patch clamp assay outside-out patch clamp assay A patch-clamp assay where a patch of the membrane is attached to the patch pipette. In this configuration, the external surface of the cell membrane is exposed as the outside of the membrane patch relative to the patch electrode. An outside-out patch starts with a gigaohm seal in a whole-cell recording configuration. The electrode is slowly withdrawn from the cell, until a fragment of membrane bulges away from the cell, which detaches and reforms as a convex membrane on the end of the electrode, with the original external surface of the membrane facing outward from the electrode. This provides the experimenter with access to the extracellular surface of the membrane via the bath and can manipulate the environment at the extracellular surface of single ion channels.