Patch clamp technique

The patch clamp technique is a versatile technique in electrophysiology used to study ion channels in isolated living cells, tissue sections, or patches of a cell membrane. 'Patch' refers to a small piece of the cell membrane and 'clamp' refers to "locking" one of the electrical variables (voltage or current) while measuring the other. Depending on the "locked" variable, the technique is more specifically called voltage-clamp method or current-clamp method. These techniques are especially useful in the study of excitable cells such as neurons.

The common elements used in this technique are:

Perfusion buffer where cells can survive (e.g. CsCl/MgCl₂)
An electrical circuit composed of:
- Pipette tip with a recording electrode (normally in contact with the cell)
- Reference ground electrode (normally in contact with the perfusion buffer)
- Cells of interest in between electrodes
Micromanipulator to control the electrodes
Different hardware and software to amplify and record the signals

This schematic shows some components of the patch clamp technique. A neuron is in a buffer solution. A pipette and recording electrode are inside the neuron. In the buffer solution, there is a reference electrode which points at the neuron.

Figure 1: Schematic representation of some of the components of the patch clamp technique.

After adding the perfusion buffer to the cells, the pipette tip with the recording electrode makes contact with a tiny area of the cell membrane. Then, depending on the goal of the experiment, there are different variants of the technique, regardless of which variable is "locked":

Cell-attached recording: Cell membrane is not disrupted. It records voltage/current through a single ion channel. Used to compare the response characteristics of different channels.
Whole-cell recording: Cell membrane is disrupted and the interior of the tip with the recording electrode becomes continuous with the cell cytoplasm. It records the voltage/current from the entire cell.
Inside-out recording: Cell membrane is disrupted but the patch of the cell membrane with the ion channel inside the pipette tip remains attached and viable. Used to record the response of the intracellular part of single channels to different media.
Outside-out recording: Cell membrane is disrupted and the patch of the cell membrane with an ion channel that remains active and viable is outside the pipette tip. When the cell membrane is repaired, the extracellular part of the channel is exposed to the media. Used to study how extracellular chemical signals influence ion channel activity.