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BA - Bridge Amplifier

BA Bridge Amplifier – For Intracellular Current Clamp and Extracellular Recordings

The BA amplifiers are wide-bandwidth high impedance amplifier designed for intracellular current clamp recordings with sharp microelectrodes. Recording scenarios are sharp microelectrodes, perforated or tight seal patch configurations as well as electroporation and iontophoresis. npi’s BA amplifiers are used in vertebrate (rat, mouse, cat, fish etc.) and invertebrate (leech, crab, snail, insect etc.) neurons, muscle cells, other excitable tissue and plant cells.

Your benefits:

  • Bridge mode recording is the most precise current clamp method.
  • High Gain and versatile high and low pass Bessel filters also allow extracellular voltage recording.
  • Perform extracellular recording, intracellular measurements and cell staining or electroporation without changing the headstage or pipette.
  • Easy cell penetration with sharp micro-electrodes, using the built-in penetration mode.

Frequently asked questions (FAQ):

Can npi’s BA amplifiers be integrated in existing e-phys setups?

Yes, the BA series amplifiers work well with all major data acquisition hardware and software (Spike2, Signal, pClamp, Patchmaster, WinEDR, WinWCP).

Can I use the BA amplifiers with high impedance electrodes (over 200 MΩ)?

Yes, the BA series amplifiers can have a bridge compensation circuit which can compensate up to 1 GΩ.

What is single cell electroporation?

The pipette tip is moved very close to the cell’s membrane. A current pulse will induce a voltage drop across the membrane, which causes the membrane to form small holes in the vicinity of the pipette tip. Charged molecules (DNA, dyes) can then move along the electrical field into the cell. In contrast to electroporation in a cuvette, this also works with lower voltages: the distance is also lower, resulting in a similar electric field.

What is juxtacellular filling?

Juxtacelular filling or juxtacellular labelling is a technique that allows labelling of extracellularly recording neurons. It is especially useful for structure-function correlation studies in living tissue and intact neural networks. The working principle is to iontophorese tracer molecules into the neuron under constant electrophysiological monitoring. (see doi:10.1007/978-1-60327-202-5_3)

Why should I use a bridge amplifier for current clamp recordings?

Patch Clamp amplifiers not as precise as bridge amplifiers (pure voltage followers) since they are not as fast and might in addition draw current from the recorded cell (see doi:10.1016/S0166-2236(96)40004-2)

What is capacity compensation?

npi’s BA series amplifiers can compensate the stray capacity of the recording electrode. To do so a square pulse is applied while the electrode is immerged in the bath, Then the potentiometer for capacity compensation is adjusted, until the capacitive artefacts disappear.

What does the “Bridge” compensate?

The Wheatstone Bridge is used to exactly determine the pipette’s resistance. To do so, a current is applied (or current pulses) and the bridge is adjusted, until no more voltage drop is visible. Here the bridge is “balanced”. Since three resistors of the bridge are known in this state, the fourth unknown resistor (pipette) can be determined.

How can I use the bridge amplifier for in vivo research?

Yes, you can. It is easy to use in head-fixed animals. Npi also provides miniature headstages for current clamp recordings in freely moving animals.

How does the penetration mode work?

There is a red pushbutton named BUZZ on the front panel. As soon as this is pushed, the amplifier’s capacity compensation goes to maximum, which results in rapid oscillations in the headstage’s output current. This effect, which is unwanted during regular recordings leads to a very localized mechanical stress to the cell’s membrane – small holes are generated, and the electrode tip can impale into the cell.

What is ELECTRODE CLEAR?

Pulses with high current can be applied to the electrode to get rid of the debris that clogs the electrode.

How can the bridge amplifier be used for extracellular recordings?

The BA series amplifiers have a high gain on the potential output (up to 1000) and also Bessel filters for lowpass and highpass filtering.

How can the amplifier be used for (single cell) stimulation?

Current or voltage pulses are applied with the pipette tip close to the cell. Due to the low distance between tip and cell, lower voltages are sufficient to stimulate the cell. Neighbouring cells will not be stimulated, as the distance to those is too large.