- whole cell
- single channel
- bilayers
- high speed current clamping
Powerful, Latest Technology, Loaded With Features
Compare the Dagan 3900A to an old technology resistive patch clamp with a new add-on computer interface that doesn't let you really control your instrument, or a stripped down, bare bones integrating technology clamp missing the features and functions you need.
The Dagan 3900A is a state of the art, powerful, latest technology instrument that is constantly being improved. We started this technology, we perfected it, and we know it. We are leading the way to new breakthroughs using this technology.
- New improved noise specifications when using capacitance compensation (i.e.,virtually no increase in noise), 0.2 pA-RMS 10 KHz bandwidth with Cp off.
- Fast current clamp. All other resistive or integrating patch clamps are about 4 to 30 times slower. The rise time of the current step for a 500Megohm/33pF with a 2 Megohm electrode whole cell model is 4µs (3902 headstage). Compare this to another integrating patch clamp that is as slow as 140µs (about 1.1 KHz bandwidth).
- Automatic polarity control is available with the flick of a switch. We give you a choice.
- Four values of seal test voltages; others only have one.
- Independent Holding Current dial for current clamp (unique to the 3900A).
- Audio monitor (especially useful for bilayers).
- Output zeroing.
- All modes, modifiers of operation, and GAIN are computer controllable.
- Twelve position 80db/decade Bessel filter.
- Automatic holding or search (i.e., track) Junction Potential.
- Rupture (Zap) generator to aid in cell impalement.
THE ULTIMATE PATCH CLAMP
Ideal capacitors, but not ideal resistors, are free of thermal noise. Technical capacitors approach their ideal more closely than resistors. Hence a capacitive transducer generates less instrumentation noise than a resistive transducer. Although the headstage of the 3900A uses a repairable design, it achieves better noise performance than all resistive headstages to date (0.20pA RMS from 0-10 KHz and <0.03pA RMS from 0-1 KHz; four pole bessel low pass). The capacitive transducer is superior also in its linearity and long term stability.
The gain of a resistive transducer is dictated by its intrinsic noise, which decreases with increasing resistance; with a 50 Gigohm resistor, the gain is 50 mV/pA. The capacitive transducer of the 3900A achieves its noise specifications at a significantly smaller gain (1 mV/pA), which makes possible significant improvements of bandwidth. Although the 3900 is designed conservatively, its bandwidth is 100 KHz. The frequency response below this limit is exquisitely flat.
A low transducer gain makes possible a wide dynamic range The 3900A can record currents up to 10 nA while operating at its minimal noise level. Present 50 Gigohm resistive headstages accept only 200 pA, yet produce more instrumentation noise. This however, is only one aspect of the 3900A's superior dynamic capabilities. The 10 nA limit applies to the range of the recorded current signal, whereas the amplitude of acceptable pipette currents is in principle unlimited: the headstage of the 3900A is not saturated by any current transient whose total charge is within 10 pC (e.g., a 100 mV voltage transition across a 100 pF membrane capacitance). Even very large membranes, such as artificial lipid bilayers, can be charged rapidly by using a built in electronic switch to temporarily shunt the headstage capacitor.
The 3900A's capability to accept large current transients makes obsolete the conventional feed-forward compensation of membrane capacitive currents. This eliminates several controls from the instrument. The compensation for series resistance also becomes simpler, as there is no interaction with a forward correction of capacity current. The high bandwidth of the 3900A is the basis for an effective series resistance compensation.
A capacitive transducer as used in the 3900A accumulates the net charge carried by the recorded current; to prevent eventual saturation of the active circuitry, there have to be means to discharge the capacitor. The 3900A provides two alternatives.
The second technique, (Mixed RC mode) of discharging permits recording to be continuous: an
electronic switch connects a 1 Gigohm resistor in parallel to the capacitor, so direct currents of up to 10 nA can be accepted without danger of saturation. The latter method increases the noise of the instrument by that of the 1 Gigohm resistor, but maintains the bandwidth and transient capability of the 3900A.
The first method, (Integrating mode) is used where the best noise performance is required (single-channel recording). With small currents, the discharging interruptions will be infrequent (e.g., every 2 seconds while recording an average net current of 5 pA). The second method, (Mixed RC mode), is typically used for whole-cell clamping (with the shunting switch used in addition when large voltage steps are applied to large membranes).
