NPI SEC-03M User manual

OPERATING INSTRUCTIONS AND
SYSTEM DESCRIPTION OF THE
SEC-03M
SINGLE ELECTRODE CLAMP
AMPLIFIER MODULE FOR EPMS
SYSTEMS
VERSION 1.8
npi 2014
npi electronic GmbH, Bauhofring 16, D-71732 Tamm, Germany
Phone [phone]; Fax: [phone]
[email protected]; http://www.npielectronic.com

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Table of Contents
About this Manual ................................................................................................................... 4
1.Safety Regulations .............................................................................................................. 5
2.EPMS-07 Modular Plug-In System .................................................................................... 6
2.1.General System Description / Operation..................................................................... 6
2.2.EPMS-07 Housing....................................................................................................... 6
2.3.EPMS-E-07 Housing ................................................................................................... 6
2.4.PWR-03D .................................................................................................................... 6
2.5.System Grounding ....................................................................................................... 7
EPMS-07 ..................................................................................................................... 7
EPMS-E-07.................................................................................................................. 7
2.6.Technical Data............................................................................................................. 7
EPMS-07 ..................................................................................................................... 7
EPMS-E-07.................................................................................................................. 7
3.Introduction......................................................................................................................... 8
3.1.Why a Single Electrode Clamp?.................................................................................. 8
3.2.Principle of Operation ................................................................................................. 10
Major Advantages of the npi SEC System .................................................................. 12
3.3.Advantages of the Modular SEC-03M System ........................................................... 12
4.SEC-03M System ............................................................................................................... 13
4.1.SEC-03M Components................................................................................................ 13
4.2.Description of the Front Panel..................................................................................... 14
5.Headstages .......................................................................................................................... 19
5.1.Standard and low-noise (SEC-HSP) headstages ......................................................... 19
5.2.Low-noise headstage (SEC-HSP)................................................................................ 21
6.Setting up the SEC-03M System ........................................................................................ 22
7.Passive Cell Model ............................................................................................................. 23
7.1.Cell Model Description ............................................................................................... 23
7.2.Connections and Operation ......................................................................................... 24
7.3.Connections and Operation ......................................................................................... 25
8.Test and Tuning Procedures ............................................................................................... 27
8.1.Headstage Bias Current Adjustment............................................................................ 27
8.2.Electrode Selection...................................................................................................... 28
8.3.Offset Compensation ................................................................................................... 28
8.4.Bridge Balance (in BR mode) ..................................................................................... 29
8.5.Switching Frequency and Capacitance Compensation (in switched modes) .............. 31
Criteria for the selection of the switching frequency .................................................. 31
8.6.Capacity Compensation - Tuning Procedure............................................................... 33
First part: basic setting................................................................................................. 33
Second part: fine tuning............................................................................................... 38
8.7.Testing Operation Modes ............................................................................................ 39
Current Clamp (in BR- or discontinuous CC mode) ................................................... 39
Voltage Clamp............................................................................................................. 39
9.Sample Experiments ........................................................................................................... 41
9.1.Sample Experiment using a Sharp Microelectrode ..................................................... 41
9.2.Sample Experiment using a Suction Electrode............................................................ 44
10.Tuning VC Performance.............................................................................................. 46
General Considerations................................................................................................ 46
Tuning Procedure ........................................................................................................ 47
11.Trouble Shooting ......................................................................................................... 48
12.Appendix ..................................................................................................................... 49

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12.1.Theory of Operation .................................................................................................... 49
12.2.Speed of Response of SEC Single Electrode Clamps ................................................. 50
12.3.Tuning Procedures for VC Controllers........................................................................ 50
Practical Implications .................................................................................................. 51
13.Literature about npi single electrode clamp amplifiers ............................................... 53
13.1.Paper in Journals.......................................................................................................... 53
13.2.Books........................................................................................................................... 64
14.SEC-03M Specifications – Technical Data................................................................. 65
15.Index ............................................................................................................................ 68

