The last several years have seen many advances in switching mode single electrode clamps, all of which have been incorporated in the new 8100-1 system. These improvements have been the result of 8100's being used in a wide range of applications that have added to our knowledge and ability to produce the very best single electrode switching damp system possible. We feel that the present 8100-1 system is truly a state-of-the-art second generation system that has proven itself in laboratories around the world. The 8100-1 Single Electrode Clamp system provides a reliable, time proven, and powerful research tool for intracellular clamping.
The Dagan 8100-1, the successor to the 8100 Single Electrode System incorporates three major technical advances.
- Background noise is reduced in half by use of lower noise/lower drift op amps and power line noise has been almost totally eliminated by the use of a novel rejection circuit
- Bandwidth, and thus the switching speed of the Headstage Probe, has been increased by a factor of 3 to 4 by decreasing the input capacitance. It is now possible to voltage clamp cell in as fast as 140 microseconds (ten megohm microelectrodes and ten megohm cell).
- Differential recording between the cell and the bath (using the 81.50 Bath Reference Amplifier probe) eliminates offset errors due to the reference electrode. Thus, bath solutions can be changed during the course of an experiment without causing an offset voltage error.
Voltage Clamping is one of the most powerful methods now used for the study of electrical events occurring in cell membranes. Under voltage clamp conditions, the membrane voltage is electronically controlled by the investigator. When special potential differences are prevented along the entire area of membrane through which current flows, and the potential is rapidly stepped to another voltage, the current which flows (following a brief capacitive transient) is the ionic current through the membrane.
The 8100-1 has been designed especially for the exacting requirements of Single Electrode Voltage and Current Clamping. With the introduction of the improved Single Electrode Voltage Clamp, Electrophysiologists now have range, capability and speed never before available. Incorporating three instruments in one, the 8100-1 is a very versatile and robust Single Electrode Voltage Clamp.
Features Include ...
- Single Electrode Voltage Clamping
- Switched Mode Current Clamping
- Bridge Mode Current Clamping
- X10 and XI00 Voltage Outputs
- Pulsed Electrode Impedance Test
- Selectable 50% or 25% Current Duty Cycle
- Two Pole Active Low Pass Filters
- 1000 Megohm Bridge Balance Range
- Transient Free Mode Selection
- Two Range Actual Current Monitor
- Low Drift, Low Noise Op Amps
- Differential Cell to Bath Recording
- Power Line Transient Rejection Circuit to eliminate Line Noise
- High Speed, Low Input Capacitance Headstage Probes
- Up to 10-13 ohms input impedance
- Micro-miniature Gold Plated Input Connector with Drive Shield
- Electronic "Buzz" Switch for Cell Impalement
- Combined Anti-aliasing Filter with Capacitance Compensation
- Independent "Holding!'controls for Voltage and Current Clamp Modes
- Headstage Output (HS/OUT) to view Output from the Probe
- Lead-Lag Phase Control
- Easy to use Ten Percent Incremented Scaling of the Step Command
- External Computer Control of Switched Clamp Modes
The need of a single electrode voltage clamp is apparent when one considers;
The impalement of a cell with only one electrode dramatically increases the chances of obtaining and maintaining a healthy cell
There are no problems with coupling between barrels of theta tubing
The difficulty of shielding the 'two electrode clamp system's" current and voltage electrode from one another is effectively avoided.
The simplicity of operation one electrode does double duty for both Current and Voltage clamping. This obviates the use of a bridge and the errors due to imbalance when electrode resistance changes.
In many cases the cell, which one is going to study cannot be visualized, so putting in two microelectrodes under the circumstances is impossible without coupling the electrodes physically. Of course, that leads to electrical coupling which makes voltage clamping difficult.
The 8100-1 can also be used in large cell when ultra fast currents are not of interest. For example, suppose one were doing a number of simultaneous studies on a cell using several micropipettes; e.g., iontophoresis, clamping and intracellular or extracellular ion concentration measurements. Using the single electrode clamp reduces the number of electrodes by one and also minimizes the complexity of the experiment
Since current damping or current stimulation is usually a large part of any Voltage Clamp procedure, great care was exercised in the design and human engineering of the current clamp portion of the 8100-1. Voltage clamp and current clamping levels are both selected on independent controls. Thus, fast precise switching from the voltage to current clamp modes is straight forward and easily accomplished. The voltage clamp "level" controls include the eleven position Command and digital dial Holding Potential controls. The current clamp level is selective via a digital dial Hyperpolarize and associated Stimulus Inputs. Current clamping can be performed in either the Bridge mode (i.e, steady state throughout the recording electrode using the Bridge Balance control) or in the Switched Current Clamp mode using a duty cycle of 50% current or 25% current. The Switched Current Clamp mode alleviates the need for a 'Bridge Balance control, thus eliminating the problem of 'Bridge ' ' unbalance during current stimulation. Electrode resistance changes, due to current passing, are no longer a problem.