Unlike other commercially available patch clamps, the 3900A maintains the pipette at virtual ground while varying the potential of the bath. This principle reduces the complexity of the instrument's circuitry, eliminates the need for driven shields (they can simply be grounded), and makes possible a much more efficient current clamp with fantastic speed.
The fact that the 3900A varies the potential in the bath rather than in the pipette is no obstacle for operating other instruments on the same or other cells in the bath, provided that these instruments do not also manipulate the bath potential. Such instruments will adapt to the varying bath potential either by using their bath reference input or a differential amplifier provided in the 3900A. Thusm you can use the 3900A to record from an on-cell patch while you voltage clamp the cell through a conventional two microelectrode voltage clamp.
Finally, the 3900A has a thorough computer interface. The gain, mode, and command parameters can be selected remotely, and analog outputs are provided for telegraphing gain and filter settings. The 3900A has a convenient one-switch control for the polarities of all signals that need to be inverted upon changing between the inside-out and outside-out orientations of the preparations. The polarity command and recorded signals can be switched to conform to your present computer programs.
The Integrating patch/whole cell clamp as implemented in the 3900A has been developed by Dr. Wolfgang Nonner, Department of Physiology and Biophysics, University of Miami, and has been extensively used in his laboratory since 1986.
- 3900A with blank panel in Expander section. Recommended for single channel, bilayer applications (where you supply triangle wave generator and step command), and whole cell applications where Cm transient removal and speed up is not needed. You may specify either the 10 nA 3901 or the 100 nA 3902 headstage.
- 3900A with 3910 Bilayer Expander. Recommended for state of the art bilayer experiments with every feature you may need. We recommend the 3901 headstage or the dedicated 3903 Bilayer headstage.
- 3900A with 3911 Whole Cell Expander. This includes Supercharging, Hypercharging for speeding up whole cell charging, Cm for passive current transient nulling, and Prefilter for control of percent compensation. Recommended for applications where total control over membrane capacitance charging currents is needed. Note that 3911's are not field upgradable. Also, the 3902 100 nA headstage is normally supplied in thisconfiguration.
The optional expander section allows room to grow. The Dagan 3900A is not easily outdated when new features and functions are needed.
- Optional supercharging and Hypercharge (automatic supercharging with blanking of current record).
- Optional Prefilter control allows highest percentage of series resistance compensation of any whole cell patch clamp.
- Optional triangle wave generator and digital capacitance meter for bilayers.
- Optional step command generator for bilayers.
- Optional whole cell capacitive transient nulling with readout of membrane capacitance.
The 3900A can be configured for special applications with a family of plug in panels each designed for more specific experiments. The 3910 EXPANDER is uniquely suited for Bilayer applications.
The Whole Cell and Bilayer capacitance to 2000 pf can instantly be displayed on the 3 1/2 digit meter. The meter also serves as an RMS noise monitor.
Cell membrane charging currents, whole cell and bilayers, can be "short circuited" to ground (Quickcharged) to reduce the amount of charging time.
The step command generator uses a pushwheel switch to digitally set an analog to digital converter to precise 100 microvolt increments for creating manual step commands up to 199.9 mV. The command can be continuous, or gated by an internal oscillator or an external signal.
- Offers vastly improved capabilities for compensating whole cell
- Features two techniques for whole cell compensation; Cm Nulling and HYPERcharge
- Eliminates current transients that result when voltage steps are applied
- HYPERcharge feature automatically fast-charges cell
Dagan's 3911A Whole Cell Expander permits you to exploit the unique features of the 3900 Integrating Patch Clamp for experiments on whole cells.
An effective whole cell clamp achieves two major tasks:
- rapid charging of the cell membrane capacitor following a command voltage step, and;
- accurate stabilization of the membran potential during ionic currents
Hypercharging Feature:
The 3911A responds to a step of command voltage that exceeds a 5mV trigger threshold by enabling Hypercharging for a time that is preset by a panel control. During this time, the feedback element in the headstage is shunted by a FET switch, so its capability to pass capacitive currents becomes virtually unlimited. A hypercharging voltage pulse is added to the command to drive a large charging current through the series resistance. During the Hypercharging, the current monitor output is blanked, so no capacity transient enters the recording system.