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About this Manual
This manual should help to setup and use SEC systems correctly and to perform reliable
experiments.
If you are not familiar with the use of instruments for intracellular recording of electrical
signals please read the manual completely. The experienced user should read at least chapters
1, 4, 8 and 10.
Important: Please read chapter 1 carefully! It contains general information about the safety
regulations and how to handle highly sensitive electronic instruments.
Signs and conventions
In this manual all elements of the front panel are written in capital letters as they appear on
the front panel.
System components that are shipped in the standard configuration are marked with ,
optional components with . In some chapters the user is guided step by step through a
certain procedure. These steps are marked with .
Important information and special precautions are highlighted in gray.
Abbreviations
Cm: cell membrane capacitance
Cstray: electrode stray capacitance
GND: ground
Imax: maximal current
Ra: access resistance
Rm: cell membrane resistance
REL: electrode resistance
SwF: switching frequency
Cm: time constant of the cell membrane
VREL: potential drop at REL

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1. Safety Regulations
VERY IMPORTANT:Instruments and components supplied by npi electronic are NOT
intended for clinical use or medical purposes (e.g. for diagnosis or treatment of humans),
or for any other life-supporting system. npi electronic disclaims any warranties for such
purpose. Equipment supplied by npi electronic must be operated only by selected,
trained and adequately instructed personnel. For details please consult the GENERAL
TERMS OF DELIVERY AND CONDITIONS OF BUSINESS of npi electronic, D-71732
Tamm, Germany.
1) GENERAL: This system is designed for use in scientific laboratories and must be
operated only by trained staff. General safety regulations for operating electrical devices
should be followed.
2) AC MAINS CONNECTION: While working with the npi systems, always adhere to the
appropriate safety measures for handling electronic devices. Before using any device
please read manuals and instructions carefully.
The device is to be operated only at 115/230 Volt 60/50 Hz AC. Please check for
appropriate line voltage before connecting any system to mains.
Always use a three-wire line cord and a mains power-plug with a protection contact
connected to ground (protective earth).
Before opening the cabinet, unplug the instrument.
Unplug the instrument when replacing the fuse or changing line voltage. Replace fuse
only with an appropriate specified type.
3) STATIC ELECTRICITY: Electronic equipment is sensitive to static discharges. Some
devices such as sensor inputs are equipped with very sensitive FET amplifiers, which can
be damaged by electrostatic charge and must therefore be handled with care. Electrostatic
discharge can be avoided by touching a grounded metal surface when changing or
adjusting sensors. Always turn power off when adding or removing modules,
connecting or disconnecting sensors, headstages or other components from the
instrument or 19” cabinet.
4) TEMPERATURE DRIFT / WARM-UP TIME: All analog electronic systems are
sensitive to temperature changes. Therefore, all electronic instruments containing analog
circuits should be used only in a warmed-up condition (i.e. after internal temperature has
reached steady-state values). In most cases a warm-up period of 20-30 minutes is
sufficient.
5) HANDLING: Please protect the device from moisture, heat, radiation and corrosive
chemicals.

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2. EPMS-07 Modular Plug-In System
2.1. General System Description / Operation
The npi EPMS-07 is a modular system for processing of bioelectrical signals in
electrophysiology. The system is housed in a 19” rackmount cabinet (3U) has room for up to
7 plug-in units. The plug-in units are connected to power by a bus at the rear panel.
The plug-in units must be kept in position by four screws (M 2,5 x 10). The screws are
important not only for mechanical stability but also for proper electrical connection to the
system housing. Free area must be protected with covers.
2.2. EPMS-07 Housing
The following items are shipped with the EPMS-07 housing:
EPMS-07 cabinet with built-in power supply
Mains cord
Fuse 2 A / 1 A, slow
Front covers
In order to avoid induction of electromagnetic noise the power supply unit, the power switch
and the fuse are located at the rear of the housing.
2.3. EPMS-E-07 Housing
The following items are shipped with the EPMS-E-07 housing:
EPMS-E-07 cabinet
External Power supply PWR-03D
Power cord (PWR-03D to EPMS-E-07)
Mains chord
Fuse 1.6 A / 0.8 A, slow
Front covers
The EPMS-E-07 housing is designed for low-noise operation, especially for extracellular and
multi channel amplifiers with plugged in filters. It operates with an external power supply to
minimize distortions of the signals caused by the power supply.
2.4. PWR-03D
The external power supply PWR-03D is capable of driving up to 3 EPMS-E housings. Each
housing is connected by a 6-pole cable from the one of the three connectors on the front panel
of the PWR-03D to the rear panel of the respective EPMS-E housing. (see Figure 1, Figure 3).
A POWER LED indicates that the PWR-03D is powered on (see Figure 1). Power switch,
voltage selector and fuse are located at the rear panel (see Figure 2).
Note: The chassis of the PWR-03D is connected to protective earth, and it provides protective
earth to the EPMS-E housing if connected.

