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INSTRUMENT OPERATION
Axopatch 200B, Copyright 1997-1999, Axon Instruments, Inc.
dither. This will effectively increase the measured membrane capacitance by 0.1 % of the
full-scale range (thus, by 0.1 pF for β = 1 or 1 pF for β = 0.1) by transiently reducing the
setting of the Whole-Cell Cap. knob by that amount. With appropriate software, these
controlled changes in capacitance values may be used in the measurement of cell
membrane capacitance changes during an experiment (for example, see Joshi and
Fernandez, Biophysical Journal (1988) 53: 885-892).
In order to use the Phase-Tracking method of capacitance measurements (for example, see
Fidler and Fernandez, Biophysical Journal (1989) 56: 1153-1162), one needs in addition to
use the DR-1 series resistance dither unit. The series resistance dither provides a short-
circuit link between the preparation and ground that increases to 500 kΩ resistor while a
TTL signal is high.
Command Potentials
Command potentials can be obtained from two internal sources, HOLDING COMMAND
and SEAL TEST, and from external sources via two rear panel BNCs.
Holding Command
In voltage clamp this control allows the user to apply a membrane holding potential of
±200 mV (with the toggle set to x1; the full range of ± 1V is available when the toggle is
set to x5). In current clamp the control allows application of a holding current of ±2 nA
with β = 1 (toggle set to x1) or ±20 nA with β = 0.1 (toggle set to x1). In current clamp,
with the toggle set to x5, the control allows application of a holding current of ±10 nA with
β = 1 or ±100 nA with β = 0.1. Turn the control fully counterclockwise for a zero
command. Use the three position toggle switch to set the polarity or to switch off. This
control is automatically switched OFF when either TRACK or I
=
0 mode is chosen.
HOLDING COMMAND RANGES
MODE Toggle x1 Toggle x5
β = 0.1 β = 1 β = 0.1 β = 1
V
CLAMP
± 200 mV ± 200 mV ± 1 V ± 1 V
I
CLAMP
± 20 nA ± 2 nA ± 100 nA ± 10 nA
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