patch clamp

A specialized and powerful variant of voltage clamp method, in which a patch electrode of relatively large tip diameter (5 m m) is pressed tightly against the plasma membrane of a cell, forming an electrically tight, "gigohm" seal. The current flowing through individual ion channels can then be measured. Different variants on this technique allow different surfaces of the plasma membrane to be exposed to the bathing medium: the contact just described is a "cell-attached patch". If the electrode is pulled away, leaving just a small disc of plasma membrane occluding the tip of the electrode, it is called an "inside-out patch". If suction is applied to a cell-attached patch, bursting the plasma membrane under the electrode, a "whole cell patch" (similar to an intracellular recording) is formed. If the electrode is withdrawn from the whole-cell patch, the membrane fragments adhering to the electrode reform a seal across the tip, forming an "outside-out patch".