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Figure 1: PWR-03D front panel view Figure 2: PWR-03D rear panel view
Note: This power supply is intended to be used with npi EPMS-E systems only.
2.5. System Grounding
EPMS-07
The 19" cabinet is grounded by the power cable through the ground pin of the mains
connector (= protective earth). In order to avoid ground loops the internal ground is isolated
from the protective earth. The internal ground is used on the BNC connectors or GROUND
plugs of the modules that are inserted into the EPMS-07 housing. The internal ground and
mains ground (= protective earth) can be connected by a wire using the ground plugs on the
rear panel of the instrument. It is not possible to predict whether measurements will be less or
more noisy with the internal ground and mains ground connected. We recommend that you try
both arrangements to determine the best configuration.
EPMS-E-07
The 19" cabinet is connected to the CHASSIS connector at the rear panel.
The CHASSIS is linked to protective earth as soon as the PWR-03D is
connected. It can be connected also to the SYSTEM GROUND (SIGNAL
GROUND) on the rear panel of the instrument (see Figure 3).
Important:: Always adhere to the appropriate safety measures.
Figure 3: Rear panel connectors of the EPMS-E-07
2.6. Technical Data
19” rackmount cabinet, for up to 7 plug-in units
Dimensions: 3U high (1U=1 3/4” = 44.45 mm), 254 mm deep
EPMS-07
Power supply: 115/230 V AC, 60/50 Hz, fuse 2 A / 1 A slow, 45-60 W
EPMS-E-07
External power supply (for EPMS-E): 115/230 V AC, 60/50 Hz, fuse 1.6/0.8 A, slow
Dimensions of external power supply: (W x D x H) 225 mm x 210 mm x 85 mm

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3. Introduction
npi electronic’s SEC (Single Electrode Clamp) systems are based on the newest
developments in the field of modern electronics and control theory (see also chapter 11).
These versatile current/voltage clamp amplifiers permit extremely rapid switching between
current injection and current-free recording of true intracellular potentials.
The use of modern high-voltage operational amplifiers and a new, improved method of
capacity compensation makes it possible to inject very short current pulses through high
resistance microelectrodes (up to 200 Mand more) and to record membrane potentials
accurately, i.e. without series resistance error, within the same cycle.
Although the system has been designed primarily to overcome the limitations related to the
use of high resistance microelectrodes in intracellular recordings, it can also be used to do
conventional whole-cell patch clamp recordings with suction electrodes or perforated patch
recordings. The whole-cell configuration allows to investigate even small dissociated or
cultured cells as well as cells in slice preparations in both current and voltage clamp mode,
while the intracellular medium is being controlled by the pipette solution.
3.1. Why a Single Electrode Clamp?
Voltage clamp techniques permit the analysis of ionic currents flowing through biological
membranes at preset membrane potentials. Under ideal conditions the recorded current is
directly related to the conductance changes in the membrane and thus gives an accurate
measure of the activity of ion channels and electrogenic pumps.
The membrane potential is generally kept at a preselected value (command or holding
potential). Ionic currents are then activated by sudden changes in potential (e.g. voltage-gated
ion channels), by transmitter release at synapses (e.g. electrical stimulation of fiber tracts in
brain slices) or by external application of an appropriate agonist. Sudden command potential
changes used to activate voltage-gated currents are especially challenging, because the
membrane will adopt the new potential value only after it’s capacitance (Cmin Figure 4and
Figure 5) has been charged. Therefore, the initial transient current following the voltage step
should be as large as possible to achieve rapid membrane charging. In conventional patch
clamp amplifiers, this requires a minimal resistance between the amplifier and the cell interior
– a simple consequence of Ohm’s law (U = R*I), i.e. for a given voltage difference (U),
the current (I) is inversely proportional to the resistance (R). In this context, R is the access or
series resistance (Rain Figure 4 and Figure 5) between the electrode and the cell interior. The
time constant for charging a cell is = REL*Cm.
Rais largely determined by certain electrode properties (mainly electrode resistance) and the
connection between the electrode and the cell. Typical Ravalues are between 5 to 10 M,
which results in a time constant of 0.5 to 1 ms for a cell with a membrane capacity of 100 pF,
i.e. the membrane needs roughly a millisecond to follow the command voltage step. Sharp
microelectrodes usually have much larger resistances (30 to 150 Mor even more).

