Figure 1.

Regulation of MORs. (A) The activation of MORs is dependent on the binding of agonist to receptors. (B) After binding, Gα and Gβγ subunits dissociate from each other. GRKs phosphorylate receptors. After phosphorylation, β-arrestin is recruited to the ligand-receptor complex to prevent further G-protein coupling. (C) The receptors together with β-arrestin then undergo endocytosis into the early endosomes, which is called receptor internalization. Receptors can be (D) dephosphorylated and (E) degraded by lysosomes or (F) resensitized through trafficking back to the cell membrane. (G) The newly synthesized receptors are transferred to the membrane for further ligand-receptor activation. MOR, µ opioid receptor; GRK, G protein-coupled receptor kinase; p, phosphorylated.