title: The extracellular patch clamp: a method for resolving currents through individual open channels in biological membranes.
abstract: The current contributions of individual ionic channels can be measured by electrically isolating a small patch of membrane. To do this, the tip of a small pipette is brought into close contact with an enzymatically cleaned membrane of a hypersensitive amphibian or mammalian muscle fiber. Current flowing through the pipette is measured. If the pipette contains cholinergic agonist at mu-molar concentrations, square pulse current waveforms can be observed which represent the activation of individual acetylcholine-receptor channels. The square pulses have amplitudes of 1 to 3 pA and durations of 10--100ms. In order to obtain the necessary resolution, a delicate compromise had to be found between different experimental parameters. Pipettes with 1--3 micrometer internal diameter and a steep final taper had to be used, extensive enzyme treatment was necessary, and conditions had be to found in which channels open at a relatively low frequency.
mesh_terms: D000818:Animals; D001001:Anura; D002462:Cell Membrane / Q000378:metabolism / Q000502:physiology*; D004553:Electric Conductivity; D007473:Ion Channels; D009132:Muscles / Q000378:metabolism / Q000502:physiology; D010827:Physiology / Q000295:instrumentation / Q000379:methods*; D051381:Rats; D011950:Receptors, Cholinergic / Q000502:physiology
chemical_list: D007473:Ion Channels; D011950:Receptors, Cholinergic