Recording from membrane ion channels (patch clamp)
Erwin Neher and Bert Sakmann developed a technique which allows the measurement of the minute currents that flow through the ion channels of cell membranes.
Ion channels allow small, charged particles to travel into and out of cells, changing the electrochemical gradient across the cell membrane. In neurons, this allows the creation of a difference in electrical potential across the cell membrane, so that the cell acts as a capacitor. When the neuron is stimulated, the stored charge allows the cell to fire electrical impulses. For many years electrophysiologists studied squid because their large nerve cells allowed changes in current across a cell membrane to be recorded. Electrochemical properties of nerve impulses were described by Hodgkin and Huxley.
Neher and Sakmann refined their equipment to record the tiny changes in current generated by a single ion channel, and devised a way of isolating single or small numbers of channels, while using Hodgkin and Huxley’s methods to control the voltage across the cell membrane.
They worked with cells from frogs and rats, using a thin pipette – a glass tube with a tip diameter so small that it was only visible under a microscope. When the tip of the pipette contacted the cell membrane, suction was applied to pull the membrane tightly around the tip. This formed a tight seal with a very high electrical resistance between the glass pipette and the cell membrane, so that a small section of the membrane – the part sucked up inside the pipette - was electrically isolated. When an ion channel in the cell membrane opened and the charged ions moved through, the resulting current could be recorded.
Last edited: 11 November 2014 12:05