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Guide to Electrophysiological Recording
MultiClamp 700A Theory and Operation, Copyright 2000, 2001 Axon Instruments, Inc.
can also be used with lower-resistance patch electrodes, which in some cases offer
advantages. (See next paragraph.) In this chapter it will be assumed for the most part
that sharp microelectrodes are being used for the I-Clamp recording. However, some
of the general advice about I-Clamp recording applies equally well to patch electrodes.
Sharp Microelectrode or Patch Electrode?
The type and resistance of the electrode will depend on the particular application, and
ultimately on personal preference, but there are a few points that should be considered.
Patch pipettes offer some advantages over intracellular micropipettes. First, the
recording configuration is often more mechanically stable. Second, stable recordings
can be obtained with patch pipette resistances one to two orders of magnitude lower
than those of micropipettes.
This second point is most important and a number of benefits accrue. Due to its low
resistance, a patch pipette used for voltage recording will have a better frequency
response and lower noise level than a micropipette. Furthermore, the tip potential of
high resistance intracellular micropipettes is often unstable and can change erratically
as the cell is penetrated. In contrast, the tip (or junction) potential of patch pipettes is
stable and can be accurately measured and corrected for electronically.
There are some instances where micropipettes may be more useful. If your study
requires that the contents of the cell remain relatively intact (second messenger
systems, for example), then patch pipettes may not be appropriate since the diffusible
cellular components will eventually become diluted. In such cases you may wish to
consider the “perforated patch” technique that prevents the loss of large intracellular
molecules to the patch pipette (see Patch Clamping, above). Finally, for some cell
types (
e.g.
those tightly wrapped in glial cells or connective tissue) it simply may not
be possible to obtain gigohm seals with patch electrodes.
Microelectrode Properties
Users of sharp microelectrodes spend far more time than patch clampers worrying
about the properties of their electrodes. This is because the higher resistance of sharp