Hypercharging is highly effective since it achieves the equivalent of compensating 90% or more of the series resistance.
In previous whole cell clamps subtraction of the membrane capacitance (Cm) current was necessary to prevent saturation of the headstage amplifier. The Hypercharging technique of the 3911A does not require such subtraction. The 3911A, however, provides Cm compensation for other purposes:
- measurement of Cm and Rs,
- subtraction of current noise resulting from noise inherent to an external command source, and
- elimination of resting cell capacitance from measurements of cell capacitance changes (like those associated with exocytosis).The subtracted Cm transient is adjusted by controls for RsM (i.e., measured Rs) and Cm (ranges 0.5-20Mohm and 2-100pF).
Additional Features:
A 3 1/2 digit meter instantly displays an RMS noise meter.
Series Resistance (Rs) Compensation (using PREFILTER)
The 3911A uses a different and safer approach to eliminate oscillations during Rs compensation.
The Rs compensation is controlled by two panel potentiometers, one setting the Rs value, located on the modifier section, the other the time constant, (called PREFILTER) located on the 3911A. The adjustment is simple; one first sets the Rs control to full value of the estimated series resistance, and the time constant (PREFILTER) control to a large and safe value. Then one enables the Rs compensation by a switch, and reduces the time constant to a minimal safe value while observing the transient associated with a small command pulse. Usually, there is a well defined optimal setting of both controls, indicated by the absence of a slow transient and a concomitant minimum in the ringing. This setting corresponds to the full compensation of Rs up to a limiting bandwidth.
Note: Requires current A version Model 3900A main frame. Please contact factory for update on older 3900's to accept the new 3911A Whole Cell Expander.
HEADSTAGE AND ELECTRODE HOLDERS
The 3900A headstage uses a unique repairable design for the critical Integrator stage. A special teflon input connector reduces the input capacitance. The electrode holder is machined from special material to achieve lowest noise levels. Standard "BNC" size electrode holders are used.
The 3901 headstage uses an internal 1000 Megohm resistor to discharge the capacitor resulting in a continuous DC current range of 10 nA(transient currents can be passed if the average DC value is 10 nA or less). The 3902 headstage uses a 100 Megohm resistor and has a range of 100 nA DC.
MAIN MODES
Standby Shorts the headstage input to ground for setup.
V-Clamp (Voltage Clamp) mode is used to clamp the pipette potential during patch clamping.
Io-Clamp (Zero current clamp) sets the pipette current to zero to allow step command changes to be made before current clamping.
I-Clamp (Current clamp) mode is used to clamp pipette current during whole cell recording. The series resistance functions as a bridge balance and the Cp compensation is also operative.
JUNCTION POTENTIAL CORRECTION
Junction or electrode offset potentials may be corrected either manually or automatically. In the "Hold mode" a digital sample and hold circuit is updated and maintains the correct voltage indefinitely. In search mode the updating is continuous and thus slow junction potential changes are automatically tracked.
COMMANDS
The Seal Test generator supplies a square wave command voltage useful in monitoring pipette seal formation and as a simple command generator. Indicator light shows that seal test is in use. Independent Holding Potential (V clamp) and Holding Current (I Clamp) ten turn dials eliminate having to readjust one control/
Six external command sensitivities cover the range of all standard levels in use. The polarity switch is easily set to match stimulator polarity.
Cell membranes may either be ruptured by the Rupture generator (1 ms to 100 ms pulse) or by suction through the port on the electrode holder.
Pushwheel set step commands are also available from the optional 3910 Expander plug-in module.
METER
The attractive green backlighted 3 1/2 digit low noise liquid crystal display shows either the current (Im) or voltage (Vm) outputs, the Bath command voltage (Vcmd), the Zeroed Im or Vm output, or a test for cleanliness of the headstage (HStest) Integrator teflon connector.
A voltage controlled oscillator can be set to accurately monitor current (Im) or voltage (Vm) signals through either the internal loud speaker or through earphones. Useful for monitoring seal formation and bilayer setup.
MODIFIER MODES
INTEGRATING mode provides the lowest noise, but either Automatic or External resetting of the headstage integrating capacitor occurs at least once every few hundred milliseconds to several minutes.
