Clamp Section - Warner OC-725C User Manual

Control Description
Current outputs are available from the I MONITOR BNC at full bandwidth (~10 kHz) and
from the I MONITOR FILTERED BNC which is filtered at 1 kHz by an integral 4-pole Bessel
filter.

Clamp Section

The CLAMP control block contains the MODE
SELECTOR switch as well as the GAIN and DC GAIN controls.
The CLAMP MODE SELECTOR switch selects for slow and fast
clamp speeds, or for off. These choices are described below.
off - In the off position, the clamp amplifier is disconnected
from the current electrode. The voltage difference between
the current electrode and the bath electrode [Ve, mV] is read
on the METER in the BATH ELECTRODES control block. This
information is also available at the Ve x10 output BNC on the
rear of the instrument.
NOTE: All CLAMP controls are disabled by turning the CLAMP
MODE SELECTOR switch to the off position. Be sure to switch this
control to the off position before handling electrodes!
SLOW - The slow clamp mode is useful for screening of oocytes or where high clamp
speeds are not required. The slow clamp speed is approximately 0.5 ms when measured
with the model membrane
(1 MΩ shunted with 0.47 µF). In this mode, measured currents are displayed on the
BATH ELECTRODES METER in units of µA.
FAST - Most oocyte clamping is performed in the fast mode. The clamp speed is limited
by the resistance of the current electrode and the oocyte membrane capacitance.
Therefore, the current electrode resistance must be kept as low as possible to obtain the
fastest clamp speeds. Currents are read on the BATH ELECTRODES METER in units of µA.
Fast clamp speeds are ~350 µs when measured with the model cell as described above.
The GAIN control is a single turn potentiometer which varies the full-bandwidth open-
loop gain from 0 to 2000. A high DC GAIN (106) can be switched in with the DC GAIN
toggle switch to provide a hard clamp when passing large currents from high expression
oocytes.
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