A possible model for the inner wall of the acetylcholine receptor channel

A structural model of the inner wall of the acetylcholine receptor (AChR) channel is developed using assumptions derived from the results of the recent labelling experiments of the MII helices by noncompetitive blockers. The assumption of steric blocking of the channel by chlorpromazine (CPZ) in the neighbourhood of the labelled serines imposes the MII helices to be in contact at this level and allows the calculation of their minimal interaxial distance. The assumption that CPZ diffuses to this position through the upper crowded part of the channel imposes that the helices are more distant in this region and permits the determination of a tilt of about 7 degrees with respect to the central axis. Electrostatic potentials are used to demonstrate the effect of the charged residues at the exit of the pore. A discussion is given on the possible aptitude of MI to satisfy the contacts necessary with the MII/s at the different heights of the model.