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Setup
The following instructions are designed to guide the user, step-by-step, through a typical
recording session involving a Xenopus oocyte. It is assumed that the user is already
familiar with the techniques of Xenopus oocyte excision and microinjection (for a review
of those techniques, see Colman, 1984). It is also assumed that the user has some
familiarity with the basic circuitry of a two-electrode voltage clamp (for review, see Hille,
1984).
Pipettes
Microelectrodes can be made using the same glass (tubing and dimensions) as those
used for a typical patch pipette and are usually filled with 3 M sterile filtered KCl.
Unlike the pipettes used as patching electrodes, microelectrode pipettes do not require
fire polishing nor coating with Sylgard. They will need to be broken off, however, to a
relatively large diameter to insure a fast response time by the clamp.
For the voltage electrode, the pipette tip should be broken back to an O.D. of 3-5
µm. The current electrode pipette should be broken back to an O.D. of 7-9 µm. The
resistances of these pipettes should be about 2 MΩ and
1 MΩ (or less), respectively.
When installed, the current electrode pipette should be shielded from the voltage
electrode and that shield should be grounded to the circuit ground. This can be
accomplished by wrapping the current pipette with aluminum foil or by mounting a
metal screen or plate between the two pipettes. In either configuration, the shield can
be grounded by connecting it to the "ground" mini-jack on the side of the bath probe.
When using the aluminum foil method, care must be taken to prevent the foil from
touching the surface of the bath solution at the bottom end of the pipette or the silver
electrode wire at the top end.
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Publication 5720-001 REV1.0
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