36 • Guide to Electrophysiological Recording
MultiClamp 700A Theory and Operation, Copyright 2000, 2001 Axon Instruments, Inc.
In patch clamping, and particularly if you are a beginner, it is very useful to have a
means of calibrating the amount of pressure or suction that is applied. This allows you
to reproducibly apply successful patch clamping strategies, or to systematically alter
unsuccessful ones. Ideally, you would attach a manometer to your suction system. A
less accurate but cheaper way is to use a 10 cc syringe. Set the syringe at the 5 cc mark
and attach it to the headstage suction tubing. The pressure in the tubing (in millibars)
is then given approximately by the formula
Pressure (mbar) -70*x + 350
where x is the mark on the syringe to which the plunger is depressed or withdrawn.
For example, depressing the syringe to 4 (cc) will give about 70 mbar of pressure.
This formula assumes about 2 m of 1/16 i.d. tubing is attached to the headstage
holder. Be aware that any air leaks in your system will nullify this estimate. If you do
not explicitly check for leaks, the only indication that a leak exists may be an inability
to get seals.
Some researchers prefer to apply pressure and suction by mouth. In this case, it might
be useful to roughly “calibrate your mouth” using the syringe method.
Note the following pressure conversion factors:
1 psi 70 mbar
100 mbar 75 mm Hg
The pipette holder is a potential source of electrical noise if it becomes moist. For this
reason, electrodes should be filled with solution only far enough that the end of the
holder wire or pellet is immersed. Further details are given under “Low Noise
Techniques”, below.
Forming a Gigaseal
Start with the MultiClamp 700A in voltage clamp mode (VC). Fill a patch pipette with
internal solution and secure it firmly in the pipette holder (fill the patch pipette with
external solution if cell-attached recording is the goal). Be sure to support the
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