acetylcholine bindin site lipid channel bilayer ore 4 nm CYTOSOL gate A Model for the structure of the nicotinic(烟碱型) Acetylcholine Receptor Five homologous subunits combine to form a transmembrane aqueous pore. n its closed conformation, the pore is thought to be occluded by the hydrophobic side chain of five leucine residues which form a gate near the middle of the lipid bilayer.A Model for the Structure of the Nicotinic(烟碱型) Acetylcholine Receptor Five homologous subunits combine to form a transmembrane aqueous pore. In its closed conformation, the pore is thought to be occluded by the hydrophobic side chain of five leucine residues which form a gate near the middle of the lipid bilayer