The 8100-1 can function as an independent "stand alone' preamplifier with all voltage and current clamp modes disabled. In the "Preamp only' mode, only the Capacity Compensation, DC Offset Voltage, Impedance Test, and Bandwidth controls function. This provides the user with a simple to use low noise, ultra high speed Intracellular Preamplifier convent for all your experimental needs. Since the 8100-1 is referenced to ground, (i.e., needs no special grounding requirements such as floating bath, etc.), it is compatible with other instrumentation including another 8100-l
Specifications ...
Preamp Only
- DC Offset: Adjustable -1000 mV, ten turn control
- X10 Output Impedance: 220 ohm
- Calibrate Voltage Input Sensitivity: 1 mV/Volt, 1 Megohm Input z
- Capacitance Compensation: Adjustable, 0 to 15 picofarads, (Optional 100pF). Ten turn control
- Input: Single ended (Non-Inverting). Via Sub-Miniature coax connector.
- Filtering: 3 KHz, 30 KHz and WB (Wideband), active two pole filter
Probe Electrical Specifications
- Input Resistance (Range): (X0.01) 10to13th Megohm, (X0.1) 10to12th Megohm. (X1) 10to11th Megohm. (X10) 10to10th Megohm
- Input Bias Current (Range): (x0.01) 0.5 pA,. (X0.1.l) 1 pA, (Adjustable to zero at probe), (XlO) 10 pA, (x10) 20 pA
- Input Capacitance: (Single Range Probes 8160, 8170, 8190, and 8190,.02 pf). (Dual Range Probes, 8110, 8120 and 8130), (.04)
- Rise Time (Xl Range): 7us 10 to 90% through 10 megohm resistor
- Auxiliary Command Input Sensitivity: --1 volt for +l00mV Clamp, 100Kohm Input Z
- Compliance Voltage: 14 volts
Mode Switch:
1. PREAMPLIFIER ONLY (BRIDGE CURRENT CLAMP)
2. PREAMP and SWITCHED CURRENT STIMULATOR (SWITCHED CURRENT CLAMP).
3. PREAMP and SWITCHED VOLTAGE CLAMP (SWITCHED VOLTAGE CLAMP)
Current and Voltage Clamp
- Speed: 140 us (70 us attack, + 70 us rise time) to 90% Voltage Clamping (10 mV step) of a cell model with a microelectrode resistance of 10 megohms and a cell resistance of 10 megohms in parallel with a cell capacitance of 1000pF.
- Impedance Test: Pulse I mV/M (Xl probe)
- Stimulus Input Sensitivity: + 100 nA per + 10 volt stimulus signal, 50K ohm Input Z (Both Front and Rear) (XI probe)
- Switching Frequency: Adjustable 500Hz to 25 KHz (optionally slower) Internally adjustable to 50 KHz.
- Voltage Sample and Hold Acquisition Time: Preset at 10 microseconds, internally adjustable
- Current Sample and Hold Acquisition Time: Reset at 10 microseconds, internally adjustable
- Switched Current Duty Cycle: Exactly 50% or 25% (digitally controlled).
- Current Monitor: Actual injected peak Current, two ranges 10 nA/Volt and 100 nA/Volt (usable sub nA to 1000 nA) (XI probe).
- Current Monitor Filter: 300Hz, 3KHz and WB(Wideband), Active Two Pole Filters.
- Current Test Input Sensitivity:10 nA/Volt, 10K ohm Input Z
- Voltage Clamp Level: Eleven position switch attenuates (scales) Command Input in 10 percent steps from 0 to 100%. For 10 volts in, each step is 10 mV.
- Voltage Command Input Sensitivity:10 Volts for 100% equals 100 mV (i.e., 10 mV steps) Input Z
- Voltage Clamp Gain Control: Adjust gain in Voltage Clamp mode only (MIN.. 5, Max 5000) Ten turn control
- Voltage Clamp Holding Pot: + 0 to 1000 mV Ten turn digital dial.
- Current Stimulation Holding Pot: + 0 to 100 nA (Hyperpolarize/Depolarize) or +/-0 to 10 nA (X1 Probe)