TEC-B-01 User Manual
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version 1.1
page 17
5.5. Testing
Operation
Modes
Current Clamp
The cell's response to current injections is measured in the current clamp (CC) mode. Current injection
is performed by means of a current source connected to the current injecting microelectrode.
Important
: In current clamp, the current stimulus is applied to the BA-03X. In DUAL mode,
STIMULUS INPUT scalings are adapted for oocytes. STIMULUS INPUT (#
23
) is scaled to 0.1 µA/V
and STIMULUS INPUT (#
24
) is scaled to 1 µA/V.
Set the amplifier to CC mode using the MODE OF OPERATION switch (#
1
).
If not already done tune the BIAS current to 0 (see chapter 5.1).
Set the CURRENT OUTPUT SENSITIVITY (#
5
) to 1.
Compensate the offsets of the current- and voltage electrode (see chapter 5.2).
Set R
m
at the cell model to 10k (see chapter 4.3).
Set the holding current to –1 µA using the HOLD potentiometer (#
6
) (setting: 100, reading:
-1.00 µA) and the HOLD current polarity switch (#
7
) (set to -).
Make sure that the display selector switch (#
10
) is set to I
CEL
and the ELECTRODE
RESISTANCE test is not active.
The POTENTIAL display (BA-03X) should read –10 mV (according to Ohm's law). The
voltage at P
EL
(#
36
) should be –100 mV.
Remember
: The voltage at P
EL
is the membrane potential multiplied by 10!
Disable the holding current and apply a test pulse of 2 µA to the cell model by giving a voltage
step of 2 V to STIMULUS INPUT (#
23
). The length of the test pulse should be at least 50 ms.
You should see a potential step of 200 mV amplitude at POTENTIAL OUTPUT (#
36
). Due to
the membrane capacity the step is smoothed.
Note
: If you expect the POTENTIAL display to show the value of the potential step (in this case 20
mV amplitude) remember that the display is rather sluggish and may not display the right value
(depending on the length of the step). The same is true for the CURRENT display.
Voltage Clamp
In voltage clamp mode, the membrane potential is forced by a controller to maintain a certain value or
to follow an external command. That allows measurement of ion fluxes across the cell membrane. This
is the most complex mode of operation with the TEC-B-01. Special precautions must be taken while
tuning the control circuit in order avoid stability problems.
Make sure that the amplifier works correctly with the cell model in CC mode (see above).
Set the holding potential to –50 mV using the HOLD potentiometer (#
6
, setting: 050, reading:
050 mV) and the HOLD potential polarity switch (#
7
, set to -).
Set the CAPACITY COMPENSATION (#
13
) to 0 and the GAIN (#
2
) to 1.
