3900A Integrating Patch Clamp
|For several years the engineers at Dagan Corporation have been enthusiastically making researchers aware of the benefits of using integrating and semi-integrating patch clamps for:
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.
| Unequalled Features
THE ULTIMATE PATCH CLAMP
| The Dagan 3900A patch/whole cell clamp breaks new ground with a new concept: the Integrating headstage. Whereas conventional headstages measure pipette current as the voltage across a resistor, the headstage of the 3900A integrates the current on a capacitor, then differentiates the charge signal into a current signal. The new technique improves substantially on noise, bandwidth, dynamic range, voltage and current clamping efficacy, and simplicity of handling.
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 first technique, (Integrating mode), uses an electronic switch to shunt the headstage capacitor during 40 µs reset intervals. Such discrhaging events can be triggered at externally determined times, or are forced to occur by an internal monitor of capacitor charge. This method of discharging produces brief interruptions of the recording.
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.
| Available in Three Configurations .......
The optional expander section allows room to grow. The Dagan 3900A is not easily outdated when new features and functions are needed.
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.
|3911 Whole Cell Expander
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:
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:
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.
|Operational Features ...
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.
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.
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.
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.
| AUDIO MONITOR
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.
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.
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.
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.
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.
|PANEL METER: Low noise 3.5 digit lighted LCD meter monitors the current Im in pA, and the output voltage Vm, Offset voltage, and Command (Bath) voltage Vcmd in mV, and the output of the Headstage (HS Test).
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.
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.
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).
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)
|3900A||Includes 3900A with one probe (specify 3901,3902,3903 or 3904: see below) and HB180 pipette holder.|
|3910||Expander Module (Recommended for Bilayers). (Typically used with 3901 or 3903 Headstages) Contact Dagan|
|3911A||Whole Cell Expander with HyperCHARGE(tm) (Optimized for use with 3902 Headstage)|
(Detunes Whole Cell Capacitance Compensation by .1pF with TTL Pulse)
|V||Voltammetry Option (enables commands up to 5 volts)|
|3901||10nA Integrating Single Channel/10nA Whole Cell Headstage (1Gig)|
|3902||10nA Integrating Single Channel/100nA Whole Cell Headstage (100 M)|
|3903||10nA Integrating Single Channel/10nA (1 nA DC) Bilayer (Requires modification to main frame)(10 Gig)|
|3904||10nA Integrating Single Channel/1000nA Large Whole Cell (Requires modification to mainframe (10M)|
Accessories (Also see Pipette Holders and Parts section)
|HB180||Universal Pipette holder for use with 1.0 to 1.8 millimeter glass. (May be drilled out for larger glass)||
|Other Patch Clamps:|
Download the Manual (PDF)
Please note that this is a legacy page. The 3900A is no longer available, but we have left this page up for informational purposes.
Warning: This equipment is not intended for use in human applications or human experimentation.
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