Spontaneous openings of large and small conductance acetylcholine receptor channels in Xenopus myocytes.

Spontaneous openings of acetylcholine receptor channels were investigated using Xenopus myotomal muscle cells in culture and patch clamp recording methods. Two classes of channels with conductances close to 40 and 60 pS and reversal potentials near 0 mV were found to open in the absence of agonist. The open time of the low-conductance channel was about 3 times longer than that of the high-conductance channel. Open times were shorter by a factor of 3-5 than those of acetylcholine-activated channels in Xenopus myocytes and showed no significant voltage dependence. These studies indicate that the two predominant classes of acetylcholine receptor channels in this preparation can open spontaneously.