Table 1. Desensitization of wild and mutant types OPRM1 by 100nM DAMGO pretreatment in HEK293 cells.

DAMGO-induced [Ca²⁺]_i release concentration-reponse curves were determined as described in Fig 1B, and EC₅₀ values of DAMGO were calculated by log(agonist)vs. response formula. 100nM DAMGO-induced desensitization in wild type or mutant types OPRM1 was examined and data were analyzed as described in figure legend of Figure 2B. K values of DAMGO-induced OPRM1 desensitization were calculated by one phase exponential decay using the data analysis program GraphPad Prism. Maximum desensitization(des) level data were obtained after 30 min agonist pretreatment. Receptor expression level was determined by radioligand binding experments as described in material and methods. Data were showed as the averages of n≥3 experiments.

HEK293-OPRM1	Response	Desensitization		Receptor desensity, (pmol/mg)
	EC50,DAMGO (nM)	K, (min−1)	Maximum des level,(%)
WT	19 ± 6.9	0.31 ± 0.12	65 ± 4	2.2 ± 0.4
S363A	60 ± 19	0.46 ± 0.32	59 ± 5	1.8 ± 0.3
T370A	65 ± 31	0.40 ± 0.11	60 ± 9	1.6 ± 0.3
S375A	58 ± 53	0.37 ± 0.19	28 ± 11*	1.3 ± 0.4
370/375	11 ± 9.1	0.41 ± 0.10	21 ± 10*	2.5 ± 0.7
363/370/375	17 ± 3.6	0.35 ± 0.18	15 ± 14**	1.7 ± 0.5

means ± SEM (n ≥3)

^*p < 0.05

^**p < 0.01.