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Figure 4: Model circuit for whole cell patch clamp recording using a suction electrode
Cm: membrane capacitance, Cstray: electrode stray capacitance, REL: electrode
resistance, Rm: membrane resistance
Figure 5: Model circuit for intracellular recording using a sharp electrode
Cm: membrane capacitance, Cstray: electrode stray capacitance, REL: electrode
resistance, Rm: membrane resistance

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Besides slowing the voltage response of the cell, Racan also cause additional adverse effects,
such as error in potential measurement. Ra, together with the membrane resistance (Rm) forms
a voltage divider (see Figure 4 and Figure 5). Current flowing from the amplifier to the
grounded bath of a cell preparation will cause a voltage drop at both, Raand Rm. If Ra<< Rm,
the majority of the voltage drop will develop at Rmand thus reflect a true membrane potential.
If, in an extreme case, Ra= Rm, the membrane potential will follow only one half of the
voltage command. In order to achieve a voltage error of less than 1% Ramust be more than
100 times smaller than Rm. This condition is not always easily to accomplish, especially if
recordings a performed from small cells. If sharp intracellular microelectrodes are used, it is
virtually impossible. If Rais not negligible, precise determination of the membrane potential
can be achieved only if no current flows across Raduring potential measurement. This is the
strategy employed in npi electronic’s SEC amplifier systems.
The SEC amplifiers inject current and record the potential in an alternating mode (switched
mode). Therefore, this technique is called discontinuous SEVC. This ensures that no current
passes through Raduring potential measurement and completely eliminates access resistance
artefacts.
After each injection of current, the potential gradient at the electrode tip decays much faster
than the potential added at the cell membrane during the same injection. The membrane
potential is measured after the potential difference across Rahas completely dropped (see
chapter 3.2). The discontinuous current and voltage signal are then smoothed and read at the
CURRENT OUTPUT and POTENTIAL OUTPUT connectors.
3.2. Principle of Operation
Figure 6: Model circuit of SEC systems

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Figure 7: principle of SEVC operation
Figure 6 and Figure 7 illustrate the basic circuitry and operation of npi SEC voltage clamp
amplifiers.
A single microelectrode penetrates the cell or is connected to the cell interior in the whole-cell
configuration of the patch clamp technique. The recorded voltage is buffered by a x1
operational amplifier (A1 in Figure 6). At this point, the potential (V[A1] in Figure 7) is the
sum of the cell’s membrane potential and the voltage gradient which develops when current is
injected at the access resistance. Due to npi’s unique compensation circuitry, the voltage at
the tip of the electrode decays extremely fast after each injection of current and therefore
allows for a correct measurement of Vmafter a few microseconds. At the end of the current-
free interval, when the electrode potential has dropped to zero, the sample-and-hold circuit
(SH1 in Figure 6) samples Vmand holds the value for the remainder of the cycle (VSH1 in
Figure 7).
The differential amplifier (A2 in Figure 6) compares the sampled potential with the command
potential (Vcom in Figure 6). The output of this amplifier becomes the input of a controlled
current source (CCS in Figure 6), if the switch S1 (Figure 6) is in the current-passing position.
The gain of this current source increases as much as 100 µA/V due to a PI (proportional-
integral) controller and improved electrode capacity compensation. In Figure 6 S1 is shown in
the current-passing position, when a square current is applied to the electrode. When the
current passes the electrode a steep voltage gradient develops at the electrode resistance. Vcell
(Figure 7) is only slightly changed due to the slow charging of the membrane capacitance.
The amplitude of injected current is sampled in the sample-and-hold amplifier SH2 (Figure
6), multiplied by the fractional time of current injection within each duty cycle (1/8 to 1/2 in
SEC-05 and SEC-10, 1/4 in SEC-03 systems) and read out as current output (ISH2 in Figure 7).
S1 then switches to the voltage-recording position (input to CCS is zero). The potential at A1
decays rapidly due to the fast relaxation at the (compensated) electrode capacity. Exact
capacity compensation is essential to yield an optimally flat voltage trace at the end of the

