Characterization of a Small Domain in the I3 Loop of the Human Muscaarinic M1 Receptor

Abstract

Muscarinic M1 acetylcholine receptors are the most abundant subtype of muscarinic receptor expressed in the CNS. When expressed in heterologous cell lines, M1 receptors internalize when exposed to agonists, but the mechanism by which it occurs is poorly understood and may have important therapeutic implications. This study was designed to characterize the small domain 252-265 previously found to affect internalization of the hM1 receptor in transiently expressing CHO-K1 cells. Various mutations were made inside the small domain in order to characterize the amino acids that affect internalization. Studies conclude that the cysteines located at 262 and 263 are very important in the internalization rate of hM1 receptors. The agonist-dependent internalization was affected by the mutations but the affinity of the receptor for the ligand and the function of the receptor are not affected.