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. Author manuscript; available in PMC: 2015 Oct 1.
Published in final edited form as: Neurogastroenterol Motil. 2014 Oct;26(10):1361–1367. doi: 10.1111/nmo.12443

Figure 1.

Figure 1

General scheme of the role of β-arrestin2 in the tolerance to morphine in the ileum and colon. Agonist binding to the μ-opioid receptor activates G-protein signaling, and phosphorylation of the receptor by G-protein receptor kinase or protein kinase C dependent on the specific agonist. Phosphorylation leads to recruitment of β-arrestin2. In the ileum, repeated administration of morphine results in down-regulation of β-arrestin2 levels and development of tolerance. In the colon, repeated morphine administration does not affect β-arrestin2 levels and tolerance does not develop. Tolerance in the colon develops in the β-arrestin2 knockout mouse.