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current free interval when Vcell is measured (see also Figure 17). The cellular membrane
potential, however, will drop much slower due to the large (uncompensated) membrane
capacitance. The interval between two current injections must be long enough to allow for
complete (1%) settling of the electrode potential, but short enough to minimize loss of
charges at the cell membrane level, i.e. minimal relaxation of Vcell. At the end of the current-
free period a new Vmsample is taken and a new cycle begins.
Thus, both current and potential output are based on discontinuous signals that are stored
during each cycle in the sample-and-hold amplifiers SH1 and SH2. The signals will be
optimal smooth at maximal switching frequencies.
Major Advantages of the npi SEC System
npi electronic’s SEC amplifiers are the only systems that use a PI controller to avoid artificial
recordings known to occur in other single electrode clamp systems (“clamping of the
electrode”). The PI controller design increases gain to as much as 100 µA/V in frequencies
less than one-fourth the switching frequency. The result is very sensitive control of the
membrane potential with a steady-state error of less than 1% and a fast response of the clamp
to command steps or conductance changes.
The use of discontinuous current and voltage clamp in combination with high switching
frequencies yields five major advantages:
1. The large recording bandwidth allows recordings of even fast signals accurately.
2. High clamp gains (up to 100 µA/V) can be used in voltage clamp mode.
3. Very small cells with relatively short membrane time constants can be voltage-
clamped.
4. Series resistance effect are completely eliminated for a correct membrane potential
control even with high resistance microelectrodes.
5. The true membrane potential is recorded also in the voltage clamp mode (whereas
continuous feedback VC amplifiers only reflect the command potential).
3.3. Advantages of the Modular SEC-03M System
The SEC-03M system is based on the well proven npi SEC technology and designed as a
module for the EPMS-07 system. Several combinations with other modules are possible.
Because this amplifier is small and handy, it is possible to combine up to three synchronized
SEC-03M in one 19” EPMS-07 housing, e.g. for recording from coupled cells simultaneously.
For recording from one cell only, it is recommended to add one or two filters to the SEC-03M
module. Such a recording system can further be enhanced by adding a stimulus isolator, a
iontophoretic amplifier or a controller for pressure ejection.
When using CellWorks the combination with the modular breakout box INT-20M facilitates
building-up a setup. All signals from or to amplifiers or filters in an EPMS housing can be
linked to each other, and directly to the breakout box making additional BNC cabling
unnecessary.
Two additional modules (HVC-03M and PEN-03) can supplement an SEC-03M amplifier in
order to allow one and two electrode voltage clamp experiments with enhanced cell
penetration facilities.
Please ask npi for an optimal configuration according to your needs.

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4. SEC-03M System
4.1. SEC-03M Components
The following items are shipped with the SEC-03M system:
Amplifier module for the EPMS-07 system
Headstage
GND- and DRIVEN SHIELD (2.6 mm banana plug) connectors
Please open the box and inspect contents upon receipt. If any components appear damaged or
missing, please contact npi electronic or your local distributor immediately
([email protected]).
Optional accessories:
Electrode holder set with one holder for sharp microelectrodes (without port), one suction
(patch) electrode holder (with one port) and an electrode holder adapter (SEC-EH-SET)
Active cell model (SEC-MODA)
Passive cell model (SEC-MOD, see chapter 7)
Low noise / low bias current headstage (SEC-HSP) with a reduced current range (:10
headstage, i.e. maximal current is ±12 nA)
Headstage with differential input (SEC-HSD)
Headstage for extracellular measurements (SEC-EXT)
Filter for the EPMS system
Data acquisition module
Stimulus isolator module
Iontophoresis module
Pressure ejection module
CellWorks hard- and software

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4.2. Description of the Front Panel
Figure 8: SEC-03M front panel view
In the following description of the front panel elements each element has a number that is
related to that in Figure 8. The number is followed by the name (in uppercase letters) written
on the front panel and the type of the element (in lowercase letters). Then, a short description
of the element is given. Each control element has a label and frequently a calibration (e.g.
CURRENT OUTPUT, 10nA/V).

