Recovery from the rapid desensitization of nicotinic acetylcholine receptor channels on mouse muscle

Pulses of acetylcholine (ACh) applied to outside-out patches of embryonic-like muscle membrane elicited channel currents which declined rapidly (τ_d = 10-60 ms) due to desensitization. Recovery from desensitization was determined by pulse pairs, varying the pulse interval. When the pulse interval was about 300 ms, the response to the second pulse was about half that to the first pulse, i.e. about half of the channels had recovered from desensitization. The results are discussed in the frame of a cyclic reaction scheme. If this scheme includes high affinity binding of ACh to desensitized receptors, it can also explain the finding that low ACh concentrations (≤ 1 μM) largely desensitize the receptors, but elicit very little channel opening.