TABLE 1.

Summary of biased agonism among several different μOR agonists with regard to different cellular responses

Relative efficacy ratios were extracted from quantitative studies in HEK-293 cells.

	DAMGO	Morphine	Methadone	Fentanyl	Etorphine	Herkinorin
[35S]GTPγS binding	+++a,b	+++a,c	+++a	+++a,c	+++a,c	+++b
ERK1/2 phosphorylation	+++d	+++d	N.D.	N.D.	N.D.	+++d
μOR phosphorylation	+++a,d,e	+a,d,e,f	+++a	+++a	+++a,f	+e
β-Arrestin2 recruitment	+++a	+a,c	+++a	++a,c	+++a,c	–e
μOR internalization	+++a,e	+a	+++a	++a	+++a	–e

N.D., not determined.

^a McPherson et al., 2010.

^b Xu et al., 2007.

^c Molinari et al., 2010.

^d Schulz et al., 2004.

^e Groer et al., 2007.

^f Zhang et al., 1998.