31
www.warneronline.com
Special Circumstances
High Side Current Measuring
In studies of single oocytes, current is monitored by the bath clamp headstage.
Experiments involving two oocytes in a common bath (such as gap junction studies)
requires monitoring currents from each oocyte. This is done in the current output leg (in
series with and ahead of the current electrode).
Two disadvantages of monitoring the current in this manner exist.
1) The noise level of this signal is higher. However, this is usually
not a serious problem since currents are typically in the µA range.
2) The voltage drop across the solution resistance (from oocyte to
bath ground) becomes an error voltage since it is not subtracted out as when
the bath clamp headstage is used. This problem is overcome by using the
optional DIFFERENTIAL VOLTAGE HEADSTAGE.
Configuration
The OC-725C current measuring circuit can be changed to the high side
current measuring mode by setting a dip switch on the main circuit board.
1) First disconnect the power cord from the wall.
2) Remove the two screws at the rear of the top cover and it off.
3) Locate dip switch S10 on the circuit board. For normal operation S4 is on
and all other 7 switches are off.
4) To convert to high side current measuring mode, turn S4 off and turn S2, S5,
and S7 on. All other switches should remain in the off position.
Optional Voltage Headstage
The optional DIFFERENTIAL INPUT VOLTAGE RECORDING HEADSTAGE (Model 7255DI) is
used in applications where the bath clamp headstage cannot be effectively employed.
Two examples are (1) situations where the solution path from oocyte to ground is very
long and (2) when recording from two oocytes in a common bath.
Two 1 mm input jacks are located on the side of the headstage, V DIFF and GND. A
shorting jumper is supplied and is used for normal single-ended recording. For double-
ended recording, the jumper is removed and a V DIFF ELECTRODE is connected to the V
DIFF jack as shown below.
If a shield between the voltage and clamp current electrodes is used, it should be
connected to the headstage ground.