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(1) MODE OF OPERATION switch
VC: Voltage Clamp
OFF: voltage- and current clamp OFF. In this position the amplifier does not
apply any voltage or current to the cell. The potential at the electrode tip
is measured and displayed. The BUZZ function is active.
CC: Current Clamp
BR: Bridge Mode
EXT.: EXTernal control; if this position is selected, the mode of operation (VC,
CC) can be set by a TTL pulse applied to the MODE SELECT BNC (19); TTL
high = VC; TTL low = CC.
(2) POTENTIAL / RESISTANCE display
LC-Display for the POTENTIAL at the electrode tip in mV or the
electrode RESISTANCE in M.
(3) MODE OF OPERATION LEDs (VC, OFF, CC, BR, EXT, DUAL)
LEDs indicating the active mode of operation (see also #1).
If operated together with the HVC-03M module the DUAL
LED indicates that the SEC-03M works in two electrode
voltage clamp mode.
(4) M/ mV LEDs
LEDs indicating that RESISTANCE (M) or POTENTIAL (mV) is revealed in
DISPLAY (#2).
(5) CURRENT display
LC-Display for the CURRENT passed through the CURRENT electrode
in nA (X.XX nA).
(6) BR.BAL. potentiometer
If current is passed through the recording electrode the potential deflection
caused at the electrode resistance is compensated with this control (ten turn
potentiometer, clockwise, calibrated in M, range: 0-1000 M).
(7) OFFSET potentiometer
Control to set the output of the electrode preamplifier to zero (ten-turn
potentiometer, symmetrical, i.e. 0 mV = 5 on the dial), range: 200 mV.
Note: Position 5 on the OFFSET control corresponds to 0 mV offset.
(8) BIAS (bias current) potentiometer

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With this trim potentiometer the output current of the headstage (headstage BIAS
current) can be tuned to zero
(9) HOLD.CUR.(nA) potentiometer and polarity switch
10-turn digital control that presets a continuous command signal for CC
mode (HOLD current). Polarity is set by switch to the left of the control (0
is off-position).
(10) SW.FREQ. (kHz) potentiometer
Potentiometer for setting the switching frequency in VC or CC mode; range 2 kHz
to 40 kHz.
(11) SYNC. / INTERN switch
Switch for setting the synchronization mode of the switching frequency.
SYNC.: Switching frequency is synchronized with the “Master” amplifier for double cell
recordings. SW.FREQ. potentiometer (#10) is disabled and the switching frequency
is set by the “Master” amplifier.
INTERN: Switching frequency is set by SW.FREQ. potentiometer (#10) for single cell
recordings.
(12) CUR.STIM. INPUT 1 nA/V connector
Analog input BNC connector for application of signals from an external stimulus
source. The voltage signal that is connected here is transformed to a proportional
current at the electrode with a sensitivity of 1 nA/V, i.e. an input voltage of 5 V is
transformed to an output current of 5 nA. The signal form remains unchanged. The
amplitude of the output current signal (current stimulus) is determined by the
amplitude of the CUR.STIM. INPUT. Two examples are given in Figure 9. In Athe
amplitude of the CUR.STIM. INPUT is 1 V that gives a current stimulus of 1 nA, in Bthe
CUR.STIM. INPUT amplitude is 2 V that is transformed into a current stimulus of 2 nA.

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CURRENT STIMULUS INPUT current stimulus
Figure 9: Input-output relation using CUR.STIM. INPUT
Important: The current injected through the electrode is always the sum of the input signal at
CUR.STIM. INPUT (12) and the holding current set by HOLD.CUR. (9) and polarity switch.
(13) CURRENT OUTPUT 10 nA/V connector
BNC connector providing the CURRENT OUTPUT signal; scaling 10 nA / V, i.e. 1V
corresponds to 10 nA.
(14) SWITCH. FREQUENCY (SYNC.OUT) connector
BNC connector providing the switching frequency for synchronization of an
oscilloscope (triggering) for tuning the capacity compensation.
(15) HEADSTAGE connector
The HEADSTAGE cable is connected to the unit at this 12-pin connector in the
center of the module.
(16) ELECT. POTENTIAL connector
BNC connector providing the switched signal directly from the electrode. This signal
is used for tuning the capacity compensation (see also SEC-05 manual).

