Figure 2.

Summary of current evidence for mechanisms of MOR regulation in resensitization and tolerance. (A) Desensitized MOR efficiently resensitizes when GRK2, βarr-2 (k.o.) or dynamin (to block endocytosis directly) are blocked, suggesting that resensitization is very efficient in the absence of endocytosis. Directly blocking endocytosis with concanavalin-A (ConA) does not affect resensitization or dephosphorylation of MOR. (B) After chronic morphine treatment, desensitization is enhanced, and resensitization is blocked. This does not appear to involve changes in endocytosis, but impaired resesnitization is restored to control rates by inhibiting GRK2, βarr-2 or dynamin.