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 μ-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 10–100 ms.
In order to obtain the necessary resolution, a delicate compromise had to be found between different experimental parameters. Pipettes with 1–3 μm internal diameter and a steep final taper had to be used, extensive enzyme treatment was necessary, and conditions had to be found in which channels open at a relatively low frequency.
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Neher, E., Sakmann, B. & Steinbach, J.H. The extracellular patch clamp: A method for resolving currents through individual open channels in biological membranes. Pflugers Arch. 375, 219–228 (1978). https://doi.org/10.1007/BF00584247
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DOI: https://doi.org/10.1007/BF00584247