The patch-clamp technique is a powerful technichnique to study electrophysiological properties of biological membranes. It allows for recording of macroscopic whole-cell and microscopic single-channel currents flowing through ion channels.
Central to the patch-clamp technique is the patch-clamp pipette. It is a thin glass tube, which is pulled out to a width of only some micrometers. It is filled with electrolyte solution, into which a Ag/AgCl electrode is immersed. When the patch-clamp pipette is brought into close contact to the cell membrane, a tight connection between the pipette and the cell membrane forms. The seal can be enhanced by applying suction to the pipette, so that the resistance to the bath solution exceeds several GΩ.
In this cell-attached configuration the ion channels which are present in the cell membrane enclosed by the pipette opening are the only electrical connection bewteen the interior of the pipette and the interior of the cell. When one of the channels opens, a small current will flow. Its magnitude is determined by the number and conductance of the channels included in the patch and the voltage applied between the electrode immersed in the pipette and the electrode in the bath solution.
By quickly retracting the patch pipette the membrabe patch enclosed by the opening of the pipette can be excised without affecting the gigaseal connection to the cell membrane. In this inside-out configuration the intracellular side of the membrane is exposed to the bath solution, which allows to apply and study intracellular modulators of channel function.
Starting from the cell-attached configuration the patch can also be broken by applying suction to the patch pipette instead of excising it. In this way a hole is created in the plasma membrane and access to the interior of the cell is gained while not compromizing the gigaseal between pipette and plasma membrane. In this configuration the resistance between pipette and cell interior is low, so that the overall resistance between the electrode in the pipette and the bath electrode is determined by the plasma membrane of the whole cell. In this whole-cell configuration the currents flowing through ion channels in the entire plasma membrane are recorded.