Patch clamping is an experimental technique used to determine the current across a membrane. This involves attaching a sensitive electrode to a section of membrane, and measuring the current. Patch clamping can be used to measure the flow of protons, Na+, K+, and other charged species across a membrane, allowing the study of different cellular geometries:
Inside-Out This involves attaching the electrode pipette to the surface of a cell, pulling a section of membrane away to determine the flow of electrons from the inside of the cell to the outside. Due to low numbers of intracellular ion channels, this geometry is not widely used.
Whole-Cell By attaching the pipette to the cell and sucking, the cell can be attached to the electrode, allowing the study of the entire membrane surface. The electrode is inside the cell, so all ion movement into the cell can be studied (as well as outward movement).
Outside-Out This geometry is studied by attaching the pipette to the cell, sucking, and then pulling away from the cell. This allows the opposite of the inside-out geometry to be studied, with the membrane flipped. This is more useful as there are more ion channels, allowing for greater levels of transport to be studied. Therefore, there will be higher current readings recorded.