How do researchers measure ion movements through single channels?

Patch clamping is a technique that measures the electric current caused by the movement of ions across a small patch of the plasma membrane.The membrane is electrically depolarized or hyperpolarized and maintained (clamped)at that potential by an electronic feedback device.The inward or outward movement of ions across a patch of membrane can be quantified from the amount of electric current needed to maintain the membrane potential at the designated "clamped" value.