MIXED RC mode eliminates the need for any timed resetting of the headstage capacitor by continuously bleeding off charge through a large value resistor (1 Gigohm or optional 100 Megohms). Noise is approximately double (i.e., same as 1 Gigohm resistive patch clamp, but with infinitely higher current passing range).
SERIES RESISTANCE COMPENSATION (Rs) is easily done with just one control. Typical compensation levels of 90% vs 75% on competing patch clamps. In current clamp Rs functions as a bridge balance
PARALLEL CAPACITANCE COMPENSATION (Cp). The unique
integrating
capability of the 3900A eliminates the need for all but one stage (time
constant and magnitude) of capacitance compensation. In fact,
capacitance
compensation is really needed only if Series Resistance (Rs)
compensation
is used. In the Current Clamp mode Cp functions as the capacitance
compensation
potentiometer. INSIDE-OUT and OUTSIDE-OUT polarity can be easily set
up.
The Im, Vm, and Command signals are automatically inverted. Thus most
user
confusion over various polarities is eliminated. Automatically powers
up
to outside-out, so there is no confusion over polarity.
OUTPUT PROCESSING
The processed Im (membrane current) or Vm (membrane potential) output is passed through a four pole low pass bessel filter that can be easily bypassed. The filter value is telegraphed to a computer A/D channel as a proportional analog voltage.
Seal and cell leakage can be subtracted from the membrane Current (Im) output by nulling the Im signal with the Leakage Adjust control while applying a small command (such as seal test).
The Im and Vm processed Output can have a DC component removed by adjusting the Output Zero potentiometer.
DESIGN PHILOSOPHY
All BNC connectors on the front panel are also repeated on the rear panel. Special attention has been given to power supply design in the 3900A. The power transformer is a true toroid with RFI filter that produces negligible radiation.
The 3900A represents superb quality in both components, engineering and attention to detail.
HEADSTAGE
- Input: Teflon jack (low noise) accepts standard pipette holders sized for BNC. Input at virtual ground.
- Bandwith: 100 Kilohertz, all modes of operation (Square wave applied via 2pf capacitor to input, independent of capacitive input loading).
- Noise: Measured with 8 pole Bessel filter;
- DC to 1 KHz: 0.03 pA RMS (Integrating Mode)
- DC to 10 KHz 0.20 pA RMS (Integrating Mode)
- DC to 10 KHz 0.48 pA RMS (Mixed RC Mode, 3901-100 Megohm)
- Current Range: 3901 (N = 1); 10 nA Direct Current (100% Duty cycle) or 1000 nA or 1% of the time etc.) For the high current headstage 3902 (N = 10); 100 nA 100% DC, or 10,000 nA for 1% duty cycle.
- Charge Range: 20 pC (100 mV command step into 200 pf cell capacitance). (200 pC 3902 headstage)
- Capacitive Loading: Stable with 1000pf cell capacitance thru 1.0Kilohm electrode
- RESET (Integrating Mode only): Reset Time (Sampled &Held): 40 µs: Reset Transient: 0.5 pA, 1 KHz bandwidth; Time Between Resets: 10 seconds for the 1 pA DC
- Current Clamp Speed: Current Step Time Constant (3902): 4 µs (Rm=500 Meg, Cm=33 pf, Re=2 Meg)
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- Standby: Headstage Input connected to Ground
- Voltage (V) Clamp: Pipette voltage is clamped to total command voltage while recording current.
- Zero Current (Io) Clamp: Pipette current is clamped to zero (i.e., voltage recording with no current)
- Current (C) Clamp: Pipette current is clamped to total command current while recording voltage.
- Integrating/Mixed RC: Pure Integrating for lowest noise (Integrating capacitor gets discharged automatically or externally for 25 µs), or a continuously discharging resistively loaded (Mixed) integrator that requires no discharge pulse but has the noise of a 1 Gigohm resistor (100 Megohm 3902) used for Whole Cell or already noisy single channel currents
- Series Resistance Compensation: 100 Megohm; 10 Megohm (3902); 100 Megohm (3901); ten turn dial
- Capacity Compensation:10 pf MAGNITUDE (ten turn dial);10 µs TIME CONSTANT (Only needs to be used if Series Resistance is on. Capacitive transients do not saturate the headstage, and are thus more easily removed by "Quickcharging" or Blanking than by using multiple Capacity controls)
- Inside Out/Outside Out Polarity: Inverts Im, 10 Vm, and all Commands and Holding signals
EXTERNAL BLANK INPUT: Logic pulse 3 to 15 volts blanks the Im output for its duration. Useful for eliminating capacitive current transients produced by command steps.