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(17) POTENTIAL OUTPUT x10 mV connector
BNC connector monitoring the recorded membrane potential with a gain of ten.
(18) VC COMM. INPUT /10 mV connector
BNC connector for an external COMMAND in VC mode (sensitivity: /10, i.e. 0.1 V
/ V).
The voltage signal that is connected here is transformed to a proportional
COMMAND voltage in VC mode. The signal form remains unchanged. Two
examples are given in Figure 9. The amplitude of the output voltage signal (voltage
stimulus) is determined by the amplitude of the input voltage signal.
input voltage signal command voltage signal
Figure 10: input-output relation using VC COMM. INPUT in VC mode
(19) MODE SELECT connector
BNC connector for remote control of the MODE of operation. A TTL signal is
connected here to select the mode of operation remotely (HI = VC, LO = CC).
(20) INTEGR. (ms) potentiometer
Potentiometer for setting the INTEGRATOR time constant in VC mode; range: 0
to 10 ms.
(21) HOLD. POT. (mV) potentiometer
10-turn digital control that presets a continuous command signal (HOLD
potential) for VC. Polarity is set by switch to the right of the control (0 is
off-position).

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(22) REL push button
Push button for activating the resistance measurement of the microelectrode. When
pushed the microelectrode resistance is measured and shown in POTENTIAL /
RESISTANCE display (#2).
Important: An accurate measurement of REL requires that the input capacity is well
compensated (see also #24 and chapter 8.6)
(23) GAIN potentiometer
10-turn potentiometer to set amplification factor (GAIN) of the VC error signal.
To keep the VC error as small as possible it is necessary to use high GAIN
settings, but the system becomes unstable and begins to oscillate if the GAIN is
set too high. Thus, the care should be taken when setting this control. Using the
INTEGRATOR (#20) provides a virtually infinite GAIN for slow signal, e.g.
holding potential.
(24) C. COMP. potentiometer
Control for the capacity compensation of the microelectrode (ten turn
potentiometer, clockwise).
Caution: This circuit is based on a positive feedback circuit. Overcompensation leads to
oscillations that may damage the cell.
5. Headstages
5.1. Standard and low-noise (SEC-HSP) headstages
The SEC-03M comes with the standard headstage (range: 120 nA) for connecting glass
electrodes with high resistances or suction electrodes for whole cell patch clamp recordings
with lower resistances via an electrode holder.
A low noise current headstage for measurement of small currents, a headstage with
differential input and a headstage for extracellular measurements is also available (see
chapter 5.2)
The electrode filled with electrolyte is inserted into an electrode holder (optional, see Figure
11) that fits into the electrode holder adapter (optional, see also Optional accessories in
chapter 4.1). The electrical connection between the electrolyte and the headstage is
established using a carefully chlorinated silver wire. Chlorinating of the silver wire is very
important since contact of silver to the electrolyte leads to electrochemical potentials causing
varying offset potentials at the electrode, deterioration of the voltage measurement etc. (for
details see Kettenmann and Grantyn (1992)). For optimal chlorinating of sliver wires an
automated chlorinating apparatus (ACL-01) is available (contact npi for details).
GROUND provides system ground and is linked to the bath via an agar-bridge or a Ag-AgCl
pellet. The headstage is attached to the amplifier with the headstage cable (see #1, Figure 11)
and a 12-pole connector. The headstage is mounted to a holding bar that fits to most
micromanipulators.

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Note: The shield of the SMC connector is linked to the driven shield output and must not be
connected to ground. The headstage enclosure is grounded.
Caution: Please always adhere to the appropriate safety precautions (see chapter 0). Please
turn power off when connecting or disconnecting the headstage from the HEADSTAGE
connector!
Figure 11: standard headstage, electrode holder (optional) and electrode holder adapter
(optional) of the SEC-03M
The standard headstage consists of the following elements (see Figure 11):
1Headstage cable to amplifier
2Coarse capacity compensation potentiometer
3Holding bar
4GROUND: Ground connector
5 ELECTRODE: SMB connector for microelectrode
6DRIVEN SHIELD connector