Intan Technologies CLAMP User Manual page 8

Intan CLAMP System
coming from ANALOG IN channels will be applied to all
enabled headstages (see External Command Tab below).
Capacitance Compensation: This control enables and
adjusts the fast transient capacitance compensation circuit
in each headstage which is used to cancel pipette
capacitance. Capacitance compensation is typically
performed when the electrode is in the bath but prior to cell
contact. It may be refined after a gigaseal has been
obtained. See the Capacitance Compensation section
below for more details.
Status: This indicator shows the current clamp status of the
selected headstage.
Voltage Clamp Controls
Clicking on the Voltage Clamp tab displays the following
voltage clamp controls:
Pipette Offset: When a pipette electrode is placed in an
electrolytic solution, a small DC potential is generated by the
interface of dissimilar materials. This control allows the user
to adjust the pipette offset to null out this built-in potential.
Pipette offset should be nulled after the electrode is placed
in solution but prior to contact with a cell. If the Auto button
is clicked, the pipette offset will be adjusted to minimize
measured current. The lock can be clicked to prevent this
value from being changed accidentally.
The pipette offset may be adjusted manually by clicking on
the blue voltage indicator and turning the mouse scroll
wheel, moving the cursor keys up or down, or typing a
number.
Holding Voltage: This control sets a baseline clamp voltage
that is superimposed on all other voltage clamp commands.
After breaking into a cell, this is typically set close to -70 mV
to match the intracellular potential and prevent large
currents from flowing into or out of the cell.
Voltage Clamp Command: These buttons allow the user to
select between different types of voltage clamp waveforms.
Holding Only can be used to monitor spontaneous activity
in a cell. Seal Test produces a repeating voltage step, and
is typically used to monitor the pipette resistance as a
gigaseal is being formed or to estimate cell parameters (see
below). Resistance is similar to Seal Test, but adds a
running plot of resistance vs. time so that resistance trends
may be monitored visually. Multi-Step generates multiple
voltage clamp steps and superimposes the plots. Arbitrary
generates a waveform specified by a user file (see Arbitrary
Waveform Specification below for details).
Current Measurement Range: This control allows the user
to select the range of the current that is sensed by the
headstage: ±5 nA, ±10 nA, ±100 nA, or ±1000 nA. Using
the smallest acceptable range minimizes the noise floor.
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Cell Parameters: If this box is checked, the passive cell
parameters R (series resistance), R
S
resistance), and C (membrane capacitance) will be
M
estimated by fitting an exponential curve to the measured
voltage clamp data (see Estimating Membrane Parameters
below for details). Unchecking this box will "freeze" these
values.
Zap: This button must be enabled by clicking the lock icon.
Clicking the Zap button produces a brief, high voltage pulse
(typically 1 V) that can be used to break into a cell once a
gigaseal has been established (although most researchers
use pressure pulses to break the membrane).
parameters of the zap pulse can be adjusted by clicking on
the blue numerical display.
Plot total Vclamp: Checking this box adds a second plot on
the Clamp Voltage graph in the lower half of the Data Display
Window. The primary plot shows the voltage clamp
waveform generated by the Voltage Clamp Command
controls above. The second plot shows the total voltage
clamp waveform applied by the headstage, which is a linear
superposition of the software-defined voltage clamp
command, the pipette offset, and any external command
delivered to an ANALOG IN port, if this option is enabled
(see External Command Tab below).
Plot Vcell: Checking this box adds a plot to the Clamp
Voltage graph in the lower half of the Data Display Window
that shows the cell voltage V
clamp voltage minus the voltage drop across the series
resistance. This voltage drop is the series resistance (R
multiplied by the instantaneous measured electrode current.
The Intan CLAMP System does not allow for series
resistance compensation in voltage clamp mode, but
observing V can allow users to manually compensate for
cell
some aspects of the voltage drop across the series
resistance and perhaps adjust the voltage clamp waveforms
to yield the desired voltage at the cell.
Current Clamp Controls
Clicking on the Current Clamp tab displays the following
current clamp controls:
Pipette Offset: See "Voltage Clamp Controls" for a
description of this control.
Holding Current: This control sets a baseline clamp current
that is superimposed on all other current clamp commands.
This can be used to bias the cell to a desired intracellular
potential or suppress spontaneous activity.
Current button may be clicked to set the holding current to
zero quickly.
Current Clamp Command: These buttons allow the user to
select between different types of current clamp waveforms.
Holding Only can be used to monitor spontaneous activity
in a cell. Tuning produces a repeating current step, and can
(membrane
M
The
, which is defined as the
cell
)
S
The Zero
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