Acetylcholine receptor channel gating and conductance involve extracellular disulfide bond(s).

Disulfide bonds are critical determinants of the function of the acetylcholine receptor at the vertebrate neuromuscular junction. In the present study, the role of these bonds in acetylcholine receptor channel gating and conductance was investigated at the single channel level. Disulfide bond reducing agents decreased the single channel conductance of both ligand-gated and spontaneously opening acetylcholine receptor channels, indicating that the observed decrease in conductance is not due to blockade of the channel lumen by agonist molecules. In addition, the reducing agents increased the opening frequency of both liganded and unliganded acetylcholine receptor channels. Use of inside-out patches and both membrane permeant and impermeant reducing agents demonstrated that the disulfide bonds involved are all extracellular. These findings indicate that both channel gating and conductance involve conformational changes in extracellular regions of the acetylcholine receptor.