Table 1

Summary of the radio-ligand binding and electrophysiology assay data for human members of opioid receptor gene family

	Expression Level	Diprenorphine	Nociceptin	Dynorphin A
	B_max (fmol/mg protein)	K_d(nM)	K_d (nM)	K_i(nM)	EC₅₀ (nM)
hMOR	4364 ± 216	2.9 ± 0.7		1.60 ± 0.18	30 ± 5
hDOR	4901 ± 186	1.8 ± 0.4		1.25 ± 0.12	84 ± 11
hKOR	1262 ± 44	0.8 ± 0.5		0.05 ± 0.01	0.43 ± 0.08
hORL1	739 ± 38		0.81 ± 0.12	386 ± 47	30 ± 6

[³H]-diprenorphine was used as radiolabeled ligand in hMOR, hDOR and hKOR binding, [³H]-nociceptin was used in hORL1 binding. The K_i values were calculated according to the Cheng-Prusoff equation from the binding studies. EC₅₀ values were obtained from electrophysiology studies.