopatch 200B uses dual controls to speed this

response and to compensate for IR drops resulting from membrane current and series

resistance, and for the filtering effect of the membrane capacitance and series resistance.

These controls are labeled PREDICTION and CORRECTION. Non-ideal circuit

characteristics require minor readjustments of WHOLE CELL CAP., SERIES

RESISTANCE, and PIPETTE CAPACITANCE COMPENSATION potentiometers to

achieve the best performance. The procedure here is intended to familiarize the user with

these controls and with the necessary readjustments.

Users who are already skilled at adjusting both the fast electrode capacitance and whole-

cell capacitance compensation circuits may prefer to set both PREDICTION and

CORRECTION at the same time prior to readjusting the various controls to eliminate the

final transient. Be aware that if you exceed the maximum achievable % PREDICTION you

will produce unacceptable non-linearities (see Figure 4 and detailed explanation in the

Series Resistance section in

PRINCIPLES OF OPERATION

Axon Axopatch 200B User Manual

Questions and Answers: