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I. INTRODUCTION OF THE PATCH CLAMP METHOD

The Patch Clamp/Whole Cell Amplifier (PCA) model 707 provides a method first introduced by E. Neher and B. Sakmann in 1976 for recording the currents in a small patch of membrane under voltage-clamp conditions. The model 707 is the last generation (designed in 2001) model combining several advantages made capable by the development of methodology and electronic industry. In recent years a number of technical advances have occurred, most notably the discovery of the gigaseal by E. Neher (1981). The advantage of the PCA mod 707 is that intracellular recordings can be made with the same type of recording setup as used for patch recording from the cell surface, as well as a cell-free membrane. The instrument can be used to perform electrochemical measurements. For an introduction to electrochemical methods you may refer to Kawagoe, Zimmerman and Wightman, J. Neuroscience Methods, 48 (1993) 225 240. Model 100 is a low cost alternative, capable of working only in Voltage Clamp (VC) mode and in either patch-clamp or whole cell mode selected when ordering the instrument.

II. REFERENCES

  1. Neher, E., and B. Sakmann, Single channel currents recorded from membrane of denervated frog muscle fibres, Nature 260 (1976) 779 802.

  2. Hamill O. P., A. Marty, E. Neher, B. Sakmann and F. J. Sigworth, Improved patch-clamp techniques for high-resolution current from cells and cell-free membrane patches. Pflungers Arch. 391 (1981) 85 100.

  3. Neher, E., Unit conductance studies in biological membranes. In: Techniques in cellular physiology, P. F. Baker, ed., Elsevier/North Holland, 1981.

  4. Sakmann, B., and E. Neher, eds. Single Channel Recording, Plenum Press, New York, 1983.

  5. Rae, J., and R. Levis, Patch clamp recordings from the epithelium of the lens obtained using glasses selected for low noise and improved sealing properties. Biophys. J. 45 (1984) 144 146.

 

Patch Clamp Whole Cell Amplifier model PCA 707

The Patch Clamp Whole Cell Amplifier model PCA 707 from Advanced Technologies Ltd. represents the latest break through in the design of this type of instrumentation. It combines precise analogue electronics with onboard microprocessor controller which decreases noise, expands the instrument functionality and reliability, and allows bidirectional communication with a computer. The processor is powered only when a button is pressed thus it does not contribute to the noise.

Features:

  1. ultra low noise, typically less than 0.1 pA in the 10 kHz bandwidth;

  2. range-changing capability of the head stage with light indicator. Possibility to work with all object (whole cell, patches, dip-tip method, etc.);

  3. possibility to store and retrieve 6 sets of working parameters with a push of a button;

  4. works in all possible modes: Voltage clamp, Current clamp (+ command current), Test, Search;

  5. integrated transient cancellation and series resistance compensation functions. Separate capacitance compensation for the pipette and the whole cell. The whole cell compensation is calibrated thus the cell capacitance can be measured and the size of the cell estimated.

  6. built-in 4-pole Bessel low pass filter with variable cut off frequency;

  7. special functions: ZAP (electrical pulse), RESET zero the current, IRMS current noise measurement;

  8. capability to link to an IBM PC compatible computer through the built-in serial interface for recording and retrieval of the experimental setup parameters. Additional Digital-Analogue-Converter board is required for data acquisition and signal generation;

  9. 3 years full warranty and lifetime support. With the instrument we send you over 300 pages tutorial on patch-clamping. Consultation and support is always free. Competitive pricing.

Operating Modes

PCA Mod. 707 is fundamentally an instrument for measuring small electrical currents. It uses a current/voltage (I/V) converter circuit to convert the currents to an analog voltage which is then made available at the CURRENT monitor outputs for display and/or recording. At the same time that the pipette currents are being recorded the potential must be specified, and the various operating modes of the EPC-7 correspond mainly to different ways of controlling that potential. These operations include (see Fig. 2):

A. Voltage-Clamp mode (V.C.)

This is the basic patch-clamp mode. The pipette potential is derived from the signal applied to the STIM IN input with a variable offset added from the V-HOLD control. The sum of these two sources is what is displayed and monitored as the V.COMM signal. Before being applied to the pipette a further variable offset is added from the Vp-OFFSET control to allow the user to cancel electrode offsets.

B. SEARCH mode and VOLTAGE CLAMP COMMAND (V. COMM)

The SEARCH mode is essentially the same as the Voltage-Clamp mode, except that V.COMM also receives an input from the search integrator, which is an amplifier that provides negative feedback between the current monitor and pipette potential signals. It acts slowly to adjust the pipette potential to make the average pipette current zero. This mode of operation is most useful when one is first approaching a cell to make a seal, as the feedback will compensate for small electrode potential drifts that otherwise would drive the current monitor signal off-scale. The speed of the feedback is inversely proportional to the resistance between the pipette electrode and the bath, with a time constant of about 1 s at 10 MW . When a gigaohm seal is established the feedback becomes very slow. To avoid drifts in the pipette potential it is desirable to switch to the VC mode before starting a recording.

C. Current Clamp modes (CC)

The Current Clamp modes are similar in principle to the search mode, in that feedback is employed between the current monitor signal and the pipette potential. In the CC mode the feedback acts rapidly to keep the current at zero by varying Vp appropriately; in this way a high-impedance voltage follower is created, with the output voltage available at the POTENTIAL output.

In the CC mode, to measure the resting potential (or spontaneous action potentials in whole-cell recording) the membrane potential will be shown on the display. In the CC+COMM mode, a command current can be injected while the pipette potential is measured. The command current is determined by the sum of voltages from the STIM. IN signal and the VHOLD control.

 

Technical Data

NOISE

(Equivalent current input noise, the 4-pole Bessel filter is on 10 kHz, 20 GW range, model cell)

    1. - 10 kHz. 0.09 pA RMS

0 5 kHz .....................................................0.03 pA RMS

MODES OF OPERATION

VC (Voltage clamp); CC (Current clamp); CC+COM (Current clamp with command current); TEST, SEARCH

CURRENT MONITOR SIGNAL

Gain 0.5 1000

Internal Filter . 1/2/5/10/100 kHz 4-pole Low Pass Bessel

TRANSIENT CANCELATION

Compensates fast and slow transients with the control of fast and slow time constant and amplitude. Additional Whole Cell compensation circuitry which is calibrated.

SERIES RESISTANCE COMPENSATION

Controls for the time constant, % compensation, and lag.

HEADSTAGE

Current-measuring resistances.0.5/20 GW , remotely switched

LED indicator of the regime of work (Patch/whole cell)

Input connector ....BNC

Other connections.Ground sense input, Pipette command output

METER

3 1/2 digit Liquid Crystal Display with 4 side LEDs to indicate the displayed units.

Monitors: I pipette current; IRMS noise current; VP Pipette potential; VCOM membrane potential; VH holding current or voltage.

DIMENSIONS

Headstage 55 x 90 x 20 mm (without the holder and the BNC)

Headstage cable 1 m, highly flexible

Controller .. 3U 19" rack chassis

MODEL CELL

Emulates whole cell or patch. 2 BNC connectors with no switches. Shielded.

POWER REQUIREMENTS 100 - 230 V, 30 W. Please specify voltage on purchase.

OPTIONS

Model PCA 707/I is without some of the digital functions: the storage and retrieval of 6 sets of parameters, and the communication with the computer. We provide turn key solutions.

Patch-clamp amplifier model 100.

Features

  • Ultra low noise;
  • Built-in full featured function generator;
  • Work in "patch" regime or with whole cells;
  • Capability to link to a computer through an optional board, thus being able to perform and record complex experiments;
  • Integrated high-quality variable frequency filter;
  • Integrated capacitance transient cancellation and series resistance compensation functions;
  • All modes of operation including voltage clamp; current clamp; search; current clamp with command current;
  • Two indicators: for the current off zero and multifunctional LED indicator;
  • Compact design for easy system integration;]
  • Lifetime warranty;
  • Low-cost.

Specifications

NOISE

(Equivalent current input noise, measured with 4-pole Bessel filter, 50 Gohm range)

0 - 10 kHz.………………………………………………………….. 0.15 pA, RMS

CURRENT MONITOR SIGNAL

Gain 0.2 – 1000 two switch selected

    Switch x1 - 0.5 Gohm resistor

    Switch x 100 - 50 Gohm resistor

Internal Filter ……. 0.3/ 1/ 3/ 10/ 30/ Off kHz 4-pole Bessel

SERIES RESISTANCE COMPENSATION

Controls for the % compensation, slow time constant and fast time constant.

TRANSIENT CANCELLATION

Compensates fast and slow transients with separate controls of the fast and slow time constant and amplitude.

HEADSTAGE

Current-measuring resistance.………0.5/50 Gohm, remotely switched

                     Input connector ……………..………BNC

                     Other connections…………………...Ground sense input and pipette command output.

FUNCTION GENERATOR

Triangular or rectangular pulses with controls for the amplitude, polarity and frequency.

METER

3 1/2 – digit Light Emitting Diode

Monitors: VH/IH –holding current or voltage; I – pipette current; IRMS – noise current; VM – membrane potential.

POWER REQUIREMENTS

85 – 240 V autoswitching, 30 W; EMC emission free.