TABLE 2.

Cell surface expression of wild-type and mutant hδORs Stably transfected HEK293_i cells expressing the wild-type hδOR or the N18Q, N33Q, or N18Q/N33Q mutants were induced for 24 h. Cells were labeled with anti-c-Myc antibody (9E10), followed by PE-conjugated secondary antibody, or with 0.1 μm fluorescein-NTX, and the fluorescence of live cells was measured with flow cytometry. The GeoMean values were normalized to those obtained for the wild-type hδOR that were set to 100%. The data were obtained from three independent experiments, performed in duplicate, and analyzed with CellQuest Pro and GraphPad Prism.

Receptor	Total receptor level, anti-c-Myc antibody staining		Ligand-binding competent receptor level, fluorescein-NTX staining		Ratio of ligand binding competent and total receptor levels, fluorescein-NTX/anti-c-Myc antibody
	GeoMean	% of wild-type hδOR	GeoMean	% of wild-type hδOR	Ratio	% of wild-type hδOR
hδOR	1781 ± 133	100.0	751 ± 23	100.0	0.42 ± 0.01	100.0
hδOR(N18Q)	1617 ± 247	89.9 ± 7.0	682 ± 33	90.9 ± 3.9	0.42 ± 0.02	100.0 ± 4.8
hδOR(N33Q)	1422 ± 186a	79.2 ± 4.4	602 ± 54a	80.2 ± 6.9	0.42 ± 0.04	100.5 ± 9.0
hδOR(N18Q/N33Q)	1150 ± 145b	64.1 ± 3.3	375 ± 18b	49.9 ± 2.0	0.33 ± 0.02a	77.3 ± 3.8

^ap < 0.05

^bp < 0.001 is compared with the wild-type hδOR, using Tukey's post test after analysis of variance test