HEKA EPC 9 - Step 3: Whole-Cell Voltage-Clamp Recording

Testing the EPC9 EPC9 Manual 24
C-fast – using the model circuit it is not very critical to misadjust -fast. Continue
adjusting C-fast and -fast unless you see an almost flat line in the oscilloscope (red
line). This should be the case at a around 6 pF (2).
Instead of compensating C-fast ”by hand” you can also press the Auto button (4) in
the CFast section of the amplifier control panel for an automatic compensation of C-
fast and -fast. If the compensation fails, the E-field (5) in the Auto button becomes
black. If this happens, you should repeat the auto-compensation, until it succeeds
and the E-field becomes normal again. The steps listed above can be automatically
executed by clicking on the ON-CELL button or pressing the ‘2’ key on the numerical
keypad. This will execute the following predefined macro that increases the gain and
then performs twice an auto-compensation – considering a possible failure in the
first attempt.
2 : ON-CELL
E Gain: 14 ; set gain to 50 mV/pA
E AutoCFast: ; automatic C-fast compensation
E AutoCFast: ; repeat compensation
E SoundOn: TRUE ; beep
E SoundOn: FALSE ;
Step 3: ”Whole-Cell” Voltage-Clamp Recording
After compensating C-fast well you can now switch into the “0.5 GOhm” position of
the model circuit. This will simulate a “model cell” with 22 pF ”membrane
capacitance”, 500 MΩ “membrane resistance” and 5.1 MΩ “input resistance” in the
whole-cell configuration. This mode can be used to verify the C-slow controls, the
action of series resistance compensation with C-slow enabled, and the current clamp
mode (see below).
After reducing the gain to 20 mV/pA (1), the Rmem field should reflect the changed
“membrane” resistance and display a value close to 500 MΩ (2). You should see in
the oscilloscope two capacitive transients (blue line) caused by the 22 pF capacitor in
the model circuit. The “slower” time constant of the model cell – compared to the
“fast” time constant from the middle position – is τ = R
s
⋅ C
m
= 5.1 MΩ ⋅ 22pF = 112
µs. The peak current can be calculated from I
max
= C
m
⋅ U / = 22 pF ⋅ 5 mV / 112 µs
= 982 pA. With the actual gain setting of 20 mV/pA this would generate a voltage of
19.6 V at the current-to-voltage converter output, which exceeds the amplifier’s
voltage range. This is signalized by the red Clipping indicator at the amplifier and in
the ”virtual panel” in E9SCREEN (3).
Activate the C-slow compensation by selecting the 100-pF range from the Range field
(4). Now start the compensation by increasing the CSlow (5) and the RSeries (6)