Testing the EPC9 EPC9 Manual 26
3 : WHOLE-CELL
E Invert: TRUE ;
E Gain: 12 ; set gain to 20 mV/pA
E CSlow: 30.00pF ; set C-Slow value to 30 pF
E RSeries: 10.0MO ; set R-Series value to 10 MOhm
E AutoCSlow: ; automatic C-slow compensation
E AutoCSlow: ; repeat compensation
E SoundOn: TRUE ; beep
E SoundOn: FALSE ;
Step 4: ”Whole-Cell” Current-Clamp Recording
If C-Slow has been compensated so far, switch into the current-clamp mode by
selecting CC from the Mode popup (1). This should automatically select the voltage
monitor Vmon (2) to become your active channel displayed in the oscilloscope. If this
is not the case, e.g. with older versions of E9SCREEN or PULSE, change the active
channel to Vmon (2). Note, that the unit of the test pulse amplitude changes from
“mV” to “pA” as soon as you switch from voltage into current clamp mode (3).
E9SCREEN and PULSE use two different amplitudes for VC and CC modes,
therefore the test pulse is set to “0 pA” initially. Now you need to inject current into
the circuitry, 100 pA should be a reasonable value (3). The current injection will
charge the “membrane” of the “model cell” at a time constant = R
m
C
m
= 500 MΩ ⋅
22pF = 11 ms to a final value of V
max
= R
m
I = 500 MΩ ⋅ 100 pA = 50 mV. Due to the
slower time constant compared with voltage clamp conditions it takes much longer
to reach V
max
, therefore you should increase the duration of the test pulse to a more
appropriate value of 100 ms (4).
Note: In contrast to voltage clamp conditions, were τ is proportional to the access- or series
resistance (R
s
) of the pipette, in current clamp experiments τ depends on the
membrane resistance (R
m
).
The normal setting of the oscilloscope scales the voltage monitor at 250 mV per
division. You should therefore increase the gain of the oscilloscope to 16 (5) which
scales the display to be 16 mV per division. Please remember that the oscilloscope
gain is different from the amplifier gain and only scales the display, not the
acquisition of data. Using a very high oscilloscope gain together with a low amplifier
gain allows you to determine the digital resolution of the analog-to-digital converter.
The EPC9 has two feedback circuitry for current clamp recordings. The so called
“fast” current clamp mode was introduced with the “C” version of the hardware in
1995 and is also available in the EPC8. The EPC7 and older EPC9 amplifiers (“A” and
“B” version) lack the fast current clamp mode. The board version of your EPC9
amplifier is displayed in the last menu item of the EPC9 menu. If your amplifier
supports the fast current clamp speed it will be activated by default (blue line in the
oscilloscope). To turn this mode off close the oscilloscope (6), click the red button
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