Abstract
Acetylcholine (ACh) released from nerve terminals binds with numerous nicotinic ACh receptors in neuromuscular junctions, causing depolarization and muscular contractions. When bound with ACh, these receptors dynamically regulate channel closing and opening by rotational movements. ACh receptors present on end plates are commonly called mature ACh receptors and have 5 subunits. Nerve-type ACh receptors composed of α3β2 are present before synapses and contribute to remobilization of synaptic vesicles via positive feedback. Immature ACh receptors composed of an α2βγδ subunit in which an ε subunit is replaced by a γ subunit are expressed on muscles in the fetal stage or denervated muscles. This often causes clinical problems due mainly to differences in responses to suxamethonium. In addition, studies conducted in recent years have suggested the presence of α7 ACh receptors composed only of the α7 subunit in muscles under specific conditions, raising interest in their physical roles, because these ACh receptors have been believed to be present only in central nerves.
