Patch-Clamp Setup EPC9 Manual 67
8. Patch-Clamp Setup
Mounting the Probe
For low-noise recording, the pipette holder must be attached directly to the EPC9
probe. Although the probe amplifier can tolerate the additional capacitance of a
short connecting cable without instability or oscillations, we find that the dielectric
and electrostrictive properties of coaxial cables introduce excessive noise. In typical
setups, the probe is therefore mounted directly on a 3-axis micromanipulator. The
EPC9 probes are supplied with a plastic mounting plate for mounting on a flat
surface. Holes can be drilled through the protruding surfaces for attachment to a
matching plate or other surface. Please remember, that the metal case of the probe
must remain insulated from ground.
Because of the extreme sensitivity of the EPC9, special care must be taken in
grounding all surfaces that will be near the probe input in order to minimize line-
frequency interference. Even one millivolt of AC on a nearby surface, which can
easily arise from a ground loop, can result in significant 50 or 60 Hz noise. A high-
quality ground is available at the Gnd terminal of the probe; this is internally
connected through the probe's cable directly to the Signal Gnd in the main unit. The
Gnd terminal on the probe is best used for the bath electrode, and perhaps for
grounding nearby objects such as the microscope.
Ground Wires
It is a good idea to run a separate ground wire from the Signal Ground jack on the
main unit to ground large objects such as the table, Faraday cage, etc. It is best to
have the high quality ground wire run parallel to the probe's cable in order to avoid
magnetic pickup and ground loop effects. Besides 50 or 60 Hz magnetic pickup,
there may be some 35 kHz pickup from the magnetic deflection of the computer
monitor. This pickup becomes visible only when the EPC9 filters are set to high
frequencies; it can usually be nulled by changing the orientation or spacing of the
ground wire from the probe cable.
Grounding the Microscope
In most cases, the patch clamp is used in conjunction with a microscope; it and its
stage typically constitute the conducting surfaces nearest the pipette and holder. In a
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