RUPTURE: Duration: A 2 volt 0.1 to 100 mS Command pulse.
OUTPUT PROCESSING
- Gain: Front panel or remotely set gains of 1, 2, 5, 10, 20, 100, or 500 mV/pA (optionally 1000). Remote gain set by 3 data lines and strobe, 5 volt CMOS input. Telegraph output in 400 mV increments to indicate gain.
- Low Pass Filter: Four pole Bessel with -3 dB points of 20, 50, 100, 200, 500 Hz and 1K, 2K, 5K, 10K, 20K, 50k, and 100 KHz. Telegraph outpu in 400 mV increments to indicate value.
- Leakage Adjust: Corrects for current leakage from pipette to bath from 5 gigohms to infinity.
- Output Zero: Removes DC component of output
DIFFERENTIAL AMP: Bath (Vcmd) applied internally to - input, + input and output at BNC connectors (10Kohm input)
BATH (Vcm) OUTPUT: 90 ohms, Inverse of command referred to pipette.
MAIN AND MODIFIER MODE SET: Edge sensitive (>2 to 15 volt)with one state sensitive converter that can convert any main mode.
DIMENSIONS
HEADSTAGE DIMENSIONS Not including Teflon Input connector:0.85 X 1.48 X 3.62 inches (22 X 38 X 92 mm) Mounting plate with four holes extends 0.31" (8 mm) past each end of case. Ten foot cable. 1/4 diameter (6.3 mm, 7.6 cm) 3 inch mounting rod.
CABINET DIMENSIONS 7.0 high x 19.0 wide x 10.0 deep inches( 17.7 x 48.3 x 25 mm) Standard rack or benchmount with handles
WEIGHT: 20 lbs.
ELECTRODE HOLDERS: HB120: accepts glass 1.0 to 1.2 mm OD HB180: accepts glass 1.5 to 1.8 mm OD (silver wire internal, 1 mm suction port)
POWER REQUIREMENTS: 100 to 125 VAC or 200 to 250 VAC internal switch. 20 watts, 50 or 60 Hz, fused 1 Amp.Line cord is shielded and enters cabinet through EMI/RFI filter power interlock connector.
3910 SPECIFICATIONS
Digital Capacitance Meter: 0 to 1.999 pF using a 5 mV (Hi Stim) or 0.5 mV (Lo Stim) internal triangle wave generator.
Digital Noise Meter: True RMS meter with ranges of 1.999 pA and 19.99 pA (5KHz four pole bessel filter process meter).
Quick Charge: Trigger circuit shorts the headstage input to ground through 4,000 ohms for 20 µs to 3 ms range. Trigger may be from internal Step Command or from an external source. (TRIG in BNC >2 to 15 volt 10 K input) A external state sensitive BNC (EXT QC TIME, > 2 to15 volt 10K input timing input is also provided.. (.i.e., Quick charge time determined externally, not by front panel time potentiometer.
Step Command: Analog to digital converter driven by a thumbwheel switch.100µv increments to 199.9 mv with selectable polarity. Gated on by external input , continuously (i.e., DC) or by internal 1, 10 , 100 Hz oscialltor with 50% duty cycle. BNC Input for Gate (> 2 to 15 volt is only, 10K input) BNC Output for STEP SYNC TIME (5 VOLT CMS, 560õ output).
3911 SPECIFICATIONS
Hypercharge: Auto Trigger: Command>5mV Time: 40-400 µseconds Shape: .5-100 µseconds
Prefilter: Stabilizes Rs compensation by reducing the bandwidth to less than 100kHz (two ranges)
Cm Nulling: Cm: 0-100pF max Rs: .5 to 20Megohm
Digital Noise Meter: Range: 1.999 pA (5kHz four pole
bessel filter
(True RMS meter)
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To view an application example showing the improved results obtained when a temperature controller is used in conjunction with a voltage clamp experiment, click here. |