Figure 3.

Patch clamp technique for the measurement of ion channel activity. A – Cell-attached mode. The micropipette used for patch-clamping is brought up to the cell membrane and gentle suction applied so that a ‘patch’ of membrane is isolated in the tip of the pipette by a high resistance seal. Using this technique the properties of single channels or groups of channels in the patch can be defined when intracellular contents are left intact. The effect of extracellular agents on channel activity can be studied by adding the agents to the pipette solution. B – Inside-out mode. Once the seal between pipette and membrane patch is established the patch is ‘torn’ away from the rest of the cell and the intracellular surface of the membrane is exposed. This makes it possible to control the intracellular environment artificially and to study channel activity after exposure of the cytoplasmic membrane surface to channel agonists and antagonists. C – Whole cell mode. A cell-attached patch is established, then extra suction is applied to suck out the patch of membrane, leaving the pipette in contact with the intracellular contents. Using this mode current and conductance, which are the sum of the properties of all the channels in the membrane, are measured. Properties of different channel types can be determined by examining the effect of extracellular or intracellular channel agonists and antagonists on membrane current and conductance.